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th5 ECNP Young Scientist Conference
th& 9 ECNP Short Course on Functional polymers
2 4
Prague, Czech Republic
April 2 - 2 , 2012
Book of Abstracts
www.ecnp-eu.org
Published by the Institute of Macromolecular ChemistryAcademy of Sciences of the Czech RepublicPrague, Czech RepublicISBN 978-80-85009-70-5
Abstracts are printed without editing.
Design and typography by CZECH-IN s.r.o.5. května 65, 140 21 Prague 4, Czech Republic
Introduction to Block Copolymer Vesicles
Adi Eisenberg and Renata Vyhnalkova,
Department of Chemistry, McGill University,
Montreal, Quebec, Canada
Block copolymer vesicles (BCVs) have become the subject of considerable activity in the
last two decades, both because of academic interest and potential applications. BCVs are hollow
spheres (usually 100 – 1000 nm in diameter) consisting of a hydrophobic wall (ca 20 -30 nm
thick) with attached hydrophilic polymer segments on both sides of the wall, which renders them
water compatible. BCVs bare a strong resemblance to phospholipid vesicles (liposomes) as well
as a range of naturally occurring cellular of sub-cellular structures. In contrast to the liposomes,
BCVs, which are frequently referred to as polymersomes, are much more robust and can be
stable under much wider range of conditions.
Block copolymer vesicles are generally prepared from amphiphilic diblock copolymers
such as those consisting of polystyrene and poly(acrylic acid) (PS-b-PAA). Polystyrene is just
one of a number of possible hydrophobic segments. Poly(acrylic acid) is also one of several
possible hydrophilic moieties, other examples being poly(ethylene oxide) or poly(vinyl
pyridine). The block copolymers which yield vesicles are, typically, highly asymmetric with a
hydrophobic segment exceeding the hydrophilic one by a factor of 5 – 10 in length. A typical
example of a vesicle former is PS310-b-PAA52, where the numbers refer to the number of repeat
units in each block and the -b- denotes a block (rather than random) order.
The preparation of BCVs is somewhat more complicated than that of the liposomes.
While phospholipids are directly soluble in water and self-assemble spontaneously, the block
copolymers used to prepare BCVs are generally water insoluble so indirect methods have to be
employed. A typical example involves the dissolution of the polymer in a common solvent for
both blocks, such as dioxane or tetrahydrofuran, followed by the addition of a liquid which is a
non-solvent for the hydrophobic block but dissolves the hydrophilic one, typically water or
methanol. At some critical non-solvent concentration (called the critical water content or CWC
in the case of water) the hydrophobic blocks start to aggregate, initially to yield spheres with a
swollen hydrophobic core surrounded by the hydrophilic chains (the corona), which keeps them
water compatible. Because the length of the corona chains is typically much shorter than that of
the core forming chains, the aggregates are frequently referred to as crew-cut.
Water addition beyond the CWC eventually leads to the transformation of the spheres to
rod-like micelles, and upon further water addition, conversion to vesicles takes place. The
mechanism of rod formation from spheres involves the generation of an intermediate irregular
pearl-necklace which, with time, becomes of a smooth rod of a thickness comparable to that of
the original sphere. The change of a rod to a vesicle takes place via the transformation of the rod
initially into a spoon-like structure. With time, the “handle” of the spoon becomes shorter, which
enlarges the bowl. Once the handle is completely retracted, the bowl closes spontaneously into a
vesicle.
A morphological phase diagram can be constructed which gives the regions of stability of
the various morphologies as a function of polymer concentration and water content. Such a phase
diagram is shown in Figure 1 for PS310-b-PAA52 in dioxane/water (from H. Shen and A.
Eisenberg, J. Phys. Chem. B 1999, 103, 9473). As can be seen with increasing water content at
constant polymer concentration, the morphologies change progressively from spheres (S), to a
mixtures of spheres and rods (S+R), to rods (R), to a mixture of rods and vesicles (R+V),
Figure 1. Phase diagram Figure 2. Different types of vesicles
and finally to vesicles (V). Clearly, the vesicle region is a very large one in the phase diagram.
The size of this region makes it very easy to prepare vesicles, because all that is necessary is to
prepare a solution at the right polymer and water concentration, and the vesicles form naturally
within that region. It is worth noting that a wide range of vesicles can be prepared depending on
the polymer composition, solvent nature, water content and polymer concentration. Typical
examples are shown in Figure 2 (from S. Burke and A. Eisenberg, Macromolecular Symposia,
Warsaw, IUPAC meeting, 2000) .
The curvature stabilization mechanism in vesicles has been elucidated. In liposomes the
closure into a spherical structure requires energy to overcome the bending modulus, which
appears not to be the case in BCVs. The explanation is based on block length heterogeneity of
the corona chains which allows the vesicles, if formed under equilibrium conditions, to segregate
the long corona chains to the outside and short corona chains to the inside of the vesicles. Since
the repulsion among the longer corona chains is stronger than among the shorter ones, and since
the longer chains are on the outside of the vesicle, the curvature is stabilized.
Chain segregation by length offers the opportunity of preparing vesicles with different
corona chains on the inside and outside interface. For example, BCVs have been prepared in one
step with the outside corona consisting of poly(vinyl pyridine) (PVP) and the inside of
poly(acrylic acid) (PAA), by making the vinyl pyridine block much longer than the poly(acrylic
acid) block.
Vesicles which can be turned inside out have been prepared from a bi-amphiphilic tri-
block copolymer PAA-b-PS-b-P4VP with the PS long and the PAA and the PVP short. Under
acidic conditions, the P4VP is protonated and thus becomes subject to the polyelectrolyte effect,
which enlarges the coil. The PAA remains non-ionic. Vesicles prepared under these conditions
have the PVP chains on the outside because they are longer than the PAA chains, which form the
interior corona. Conversely, at high pH, the acrylic acid is deprotonated and ionic while the PVP
is neutral. Vesicles prepared under those conditions have the PVP on the inside and the PAA on
the outside. If these latter vesicles are subjected to a decrease in pH, the now non-ionic PAA
chains become shorter and can diffuse to the inside of the vesicle. The PVP chains, once they
diffuse to the outside of the vesicle, become protonated and cannot diffuse back in because the
wall is hydrophobic and the PVP has become ionic.
Both the wall thickness and the size of the vesicles can be controlled. Control of the wall
thickness can be accomplished via a change in the hydrophobic block length. The size can be
controlled by appropriate manipulation of the polymer concentration and the water content in the
region where the vesicles are stable.
BCVs are being explored for a range of potential applications, among them drug delivery.
The interior of the vesicle is a natural location for a hydrophilic drug, which is protected by the
wall from hostile elements in the body, e.g. stomach acids. Inserting the drug into the hollow
cavity requires active filling. Passive filling, which involves preparation of vesicles in the
presence of the drug, results in the incorporation of an amount proportional to the ratio of interior
volume to the exterior volume, which is usually in the range of 1/100 to 1/1000. Active filling,
on the other hand, involves the insertion of the drug after vesicles are prepared but under
conditions which favour internalization. For example, doxorubicin (a potent anticancer drug)
contains an amino group. To facilitate active filling, the vesicles are prepared under acidic
conditions, and once they are formed, the external pH is raised to neutral. The interior pH
remains low because the wall is hydrophobic. The drug is introduced on the outside of the
vesicles. Since it is non-ionic, it can diffuse to the interior. Once it is exposed to the low pH of
the interior, it becomes ionic, and is thus trapped because it cannot diffuse out over short time
scales through the hydrophobic wall. The wall can remain mobile in the presence of small
quantities of organic solvents, such as dioxane, or can be rendered impermeable if the organic
solvent is removed by dialysis. By such active filling techniques, it is possible to insert all of the
drug into the interior volume. The excess drug, if any, can be removed by dialysis. Diffusion out
of the vesicles is Fickian, and can be controlled by wall plasticization. The magnitude of the
diffusion coefficient can thus be altered by more than an order of magnitude.
Not surprisingly, as our experience with the manipulation of vesicles has improved, the
number of potential applications has increased. This can be seen in the dramatic raise in number
of published paper dealing with block copolymer vesicles over a decade. In the year 2010, the
number of paper exceeded 1000 from less than 10 a decade earlier. We can anticipate that the
number will continue increasing as applications in such areas as drug delivery, nano-reactors,
catalysis, etc. continue to evolve.
ANALYTICAL IMAGING OF POLYMERIC MATERIALS : the link between chemical
composition and macroscopic properties
Olivier LAVASTREa, Guillaume Darsy
a, and Guillaume Husson
a,
aCNRS, IETR UMR 6164 Rennes University, France; [email protected]
Polymers, and more particularly their physical properties, are really sensitive to their chemical composition.
However the 2D and 3D chemical distributions are also a key point to understand and to explain macroscopic
properties for both copolymers or polymer-based composites.
Introduction to analytical imaging of polymers (using classical camera, Raman imaging system as well as
nanodomains visualization with mass spectrometry (NanoSims) will be presented. Selected examples
including Ligth Emitting Diodes (LED's), biodegradable materials, hydrophobic films, stability of polymers,
... will be discussed.
Acknowledgements. The CNRS, Total company are acknowledged. MENRT, FEDER, Conseil Régional de
Bretagne, Ille et Vilaine and Rennes Metropole are acknowledged for the EUROPIA ONIS Imaging platform
funding. .
SEMICONDUCTING POLYMERS IN ORGANIC ELECTRONICS: SYNTHETIC
STRATEGIES, CHARACTERIZATION AND STRUCTURATION
Adam Pron and Malgorzata Zagorska
Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland;
e-mail: [email protected]
This tutorial lecture will focus on specific chemical and physicochemical requirements which must be met
for polymers to be considered as promising materials for applications in organic electronics. Although
emphasis will be put on macromolecules suitable for fabrication of field effect transistors (FETs), a large
fraction of the discussed compounds can also be applied in other organic or hybrid (organic–inorganic)
electronic devices such as photodiodes, light emitting diodes, photovoltaic cells, etc.
In the first part of the lecture the methods of the semiconducting homopolymers and copolymers
synthesis will be discussed. This will involve chemical or electrochemical oxidation of suitable monomers or
macromonomers, Grignard metathesis condensation, as well as other condensation methods such as Stille,
Suzuki, Yamamoto couplings or recently discovered direct C-C coupling.
The second part of the lecture will be devoted to the detailed description of the characterization
methods, including those which give access to the positions of the HOMO and LUMO levels of polymeric
semiconductors. These would involve cyclic voltammetry, UV-vis-NIR and Raman spectroelectrochemistry
and photoelectron spectroscopy.
In the third part of the lecture 2D and 3D supramolecular organization in thin films of
semiconducting polymers will be discussed, completed by instructive STM images and X-ray diffraction
patterns.
The lecture will be completed by the description of the processing techniques and their effect on the
electrical parameters of the fabricated transistors and photovoltaic cells.
Acknowledgements. This work was partially supported by NoE FlexNet Project, UE ICT 247745 (7FP).
ADVANCED POLYMER BIOMATERIALS: FROM CONTACT LENS TO
BIOMIMETIC POLYMER SCAFFOLDS
František Rypáček
Institute of Macromolecular Chemistry of the AS CR, Heyrovský Sq. 2,
16206Praque 6, Czech Republic
The term biomaterial indicate any xenobiotic material or substance (other than
a drug) that constitutes parts of a medical implant or device designed to treat,
augment or replace any tissue or organ in a living body or to support its function.1
The common denominator of all biomaterials is their direct contact with the inner
environment of the body. Therefore, their interactions with components of body
fluids, cells and tissues become always and integral part of evaluation of the
biomaterial performance.2 Synthetic materials, such as metals, ceramics or
polymers, as well as materials of natural origin based on proteins, polysaccharides
or modified whole tissues are being used as biomaterials.3
Synthetic polymers have been widely used for various medical applications,
such as disposable supplies, extracorporeal devices, wound dressings, surgical
implants, orthopaedic devices, vascular grafts, encapsulants, pharmaceutical
excipients and drug delivery systems. As biomaterials, synthetic polymers exhibit
significant advantages providing for materials with wide range of physical and
mechanical properties, easy processability into products with various shapes and
structures, availability and reasonable costs. Taking into account that the living
matter and the bodies of all living species are build from macromolecular
compounds, e.g., proteins, polysaccharides, i.e., natural polymers, the synthetic
organic polymers can be considered to be their closest relatives. With the
expanding options of synthetic methods the polymer chemistry offers a vast range
of materials and complex macromolecular systems their properties can be tuned to
match the various needs of biomedical applications.
Rapid expansion of polymer biomaterials research began with the 2nd WW,
which brought about an enormous need of prosthetic materials. As the first choice,
polymers known from other fields were used, such as polymethylmethacrylate
(PMMA), polyvinylchloride (PVC), polyethylene (PE), polyamides, polyesters,
fluorocarbon polymers (e.g. PTFE). In late fifties and sixties of the 20th century,
a special field of medical polymers emerged with development and applications of
hydrophilic methacrylate gels – hydrogels, the most known example of which was
poly(hydroxyethyl methacrylate), (polyHEMA), the first material for soft contact
lenses.4 The success of methacrylate hydrogels started a boom of tailor-made
polymer biomaterials, the strength, rheological properties and water content of
which could be tuned to match the properties of tissues to be replaced. The
biocompatibility of polymer biomaterials was sought based primarily on their
inertness and producing minimum interactions with the living systems, such as
adsorption of proteins, adhesion platelets, thrombogenicity, immunogenicity, etc.
The field of research of polymer biomaterials developed and changed
significantly during the last twenty years. From the original biocompatibility
concept, based primarily on inertness of the material with minimal interactions or
interference with biological environment, the focus is shifted towards new types of
biomaterials, which may actively participate in physiological processes, or change
their properties in response to changes in biological environment or according
build-in preprogrammed scheme.
Contemporary total joint prostheses represent an example of classical concept.
In these and similar applications, in which the implant is designed to function in the
body for a long time or, optimally, for the patient lifetime, the material
characteristics of the implant are optimized to their peak quality at the time of
implantation. During the extended period after implantation its material
characteristics may only deteriorate, due to mechanical stress, wearing, chemical
and biological erosion, etc., in contrast to the healthy living tissues, the properties of
which are stable in a long-term because of its continuous renewal.
Instead of total replacement of the tissue with synthetic material, new trends in
the research of biomaterials for regenerative and reconstruction medicine are
focused rather on use of biomaterials as temporary supporting structures - scaffolds,
which can temporarily substitute the function of tissue, facilitate the tissue
regeneration and after fulfilling its supporting role be reabsorbed and, eventually,
replaced with the newly regenerated tissue. Tissue engineering emerges as an
interdisciplinary field that combines the knowledge of cell biology a stem cells
technology with polymer engineering approaches to design of the biomaterial
scaffold.5
The scaffolds are typically three-dimensional porous constructs that could be
made of various biomaterials, mostly polymers or ceramics, which serve as cell
carriers. In a broader sense, the scaffold represents and should function as a
synthetic analogue of the extracellular matrix of the tissue (ECM). Therefore, to
actively promote formation and/or regeneration of a functional tissue, the scaffold
must serve only as a mechanical support but it must also provide the additional cues
that mimic the ECM-cell signaling mechanisms. 6
The bidirectional cells-ECM communication is realized through specific cell-
membrane receptors, e.g. integrins. The integrins can specifically bind to certain
domains on proteinaceous components of ECM, such as collagen, fibronectin,
vitronectin, laminin and others. The signaling action resulting from this integrin
binding is mediated by clustering of several integrin receptors within the cell
membrane and their linking to the actin molecules of the cytoskeleton through a
complex of protein intermediates.
Instead of modification of biomaterial surfaces with whole ECM proteins, short
oligopeptide sequences known to be present in the cell-adhesion domains of ECM
proteins can be used. Due to their low–molecular-weight nature, synthetic origin
and easier chemical manipulation, they quickly turned to be favorite components in
fabrication and/or biomimetic modification of polymer scaffolds for tissue
engineering. Many peptide sequences of adhesion sites have been already
identified, the most known and exploited one being the tripeptide arginine-glycine-
aspartic acid (RGD)7 present in fibronectin and recognized by about half of known
receptors of the integrin family. Numerous studies demonstrated the capability of
immobilized RGD-derived peptides to enhance cell adhesion to biomaterial surface
and promote other cellular adhesion-dependent activities. Furthermore, not only
their presence but also the surface density of biomimetic ligands, more precisely,
their nanoscale organization on the surface is necessary for functional cell
interaction. Actually, only the surface organization of peptide ligands that makes
them available to integrins at precise distances in a tens-of-nanometers scale can
provide for a functional signal triggering from the biomaterial surface. 8, 9
A number of recent evidence shows that the molecular organization of the
biomimetic ligands on the biomaterial surface represents a key factor in functional
communication at cell/biomaterial interfaces. The focus on creation of biomimetic
biomaterial/cell interfaces will become a key issue in the future research of polymer
scaffolds for tissue regeneration.
The lecture will present some typical examples of use of polymers as
biomaterials, explains the role of the polymer in particular applications as well as
recent approaches to creation of nanoscale organized surfaces with biomimetic
groups to direct the biomaterial/cell interactions.
REFERENCES
1. Ratner, B.D., Hoffman, A.S., Schoen, F.J., and Lemons, J.E. (Eds.):
Biomaterials Science: An Introduction to Materials in Medicine. Acad. Press,
New York, NY, 1996.
2. J. Drobník and F. Rypáček, Adv. Polymer Sci., 57: 1-50, 1984
3. Bronzino, J.D. (Ed.) The Biomedical Engineering Handbook, CRC Press, Boca
Raton, FL, 1995
4. Wichterle, O., Lím, D.: Nature 185, 1960, 117
5. Langer, R., Vacanti, J. P., Science, 260, 920-926, (1993).
6. Sands, R. W.; Mooney, D. J., Curr. Opin. Biotechnol. 2007, 18, 448-453
7. Pierschbacher, M. D.; Ruoslahti, E., Nature 1984, 309, 30-33.
8. Cavalcanti-Adam, E. A.; Micoulet, A.; Blummel, J.; Auernheimer, J.; Kessler,
H.; Spatz, J. P., European Journal of Cell Biology 2006, 85, 219-224
9. E. Třesohlavá-Chánová, Š. Popelka, L. Machová, and F. Rypáček,
Biomacromolecules 11 (1):68-75, 2010.
DESIGN AND PREPARATION OF THREE DIMENSIONAL SURFACE FUNCTIONALIZATIONS
Andreas Holländer
Fraunhofer-Institut für Angewandte Polymerforschung, Potsdam, Germany
Introduction.
Many tools for biological diagnostics rely on probe molecules which are immobilized to a solid substrate.
For example, the application of microarrays made a substantial contribution to the human genome project. A
microarray is a sheet of glass with a functionalized surface where DNA molecules with different short and
defined sequences are bonded in small spots which are arranged to an array. The sample contains a mixture
of DNA fragments which were labelled with fluorescence dyes. These fragments bind to the probe molecules
if they have a complementary sequence. The fluorescence pattern of the array provides information about the
sample. This basic approach has found many applications.
The surface chemistry of the DNA microarrays is relatively simple and based on coatings with polylysine1,
aminopropyl triethoxysilane2, or glycidylpropyl triethoxysilane
3. Recently, a number of driving forces
emerged to develop new approaches. One of them can be found in the fact that so far microarrays have been
used almost exclusively in academic research. This means that there is a demand for only a relatively small
number of pieces. In the event that microarrays penetrate into the medical diagnostics market, the demand
for substrates will increase by two or even three orders of magnitude. The current production technology will
not be able to provide this amount of microarrays at an appropriate quality and an acceptable price.
Secondly, after DNA sequencing has made huge progress during the last decade, the scientists’ interest has
shifted towards the proteins produced according to the DNA and the studying of their function and possible
relations to deceases. It turned out that the immobilization of proteins is much more complicated than
immobilizing DNA and it requires new procedures.
In this tutorial we will discuss solutions for the second problem, i.e. how to functionalize a surface in order
to make it a suitable host for proteins and their substrate molecules.
Surfaces for protein immobilization.
In the state of the art pieces of glass are the substrate for microarray type devices. For a considerable
improvement of the productivity in their preparation it is suggested to switch from the pieces to a film and
from glass to a polymer. Polymer substrates offer a greater variety of surface chemical approaches. The films
can be handled efficiently with roll-to-roll equipment.
Since most polymer materials are relatively inert, highly energetic means are used to activate the surface.
Electrical discharge plasmas have proven to be suitable tools for the efficient alteration of the chemical
structure at the surface4. For example, corona (barrier) discharges have found large scale industrial
applications for the treatment of polymer films for packaging applications. The process of activation is
largely based on radical oxidation reactions. These reactions run with a high rate and they result in a rather
broad variety of functional groups. For the activation of packaging films this heterogeneity does not matter.
Other applications like the immobilization of proteins rely on a specific functional group. In literature there
are reports about various approaches to create a defined surface chemistry5. However, the functionalization
of more or less flat surfaces is not the best way for the immobilization of proteins as can be seen in Figure 1.
The typical concentration of amino groups for the immobilization is rather high compared to the protein
molecules. The volume where an interaction can take place is small. The situation can be improved be using
a spacer molecule instead of the short ethylene diamine. But still the structure is far from being optimal and
the reason for the denaturation of the protein molecule is obvious.
If the protein is supposed to be immobilized in a way that it is situated like in a physiological environment
the actual immobilization sites must be very few and the rest of the bonding structure must be “invisible”.
This means a network is required which is constructed of hydrated molecular chains in order to prevent
interactions that would result in a denaturation. The mesh size of the network must be sufficiently large to
accommodate the protein molecules together with the substrate molecules in interaction studies. And there
must be a well adjusted concentration of immobilization sites.
Figure 1. In scale scheme of a polyethylene surface which was oxidized and then aminated in relation with a DNA
fragment, a small and a large protein molecule.
In literature it was suggested to graft polymer chains to the surface6 or to construct a network
7.
Graftpolymers have quite some disadvantages with respect to the demands stated above. For example, small
concentrations for the immobilization groups are difficult to handle.
The network construction via a cross-grafting type approach is more promising. The reaction of difunctional
poly(ethylene glycol)s (PEG) as branch molecules with trifunctional linkers was found to be a suitable
scheme which allows to adjust the properties according to the demands. PEGs with amino end groups were
used in the first investigations. They were linked, for example, with trifunctional epoxides or acid chlorides.
For the coupling of the network the surface can be equipped with amines (Figure 2) or thiol groups8.
Figure 2: Synthesis scheme for the construction of a surface bonded network.
The network formation reaction does not run to completion. Some amino end groups remain unreacted at the
end and some epoxide groups or carboxylic acid groups in the case of epoxide and acid chloride networks,
respectively. All of these groups can be used for further reactions or for the immobilization of biomolecules.
Chemical analysis of the networks.
The surface of a polymer is a rather complex object, in particular after it was exposed to an activation
process. A more detailed discussion on this subject can be found in reference 9. The analysis of chemically
heterogeneous surface layers is a very challenging task for modern analytical technology.
The combination of surface chemistry with instrumental methods creates powerful tools for the
determination of functional groups on organic surfaces. Derivatization or labeling reactions are used to
identify functional groups and to determine their concentration. During the last 30 years numerous reactions
and procedures have been suggested for the determination of various functional groups10
. The reaction of
trifluoroacetic anhydride (TFAA) with hydroxyl groups is one of the most straightforward derivatization
reactions for X-ray photoelectron spectroscopy (XPS). TFAA can also react with amino groups.
DNA(20 base pair
PDB 1gj1)
ethylene diamine
oxidized polyolenfin
antibody(PDB 1igt)
insulin(PDB 2omi)
NH2 NH2NH2 NH2 NH2
PE/COC
OOOO
O
O
HN
OH
OHHO
NH2
OO
Recently, experimental evidence was published which suggests that the concentration of amino groups and
hydroxyl groups can be determined side by side11
. The binding energy (BE) of the CF3 carbon atom in a
trifluoro acetate group is remarkably higher than that of the same kind of carbon atom in a trifluoro
acetamide. Moreover, the density of hydroxyl groups in the molecule influences the BE of the CF3 carbon12
.
This side-by-side determination of hydroxyl groups and amines allows the detailed analysis of the structure
of the networks discussed above.
From the viewpoint of the application as host structures for proteins and their complexes the PEG based
networks are described by structural parameters such as the mesh size (distance between branching points)
and the concentration of coupling groups for the immobilization. The procedure for the determination of the
network architectural parameters will be explained for the PEG-amine epoxide networks. It works in a
similar way also for the acid chloride networks7 and probably also for others.
The reaction between the PEG diamine and the trifunctional epoxide can result in three kinds of products:
1) The complete reaction of all epoxide groups with amines results in the formation of a branching point.
Each epoxide group is converted into one hydroxyl and one amino group ([OH] : [NH] = 3 : 3).
2) The reaction of two epoxide groups with amino groups results in the formation of a linear linkage and the
hydrolysis of the remaining epoxide groups gives rise to two hydroxyl groups. ([OH] : [NH] = 4 : 2).
3) The reaction of one of epoxide groups with an amino group results in the formation of an unlinked end
and the hydrolysis of the remaining epoxides generates four hydroxyl groups. ([OH] : [NH] = 5 : 1).
After derivatization with TFAA the C1s spectrum shows additional signals for CF3 carbon atoms and the
carbon atoms in the ester and amide groups. A 1 : 1 ratio would be found in the case that we have a complete
reaction of the epoxides. The average distance between two branching points would be the length of a PEG
chain. The higher the concentration of hydroxyl groups with respect to the amines the fewer branching points
are in the network. If we neglect the unlinked ends (case 3) which is a reasonable assumption for many real
samples, the analytical data can be explained as a mixture of the cases 1) and 2). The average distance
between two branching points can be calculated. It was found to be in the range of some nm to some 200 nm.
The determination of the concentration of the functional groups which can be used for immobilization is
usually performed by fluorescence labeling techniques as described in reference 13. The coupling chemistry
is similar to the one used for the immobilization of proteins. In the case of the PEG diamine epoxide
networks, the epoxide groups were determined using dansyl cadaverine. A typical concentration is
90 pmol/ cm2 for a network with a dry thickness of about 30 nm. The concentration of the primary amino
groups was determined by labeling with Fluorescamine. A value of 1.5 pmol/ cm2 was obtained for the
aminated flat surface of polyethylene. The preparation of a 30 nm thick network results in a higher amine
concentration with a typical value of 5 pmol/ cm2. The NH2 groups are mostly PEG diamine end groups.
In a similar way the concentration of other coupling groups can be determined.
Proteins inside the network.
The type and the concentration of functional groups in the network can be influenced by the reaction
conditions, the ratio of the components of the reaction mixture, by adding substances to the reaction mixture,
and by reactions after the end of the network formation. Adding heterodifunctional molecules to the reaction
system is a very versatile path to modify the properties of the network. For example, an increased
concentration of carboxylic acid groups can be obtained by adding an amino acid like alanine.
Adding an amino functionalized biotin to the reaction will result in networks with biotin moieties. For
demonstrating the performance of such a surface bonded network, a sequence of coupling reactions was
carried out. Streptavidin is a protein with a molecular mass of about 53 kDa. It is capable of binding four
biotin molecules. This molecule was coupled to the biotin in the network. Then, biotinylated protein A was
immobilized at one of the remaining binding sites of the streptavidin. Finally, the protein A was detected by
a fluorescence labeled antibody (FITC-IgG). The whole complex has a molecular mass of more than
210 kDa. The fluorescence signal from the FITC suggests a concentration of the IgG which is 4times larger
than on a flat surface (Figure ).
Figure 3: Fluorescence spectra of FITC-labelled antibodies coupled to a network containing biotin (upper curve) and
without biotin (lower curve, see text for complexation sequence)
In an experiment for testing the unspecific interactions of proteins with the network, the complete coupling
sequence was carried out with a network which does not contain any biotin. The very low fluorescence
signal (lower curve in Figure 3) indicates very few interactions.
Conclusions.
The preparation of surface bonded networks via polyaddition reactions allows the quantification of all
structural features and it provides very detailed information about the network architecture. The accessibility
of this kind of information allows the engineering of the network to the needs of a particular application. The
networks can be constructed on a molecular scale.
The structure of the networks was shown to be well suited for hosting proteins for interaction studies.
Acknowledgements.
The author likes to thank Dr. Falko Pippig and Dr. Sanaa Sarghini for their diligent work which was the basis for the
material presented here.
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3 D. Call, D. Chandler, F. Brockman, Biotechniques 2001, 30, 368.
4. d’Agostino R, Favia P, Oehr C, Wertheimer MR (eds.). Plasma Processes and Polymers, Wiley-VCH; 2005.
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Oehr, M. Müller, B. Elkin, D. Hegemann, U. Vohrer, Surface and Coatings Technology 1999, 116-119, 25; S.
Wettmarshausen, G. Kühn, G. Hidde, H. Mittmann, J. F. Friedrich, Plasma Processes and Polymers 2007, 4, 832;
E. Wischerhoff, N. Badi, A. Laschewsky, J. Lutz Advances in Polymer Science, 2011, 240, 1.
6. S. Edmondson, V. L. Osborne, W. T. Huck, Chemical Society Reviews 2004, 33, 14; R. Barbey, L. Lavanant, D.
Paripovic, N. SchuÌwer, C. Sugnaux, S. Tugulu, H. Klok, Chemical Reviews 2009, 109, 5437.
7 F. Pippig, A. Holländer, Macromolecular Bioscience 2010, 10, 1093.
8 A. Holländer; F. Pippig in N. Dumitrascu, I. Topala (editors) Biomaterials and Plasma Processing. Editura
Universitätii Alexandru Ioan Cuza, Iasi, 2011. p. 157 - 173.
9 A. Holländer, S. Kröpke, F. Pippig, Surface and Interface Analysis 2008, 40, 379.
10 A. Chilkoti; B. D. Rattner in L. Sabbatini and P. G. Zambonin (editors) Surface Characterization of Advanced
Polymers. VCH Verlagsgesellschaft, Weinheim, 1993. p. 221 – 256; A. Holländer, Surface and Interface Analysis
2004, 36, 1023.
11 A. Holländer, F. Pippig, M. Dubreuil, D. Vangeneugden, Plasma Processes and Polymers 2008, 5, 345.
12 F. Pippig, S. Sarghini, A. Holländer, S. Paulussen, H. Terryn, Surface and Interface Analysis 2009, 41, 421.
13 B. Ivanov, J. Behnisch, A. Holländer, F. Mehdorn, H. Zimmermann, Surface and Interface Analysis 1996 24, 257.
CIg
G-F
ITC
(pm
olcm
-2)
500 550 600 6500
100
200
300
400
500
0
5
10
15
20in
ten
sity
(Mcp
s)
wavelength (nm)
SELF-HEALING AND POLYMER-BASED MATERIALS
Jean-François Gérard Ingénierie des Matériaux Polymères UMR CNRS 5223, Université de Lyon – F69621 Villeurbanne (France)
Biological materials which respond to damage via an autonomic healing response inspire the development of
new approaches for designing synthetic polymer-based materials for various applications. The different
routes which could be applied and the application to structural materials, matrices of composites as well as
coatings are described in this lecture.
In the first part of the lecture, the fracture mechanisms of polymers, i.e. for both thermoplastics and
thermosets, are described in order to understand what kind of defects need to be repaired via healing
processes. The conventional solutions will be also reported.
In a second part of the lecture, the self-healing solutions for thermoplastics will be listed and detailed (for
each of them, the basic phenomena will be reported and commented). The following approaches will be
considered: molecular interdiffusion, photo-induced healing, recombination of chain ends or via reversible
bond formation as well as development of specific materials such as organo-siloxane, ionomers, living
polymers, and nanoparticle addition.
The case of thermosets will be considered in the third part. A special attention will be given to self-healing
via addition of microcapsules containing healing components, i.e. monomers or polymers, which was
described in many papers in the literature. Routes using high glass transition temperature thermoplastics and
thermally reversible matrices as well as metal-ion-mediated healing processes will be also reported. Due to
the fact that thermosets are widely used as matrices and coatings, specific approaches developed for such
applications will be described. One can mention the introduction of hollow fibers which is proposed for
composite materials and corrosion inhibition active coatings, respectively.
The lecture will also report the numerous approaches considering shape memory and swollen materials and
the proposed modelling of self-healing process with a special attention to its kinetics.
References
1. Self-healing materials: Fundamentals, Design strategies, and applications, Ed. S.K. Ghosh, Wiley-VCH, 2009
2. Self-Healing Polymers and Composites, B.J. Blaiszik, S.L.B. Kramer, S.C. Olugebefola, J.S. Moore, N.R.
Sottos, S .R.White, Annu. Rev. Mater. Res. 2010. 40:179–211
3. Self healing in polymers and polymer composites. Concepts, realization and outlook: A review, Y. C. Yuan, T.
Yin, M. Z. Rong, M. Q. Zhang, eXPRESS Polymer Letters, 2008. 2(4):238–250
4. Self-healing polymeric materials: A review of recent developments, D.Y. Wu, S. Meure, D. Solomon, Prog.
Polym. Sci., 2008. 33:479–522
5. A critical appraisal of the potential of self healing polymeric coatings, S.J. García, H.R. Fischer, S. van der
Zwaag, Progress in Organic Coatings, 2011, 72:211– 221
RESPONSIVE AND SMART MATERIALS FOR SENSING AND BIOMEDICINE
Brigitte Voit
Leibniz-Institute of Polymer Research Dresden, Hohe Strasse 6, Dresden, Germany
E-mail: [email protected]
A large variety of so-called “smart” polymer systems have been prepared in the recent years.1,2
This
term is usually applied for any material which responds to an external trigger with a defined change
in material properties e.g. changes in solubility, hydrophilicity or hydrophobicity, aggregation and
physical interaction behavior, optical properties, and so forth. Triggers applied can be manifold, e.g.
heating, cooling, irradiation, changes in chemical environment e.g. variations in pH, salt
concentrations or solvent, changes in pressure, a magnetic impulse and others. However, one has to
admit that the term “smart” is used today in a much broader aspect, often for many functional
polymer materials taking over a specific task without any specific physical change.
First, some examples will be given on polymeric materials used for chemical sensors where the
absorption of a chemical leads to a fast and defined change in film properties like thickness,
refractive index and weight, changes which can be detected in a sensor device. Hyperbranched
polymers will be used as an example. Furthermore, polymers applied in microfluids, which have as
well a sensor function and act on that e.g. with a strong volume change, allowing the use as
actuators will be addressed.
Responsive polymeric materials are certainly highly essential and very popular for a variety of
biomedical applications, most prominent as carrier material in which drug release can be triggered
by heat, pH changes, irradiation or a (bio)chemical reaction. E.g. for stents, catheter, implants,
membranes, cell cultures or even syringes, a biocompatible and smart surface is required which
prevents infection or blood clotting, reduces protein adsorption or increases just hydrophilicity.
Several hydrophilic, amphiphilic and thermo- and pH responsive polymers have been developed in
our group which can be attached to polymeric and metal substrates using different methods. Stable
polyacrylic acid hydrogel formed from a thin macroinitiator layer could be used to reduce the
friction of polymeric catheters and to allow a better sliding into the blood vessels without damaging
tissue but can also be used for the incorporation and release of a drug. Copolymers of NiPAAm
with poly(oligo)ethyleneoxide macromonomers as thermoresponsive materials could be
immobilized on surfaces by a plasma induced process. Cell growth on these modified substrates
could be stimulated and by changing the temperature, a smooth and cell friendly release of the cells
into the cell culture medium was possible. Double-responsive hydrogel nanoparticles have been
prepared through selective crosslinking of micellar structures through e-beam irradiation. Dendritic
glycopolymers which interact with analytes pH dependent have been developed as globular carrier
systems for targeted multicompartment drug delivery systems or in studying biological processes
but also as smart thin layers for biosensing and bioseparation techniques.
Smart Polymers: Applications in Biotechnology and Biomedicine, Second Edition, Igor Galaev, Bo
Mattiasson (Eds.), 2007, CRC Press.
Chemical Design of Responsive Microgels, Adv. Polym. Sci., Vol. 234, 2011, Springer.
S. Zschoche, J. C. Rueda, M. Binner, H. Komber, A. Janke, K.-F. Arndt, B. Voit, Macromol. Chem. Phys.,
2012, 213, 215.
N. Polikarpov, D. Appelhans, P. Welzel, A. Kaufmann, P. Dhanapal, C. Bellmann, B. Voit, New Journal of
Chemistry, 2012, 36, 438.
Smart Photo Crosslinked Polymersomes as Multifunctional Device for Drug Delivery and Biological Tasks
Mohamed Yassin, Dietmar Appelhans and Brigitte Voit
Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, D-01069 Dresden, Germany E-mail: [email protected]
Self-assembly of amphiphilic block copolymers into hollow spheres, so called polymersomes has attracted increasing scientific interest in the past decade. This interest is derived from their numerous potential applications such as carriers for drug delivery and as naoreactor for synthetic biology[1]. We are interested in establishing of shape-persistence polymersomes with a pH-tunable membrane. As well as functionalization of their surface with different targeting groups is highly desired to give them smartness to deliver drug to the desired cell [2].
Here we present a new class of photo crosslinked polymersomes based on poly(ethyleneglycol)-block-poly[2-(diethylamino)ethylmethacrylate-stat-2-hydroxy-4-(methacryloyl-oxy) benzophenone], PEG-b-P(DEA-stat-BMA). Thus, BMA act as a photo crosslinker providing stable polymersomes against lower pH. However, the pH sensitivity of the membrane is derived from DEA units. Irradiation of these polymersomes for only five minutes provided crosslinked polymersomes with a vesicular shape-persistent over the whole range of pH. Moreover, polymersomes showed also a defined pH-responsivity around pH 7. Thus, at pH 3 the membrane undergoes swelling resulting in polymersomes of about 200 nm which shrink reversibly to 120 nm at pH 10 (scheme 1). This feature provides polymersomes with controllable gates within their membrane, where they can undergo “on-off” switching according to the pH. Doxorubicin as anticancer drug and Ribavirin as a nucleotide analogue for the treatment of Hepatitis C virus (HCV) have been used as two different drug models. Our polymersomes show the potential to uptake, retain and release the drugs according to the pH. Furthermore, surface of polymersomes has been functionalized with amino and alkyne groups in order to couple different targeting agent on the surface of polymersomes.
Scheme 1. shape-persistence polymersomes with a pH-tunable membrane and functionalized surface
References
1. F. H. Meng, Z. Y. Zhong, Journal of Physical Chemistry Letters 2011, 2, 1533. 2. J. Gaitzsch, D. Appelhans, D. Grafe, P. Schwille, B. Voit, Chemical Communications 2011, 47, 3466.
DESIGN OF EDIBLE COATINGS BASED ON A NEW MICROBIAL POLYSACCHARIDE
FOR THE IMPROVEMENT OF FOOD PRODUCTS QUALITY
A. Rita Ferreiraa, Vítor D. Alves
b and Isabel M. Coelhoso
a
aRequimte/CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de
Lisboa, Campus de Caparica, 2829-516 Caparica, Portugal bCEER – Biosystems Engineering, Instituto Superior de Agronomia, Universidade Técnica de Lisboa,
Tapada da Ajuda, 1349-017 Lisboa, Portugal
Edible coatings may be defined as a thin layer of material that covers the surface of the food and can be eaten
as part of the whole product. This technology is innovative and can increase shelf-life of food products.
Beyond that, edible coatings may be functionalized with the incorporation of bioactive components.
The coatings may be produced from diverse materials recovered from renewable natural resources, such as
polysaccharides extracted from natural resources (e.g. pectin and chitosan) or produced by microbial
fermentation (e.g. gellan); proteins (e.g. whey proteins) and lipids (e.g. waxes)1.
In this work, innovative edible coatings will be developed based on a new microbial exopolysaccharide
(EPS) produced by a non-pathogenic Pseudomonas oleovorans strain2. This EPS is produced using a
glycerol by product from biodiesel industry, as carbon source, with attractive productivities and polymer
yield. Process and product are innovative and had been the subject of an international patent3.
The new EPS is a high molecular weight negatively charged heteropolysaccharide, composed by sugars
(galactose, glucose, fucose, mannose and rhamnose) and acyl groups (pyruvil, succynil and acetyl)4.
The ability of the new EPS to produce cohesive films (without additives) and a detailed characterization of
their properties, namely, transparency, water sorption, solubility and swelling behaviour, barrier and
mechanical properties was studied.
The films obtained from this microbial biopolymer are quite transparent with a good physical integrity when
handled, although showing some stiffness when subjected to tensile tests with a low strain at break (9.5 ±
3.9%) and a high Young modulus (1738 ± 114 MPa).
The EPS films are hygroscopic with poor water vapour barrier properties, with water vapour permeability
between (1.1 ± 0.2) x 10-11
and (5.4 ± 0.8) x 10-11
mol/m s Pa, depending on the driving force used. However,
they exhibited a good barrier to carbon dioxide, with a permeability of (0.20 ± 0.03) x 10-15
mol/m s Pa,
which was dependent on the water content of the polymer matrix5.
Single and bi-layer coatings will be developed using the EPS (alone or mixed with commercial
polysaccharides) to form hydrophilic layers, and beeswax as hydrophobic layer.
The EPS aqueous solutions will be complemented with plasticizers (e.g. glycerol) and food grade cross-
linking agents. They will be also mixed with other polysaccharides (e.g. pectin from fruit residues, chitosan)
in different proportions, to form coating solutions based on biopolymers with dissimilar chemical
composition and properties.
In addition, composite coating solution based on emulsions will be developed; melted beeswax containing an
emulsifier agent will be dispersed by homogenization in the polysaccharide solution. Also bioactive
ingredients addition to the coating solution will be studied. Depending on their chemical properties, the
functional molecules will be included either in the polysaccharide or in the beeswax phase.
It is expected to design formulations with bioactive activity to be used in coating formulations for specific
fruit products.
Acknowledgements. The authors would like to acknowledge FCT-MCTES, Portugal, for funding of project
PTDC/AGR-ALI/114706/2009 - “New edible bioactive coatings for the improvement of food products quality”
References
1. Daniel Lin and Yanyun Zhao; Innovations in the Development and Application of Edible Coatings for Fresh and
Minimally Processed Fruits and Vegetables; Comprehensive Reviews in Food Science and Food Safety, 6 (2007)
60-75.
2. Andrade de Freitas, Maria Filomena; Delgado Alves, Vitor Manuel; Oliveira Pais, Joana; Carvalho Fernandes de
Miranda Reis, Maria Ascensão; Freitas Oliveira, Rui Manuel; Pereira da Cunha Rodrigue; Galactose-rich
polysaccharide, process for the production of the polymer and its applications, CA2683817(A1), 2008.
3. Galactose-rich polymer, process for the production of the polymer and its applications. PCT nº PT 2008/000015,
April 2008. Inventors: Maria A. Reis, Rui Oliveira, Filomena Freitas, Vitor D. Alves, Joana Pais, Cristina Oliveira.
International Publication Number WO 2008/127134 A1.
4. Filomena Freitas, Vitor. D. Alves, Joana Pais, Nuno Costa, Cristina Oliveira, Luis Mafra, Loic Hilliou, Rui Oliveira,
Maria A.M. Reis, Characterization of an extracellular polysaccharide produced by a Pseudomonas Strain grown on
glycerol, Bioresource Technology,100 (2) (2009) 859.
5. Vitor D. Alves, Ana R. Ferreira, Nuno Costa, Filomena Freitas, Maria A. M. Reis, Isabel M. Coelhoso;
Characterization of biodegradable films from the extracellular polysaccharide produced by Pseudomonas
oleovorans grown on glycerol byproduct. Carbohydrate Polymers; 83 (2011) 1582-1590.
Deformation mechanisms in Organoclay-Polylactic acid/Natural rubber bionanocomposites as
revealed by Synchrotron X-ray scattering
N. Bitinisa*
, A. Sanzb,c*
, A. Nogalesb, R. Verdejo
a, M.A. Lopez-Manchado
a,
T.A. Ezquerrab
a Instituto de Ciencia y Tecnología de Polímeros, ICTP-CSIC, Juan de la Cierva, 3 28006-Madrid, Spain
b. Instituto de Estructura de la Materia, IEM-CSIC, Serrano 121, Madrid 28006, Spain
c Instituto de Química Física ´Rocasolano´, IQFR-CSIC, Serrano 119, Madrid 28006, Spain
Polylactic acid (PLA) is a biodegradable material derived from renewable resources, which
possesses favourable properties to be used as a packaging thermoplastic polymer and thus could be a good
candidate for replacing petroleum-based polymeric material. However, some of its properties such as its
brittle behaviour or gas barrier properties need to be improved for many end-user applications, especially for
food packaging applications.[1]
In our previous study on polylactic acid, we demonstrated the production of ductile PLA through the
addition of natural rubber (NR).[2]
Subsequent developments of this blend enabled further improvements of
the mechanical properties by adding small amounts of organoclays due to their location at the PLA/NR
interface.[3]
Here, our main goal is to gain a better understanding of the micromechanical deformation
mechanism of thermoplastic/elastomeric blend nanocomposites based on PLA, NR and organoclays, by in-
situ SAXS-WAXS measurements under tensile conditions. Deformation mechanisms using synchrotron light
have already been studied for polymer blends and polymer nanocomposites since it enables linking the
macroscopic deformation to the structural changes at both microscopic and mesoscopic levels.[4-5]
We
combined in situ WAXS and SAXS measurements during stretching to obtain a broader understanding of the
deformation mechanisms. While WAXS mainly provides information about length scales associated to inter-
chain correlations of the matrix, SAXS informs us of the nanometer scale phenomena, such as microvoid
formation, crazing, shear yielding or debonding. Moreover, because of the layered structure of the
organoclays, SAXS patterns also give us information about the interlayer distance and orientation of the
clays in the blends through the main diffraction peak.
Compounds were prepared by melt blending PLA, NR and the organoclay, dimethyl, dehydrogenated tallow, quaternary ammonium modified montmorrillonite (Cloisite C15A). In situ WAXS and SAXS measurements were recorded simultaneously during longitudinal deformation of the samples at a speed of 5 mm/min. Time-resolved WAXS and SAXS were performed at the Spanish beamline BM16-CRG of the European Synchrotron Facility (ESRF) in Grenoble, France.
The deformation mechanisms of each material were analysed and identified through the study of SAXS and
WAXS patterns.
Figure 1. Example of scattered intensity for PLA/NR/C15A 3wt%. a) WAXS 2D pattern: orientation of
polymer chains and SAXS pattern: b) orientation of nanoclays and c) microvoid formation and orientation
1. Auras, R.; Harte, B.; Selke, S., Macromol. Biosci. 2004, 4, 835-864.
2. Bitinis, N.; Verdejo, R.; Cassagnau, P.; Lopez-Manchado, M., Mater. Chem. Phys. 2011, 129, 823-831.
3. Bitinis, N.; Verdejo, R.; Maya, E. M.; Espuche, E.; Cassagnau, P.; Lopez-Manchado, M. A., Compos. Sci.
Technol. 2012, 72, 305-313.
4. l'Abee, R. M. A.; van Duin, M.; Spoelstra, A. B.; Goossens, J. G. P., Soft Matter 2010, 6, 1758-1768.
5. He, C. B.; Donald, A. M.; Butler, M. F., Macromolecules 1998, 31, 158-164.
INCORPORATION OF BIODEGRADABLE NANOPARTICLES INTO N-
ISOPROPYLACRILAMIDE HYDROGEL FOR BIO -APPLICATION
Nicoletta Rescignanoa, Ilaria Armentano
a, Carmen Mijangos
b, Rebeca Hernandez
b and Josè M.
kennya,b
aMaterial engineering Center, UdR INSTM University of Perugia, Italy, [email protected] b Institute of Polymer Science and Technology, CSIC, C/lle J. De La Cierva, 3 Madrid Spain
Introduction. Thanks to the capability of their rapid response to environmental stimuli, “smart” hydrogels
constitute a fast growing area of polymer science. Examples of this behaviour include change in swelling
ratio of a pH-sensitive hydrogel due to a change in the pH of the swelling agent [1], change in hydrophilic
and hydrophobic properties of a thermosensitive hydrogel due to a change in temperature [2], and change in
the dimensions of an ionic hydrogel due to a change in the ionic strength of a surrounding solution and
electrical potentials [3-4]. Based on these characteristics, stimuli-sensitive hydrogels can be widely applied
in biomaterials such as controlled drug release and delivery system [5-7.], on–off switching materials [8],
artificial muscles [9], biosensors, separations, and adsorptive materials [10]. Hydrogels are usually polymers
with three-dimensional networks structures that permit a high permeability to drug molecules and have been
used for the controlled release of pharmaceutically active compounds. Thermosensitive hydrogels based on
poly(N-isopropylacrylamide) [poly(NIPAAm)] or related copolymers were studied in the past [5-6].
Poly(NIPAAm) hydrogel in aqueous solution exhibits a rapid and reversible hydration–dehydration change
in response to small temperature changes around its lower critical solution temperature (LCST) [2]. The gel
forms a dense polymer skin layer at the surface when a swelling poly(NIPAAm) hydrogel is immersed in
water above the LCST [11]. This prevents the permeability of water or solute. Promotion of the application
of hydrogels for drug release or fast responsive materials, such as artificial muscles, reducing the dense skin
layer formation is an important point of this research. During the past few years a number of strategies have
been developed to control the release of proteins on the basis of time. Proteins are sensitive to exposure to
high and low temperatures, the presence of hydrophobic surfaces (many organic solvents), high shear, high
and low pH, and the removal of water. Henceproteins or bioactive molecules could be encapsulated in
biodegradable polymeric nanoparticles in order to protect them from external stimuli.
The incorporation of porous biodegradable nanoparticles loaded with bioactive molecules into N-
isopropylacrylamide hydrogels, in order to develop nanocomposite hydrogel, represents a perfect tool for the
biological applications envisaged.
Materials and Methods: Poly(DL-lactide-co-glycolide), PLGA (I.V. 0.95-1.20dL/g) ether terminated, with
a 50/50 ratio (PLA/PGA) was used as biodegradable polymers. Polyvinyl alcohol (PVA) (31,000-50,000 87-
89% hydrolyzed) was used as surfactant and chloroform (CHCl3) from Sigma Aldrich as solvent. Vitamine
B12 was purchased from sigma Aldrich as a bioactive molecule. The N-isopropylacrylamide (N-AAm)
(Panreac), the initiator potassium persulphate (Fluka), the crosslinker N,Nmethylene bisacrylamide
(Bis)(Aldrich), and the accelerator N,N,N,N-tetramethylethylendiamine (TEMED) (Bio Rad) were used as
received. Alginic acid sodium salt from brown algae with a 65–70% guluronic acid and a Mw ¼100–200 K
according to the manufacturer was purchased from Aldrich and used as received. Alginate stock solutions
were prepared by dissolving alginate powder in distilled water to yield 1 g per 100 mL solutions.
Biodegradable nanoparticles were prepared by double emulsion (water/oil/water) method, with subsequent
solvent evaporation. The PLGA nanoparticles (Nps) were suspended in distilled water after several washes
and centrifuges. Briefly PLGA was dissolved in chloroform by magnetic agitation. This solution was
emulsified with phosphate buffered saline solution (PBS) using the tip sonicator (VIBRA CELL Sonics mod.
VC 750, USA ). The resulting emulsion is mixed with 2 %wt/v of PVA aqueous solution, by sonication
treatment, for the formation of second emulsion. For the solvent evaporation the second emulsion was
transferred in 0,2 %wt/v PVA aqueous solution and was magnetically stirred over night at room temperature.
The nanospheres were collected by centrifugation and were washed four times with distilled water.
Semi-interpenetrating polymer networks (INPs) constituted by alginate and PNiPAAm (Alg-PNiPAAm)
were obtained by polymerizing of N-AAm and Bis in 1 %wt alginate aqueous solution. Before that the
polymerization starts, the PLGA Nps were added in alginate solution (1 %wt Nps in alginate solution) the
polymerization was initiated by the potassium persulphate/TEMED redox system and carried out at room
temperature. Solutions were poured into Petri dishes and allowed to react at room temperature for 24 h. The
samples obtained were dialyzed against fresh water over 2 d to remove all the unreacted monomer [12].
PLGA Nps and gel morphological characterization were performed by field emission scanning electron
microscope (FESEM Supra 25, Zeiss). Thermogravimetric analysis (TGA) was performed on 10 mg samples
on a Seiko Exstar 6000 TGA quartz rod microbalance in Nitrogen atmosphere from 30 to 600 °C, 10 °C/min.
Thermo-mechanical characterization was carried out by TMA 7, Perkin Elmer from 12 to 65 °C at a heating
rate of 10 °C/min.
Experimental, Results and Discussion: The FESEM analysis of PLGA Nps loaded with Vitamin B12
shows a mostly spherical smooth shape for all nanoparticles, demonstrating the success of the parameters
selected for the particle formation process. High magnification images show that the nanoparticles have a
porous surface. This porous nature of the nanoparticle surface is the major characteristic of biodegradable
nanoparticles responsible for the controlled release of entrapped materials from the nanoparticles. The pore
size is not detectable by FESEM, since the very low pore diameters.
The morphology of the Alg-PNiPAAm gel void and the gel with PLGA Nps were examined by FESEM in
figure 1. The crosslinked gel presents a porous structure that consists in big holes and smalls pores. The
pristine gel has a regular porous structure while the nanocomposites gel presents an irregular porous
structure, with PLGA Nps well dispersed and distributed on the pores walls and in the inner part of the pores.
PNiPAAM is the most popular temperature-responsive polymer since exhibits a sharp phase transition in the
water, the lower critical solution temperature (LCST) at around 32°C, in Alg-PNiPAAm LCST this value
shifts to high temperature at 36,6 °C, measured by TMA and the PLGA Nps presence does not influence this
data. The thermal gravimetrical analysis presents the typical peak of PNiPAAm to 450 °C.
Conclusions: PLGA nanoparticles loaded with vitamin B12 were successfully developed by double
emulsion method and incorporated in Alg-poly(NIPAAm) gel. An homogeneous dispersion of PLGA Nps
was observed, and it does not affect the LCST of the gel.
References 1. L.B. Peppas, N.A. Peppas, Biomaterials 1990 11, 635.
2. K. Makino, J. Hiyoshi, H. Ohshima, Colloids and Surfaces, B: Biointerfaces 2000, 19197.
3. W.F. Lee, C.H. Shieh, Journal of Polymer Research 1999 641.
4 W.F. Lee, W.Y. Yuan, Journal of Applied Polymer Science 2000, 77 1760.
5. C.L. Bell, N.A. Peppas, Journal of Controlled Release 1996, 39, 201.
6 L K. Makino, J. Hiyoshi, H. Ohshima, Colloid and Surfaces, B: Biointerfaces 2001 20, 341.
7. A. Gutowska, J.S. Bark, I.C. Kwon, Y.H. Bae, Y. Cha, S.W. Kim. Journal of Controlled Release 1997, 48, 141.
8. R. Dinarv, A. D’Emanuele, Journal of Controlled Release 1995, 36, 221.
9. Y. Li, Z. Hu, Y. Chen, Journal of Applied Polymer Science 1997, 63, 1173.
10. Y. Seida, Y. Nakano, H. Ichida, Kagaku Kogaku Ronbunshu 1992, 18, 346.
11. T. Okano, Y.H. Bae, H. Jacobs, S.W. Kim, Journal of Controlled Release 1990, 11, 255.,
12. R. Hernandez, C. Mijangos, Macromolecular rapid communications, 2009, 30, 176.
Biodegradable poly(sorbitol sebacate malate): Mechanical and thermal properties
W. H. Tham1, M. U. Wahit
1*, M. R. Abdul Kadir
2, T. W. Wong
1
1 Enhanced Polymer Research Group, Department of Polymer Engineering, Faculty of Chemical
Engineering, Universiti Teknologi Malaysia, Johor Bahru, 81310, Malaysia. 2 Medical Implant Technology Group, Faculty of Biomedical Engineering & Health Sciences,
Universiti Teknologi Malaysia, Johor Bahru, 81310, Malaysia.
*e-mail: [email protected]
Abstract-A new class of biodegradable polyesters was synthesized by polycondensation of
sorbitol, sebacic acid, and malic acid without the presence of catalyst. The resulting polymer
was designated as poly(sorbitol sebacate malate) (PSSM). The effects of different mole ratio
of malic acid to the mechanical properties PSSM polymers were investigated. Fourier
transform spectroscopy, differential scanning calorimetry and tensile test were conducted to
characterize the polymers. The results of DSC demonstrated that the glass transition
temperature (Tg) increased with higher concentration of malic acid. Tensile testing of PSSM
polymers showed that increasing malic acid content in the polymer formulation cause a
significant increase in the tensile strength and Young’s modulus but a decrease in elongation
at break.
MULTIFUNCTIONAL POLYMERSOMES AS VERSATILE AND BIOCOMPATIBLE
NANOREACTORS
Jens Gaitzscha, Dietmar Appelhans
a, Petra Schwille
b, Giuseppe Battaglia
c and Brigitte Voit
a
a Leibniz Institute of Polymer Research Dresden e. V.,Hohe Straße , 01069 Dresden, Germany,
[email protected] b TU Dresden, Biotechnological Centre, Tatzberg 47-49, 01307 Dresden, Germany
c University of Sheffield, Dept. of Biomedical Science, Western Bank, Sheffield S10 2TN, United Kingdom
Over the past decade, researchers have tried to develop feasible polymer-based systems for biomedical
applications, such as drug delivery systems or artificial organelles1. Polymersomes have proven to be a
promising candidate for such systems. Compared to their biological counterpart, the liposomes, there
membrane is considerably thicker and show increased mechanical and chemical strength2. This strength can
yet be improved by introducing chemical bonds within the membrane, e.g. to cross-link it. We combine this
cross-linking with a well-known pH sensitive polymer to give a highly stable polymersome with strictly
controlled trans-membrane diffusion by reversible pH switches3.
OO
O
OO
45
N
Br
O O
NO O
100
2
0 1 2 3 4 5
0,7
0,8
0,9
1,0
1,1
1,2
1,3
1,4
1,5
1,6
1,7
Re
latio
n t
o o
rig
ina
l siz
e
Cycles
C4-20, 30 s
pH = 3
pH = 10
a b c
Figure 1: (a) PEG-b-PDEAEM-s-PDMIEM block-copolymer used to form polymersomes. (b) Once crosslinked, the
polymersomes show a definite, reproducible swelling behaviour. (c)Images of polymersomes using laser scanning
microscopy and TEM.
Polymersomes consist of amphiphilic block-copolymers, which eventually self-assemble into hollow
vesicles (Fig. 1c). We use polyethyleneglycol (PEG) as a biostable hydrophilic block, which is combined the
pH sensitive polydiethylaminoethylmethacrylate (PDEAEM) and photo cross-linkable
polydimethylmaleimidobutylmethacrylate (PDMIBM) as hydrophobic components (Figure 1a)3. The content
of the PDMIBM is high enough to provide effective cross-linking after 30 s of UV irradiation, while the pH
sensitivity remains. While pH sensitive polymersomes usually disassemble upon acidification, ours show a
definite swelling, since the cross-linked membrane remains intact. This swelling is due to protonation of the
pH sensitive PDEAEM and completely reversible as well as reproducible, indicating a highly stable cross-
linking (Fig. 1b). Additionally, we were able to produce large structures with 150 µm in diameter using
electroformation. (Fig. 1c)
0 h
24 h
0 %
85 %
a b c
Figure 2: (a) Scheme of a pH dependent enzymatic reaction within an polymersome. Only at pH 6 substrate is able to
penetrate the polymersome membrane. (b) Cell viability after polymersome incubation at different concentrations. The
time indicates the amount of UV irradiation. (c) Cellular uptake studied via flow cytometry.
These vesicles provide a very good basis for a synthetic bionanoreactor. While the membrane is not open for
diffusion traffic in the basic state, small molecules are able to diffuse inside in an acidic state. Additionally,
they are non-toxic and show good cellular uptake into different cell types. Therefore, a bioactive protein
(myglobin) is incorporated into the vesicle. Only, if the membrane is made open for diffusion, the myoglobin
can react with substrate added to the solution. Therefore, an enzymatic reaction is observed at pH 6, but not
at pH 8 (Fig. 2a).
Since our polymersomes are designed for synthetic biology, we also examined their cellular toxicity and
uptake properties. We discovered a great dependence of the buffer used during polymersome crosslinking
and toxicity level. While polymersomes crosslinked in PBS buffer showed high levels of toxicity, no toxicity
was observed, if they are crosslinked in a phosphate-free environment. Under these conditions, cell
viabilities of 90 % and higher were obtained at low concentrations (0,02 mg/ml). However, once applied in
larger amounts, cell viability dropped considerably. This is due the positive charges evolving in the
membrane, once the polymersomes are taken up into an endosome. Since endosomes have a pH of 6.5 or
lower, the pH sensitive PDEAEM gets protonated, e.g. positively charged. To shield this positive charge
from the cells, we increased the crosslinking density by applying UV irradiation for a longer time. The non-
toxic PEG corona is now able to shield the positive charge of the pH sensitive PDEAEM (Fig. 2b). Once the
amount of crosslinking bonds was high enough, high levels of cell viability could be observed, also for large
concentrations of up to 0,4 mg/ml.. We were now able to study cellular uptake using flow cytometry and
polymersomes with marked cargo. This revealed polymersome uptake in 85 % of the cells after 24 h of
incubation (Fig. 2c).
Thus, we demonstrate that our system is capable as a non-toxic bionanoreactor for applications in synthetic
biology and may be the starting point in creating a synthetic organelle.
Acknowledgements. Financial Support of the Rosa-Luxemburg-Foundation and DIGS-BB is gratefully acknowledged.
References 1. Blanazs, S. P. Armes, A. J. Ryan, Macromol. Rapid Commun. 2009, 30, 267.
2. LoPresti, H. Lomas, M. Massignani, T. Smart, G. Battaglia, J.Mater.Chem. 2009, 19, 3567.
3. J. Gaitzsch.; D. Appelhans; D. Gräfe; P. Schwille; B. Voit; Chem. Commun. 2011, 47, 3466.
FORMATION OF THERMAL AND ELECTRICAL CONDUCTIVE PATH S IN EG-TPU COMPOSITES PREPARED VIA MELT MIXING AND FROM SO LUTION
Francesco Piana, Jürgen Pionteck
Leibniz-Institut für Polymerforschung Dresden e. V., Hohe Str. 6, 01069 Dresden, Germany; [email protected]
New special applications require conductive composites to match the mechanic properties of polymeric matrices with thermal and electrical conductivity of fillers1. Graphite is very cheap and available filler, whose structure can be easily expanded via thermal shock after oxidation2. The new high-porosity structure of EG is easier to disperse and it is possible to obtain a conductivity in the range of semiconductors with lower content of filler than using normal graphite3. As expected some mechanical properties are enhanced by introduction of EG, like hardness and storage modulus, others decrease like stress and strain at break4. For this reason it is needed to chose the right amount of EG to obtain the best performances and to have high conductivity with the lowest EG concentration. We prepared TPU-EG composites by three different methods: via melt mixing, from solution and by in-situ polymerisation using commercial expanded graphite and both commercial and self prepared TPU. Materials have been characterized by SEM, TEM, X-ray, and DSC to evaluate the dispersion of EG and variation on microstructure. Moreover, thermal, electrical and mechanical behaviors have been investigated. Acknowledgements. We are grateful for the support of the project by the Deutsche Forschungsgemeinschaft (DFG) and to SGL Carbon for providing the graphite. References
1. X. Wang, L.-J. Zhi, K Mullen, Nano Letters 2008, 8, 323. 2. B. Zhao, P. Liu, Y. Jiang, D.-Y. Pan, H.-H. Tao, J.-S. Song, T. Fang, W.W. Xu, Journal Of Power
Sources 2012, 198, 423. 3. K. Hyunwoo, Y. Mi, C. W. Macosko, Chemistry Of Materials 2010, 22, 3441. 4. A. Yasmin, J.-J. Luo, I. M. Daniel, Composites Science and Technology 2006, 66, 1182.
THERMORESPONSIVE SHAPE-MEMORY POLY(-CAPROLACTONE)
CROSS-LINKED BY SOL-GEL PROCESS
Massimo Messoria, Katia Paderni
a, Stefano Pandini
b, Simone Passera
b,
Francesco Pilatia, Theonis Riccò
b, Maurizio Toselli
a
aUniversity of Modena and Reggio Emilia, DIMA,Via Vignolese 905/A – 41125 Modena (Italy);
[email protected] bUniversity of Brescia, DIMI, Via Branze 32 – 25133 Brescia (Italy)
Introduction
Shape Memory Polymers (SMPs) are an emerging class of smart materials, capable of changing their shape
in response to an external stimulus, typically a thermal one. In recent years much interest has been focused
on SMPs for biomedical applications, such as smart medical devices and minimally invasive surgical
implantsa. In this work, an alternative method is proposed to synthesize SMPs under very mild conditions.
This method enables the synthesis of covalently cross-linked poly(e-caprolactone)-based (semi-crystalline
polymers starting from alkoxysilane terminated PCL via sol-gel processb. The melting transition is exploited
to activate shape recovery. Our approach permits to extrapolate affordable correlations among molecular
structure, degree of cross-linking and shape memory properties.
Materials
α,ω-Hydroxyl terminated poly(ε-caprolactone) with different number-average molecular weights (900, 2200,
3300 and 10900 gmol-1
, PCL_x in which x = 1, 2, 3 or 10 indicates the rounded molecular weight of the
polymer, respectively), 3-(triethoxysilyl)propyl isocyanate (ICPTS), tetrahydrofuran (THF), ethanol (EtOH),
water and hydrochloric acid (37%) were purchased from Sigma-Aldrich (Milan, Italy) and used as received
without any further purification.
Experimental
Synthesis of PCLs ethoxysilane terminated and their curing: PCLs triethoxysilane terminated (PCL_x_Si)
were obtained starting from PCL_x through bulk reaction with ICPTS at 130°C for 2 h. The subsequent
cross-linking of PCL_x_Si was carried out by means of sol-gel method: after complete dissolution of
PCL_x_Si in THF, EtOH (to favour miscibility), water (for the hydrolysis reaction) and HCl (as catalyst)
were added at the following molar ratios (with respect to ethoxide groups of PCL_x_Si): EtO-
:EtOH:H2O:HCl =1:1:1:0.01. The solution was then cast into a silicone mould to allow gelation, induced by
the formation of cross-linked silica domains after sol-gel reactions before solvent evaporation. The obtained
materials were coded as X-PCL_x_Si.
Degree of swelling and gel content: after curing, specimens having initial mass mo were placed in 20 ml of
THF at room temperature. The mass of the swollen specimen at equilibrium (ms) was determined after 24 h.
The solvent was then removed and the swollen specimens were subsequently dried at room temperature until
constant weight in order to determine the residual mass after extraction (md). The degree of swelling (Q) and
the gel content (G) were calculated according to the following equations:
Q 112
ms
md1
and
G md
mo
where ρ1 and ρ2 are the densities of the swelling solvent and PCL, respectively.
Thermal analysis: thermal properties were investigated by using differential scanning calorimetry (DSC) at a
heating/cooling rate of 20°Cmin-1
over the range -30/100°C by using a TA Instrument DSC 2010 purged
with nitrogen.
Shape memory behaviour: the method of bending testc was adopted to evaluate shape memory properties, in
terms of capacity to fix the temporary shape below the transition temperature, Ttrans, (related to the melting
temperature), ability to recover the permanent shape above the Ttrans and time necessary for full recovery.
Results and Discussion
Triethoxysilane terminated PCLs were prepared by bulk reaction of PCL diols with ICPTS (Figure 1). In
particular PCL diols with four different number-average molecular weights of 1000 (PCL_1), 2000 (PCL_2),
3000 (PCL_3) and 10000 gmol-1
(PCL_10) were used. FT-IR spectroscopy was used to follow the progress
of the reaction, while 1H-NMR was used to confirm the expected molecular structure of the products. Cross-
linking of alcoxysilane terminal groups was carried out by means of sol-gel method, as briefly described in
experimental section, and a scheme of hydrolysis and condensation reactions of alcoxysilane groups to
generate silica-like cross-linking points is reported in Figure 1:
QuickTime™ e undecompressore
sono necessari per visualizzare quest'immagine.
Figure 1: synthesis of the cross-linked networks starting from PCL diols
These polymers were able to show shape memory properties due to a suitable morphology consisting of
crystalline domains, that represent the molecular switches between the temporary and permanent shapes, and
chemical net-points, that permit the recovery. It was found that melting temperature, degree of crystallinity
and cross-linking density (related to gel content and swelling degree), all representing fundamental
parameters for defining shape memory properties, could be easily tuned by an accurate choice of the
molecular weight of PCL precursor.
Table1: thermal properties, gel content (G) and degree of swelling(Q) of cross-linked materials
X-PCL_x_Si Tm (°C) Degree of crystallinity (%) G (%) Q
X-PCL_1_Si Not present 0 89 2.1
X-PCL_2_Si 26 21 93 3.8
X-PCL_3_Si 42 30 82 4.3
X-PCL_10_Si 55 37 93 5.9
All the materials prepared showed good shape fixity at T<Ttrans also over long times with the exception of X-
PCL_1_Si. This material showed no melting transition indicating a complete inhibition of the crystallisation
process due to restrictions imposed by cross-linking. On the contrary, X-PCL_2_Si, X-PCL_3_Si and X-
PCL_10_Si samples exhibited an evident shape memory behaviour and the
time necessary to recover the permanent shape (trec) at T=Ttrans+20°C was found
to be strongly affected by the molecular structure, that is molecular weight of
the PCL precursors and, to a minor extent, the resulting cross-linking density.
The values of trec as a function the molecular weight of linear PCL precursor
are reported in Figure 2 from which a straightforward correlation is well
evidenced. The amount of cross-linking points, responsible of the shape
recovery phenomenon and the average molecular weight of PCL segments
between two adjacent cross-linking points represent the key parameter for
control of the shape memory behaviour.
Conclusions
A new method to synthesize SMPs exploiting sol-gel chemistry to cross-link alkoxysilane-terminated PCLs
has been reported. It permitted to obtain covalently cross-linked PCL-based SMPs, with Si-O-Si domains
behaving as net-points necessary for shape memory behaviour and to tune shape memory properties, such as
thermal transition range and the recovery time of the permanent shape, through an accurate design of the
molecular structure. The biodegradability and biocompatibility of PCL and the mild reaction conditions
required by the sol-gel process are further advantages that support the easy way proposed to synthesize
biomedical SMPs.
Acknowledgements The authors would like to acknowledge INSTM (Firenze, Italy) and Regione Lombardia for providing financial support
to the present research.
References
a. K. Paderni, S. Pandini, S. Passera, F. Pilati, M. Toselli, M. Messori (2012) J Mater Sci 47:4354
b. M. Messori, M. Toselli, F. Pilati, E. Fabbri, P. Fabbri, S. Busoli (2003) Surf Coat Int Part B: Coat
Transact 86:181
c. C.D. Liu, S.B. Chun, P.T. Mather, L. Zheng, E.H. Haley, E.B. Coughlin (2002) Macromolecules 35:
9868
Figure 2: trec as a function of
molecular weight of linear
PCL precursor
INVESTIGATION OF POSS NANOCLUSTERS FOR FIRE RETARDANCY OF HYBRID
THERMOSET POLYMERS
Suzanne Laika, Jocelyne Galy
a, Jean-François Gérard
a, Marco Monti
b, Giovanni Camino
b,c
a Université de Lyon, F-69003, Lyon, France ; INSA Lyon, CNRS, UMR 5223, Ingénierie des Matériaux
Polymères, F-69621, Villeurbanne, France
[email protected] b Proplast Consortium, Strada Comunale Savonesa 9, 15057 Rivalta Scrivia (AL), Italy
c Politecnico di Torino - Sede di Alessandria, V.le T. Michel 5, 15121 Alessandria, Italy
Abstract
Thermoset polymer composite materials, already used in many application domains, are particularly
developed in the transports sector. However, the poor fire resistance of most of the polymer matrices limits
their use for obvious safety and security issues. The present study aims at investigating how the fire
retardancy of hybrid epoxy networks can be improved by incorporating Polyhedral Oligomeric
Silsesquioxanes (POSS). The systems are based on a model epoxy matrix synthezided from DiGlycidylEther
of Bisphenol A (DGEBA) and 4,4′-Methylene bis-(2,6-DiEthylAniline) (MDEA) as curing agent, in which
1.5 inorg.wt.% of POSS is added. Several POSS have been selected, either non-reactive (ex: isoOctylPhenyl
POSS, OctaPhenyl POSS) or reactive (ex: GlycidylPhenyl POSS, N-PhenylAminoPropyl POSS,
TrisilanolPhenyl POSS). The fire retardancy and the thermal stability of the different networks were then
assessed by the UL-94 test and TGA, respectively. Their glass transition temperature was determined by
DSC and DMA. The morphology of the networks and the dispersion of the POSS were investigated by
means of SEM and XRD. The structure of POSS and the preparation of the networks, by governing the
POSS dispersion, are two important parameters influencing the flammability of the networks.
EPDM/SiO2 nanocomposites obtained by in situ generation of silica
Davide Morsellia, Massimo Messoria, A. S. Luytb and Federica Bondiolia aUniversità di Modena e Reggio Emilia, Via Vignolese 905/A, 41125, Modena, Italy;
[email protected] bUniversity of the Free State (Qwaqwa Campus), Private Bag X13, Phuthaditjhaba, 9866, South Africa
Introduction Carbon black is one of the most used reinforcing filler for rubbery materials, especially in the tyre industry. Nowadays silica (SiO2) nanoparticles represent one of the most interesting and alternative filler employed for reinforced elastomeric composites. Silica offers several advantages compared to the carbon black, such as whiteness, excellent tear strength, abrasion resistance, and heat build up reduction. One of the main drawbacks related to the use of nanometric silica, prepared ex situ by several methods, is the agglomeration of the inorganic grains within the matrix, due to the strong particle-particle interactions, which usually leads to high compound viscosity causing a difficult mixing and processing. Furthermore, the incompatibility between silica and elastomeric systems (such as ethylene-propylene diene monomer rubber (EPDM), styrene-butadiene rubber or natural rubber1) leads to poor filler-rubber interaction that is commonly improved by the use of coupling agents to preserve nanometric size of the filler and to obtain a good dispersion and distribution. In order to overcome the problems related to the incorporation of preformed fillers by mechanical mixing (ex situ process), an alternative and innovative approach may be the in situ generation of inorganic oxides (such as silica but also titania2, alumina, zirconia, etc.) by means of the sol–gel reactions, according to a bottom-up approach for the purpose of obtaining nanostructured organic–inorganic hybrid materials. Materials EPDM rubber (Polimeri Europa Dutral® TER 4038, density ρEPDM = 0.91 g·cm3) was kindly provided by ATG Italy (Castel d’Argile, BO, Italy). Tetraethyl orthosilicate (TEOS), dibutyltin dilaurate (DBTDL), dicumyl peroxide (DCP), ethanol (EtOH) and toluene were purchased from Sigma-Aldrich (Milan, Italy) and were used without further purification. Experimental EPDM/SiO2 nanocomposites were prepared by means of in situ generation of silica employing a hydrolytic sol-gel reaction (HSG). About 6 g of EPDM was dissolved in 100 ml of toluene; the right amount of sol–gel reagents (TEOS:H2O:EtOH:DBTDL, 1:4:4:0.04) was added to the solution previously obtained. The reaction was carried out in a round bottom flask at 80°C (in an oil bath) and under vigorous stirring for 6 hours. The suspension obtained was partially dried (around 50%) before the addition of the thermal–initiator (DCP, 2 phr). The remained suspension was cast into Petri dish and the volatiles were completely eliminated by maintaining the system under an aspiration hood overnight. Three nominal filler concentrations were prepared (5, 15 and 30 phr, respectively) and, as a comparison, the pristine rubber. The specimens (about 0.5 mm thick) were vulcanized under hot press at 160°C for 20 min. Results and Discussion The conversion of TEOS in SiO2 is practically 100% for all samples, in fact the actual and nominal content of silica are almost equal as shown in the thermal gravimetric analysis (TGA) data reported in Table 1. Scanning electron microscope (SEM) micrographs showed that the particles were uniformly distributed and
well dispersed without significant particle-particle aggregations (Figure 1) as expected by the bottom up approach for the filler synthesis. Equilibrium swelling analysis and extractable fraction were performed using toluene, in order to evaluate the qEPDM (swelling ratio) and fEPDM (absolute extractable fraction) as reported in Table 1 (both normalized to the EPDM weight). From swelling and extraction tests, it was possible to conclude that the in situ generation of silica particles by means of the sol–gel process, led to a hindering effect on the vulcanization process that limited the extent of the crosslinkings in the EPDM phase, as already observed for similar materials based on isoprene rubber3.
Figure 1 – SEM micrograph of sample with 5 wt% of silica (EPDM_5 as representative for all samples)
Table 1 – Compositions and properties of the prepared materials The tensile test results showed a remarkable increment of both stress at break (σb, reported in Table 1) and
initial elastic modulus (Ein) when the silica content increases, if compared to the unfilled rubber. The Ein values obtained by tensile tests were compared in Figure 2 to the calculated data by the well-known Smallwood-Guth-Einstein equation4. The gap found could be due to the structure effects (a filler aggregates into chair-like structures producing a greater stiffening) and to the introduction of additional physical cross-links into the network by the filler.
Figure 2 – Comparison between experimental initial elastic modulus values and calculated data by Smallwood-Guth-Einstein equation as a function of volume fraction In addition, the presence of SiO2 is also able to increase the E’ modulus of the rubber in the rubbery region (T=Tg+100°C) as clearly shown in DMTA curves reported in Figure 3 (values in Table 1); on the contrary the glass transition temperature (Tg) is not affected by the nanoparticles as also confirmed by differential scanning calorimetry (DSC, Table 1).
FFigure 3 – Storage modulus (E’) as a function of temperature evaluated by DMTA
Conclusions EPDM/SiO2 nanocomposites were prepared by means of in situ HSG that allowed obtaining very good dispersion and distribution of the filler within the matrix. The sol-gel reaction is not affected by the presence of rubber in the reaction mixture; this aspect leads to silica contents closed to the nominal one. When the amount of silica increases from 5% to the 30%, the samples showed many enhanced mechanical properties such as an increment of initial elastic modulus in the low deformation region and stress at break in the large deformation region. In conclusion, through the DMTA was found an increase of E’ in the rubbery region, trend in agreement with the tensile data at low deformation. References
1. M.Messori: In Situ Synthesis of Rubber Nanocomposites. In: V. Mittal et al. editors. Recent Advances in Elastomeric Nanocomposites. Advanced Structured Materials. Berlin: Springer-Verlag Berlin and Heidelberg GmbH & Co. K, 2011.p. 57 – 88.
2. D. Morselli, F. Bondioli, M. Sangermano, M. Messori, Polymer 2012, 53, 283 3. M Messori, M Fiorini Journal of Applied Polymer Science 2011, 119, 3422 4. G Kraus: In: G. Kraus editor. Reinforcement of elastomers. New York: Wiley, 1965.
Sample Code
SiO2 Nominal Content
(%)
SiO2 Actual Content (%)
by TGA
SiO2 Conversion
(%)
Volume fraction φ
(-) q (-) f
(%)
Tg by DMTA
(°C)
Tg by DSC (°C)
σb (MPa) E’
T=Tg+100°C (MPa)
EPDM_0 0 0.0 -- 0.00 3.0 5.3 -42 -50 1.57 1.89 EPDM_5 5 5.0 100 0.03 3.7 7.2 -43 -51 2.07 2.44
EPDM_15 15 15.0 100 0.17 4.3 8.5 -42 -51 2.32 2.94 EPDM_30 30 26.7 89 0.27 7.0 20.9 -41 -52 2.09 6.27
FABRICATION OF POLYMER AND POLYMER-BASED COMPOSITE NANOSTRUCTURES. A PRELIMINARY STUDY OF CRYSTALLIZATION PROCESS.
Jon MaizInstituto de Ciencia y Tecnología de Polímeros (CSIC), c/ Juan de la Cierva 3, 28006 Madrid;
and Carmen Mijangos
Introduction. In the last decade, there has been a great deal of research interest in the fabrication of nanostructured materials with nanometer scale periodicity. Such kind of structurally and dimensionally well-defined nanostructured materials is potential candidate for wide practical applications in optoelectronic, magnetic and electronic structures and devices1. Anodized aluminum oxide (AAO) has wide application as template for the preparation of polymer nanostructures of high-aspect-ratio nanopillars2-4. The formation process of AAO pores is well developed in oxalic, sulfuric and phosphoric acid solutions. The length and diameter of nanopores is easy to control in wide range of approximately 10 to 400 nm by varying electrolyte and electrochemical parameters like electrolyte concentration and anodizing voltage5. The aim of the present work is to deepen in the study of polymer properties under confinement, in particular the early stages of polymer crystallization. Experimental. Self-ordered AAO was prepared by the two-step anodization introduced by Masuda and Fukuda6. The Aluminium foil is first cleaned, degreased and electropolished. Subsequently, the aluminium foil is mounted on a copper plate serving as the anode and exposed to the acid in a thermally isolated electrochemical cell. Before proceeding with the second anodization step, the porous alumina is removed by a wet chemical etching (phosphoric and chromic acids solution). For the preparation of the Polyethylene oxide (PEO) nanotubes (dp = 400nm) the infiltration of the polymer is carried out by “precursor film” method into the nanopores at 105ºC for 60 minutes. The same method was used to infiltrate the Polyvinylidene fluoride (PVDF) and Polyvinylidene fluoride-single walled carbon nanotubes (PVDF-SWCNTs) nanostructures (dp = 25-300nm). Both polymers are melted on the surface of ordered porous alumina at 200ºC for 45 min8. All the prepared samples were morphologically characterized by scanning electron microscopy (SEM) (Philips XL-30 ESEM) as we can see in the figure 1.
200nm 1μm
a) b)
Figure 1. SEM micrographs of surfaces of prepared AAO templates; a) 35 nm and b) 300 nm in pore diameter.
The identification of the crystalline phase of the samples X-Ray Diffraction (XRD) were performed in a Bruker Advance D8 equipment by using CuKα radiation (λ=1.5418Å) . Raman spectra were collected using a Renishaw InVia reflex Raman microscope. The Raman scattering was excited with a 785-nm near-infrared diode laser. The calorimetric measurements of different samples are conducted in a Perkin Elmer 8500 Differential Scanning Calorimeter (DSC). Nonisothermal crystallization kinetics in the cooling mode from the molten state (melt crystallization) are carried out at 10 and 20ºC/min and isothermal crystallization tests were performed at different temperatures7. Results and Discussion. Raman spectroscopy is employed to investigate and to chemically characterize the distribution of SWCNTs within PVDF nanorods. Confocal Raman microscopy (CRM) is able to generate depth profiles with a ~4-5 μm spatial distribution resolution. The Raman spectrum of PVDF nanorods displays all the PVDF characteristic bands that can be observed up to depths of about 45 μm which corresponds to the AAO template thickness estimated from SEM. This result clearly confirms that the pores are completely and homogeneously filled with PVDF. In the PVDF-SWCNTs nanorods there are some
intense bands at 1375 cm-1 and 1575 cm-1, corresponding to the G and D bands of SWCNTs. The intensity of these bands changes on penetrating the interior of the material suggesting higher concentration of SWCNTs within the first 25 μm. Indeed at depths ≥ 25 μm the intensity of these peaks is still considerable suggesting that SWCNTs are present all along the PVDF nanorods. DSC experiments are carried out on bulk PEO and a sample of PEO nanotubes to study the crystallization and melting behaviour. Each sample is cooled from 110ºC to -60ºC at a constant rate of 20ºC/min. Then the sample is heated at same conditions that in the cooling sweep. We observe from these scans the exotherms and endoterms peaks of each sample. The DSC measurement of both samples shows no appreciable change in melting temperature (62ºC). Nevertheless bulk PEO crystallizes at low supercooling, that is at high temperature (43 ºC) and the sample of PEO nanotubes crystallizes at high supercooling, that is at low temperature (-8ºC) as we can see in the figure 2. The Avrami theory has been widely and successfully used for the interpretation of isothermal crystallization process. The Avrami exponent n depends on the growth geometry and the mechanism of the nucleation. The n values found to be between 1.6 to 2.1 for the bulk sample, and 1.1 to 1.2 for the PEO nanotubes.
0 40 80-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5 30 40 50 60 70 80-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
-20 0 20 40 60 80-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5 30 40 50 60 70 80-1,5
-1,0
-0,5
0,0
0,5
1,0
1,5
PEO nanotubes
PEO bulk
Heat flow
Endo u
p (m
W)
Temperature (ºC)
Figure2. Heat flow versus temperature during non-isothermal melts crystallization of a) bulk PEO and b) PEO
nanotubes at 20ºC/min both of them.
Conclusions. We have presented a simple and effective method for generating PVDF nanorods filled with SWCNTs and thanks to the confocal Raman spectroscopy technique a SWCNTs distribution gradient through polymer nanorods have been determined. In addition the crystallization of PEO appears to be strongly influenced by the confinement and the differences from the bulk behaviour which are related to the spatial confinement of the nanostructures. The crystallization temperature of PEO nanotubes in the nanoporous alumina is significantly reduced. XRD analysis shows that at room temperature the PEO in confined system is amorphous and the crystallization occurs at low temperature which gives different diffractions. Acknowledgements. This research project has been supported by CICYT MAT2008-1073 and MAT2011-24797. J. Maiz acknowledges support from FPI BES 2009-026632. References
1. R. J. Tonucci, B. L. Justus, A. J. Campillo, C. E. Ford, Science 1992, 258, 783. 2. J. Martín, C. Mijangos, Langmuir 2009, 25, 1181-1187. 3. J. Maiz, J. Sacristán, C. Mijangos, Chemical Physics Letters 2010, 484, 290-294. 4. M. Zhang, P. Dobriyal, J-T. Chen, T.P. Russell, J. Olmo, A. Merry, Nano Letters 2006, 6, 1075. 5. A. P. Li, F. Muller, A. Birner, K. Nielsch, U. Gosele, J. Appl. Phys. 1998, 84, 6023. 6. H. Masuda, K. Fukuda, Science 1995, 268, 1466-1468. 7. H. Duran, M. Steinhart, H-J. Butt, G. Floudas, Nano Letters 2011, 11, 1671. 8. J. Martín, J. Maiz, J. Sacristán, C. Mijangos, 10.1016/j. polymer.2012.01.028
15 nm
SMART BINARY POLYMER BRUSHES
RESPONSIVE SWITCHING OF WETTABILITY AND
FIXED MICROPHASE SEPARATION
Anja Rollberg, Petra Uhlmann*, Manfred Stamm
Leibniz Institute of Polymer Research Dresden, Department Nanostructured Materials, Hohe
Straße 6, 01069 Dresden, Germany [email protected]
For industrial coating processes it is necessary to develop materials that can be applied to a
surface in one step. To realize multifunctionality it is necessary therefore, to combine
different functionalities in one material or in our case in one molecule. The usage of polymer
brushes as smart coatings gives the opportunity for a responsive switching of the surface
properties. Our aim is the development of new block copolymers for a one step grafting-to
process as an effective preparation technique of binary polymer brushes.
The block copolymers were synthesized by controlled living radical polymerization,
especially via atom transfer radical polymerization (ATRP) and anionic polymerization. They
were characterized by SEC, NMR and IR measurements. The resulting polymers with a
narrow molecular weight distribution consist of a block responsible for the anchoring to the
substrate (P2VP, PGMA), a “hydrophilic” (PMAA, PAA) and a “hydrophobic” block
(PMMA, PS). This offers the possibility to combine switching wettability behaviour and the
anchoring to a substrate in one molecule. Silicon wafers were used as planar substrates for the
grafting-to process of these synthesized polymers. The wetting behaviour of the prepared
polymer brushes can be switched by external stimuli: temperature, pH-value, solvent
atmosphere, salt concentration etc. (figure 1). By usage of a selective solvent for the
“hydrophobic” block component, this polymer is stretching due to solvatisation and hence
determines the surface properties of the system, while the other block component collapses
leading to a “dimple” morphology of the film. Accordingly the polymer brush performs a
perpendicular phase separation. The characterization of the responsive polymer brush layer
was performed via ellipsometry (thickness) and contact angle (wetting and switching
behaviour) measurements. Additional, the immiscibility of the components of the amphiphilic
triblock copolymer results in a lateral lamellar microphase separation during the preparation
of the brush (figure 2). Because of the chemical bonding to the substrate (via the anchoring
block), the phase separation is fixed. Hence, the surface morphology is determined by the
microphase separation of the components and the conformation of the polymer brush itself. A
verification was done with atomic force measurements (AFM) and grazing incident small
angle x-ray scattering (GISAXS). We acknowledge funding by BMBF (project UltraSurf
02PU245).
Figure 1: switching principle of a binary (mixed)
polymer brush
Figure 2: height (left) and phase (right) AFM image of a
hydrophilic switched polymer brush layer on a silicon wafer
15.00
0.00
400 nm
0 100 200 300 4000
2
4
6
8
10
hei
gh
t z
[nm
]
distance [nm]
HIGH PERFORMANCE PEEK NANOCOMPOSITES
Leandro Casabana,b
, Antonio Iannonia, Andrea Terenzi
a, Miguel A. Lopez-Manchado
b, Jose M
Kennya,b
aUniversity of Perugia,Strada di Pentima 4, 05100 Terni, Italy; [email protected] bPolymer Science and Technology Institute, Juan de la cierva 3, 28006 Madrid, Spain
Poly(ether ether ketone) (PEEK) is a high performance thermoplastic polymer with an aromatic backbone.
PEEK has been used in military, aerospace and chemical industry. It is a crystalline polymer with a melting
point around 343ºC and a glass transition temperature around 145ºC. It has outstanding mechanical and
chemical properties, such as elastic modulus of 3.6GPa and tensile strengths of 100MPa1, solvent and
abrasion resistance2–5
, and it can persist for long time under 250ºC6.
Since the discovery of the carbon nanotubes and graphenes, several reports have been published where these
materials were used as nanofillers to improve the electrical, mechanical or thermal properties of the polymer
matrices. These materials present remarkable properties, like elastic modulus of 1TPa and elastic strengths of
150GPa7,8
.
A small number of studies have been made with nanofillers and high-performance polymers, and fewer
studies have been made to compare the effect of the loading type within the matrix. The aim of this work is
to analyse the influence of different nanofillers in PEEK-based nanocomposites: graphenes, multi-wall
carbon nanotubes (MWCNT) and carbon nanofibres (CNF).
Poly(ether ether ketone)/nanofiller composites were prepared by melt-compounding using a twin screw co-
rotating extruder.
Typical concentrations of the nanofillers were: Graphenes: 0.1%, 0.5% wt
Carbon nanotubes: 0.1%, 0.5%, 1% wt
Carbon nanofibres: 0.1%, 0.5%, 1% wt
The resulting materials were characterized by scanning electron microscopy (SEM), differential scanning
calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA).
a) b) c)
Figure 1. SEM images of neat PEEK (a), 0.5wt% graphene (b) and 0.5wt% CNT (c).
After analysing the results obtained, it can be concluded that the fillers does not modify the melting or the
crystallization temperature of the resulting composites. However, the crystallization temperature slightly
tends to increase with higher filler content for carbon nanotubes and carbon nanofibres. The thermal stability
of the resulting composites depended on the type of filler, addition of graphene into the polymeric matrix
does not alter the thermal stability. Addition of carbon nanotubes or carbon nanofibres diminished the
degradation temperature of composites.
(1) Gensler, R.; B�guelin, P.; Plummer, C. J. G.; Kausch, H.-H.; M�nstedt, H. Polymer Bulletin 1996, 37, 111-
118.
(2) Blundell, D. J.; Osborn, B. N. Polymer 1983, 24, 953-958.
(3) Díez-Pascual, A. M.; Naffakh, M.; Gómez, M. A.; Marco, C.; Ellis, G.; Martínez, M. T.; Ansón, A.; González-
Domínguez, J. M.; Martínez-Rubi, Y.; Simard, B. Carbon 2009, 47, 3079-3090.
(4) Deng, F.; Ogasawara, T.; Takeda, N. Composites Science and Technology 2007, 67, 2959-2964.
(5) Sandler, J.; Werner, P.; Shaffer, M. S. P.; Demchuk, V.; Altstädt, V.; Windle, A. H. Composites Part A: Applied
Science and Manufacturing 2002, 33, 1033-1039.
(6) Jones, D. P.; Leach, D. C.; Moore, D. R. Polymer 1985, 26, 1385-1393.
(7) Lee, C.; Wei, X.; Kysar, J. W.; Hone, J. Science 2008, 321 , 385-388.
(8) Yu, M. Science 2000, 287, 637-640.
Nanostructured polyurethane-clay clear coatings with enhanced performance properties: an inspiration from the ancient ‘Maya Blue’ paintings
Gaurav Vermaa, Anupama Kaushika, and Anup K Ghoshb,
a University Institute of Chemical Engineering & Technology, Panjab University, Sector 14 Chandigarh, India.; [email protected], [email protected]
b Centre for Polymer Science & Engineering, Indian Institute of Technology, IIT Delhi, Hauz Khas New Delhi, India
Introduction Maya blue pigment is a composite of organic and inorganic constituents, primarily indigo dyes combined with palygorskite, a natural clay1. Despite time and the harsh weathering conditions, paintings colored by Maya Blue have not faded over time. What is even more remarkable is that the color has resisted chemical solvents and acids since 6th century. It thus inspires to prepare protective coatings using clay as a nano-reinforcement with improved barrier & surface properties. Hence nanocomposite coatings using clay in low loadings (e.g. 2 weight %) was prepared to improve a clear polyurethane formulation. These nanostructured coatings have a potential to be used in preserving ancient sculptures & paintings from degrading due to ever-changing environmental conditions. We present here this novel idea to counter detrimental environmental conditions especially sunlight and moisture which are a constant threat to the ancient heritage. Materials and Methods A two pack polyurethane (PU) coating formulation consisting of a binder: hydroxyl polyester (Desmophen 680BA~D680) and a hardener: an isocyanate trimer (Desmodur 3390BA~D3390) is modified by organoclay (Cloisite 30B~C30B) in low loadings (0-5 wt%). Raw material for PU has been procured from Bayer Materials, Germany while Cloisite 30B was procured from Southern Clay Products, USA. Experimental PU-clay coatings were prepared as per detailed processing procedure mentioned elsewhere2. The processing protocol consisted of a combination of sonication, high shear homogenizing and low-speed mechanical stirring devices. The prepared formulations were spray coated onto various substrates for further characterisation3. TEM (Hitachi H-7500) was carried out on C30B/D680 dispersions, while an AFM (Veeco Bioscope II) tip was tapped on surface of the solid coatings deposited on a glass substrate. XRD (Philips X-Pert Pro) also evaluated the state of dispersion. After ascertaining the morphology and structure of the samples, gloss (Sheen T160), mar resistance (Sheen) and FTIR-ATR (Perkin Elmer) were done to characterize the properties. Performance was evaluated by subjecting the coatings to 1000 hours of Ageing (QUV Q-panel) tests. FTIR-ATR and CIElab (GretagMacbeth CE7000A) parameters assessed the damage done due to ageing. The results are discussed for pristine PU and 2wt% nanocomposite PU coatings only (PU2C30B). Results and Discussion TEM analysis shows exfoliated platelets of C30B in Figure 1. This nanostructure inside the bulk of the coatings acts as a barrier to etching solvents and even moisture4. Figure 2(inset) shows XRD diffractograms of PU, C30B and PU-2wt%C30B coating samples. The inherent peak at 2θ= 4.78° for C30B is observed, corresponding to a basal spacing of d001=18.5A°, which almost completely disappears in the nanostructure sample indicating delamination of platelets as also observed through TEM. AFM images show the change in surface morphology of PU (Figure 2) due to addition of C30B. The surface tends to form nanostructured barracks (~60nm) under influence of C30B. These barracks not only reinforce the PU matrix but may also act as a protective shield against any external degrading stimulus.
Table 1 shows the comparative surface properties of the samples. The reduction in gloss is insignificant (~3%) while improvement in mar resistance is considerable (~31%). Gloss reduces because of increased surface roughness which has been measured through the AFM Nanoscope Realtime software.
Figure 1. TEM image. Figure2.AFM image(5x5μm) of PU & PU-2wt%C30B. Inset: XRD diffractograms. The increase in mar-resistance can be ascribed to the reinforcing effect of C30B which resists plastic deformation on the surface. In addition to this the presence of nanosized barracks on the surface may also contribute to this increased resistance. Figure 3 shows the comparative IR of coatings before and after ageing. PU-2C30B clearly shows better preservation of urethane structure and lesser tendency to get oxidised. Again C30B platelets act as a barrier to the combined UV/H2O attack in the QUV chamber. The nano barracks also may act as a blockade against the water molecules and UV rays.
Figure 3 Comparative IR of unaged and aged (X) samples. CIELab scale assesses the yellowing due to ageing through calculation of Δb* parameter5. Table 1 shows that PU2C30B has decreased the yellowing due to degradation indicating lesser damage versus PU. Thus both IR and Δb* studies indicate better anti-ageing characteristics in PU2C30B. Conclusions C30B acts as reinforcing filler which modifies the nanostructure of PU coatings thus giving it better performance attributes versus pristine PU. The nanoscale structure of C30B ascertained through images resembles the fillers used in ‘Maya Blue’, and thus the idea is inspired from the ancient technology. References 1. F.A. Bergaya, Microporous & Mesoporous Materials 2008, 107, 141. 2. G. Verma, A. Kaushik, A.K. Ghosh, submitted to Journal of Plastic Film and Sheeting 2012. 3. ASTM standard D823 - 95(2007), “Standard Practices for Producing Films of Uniform Thickness of Paint, Varnish, and Related Products on Test Panels”, ASTM International, West Conshohocken, PA, 2007, DOI: 10.1520/D0823-95R07, www.astm.org. 4. C.S.Chou, E.E. LaFleur, D.P. Lorah, R.V. Slone, K.D. Neglia US Patent 6,838,507: 2005. 5. C. Decker, K. Zahouily, Polymer Degradation & Stability 1999, 64, 293.
500
1000
1500
2000
2500
3000
3500
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wavenumbers [1/cm]
trans
mitt
ance
/ int
ensi
ty
PU2C30BX
PU2C30B
500
1000
1500
2000
2500
3000
3500
-0.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Wavenumbers [1/cm]
trans
mitt
ance
/ int
ensi
ty
PUX
PU
0
Rel
ativ
e In
tens
ity
Position [°2Theta] (Copper 4 6 8 10
PU-2C30B
PU
C30B
PU-2C30B PU
100 nm
Table 1 Performance properties Samples PU PU2C30B
Gloss units 95.45 92.57
Mar (g) resistance
1600 2100
CIELab Δb*
9.365 7.865
Nanosized barracks
Synthesize and Characterization of Novel Poly (Xylitol-co-Adipate)/Hydroxyapatite Composites
TuckWhye Wong1, Mat Uzir Wahit
1*, Mohammed Rafiq Abdul Kadir
2,
Munirah Moktar1, A.A. Yusuff
3, WengHong Tham
1
1Department of Polymer Engineering, Faculty of Chemical Engineering,
Universiti Teknologi Malaysia, Skudai 81310, Malaysia
2Department of Biomechanics & Biomedical Materials, Faculty of Biomedical Engineering & Health Science,
Universiti Teknologi Malaysia, Skudai 81310, Malaysia
3Petroleum Research and Studies Center, Kuwait Institute for Scientific Research, Kuwait
* [email protected], Tel.: + (6)07-5535909; Fax: + (6)07-5588166
Abstract
Novel poly (xylitol-co-adipate) (PXA) was successfully prepared via a simple catalyst-free condensation reaction
between xylitol and adipic acid. Hydroxyapatite particles (HA) were added to enhance the mechanical properties
of PXA and to potentially induce osteoconductivity. FTIR analysis revealed that both pure polymer and
composites contained the same amount of ester bonds and that no chemical interaction took place between PXA
and HA. DSC results showed the lowering of Tg of the composites as HA content increased. The Young’s
modulus and tensile strength significantly improved but elongation at break gradually decreased with increasing
HA content. Interestingly, all composites remained flexible despite increased HA content.
Keywords: Polymeric Composites; Elastic Properties
TRANSPARENT AND SUPERHYDROPHOBIC COATINGS FROM ORGANOSILICA
Raquel de Francisco, Nuria García. Pilar Tiemblo. [email protected]
Instituto de Ciencia y Tecnología de Polímeros (CSIC), Juan de la Cierva 3, 28006 Madrid. Spain.
A surface that exhibits a water contact angle 150º or greater and where droplets roll off easily is considered to be superhydrophobic. Surfaces with both superhydrophobic1,2 behaviour and high transparency would be very desirable for applications such as self-cleaning windows and paints, anti-fogging and anti-icing surfaces. The wetting behaviour is dependent on both the surface chemistry (surface energy) and surface topography (physical roughness).However surface roughness and transparency are competitive properties. Thus, topographical features out of the size range of visible light wavelength3 are necessary to obtain transparent coatings. With this aim in mind, superhydrofobic coatings have been achieved taking advantage of the fractal structure of Aerosil 200 nanosilica to introduce the necessary roughness and modifying surface energy of silica with appropriated hydrophobic reagents. We report in this work the preparation of highly transparent superhydrophobic coatings of nanosilica particles coated with PDMS chains of different lengths. The surface of silica nanoparticles has been modified using two different methods.
Chemisorption: PDMS chains were grafted onto the nanoparticles surface using p-toluenesulfonic acid as the catalyst in toluene reflux4.
Physisorption: Simple blends of PDMS and silica in toluene. These as-modified particles were dispersed in ethanol and isopropyl alcohol. Subsequently these suspensions were used to prepare the final coatings on glass support by spin coating. Characterization of the organic loading and structure has been carried out by microanalysis, BET surface, 29 Si and 13C CP/MAS NMR and thermogravimetric analysis. The organosilica aggregate size in ethanol and isopropyl alcohol has been analyzed by dynamic light scattering (DLS).The surface structure and properties of these coatings were evaluated by water contact angle measurements, AFM imaging and SEM. The optical transparency of the glass substrates was analyzed. The results show an effective incorporation of PDMS chains onto silica surface, and a dependence of the nanosilica aggregate size on both the method of preparation, the solvent used to prepare the coatings and on the time elapsed between the preparation of the modified nanoparticles and the preparation of the coating. By controlling these three experimental factors it is possible to obtain small hydrophobic nanosilica aggregates which enable the preparation of highly transparent superhydrophobic coatings. .In both cases, an evolution of the surface structure with time has been observed.
Figure1: Image of transparent superhydrophobic coating.
Acknowledgements. We acknowledge financial support from the Spanish Science and Innovation Ministry (MAT2008-06725-C03-01) and CSIC (JAE-Doc grant to R.d.F) References.
1 Zhang, X.; Shi, F.; Nit, J.; Wang, Z. J. Mater. Chem. 2008, 18, 621. 2 Shirtcliffe, N.J.;McHale, G.; Newton, M.I. Polymer Physics 2011, 49, 1203. 3 Levkin P. A. ; Svec F. ; Fréchet J. M. Adv. Funct. Mater. 2009, 19, 1993. 4 García, N.; Benito, E.; Guzmán, J.; Tiemblo, P. J. Am. Chem. Soc.2007, 159, 5052.
GRAPHENE NANOPLATELETS AS CONDUCTIVE FILLERS FOR STRAIN SENSING IN EPOXY NANOCOMPOSITE
Marco Rallinia, Leonel M. Chiacchiarellia, Maurizio Natalia, Debora Pugliaa, José M. Kennya,b, Luigi Torrea
aUniversity of Perugia, Civil and Environmental Engineering Department, Strada di Pentima 4, 05100 Terni
(Italy); [email protected] bICTP-CSIC, Juan de la Cierva 3, 28006 Madrid, Spain
INTRODUCTION In the last decade, the study of carbon-based fillers, such as carbon nanotubes, became more and more important
because of the extraordinary properties they confer to the matrix in which they are embedded. However, the use
of these nanofillers is often limited by the cost, their anisotropy and the high viscosity of the systems in which
they are dispersed. Consequently, graphene nanoplatelets (as one or more layers) assumed a relevant role as a
valid substitute of carbon nanotubes because they show the same properties with a lower viscosity of the blends
and a lower cost1,2
. Particularly it was demonstrated3,4
that it is possible to obtain a polymeric nanocomposite
with enhanced electrical conductivity using exfoliated graphite instead of carbon nanotubes. These conductive
materials can be employed in all the applications in which detecting the presence of strain accumulation and
even the presence of any damages it is very important. A non-invasive and an inexpensive way to monitor
damages is based on the use of a conductive coating on the external skin of the material. In this way the
conductive strip can act as a detector of deformation also in fiber-reinforced composites with non-conducting
fibers. So in this work we investigated the possibility to use graphene nanoplatelets (GNPs) as a filler for epoxy
nanocomposites in order to develop a conductive plastic material. This conductive nanocomposite was applied as
a paint to the surface of a fibre reinforced composite material. The experimental results confirmed that the paint
can act as a sensor and it is able to detect conductivity variations during the deformation also at low strain
values.
MATERIALS AND METHODS GNPs were added to chloroform (CHCl3) (2 mg/ml) and the suspension was sonicated with an ultrasonic tip in
an ice bath for 1 hour with an amplitude of ultrasonic waves of 40 %. Epoxy monomer (Epikote 862), kindly
supplied by Hexion, was added to the suspension and the new mixture was further sonicated for 1 hour with an
amplitude of 30 %. The sonicated mixture was stirred with a magnet on a hot plate to remove solvent and then
Diethyltoluenediamine (DETDA) was added as hardener (26.4 phr). A GNPs concentration of 2 % wt was
chosen, according to previous results obtained studying the electrical percolation of GNPs in the selected epoxy.
The reactive system was used to paint a 50 mm long and 6 mm wide area on the surface of carbon fibre/epoxy
specimens for flexural tests previously electrically insulated with acrylic paint. The thickness of the conductive
paint was about 0.6 mm. In this study, the mechanical behaviour of the materials was observed simultaneously
with the electrical resistance, in order to check if it is possible to correlate the presence of a tensional state or a
damage, with an increase of electrical resistance. In all cases, a Keithley electrometer, model 6517B, was
employed to measure electrical resistance. Two aluminium electrodes were glued at the end of a conductive
strip. A voltage of 100 V was applied trough the electrodes and the fibre reinforced specimen was subjected to a
flexural load (three-point bending) up to fracture monitoring the resistance variation. The specimen was also
tested with cyclic flexural loads. In each flexural cycle, the amount of deformation was increased maintaining
the materials in the elastic range and avoiding the fracture of the film or of the fibre reinforced composite. The
change in conductivity was monitored during the cycles and the electrical resistance variation was calculated.
RESULTS
Observing Figure 1, it is possible to see how the mechanical failure of the sample obviously corresponds to a
strong increase of electrical resistance, due to the breakage of the continuity of the material, involving both the
fracture of the composite material and the rupture of the paint. These simultaneous events can be detected as two
breaking events in the mechanical and electrical profiles.
The cyclic deformation (load-unload tests in Figure 2) clearly demonstrated that this coating can be successfully
applied for detection of relatively small deformations of the material. The increase of ∆R/Ro as a function of
time during the loading phase can be modelled using a theoretical function that does not change with the
growing value of load in the elastic limit of deformation and that takes in account the changes in the inter-
particle distance and the destruction of the conductive network among GNPs during the deformation.
CONCLUSIONS GNP has turned out to be a very interesting tool to modify electrical properties of a thermosetting matrix that can
be exploited as a tool for strain and damage sensing, especially in applications in which the constant knowledge
of the health status of the material is a key factor for its use, for example in structural applications.
Figure 1. Load (N) and resistance variation (%) as a function of time in a static flexural test.
Figure 2. Load (N) and resistance variation (%) as a function of time in cyclic flexural test (1 mm/cycle for a maximum
value of 7 mm ).
REFERENCES
1. I. Zaman, T.T. Phan, H. Kuan, Q. Meng, L.T. Bao La, L. Luong, O. Youssf, J. Ma, Polymer 2011, 52, 1603-1611.
2. M.A. Rafiee, J. Rafie, Z. Wang, H Song, Z. Yu, N. Koraktar, ACS Nano 2009, 3, 3884-3890.
3. S. Biswas, H. Fukushima, L.T. Drzal, Composites: Part A 2011, 42, 371-375.
4. K. Hyunwoo, A. A. Abdala, C. W. Macosko, Macromolecules 2010, 43, 6515-6530.
NANOSTRUCTED POLYMERS BASED ON EPOXY RESIN:
NONAQUEOUS SOL-GEL PROCESS
S. Ponyrko, J. Plestil, M. Pekarek, L. Matejka
Institute of Macromolecular Chemistry AS CR, v.v.i.
Heyrovsky Sq. 2, 162 06 Prague 6, Czech Republic
Organic-inorganic hybrids with silica nanostructures have been prepared and studied.
Non-aqueous synthesis of nanosilica in diglycidyl ether of bisphenol A epoxy (DGEBA) resin
has been successfully achieved by the sol-gel process. Boron trifluoride monoethylamine
(BF3MEA) was proved to be an effective catalyst for the in-situ formation of nanosilica in
epoxy network under thermal heating process.
The DGEBA type epoxy was modified by different coupling agents in order to enhance
silica-epoxy interfacial interaction and to improve mechanical properties. Epoxy resins were
cured with different amines including oligomeric diamines (Jeffamines), aromatic diamine
diaminodiphenylmethane (DDM) and cycloaliphatic 3,3'-dimethyl-4,4'-
diaminocyclohexylmethane (Laromin C260). We have proved a significant increase in shear
storage modulus in rubbery state and glass transition temperature of the studied hybrid epoxy
networks.
Hexamethylenediisocyanate was used for the tailoring shape memory properties for
epoxy-resins.
The structure, morphology, chemorheology and mechanical properties were followed by
FTIR, SAXS, TEM and DMA.
Acknowledgement: The authors thank the Academy of Sciences of the Czech Republic in the
frame of Program for international cooperation, Project Nr. M200500903 for financial
support of this work.
Keywords: epoxy-silica nanocomposite, boron trifluoride monoethylamine, tetraethoxysilane,
shape memory polymer.
CARBON NANOTUBES MODIFIED CFRP FOR IMPROVED RESIN CONTROLLED PROPERTIES OF
AEROSPACE COMPOSITE STRUCTURES
Mathieu Fogela, Hans Luingea, Anne-Lise Maillot a EADS Innovation Works, Composites Technologies, 81663, Munich, Germany
e-mail: [email protected]
Over more than 30 years, the use of Carbon Fiber-Reinforced Polymers (CFRP) in the aerospace industry has been significantly increasing. Almost insignificant 40 years ago, it now represents around 50 % of the total amount of materials implemented in developing projects currently carried out, such as the Airbus A350.
Fig. 1 Amount of composite materials in various aircrafts
Carbon fiber-reinforced polymers have gained popularity over the years, replacing traditional metallic-based structures due to the fact that they offer a better mechanical properties/weight ratio, allowing manufacturers to reduce the weight-per-passenger ratio of their aircrafts. As a result, fuel consumption is reduced; flight range and payload are increased and the environmental balance is improved.
However by replacing metallic structures with CFRP some inherently integrated electrical functions are lost: lightning strike protection, systems bonding, grounding and electrical discharge. This is why a dedicated Electrical Structure Network (ESN) has to be implemented to ensure these properties, causing a weight penalty.
The aim of this work is to enhance the damage tolerance of the CFRP material and to increase the electrical conductivity in the transverse direction in order to reintegrate some of these ESN functions in the CFRP material. This study focuses on CNT modification of the preform prior to infusion. Since their discovery in 1991, Carbon Nanotubes (CNT) have attracted attention due to their extraordinary mechanical and electrical properties [1]. Some significant improvements in resin systems have already been reported in literature [2].
In this work, we focused our attention on commercially available epoxy matrices and non-crimp carbon fabric, as well as on commercially available carbon nanotubes (MWCNTs) regarding nanofillers. CRFP Plates were manufactured using the EADS patented Vacuum Assisted Process (VAP). Morphology of the composite is being observed using SEM images. The mechanical characterization of the material is being carried out using GIc/GIIc and ILSS testing.
Fig. 2: CFRP interlayer with a high carbon nanotubes load.
A good dispersion of the CNTs in the epoxy resin has already been achieved with commercially available carbon nanotubes and we compared their influence on CFRP made of non-crimp fabrics and epoxy resin. However, the resulting increase of the viscosity does not allow using infusion processes for the production of CFRPs.
We present a route towards the incorporation of CNTs in C-fiber materials which overcomes the processing difficulties. The CNTs are introduced in the dry preform between the NCF layers and the whole assembly is then infused using the VAP process with neat resin. In this way laminates can be successfully infiltrated.
We will present the results on the electrical conductivity as well as on the mechanical performance of these CNT modified composites, in terms of fracture toughness and impact resistance.
References
[1] B. Fiedler et al., Fundamental aspects of nano-reinforced composites, Composites Science and Technology, 66, 3115–3125 (2006)
[2] F. Marcq et al., Carbon Nanotubes and Silver Flakes Filled Epoxy Resin for New Hybrid Conductive Adhersives, Microelectronics Reliability 51, 1230-1234 (2011)
“CLICK”-CHEMISTRY AS A POWERFUL TOOL FOR POST-POLYMERIZATION MODIFICATION OF SUBSTITUTED POLYACETYLENES
Radoslava Sivkova, Jan Sedláček, Jiří Zedník and Jiří Vohlidal
Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030/8, Prague 2, Czech Republic, CZ-12843
Conjugated polymers are permanently subject of materials research due to the fact that their properties
are suitable for various practical applications. Polyacetylenes are probably best known subclass of conjugated polymers. Their functional properties can be tuned through: a)the configurational structure of main chains, and b)the introduction of substituents favorably affecting their electrical, optical and other properties towards the desired function. One of the possible approaches of introduction of functional group to polymer backbone is the 1,3-dipolar Huisgen cycloaddition of the ethynyl and azide group catalyzed by copper(I) salt which takes place under mild conditions and is therefore ranked among the click reactions. This highly selective reaction is tolerant to many types of functional groups and already has been successfully used for modification of polymers including PDAs (for the introduction of chromophore and organometallic side groups). Thus, it may potentially be used to introduce fluorophores into PDA chains.
In this contribution we report the combination of polyacetylene and Huisgen-type chemistry for the preparation of new PDAs that contain a newly designed 1,8-naphthalimide fluorophore bound as a pendant to the PDA chains.
~ ~
Cl
~ ~
N3
~ ~
N
NN
NN
samples A samples B samples C
NaN3, DMF40 °C, 24h
PN, CuI, DMF
40 °C, 4hpiperidine
Scheme 1. Synthetic route for polyacetylenes
The two step post-polymerization modification of statistical copolymers of 1-phenylhex-1-yne and 1-(4-
tert-butylphenyl)-6-chlorohex-1-yne consisting of the exchange of Cl atoms of pendant groups with N3 groups and subsequent Huisgen “click” reaction of N3 groups with ethynyl groups of a new fluorophore: N-(prop-1-yne-3-yl)-4-(piperidine-1-yl)-1,8-naphthalimide (PN) has been performed as a feasible method for the preparation of PDAs with significantly increased fluorescence efficiency. The polymer-modification strategy used represents a synthetic path that generally allows incorporation of a group that is not compatible with polymerization catalyst to chains of conjugated polymers such as PDAs.
Fluorescence properties of the PN fluorophore remained preserved after binding PN to PDA chains with a small decrease in the fluorescence quantum yield. The observed convergence of fluorescence characteristics of linked PN fluorophores toward those of the free PN molecules at increasing content of PN species in PDA can be ascribed to the increasing conformational rigidity of PN-rich chains. The time-resolved fluorescence measurements indicate a participation of the excitation-energy transfer from PDA main chains to pendant PN groups in the overall fluorescence process. Acknowledgement: Financial supports from Ministry of Education of Czech Republic (MSM002160857), Czech Science Foundation (Project No. 104/09/1435) are gratefully acknowledged.
THERMOREVERSIBLE POLYURETHANE NETWORKS VIA DIELS-ALDER
REACTION
Nidhal OKHAYa, Nathalie MIGNARD
a, Corinne JEGAT
a and Mohamed TAHA
a
a Université de Lyon, F-42023, CNRS, UMR 5223, IMP@UJM, Université de Saint Etienne, Jean
Monnet, F-42023, Saint Etienne, France
Introduction
Recently, the interest in self-healing and thermosensitive polymer networks is growing. One of the
concepts used in order to obtain such polymers is the use of thermoreversible reactions1: Under the
effect of temperature, a network can be dissociated giving monomers, oligomers or branched
polymers. One of the most investigated reactions used to achieve such materials is the Diels-Alder
(DA) cyclo-addition2,3,4
. The use of DA cycloadditions, most specifically those between various
maleimide and furan derivatives, was facilitated by both the commercial availability and chemical
accessibility of these functional groups5.
In this study, furan (or maleimide) functionalized polyurethane (PUR) were first prepared, then their
crosslinking achieved via reaction with maleimide (or furan) based coupling agent. The obtained
networks were thermosensitive and had self-healing and shape-memory properties.
Materials and methods
4,4'-Methylenebis(cyclohexyl isocyanate), furfuryl alcohol (98%), maleic anhydride, nickel (II)
acetate, acetic acide, triethylamine, diethylene glycol, glycerol, furfuryl glycidyl ether, hexamethylene
diamine, furfuryl amine, triethylene tetramine and different solvents (THF, Chloroform, DMF, and
ethanol) were purchased from SIGMA ALDRICH. 1,6-diaminohexane was purchased from ACROS
ORGANICS.
JEFFAMINE T-403 (average molar weight of 440g.mol-1
) used for the synthesis of the coupling agent
was offered by HUNTSMAN.
Rheological studies were conducted in an ANTON PAAR rheometer using parallel plate geometry
(25mm). The experiments were conducted within the linear viscoelastic regime under the dynamic
oscillation mode at a 1 rad.s-1
frequency. The gap between plates was maintained at 2 mm.
Experiments were run from 150 °C to 60 °C at a constant 1 °C min−1
cooling rate then heated at the
same rate from 60°C to 150°C.
Experimental
Networks were prepared from stoechiometric quantities of functionalized polymer and coupling agent.
The two constituents were first dissolved in chloroform until homogenization. Then, the solvent was
evaporated and the obtained thin film was heated in an oven before cooling to room temperature.
Results and discussion
First, functionalized PUR were synthesized and characterized. 1H NMR was used to calculate the
average functionality of polymers. Three different functionalities (3, 4, 7) were obtained for each
polymer (furan functionalized PUR (PUR-F) and maleimide functionalized PUR (PUR-M)). The
thermal properties of these polymers were determined by Differential Scanning Calorimetry (DSC)
and thermogravimetric analysis (TGA).
The obtained polymers then reacted with different coupling agents (maleimide based coupling agents:
BMI (bismaleimide) and TMI (trimaleimide) and furan based coupling agents: TF (trifuran), TEF
(tetrafuran) and HF (hexafuran). The obtained networks were firstly characterized by solubility tests in
DMF (Figure 1). At room temperature, the network remained insoluble (Figure 1 (b)). When the
sample was heated to 130°C it became soluble. That means that the crosslinking is reversible. This
result was confirmed by rheological tests. Indeed, we can observe a cross-over between G’ (storage
modulus) and G” (loss modulus) between 80°C and 95°C. This temperature appeared to depend on the
system studied.
Figure 1. Solubility tests in DMF: (a) PUR-F without crosslinking at room temperature, (b) PUR-F crosslinked
with TMI at room temperature, (c) specimen (b) at 130°C
Thermosensitive PUR networks were identified as shape-memory and self-healing polymers after a
thermal treatment involving DA-retro-DA thermoreversible reaction.
Conclusion
The use of Diels-Alder reaction to form thermoreversible PUR networks was investigated. A
reversible network was obtained by mixing furan (or maleimide) functionalized PUR with maleimide
(or furan) based coupling agent. The reversibility was confirmed by solubility tests and rheology in
melt. New characteristics were conferred to PUR: shape-memory and self-healing.
References
1. A. Gandini, A.J.D. Silvestre, D. Coelho, J. Polym. Sci. P A: Polym. Chem. 2010, 48(9), 2053
2. X. Chen, M. A. Dam, K. Ono, A. Mal, H. B. Shen, S. R. Nutt, K. Sheran, F. Wudl, 2002, 295, 1698
3. M. Reinecke, H. Ritter, Makromol. Chem. 1993, 194, 2385
4. N. Okhay, C. Jegat, N. Mignard, M. Taha, submitted 2012
5. A.J. Inglis, L. Nebhani, O. Altintas, F.G. Schmidt, C. Barner-Kowollik, Macromolecules 2010, 43, 5515
(a) (c) (b)
EFFECT OF CARBON NANOFILLERS ON PU FOAMING FROM A CHEMICAL AND
PHYSICAL PERSPECTIVE
M.Mar Bernala, Mario Martin-Gallego
a, Laura J. Romasanta
a, Samuel Pardo-Alonso
b, Eusebio
Solórzanob, Miguel Ángel Rodríguez-Pérez
b, Miguel Ángel López-Manchado
a and Raquel Verdejo
a
a Instituto de Ciencia y Tecnología de Polímeros (ICTP-CSIC), C/Juan de la Cierva 3, 28006, Madrid,
Spain; [email protected] bCellular Materials Laboratory (CellMat), Condensed Matter Physics Department, University of Valladolid,
47011, Valladolid, Spain
Polymer nanocomposite foams are receiving increasing attention due to the combination of the foam
technology and the properties of the nanoparticles, generating multifunctional and lightweight materials that can find interesting applications.
1, 2 In particular, polyurethane (PU) foams are one of the most versatile
polymeric materials because they can be formulated to meet specific requirements but they require the
inclusion of conductive particles. The use of high aspect ratio conductive fillers, such as carbon nanotubes and graphene can therefore be an attractive alternative. The introduction of carbon nanoparticles (CNPs) in
polymer foams can enhance not only the electrical conductivity3 but also the mechanical strength, thermal
stability, and surface quality.4-6
Water-blown PU nanocomposite foams are formed by the simultaneous polymerisation and expansion of
relatively low molecular weight reactive liquids, resulting in solid cellular materials. The aim of this work is
to understand the effect of different CNPs on chemical and physical events involved on the evolution of the PU nanocomposite foams.
Multi-walled carbon nanotubes (MWCNTs) were synthesised in-house by a chemical vapour deposition (CVD) process.
7 Functionalisation of MWCNTs was carried out in a mixture of acids at 120ºC for 30
minutes and then filtered with distilled water until neutral pH. Functionalised graphene sheets (FGS) were
produced from the adiabatic expansion at 1000ºC of graphite oxide under argon atmosphere.5 Flexible PU
foams were synthesised in a two-step procedure. First, a fixed amount (0.5 phpp, approximately 0.3 wt.-% in the final foam) of the different carbon nanofillers were mixed in the polyol for 6 hours to achieve a good
dispersion before foaming.
The reaction kinetics of PU nanocomposites foams is monitored by FT-IR spectroscopy while the
morphology development is investigated by synchrotron SAXS. The physical events taking place during the
expansion of the foam were followed by X-ray radioscopy. The different morphologies of the CNPs
influenced the kinetics of polymerisation and foaming.
The polymerisation reaction and the development of the phase-separated structure of flexible PU foams were
strongly influenced by the presence of carbon nanoparticles with different morphologies and surface bearing groups. FT-IR analysis confirmed a deceleration on the kinetics of polymerisation attributed to a restriction
of the mobility of the systems. This rate was further slowed down by the presence of oxygen bearing groups
on the surface of the nanofillers. Meanwhile, synchrotron SAXS analysis confirmed the delay of the morphology development.
X-ray radioscopy confirmed a deceleration on the foaming evolution of PU foams with CNPs related to the
high viscosity of the initial dispersions of CNPs. The rate of foaming was determined by the density changes observed during foaming.
FTIR and SAXS showed a similar trend on the kinetics of polymerisation and the kinetics of phase separation of hard segments. The effect of the nanoparticles on the polymerisation and microphase structure
depended on their rigidity and the type of functional groups on their surface. Meanwhile, the evolution of the
density is influenced by the rheological behaviour of the CNP/polyol mixtures at the initial stages of foaming.
Figure 1. X-ray radiographs of expanding PU nanocomposite foams.
Acknowledgements. The authors gratefully acknowledge the financial support of the Spanish Ministry of Science and
Innovation (MICINN) through MAT 2010-18749 and the 7th Framework Program of E.U. through HARCANA
(NMP3-LA-2008-213277). MMB and MMG also acknowledge the FPI and JAE-Pre programs from MICINN and
CSIC, respectively.
References 1. L.J. Lee, C.Zeng, X.Cao, X.Han, J.Shen, G.Xu, Composites Science and Technology, 2005, 65, 2344-2363.
2. C.C.Ibeh, M.Bubacz, Journal of Cellular Plastics, 2008, 44, 493-515.
3. X.B. Xu, Z.M. Li, L. Shi, X.C. Bian, Z.D. Xiang, Small, 2007, 3, 408-411.
4. D.X. Yan, K. Dai, Z.D. Xiang, Z.M. Li, X. Ji, W.Q. Zhang, Journal of Applied Polymer Science, 2011, 120,
3014-3019.
5. R. Verdejo, F. Barroso-Bujans, M.A. Rodriguez-Perez, J.A. de Saja, M.A. Lopez-Manchado, Journal of
Materials Chemistry, 2008, 18, 2221-2226.
6. G. Harikrishnan, S.N. Singh, E. Kiesel, C.W. Macosko, Polymer, 2010, 51, 3349-3353.
7. C.Singh, M.S.P. Shaffer, A. H. Windle, Carbon, 2003, 41, 359-368.
FILLER PERCOLATION IN CARBON NANOTUBE AND GRAPHENE EPOXY NANOCOMPOSITES
Mario Martin-Gallegoa, M. Mar Bernala, Marianella Hernandeza, Raquel Verdejoa and Miguel Angel
Lopez-Manchadoa. a Instituto de Ciencia y Tecnología de Polímeros, CSIC, Juan de la Cierva, 3 28006-Madrid, Spain.
Introduction: Multi-walled carbon nanotubes (MWNT), acid treated carbon nanotubes (f-MWNT) and functionalized graphene sheets (FGS) were synthetized and added into an epoxy resin. The formation of a structured filler network was evaluated by rheology and electrical measurements. Depending on the degree of exfoliation and the distribution of the filler, the rheological and electrical behavior of the nanocomposites will be different. This is the main reason we chose these two strategies to study the differences in percolation networks of nanocomposites consisting of rod-like and sheet-like nanoparticles2. Materials and methods: CNTs and FGS were synthetized in-house by chemical vapor deposition and through rapid exfoliation of graphite oxide1 respectively. Nanoparticles were dispersed in the epoxy matrix (DGEBA) using an ultraturrax at 30000 rpm during 10 min and 10 min in ultrasonication at 60ºC. The rheological measurements were performed using a TA Instruments Advanced Rheometer AR1000. The geometry used was a stainless-steel parallel plate with a diameter of 25 mm. The gap was fixed to 3 mm and the measurements were recorded in frequency from 0.01 to 100 Hz at 21ºC and at a shear rate of 1s-1. Electrical conductivity of the cured nanocomposites was determined on an ALPHA high-resolution dielectric analyzer (Novocontrol Technologies) over a frequency range window of 103 to 1011 Hz at room temperature. Results and discussion: The first step in our study was to analyze the dispersion state of the samples containing MWNT and FGS. Figure 1 corresponds to TEM images of the cured nanocomposites.
Figure 1: TEM images of the samples containing a) 0.75 wt.% of MWNT and b) 1.5 wt% of FGS.
In figure 2 we show the variation of the complex viscosity versus frequency, the dots are the experimental data obtained for the different mixtures and the solid lines are their fittings with the Herschel-Bulkley model (equation 1).
(1)
where η* is the complex viscosity, ω the angular frequency, τ0 the yield stress, k the consistency index and n is the flow behavior index. When n>1, the fluid exhibits a shear-thickening behavior; for n=1 the fluid has a Newtonian behavior; when n<1 the fluid shows shear-thinning behavior. The fitting parameters are summarized in table 1.
Table 1: fitting parameters
τ0 (Pa) k (Pa·sn) n R2
DGEBA ≈0 24.3 1 0.91
0.25% MWNT 13.4 88.2 0.8 0.99
0.5% MWNT 75.7 116.9 0.8 0.99
0.5% f-MWNT 10.0 25.1 1 0.99
0.75% MWNT 510.6 191.3 0.8 0.99
0.75% FGS ≈0 49.3 1 0.96
1.5% FGS ≈0 85.6 1 0.99
Figure 2: η*vs ω of the epoxy/nanofiller dispersions. On the other hand, the results of the electrical conductivity measurements are represented in the figure 3.
Figure 3: AC Electrical conductivity of the cured samples.
Conclusions:
Rheological and the electrical conductivity results showed that CNTs could form easer a filler network than FGS. This filler percolation appeared at lower percolation thresholds and presented certain strength by itself confirmed by the presence of yield stress.
Acknowledgements: The authors gratefully acknowledge the financial support of the Spanish Ministry of Science and Innovation (MICINN) through MAT 2010-18749. MMG and MMB also acknowledge the JAE-Pre and FPI programs from CSIC and MICINN, respectively. References
1. R. Verdejo, F. Barroso, M. Rodriguez, J. de Saja, M. A. Lopez-Manchado, J. mater. chem. 2008, 18, 2221-2226.
2. J. Du, L. Zhao, Y. Zeng, L. Zhang, F. Li, P. Liu, C. Liu, Carbon 2011, 49, 1094.
Effects of Sepiolite on melt compounded Poly(ethylene oxide)/ Ethylene carbonate/Li salt based solid polymer electrolytes.
Alberto Mejía, Julio Guzmán, Nuria García, Pilar Tiemblo Instituto de Ciencia y Tecnología de Polímeros (CSIC), Juan de la Cierva 3, 28006 Madrid, Spain
e-mail: [email protected] Poly(ethylene oxide) containing lithium salt is usually considered as the most promising solid polymer electrolyte for lithium batteries due to its low cost, lack of toxicity and chemical stability. However its low Li+ ion conductivity, less than 10-5 S·cm-1 at room temperature, makes these materials to be disregarded for applications in Li cells.1,2 Blending solvents of high dielectric permittivity with these systems, such as ethylene carbonate (EC) and/or propylene carbonate (PC) has demonstrated to hinder crystallization and enhance the segmental and chain mobility, leading to conductivities higher than 10-4 at room temperature; but inevitably accompanied by the deterioration of the electrolyte's mechanical properties. The addition of inorganic fillers to the polymer electrolytes is an attractive approach for improving mechanical stability.3 We propose the use of sepiolite fibers as nanofiller in SPEs prepared with poly(ethylene oxide) (Mw =5·106 g mol–1) as polymer matrix, Lithium trifluoromethane-sulfonate (LiTf) or bis-(trifluoromethanesulfonyl)-imide (LiTFSI) and ethylene carbonate (EC) as high dielectric permittivity plasticizer. Composites were physically premixed in different compositions and then melt compounded without using masterbatches. Sepiolite was used neat and surface modified with polyethylene glycol (PEG) and D-α-tocopherol polyethylene glycol 1000 succinate (TPGS). The addition of LiTFSI precludes crystallization and almost amorphous composites are obtained, which present a Li+ conductivity up to 10-4 S·cm-1 at 40 ºC. Ethylene Carbonate (EC) may be added in order to improve the ionic conductivity; however, composites with LiTFSI loose their mechanical properties and become viscous fluids when a 20% of EC is used. In composites containing LiTf the PEO crystallinity is preserved, though for concentrations of a 40% wt. EC, again viscous fluids are obtained. However, the addition of a 5% of organosepiolite to these last composites produces solid-like electrolytes with liquid-like ionic conductivities close to 10-3 S·cm-1 at room temperature. In this work we analyze the role of sepiolite as nanofiller, its effects on the semicrystalline morphology and the matrix tortuosity, and the dependence of conductivity with the crystalline fraction. References
1. J. B. Goodenough and Y. Kim. Chemistry of Materials 22 (3), 587-603 (2010) 2. A. M. Stephan and K.S. Nahm. Polymer 47, 5952-5964 (2006) 3. H.M.J.C. Pitawala et al. Solid State Ionics 178, 885–888 (2007)
PREPARATION OF ALKYLATED GRAPHENE OXIDE LAYERS FOR POLYMER COMPOSITES
Silvia Bittolo Bona, Luca Valentinia and Josè Maria Kennya
aUniversity of Perugia, Civil and Environmental Engineering Department, Strada di Pentima,4 05100 Terni; [email protected]
Introduction. Graphene oxide has the same two-dimensional sp2 carbon nanostructure of graphene but it is characterized by the presence of hydroxyl and epoxy functional groups on the sheet surface, moreover carbonyl groups are present as carboxylic acid along the sheet edge and also as organic carbonyl defects within the sheets1,2. Graphene oxide is attracting a great research interest as the most common preparation method of graphene starts from the oxidation and exfoliation of graphite to graphene oxide (GO)3-5: afterwards it can be reduced to graphene through thermal or chemical methods. Moreover the functional groups in the GO structure give to this material hydrophilic properties allowing the easy preparation of stable and homogeneous GO dispersion in water6: wet-chemistry approaches are the most desirable methods for the large scale integration of reduced GO for the production of GO-based polymeric nanocomposites. The possibility to use soluble alkylated reduced GO nanosheets as fillers in polymeric nanocomposites films7,8 was investigated. For this approach the critical issue in terms of physical properties and film uniformity is the aggregation of the reduced GO sheets after the dispersant evaporation. The formation of aggregates of GO layers after the filler mixing with the polymer matrix can produce a worsening of the material properties: in the case of the development of transparent electrodes for applications in the area of optoelectronics it could result in the reduction of the optical transparency and conductivity of the graphene/polymer composites. Along this line, the current interest is designing new soluble polymer-modified reduced graphene oxide materials that can be directly used to fabricate graphene-based molecular photoresponsive devices. Materials and Methods. GO were purchased from Cheaptubes (Fig. 1), GO water solution (1mg/1ml) was prepared and sonicated (750W, 60% amplitude) for 1 hr and then centrifuged for 30 min at 9000 rpm. Butylamine (BAM, purchased from Sigma Aldrich) was used to modify the GO structure and properties.
Fig.1 SEM image of GO.
Infrared spectroscopy in the 500–4000 cm-1 range, was used to confirm the chemical composition of the modified GO. The surface morphology of the films were investigated by optical (Fig. 2) and field emission scanning electron microscopy (FE-SEM). UV−Vis spectroscopy was used to verify the optical transparency of the produced samples. Raman measurements were performed to verify the formation of alkylated GO.
1 µm
Results and Discussion The alkylated graphene oxide (Fig. 2) was used to produce composite films: its dispersion in a conductive polymer matrix allowed to reach a higher electrical conductivity (Fig. 3) without negative effects on other characteristics of the composite material, such as its optical transparency (Fig. 4).
Fig. 2: Optical image (500 µm X 250 µm) of the alkylated Gox film from a water dispersion
Fig. 3 I-V curves of PEDOT:PSS film and PEDOT:PSS/GO composites deposited from GO water dispersion and
BAM-treated GO in water dispersion
Fig. 4 UV-Vis spectra of PEDOT:PSS and BAM-treated GO/PEDO:PSS films.
Conclusions The alkylated GO sheets show homogeneous water dispersion leading to the deposition of large functionalized graphene oxide thin films with an enhanced electrical conductivity. These properties with the ease of preparation and solution processing capability, lead to graphene/polymer hybrid material with a combination of conductivity and transparency useful for the development of optoelectronic devices. References 1. A. Lerf, H. He, M. Forster, J. Klinowski, J. Phys. Chem. B 1998, 102, 4477. 2. H. Y. He, J. Klinowski, M. Forster, A. Lerf, Chem. Phys. Lett. 1998, 287, 53. 3. S. Park, R. S. Ruoff, Nat. Nanotechnol. 2009, 4, 217. 4. S. Park, J. H. An, I. W. Jung, R. D. Piner, S. J. An, X. S. Li, A. Velamakanni, R. S. Ruoff, Nano Lett. 2009, 9, 1593. 5. S. Stankovich, D. A. R. D. Dikin, K. A. Kohlhaas, A. Kleinhammes, Y. Jia, Y. Wu, S. T. Nguyen, R. S. Ruoff, Carbon 2007, 45, 1558. 6. T. Szabo, E. Tombacz, E. Illes, I. Dekany, Carbon 2006, 44, 537. 7. S. Bittolo Bon, L. Valentini, J. M. Kenny, Chem. Phys. Lett. 2010, 494, 264. 8. S. Bittolo Bon, L. Valentini, R. M. Moustafa, F. M. Jradi, B. R. Kaafarani, R. Verdejo, M. A. Lopez-Manchado, J. M. Kenny, J. Phys. Chem. C 2010, 114, 11252.
Graphene-containing thermo-responsive poly(N-vinylcaprolactam) nanocomposite hydrogels
Roberta Sanna,a Valeria Alzari,a Daniele Nuvolia, Sergio Scognamilloa, Davide Sanna,a Emilia Gioffredi, b Giulio Malucelli,b Massimo Lazzaric and Alberto Mariania
aDipartimento di Chimica e Farmacia, Via Vienna 2,07100, Sassari, Italy; [email protected] bDipartimento di Scienza dei Materiali ed Ingegneria Chimica, Politecnico di Torino, sede di
Alessandria,Via T. Michel 5, 15121, Alessandria, Italy; cCentre for Research in Biological Chemistry and Molecular Materials (CIQUS), University of
Santiago de Compostela, 15782 Santiago de Compostela, Spain Introduction
Poly(N-vinylcaprolactam), PNVCL, hydrogels exhibit a thermo-responsive behavior that has attracted large interest in recent years. It belongs to the same family of poly(vinylpyrrolidone), PVP, a macromolecular compound widely used in pharmaceutical and biomedical field1. PNVCL is a non-ionic polymer, soluble in aqueous media, and, similarly to PVP, able to absorb a large number of organic compounds from water. It is also a very interesting material because of its stability against hydrolysis, which makes it more biocompatible than poly(N-isopropylacrylamide), PNIPAAm. Moreover, it exhibits a critical solution temperature (LCST) at about 32-34 °C, a temperature value that makes it a valid alternative to PNIPAAm in controlled drug delivery systems2, in the immobilization of enzymes3 and in separation science.4 Anyway, the mechanical properties of the above hydrogels are often quite poor, thus limiting the number of their possible applications. To overcome these limitations and improve swelling, graphene-containing nanocomposite hydrogels were prepared5. The present work aims to the dispersing of graphene directly into the monomer (N-vinylcaprolactam, NVCL) by using an alternative and convenient route based on graphite sonication without any chemical manipulation, and to the obtainment of the corresponding thermoresponsive nanocomposite hydrogels through the use of the frontal polymerization (FP) as the synthetic technique. Moreover, we investigated the influence of graphene on the swelling behavior of the corresponding hydrogels at different temperatures, and on the mechanical properties. Experimental A graphene masterbatch dispersion was prepared by dispersing 5 wt.-% of graphite flakes in NVCL, and sonicating it for 24 h. Then, the dispersion was centrifuged for 30 min at 4000 rpm and the residual solid graphite was removed. Graphene concentration, calculated by gravimetry after filtration through polyvinylidene fluoride filters, was found to be equal to 5.0 mg/ml. The presence of graphene in this medium was confirmed by Raman spectroscopy and transmission electron microscopy (TEM) analyses. The nanocomposite polymer hydrogels of PNVCL containing graphene were prepared by varying the amount of graphene from 0.0088 to 0.4382 wt.-%, and keeping constant the amount of crosslinker (tetraethyleneglycoldiacrylate, TEGDA), and initiator (trihexyltetradecylphosphonium persulfate TETDPPS), both at 1 mol% referred to the amount of NVCL. The graphene masterbatch dispersion in NVCL was diluted with suitable amounts of NVCL, thus obtaining dispersions containing different concentrations of graphene. Each of them was introduced into a common glass test tube, and TEGDA and TETDPPS were added. FP started by heating the external wall of the tube in correspondence of the upper surface of the monomeric mixture. For all samples, front temperature (Tmax) and front velocity (Vf) were measured. To determine the swelling ratio (SR%) and the LCST of the PNVCL-graphene nanocomposite hydrogels in water, they were heated from 3 to 55 °C in a thermostatic bath. From 3 to 9 °C, temperature was increased at a rate of 3 °C/day; from 25 to 35 °C, it was raised at a rate of 1 °C/day and finally, from 35 to 55 °C, of 5 °C/day. The swelling ratio (SR%) was calculated by the following equation: SR% = (Ms- Md)/Md x 100, where Ms and Md are the hydrogel masses in the swollen and in the dried state, respectively. Results and discussion First of all, the presence of graphene in NVCL was confirmed by Raman spectroscopy and TEM. The Raman spectra exhibit the three typical signals of graphene: the D band at 1350 cm-1, the G band at 1580 cm-1 and the disorder-related 2D peak at a frequency of ca. 2700 cm-1.
The 2D band is a very important signal for graphene identification because it differs from that of graphite and has a shape that is related to the number of layers. In the example reported in Figure 1a the shape and position of the 2D band suggest that the sample is constituted of bi- and tri-layer graphene. The concentration of graphene in NVCL was found to be 5.0 mg/ml, one of the highest reported so far in literature by using any method and in any liquid. From the above graphene dispersions in NVCL, several polymer nanocomposites having concentration of graphene ranging from 0.0088 to 0.4382 wt.-% were prepared by FP. Front temperatures were not affected by the presence of graphene, with Tmax values always included between 161 and 166 °C. Besides, front velocity was characterized by a relatively larger range values. Moreover, all samples were characterized by almost quantitative conversion, independently of graphene concentration; it is noteworthy that the conversion reported here is higher than that previously reported in literature for the classical polymerization of NVCL, performed in solution at 60 °C for 192 h.6 This result confirms the reliability of FP as a convenient alternative polymerization technique.
1200 1400 1600 2600 28000
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
11000
Inte
nsity
(a.u
.)
Raman shift (cm-1)
graphite
graphene
Figure 1 Raman spectra of graphene dispersion in NVCL (a), and SR% as function of temperature for samples characterized by different amounts of graphene (b).
a) b)
Swelling studies in water at different temperature were performed on all the samples: as can be seen in Figure 1b, the swelling ratio is strongly influenced by the amount of graphene contained in the polymer nanocomposites. Namely, at 3 °C, SR% increases from 1700% for the neat polymer to a maximum of 3260 % for the nanocomposite having 0.0879 wt.-% of graphene. On the contrary the presence of graphene does not influence the LCST of the thermoresponsive polymer hydrogels, which is always comprised between 32-33 °C. Moreover, it was found that the rheological and mechanical properties of the examined nanocomposites were correlated to the graphene content: it was shown that the presence of graphene results in a decrease of both the complex viscosity and the storage modulus G'. Conclusions Graphene-containing thermo-responsive PNVCL nanocomposites hydrogels were prepared by using an alternative and convenient route. The concentration of graphene in NVCL was found to be 5.0 mg/ml, one of the highest reported so far in literature with any method and in any liquid. FP was used for the preparation of the polymer nanocomposite hydrogels, which exhibit an LCST at ca. 34 °C. The presence of graphene resulted in a large increase of the SR%: at 3 °C, it ranges from 1700% for the neat polymer to a maximum of 3260 % for graphene nanocomposite. On the other hand, LCST was not affected by the presence of graphene. Finally, the G' modulus and complex viscosity of the hydrogels were found to decrease with increasing nanofiller concentration, thus indicating a lubricant effect of graphene. References 1. Y. E. Kirsh, Water soluble poly-N-vinylamides. Chichester: Wiley; 1998, p. 1–33. 2. K. S. Soppimath, D. C. W. Tan, Y. Yang, Adv Mater 2005,17,318. 3. A. Guiseppi-Elie, N. F. Sheppard, S. Brahim, D. Narinesingh, Biotechnol Bioeng 2001,75,475. 4. H. Kawaguchi, K. Fujimoto, Smart Bioseparation 1998, 4, 253. 5. V. Alzari, D. Nuvoli, S. Scognamillo, M. Piccinini, E. Gioffredi, G. Malucelli, S. Marceddu, M. Sechi, V. Sanna, A. Mariani, J. Mater. Chem. 2011, 21, 8727. 6. S. Kozanoglu, PhD thesis, 2008, M.Sc., Department of Polymer Science and Technology.
Novel Multi-Functional Surfaces for Industrial Implementation –
Synthesis and Application of Reversible Switchable Polymer Brushes
Mandy Kunder1, Martin Messerschmidt
1, Andreas Stake
2, Thomas Lukasczyk
2,
Petra Uhlmann1, Manfred Stamm
1
1Leibniz Institute of Polymer Research Dresden, Hohe Str. 6, 01069 Dresden, Germany
e-mail address: [email protected] 2 Fraunhofer Institute for Manufacturing Technology and Advanced Materials,
Wiener Str. 12, 28359 Bremen, Germany
In recent years, multifunctionality, i.e. the integration of several functionalities in one coating
system gained much attention in the development of intelligent coatings on different
materials. Elegant self-cleaning surfaces from nature, such as lotus leaves [1]
, are a
combination of low surface energy species and a peculiar topographic feature based on dual-
size roughness. The combination of dual surface roughness and functionalisation of the
surface with switchable polymer brushes opened new paths for application in industry [2]
, e.g.
automotive and paint/lacquer industry.
Here, suitable amphiphilic diblock and triblock copolymers have been designed and
synthesized via controlled radical polymerisation and finally applied to silica nanoparticle
containing lacquer and raspberry-like silica particles to build core shell particles for intelligent
surface modification. The advantage of switchable polymer brushes and silica particles is the
combination of switchability of surface properties and stability.
The block copolymers were synthesized by radical addition fragmentation chain transfer
polymerisation (RAFT) with a narrow size distribution. The block copolymers are composed
of two respectively three functional parts: the anchoring block that include surface active
groups for the directly attachment on silica substrates; the “hydrophobic” and/or
“hydrophilic” blocks are switchable and responsible for the favoured surface properties, e.g.
wetting behaviour.
Acknowledgement: We like to acknowledge DFO, EFDS, AiF and BMWI (“Zutech”-Projekt
IGF 350 ZGB) for funding.
[1] Neinhuis, C.; Bartholett, W. Ann. Bot. 1997, 79, 667
[2] P. Uhlmann, K. Oleschko, N. Laber, G. Hüttner, B. Lehmann, Farbe und Lack 2011, 117 (9), 17
INTERMOLECULAR INTERACTIONS
IN POLY(2-(2-METHOXYETHOXY)ETHYL METACRYLATE) HYDROGELS
Olejniczaka M., Kozanecki
a M., Matusiak
b M., Kadlubowski
b S. and Ulanski
a J.
aDepartment of Molecular Physics, Faculty of Chemistry, Technical University of Lodz, Zeromskiego 116,
90-924 Lodz, Poland; [email protected] bInstitute of Applied Radiation Chemistry, Technical University of Lodz, Wroblewskiego 15, 93-590 Lodz,
Poland
Polymer hydrogels belong to a group of functional materials, which attracts most attention because
of their diverse usability. They have been successfully used in many fields of life e.g. medicine, pharmacy,
biotechnology and in food industry.
One of the most interesting group of water-polymer systems is stimuli-responsive hydrogels, which
reveal abrupt change in their properties under even small modification in environmental conditions
(temperature, pH, melectrical, mechanical or magnetical fields etc.). Properties of the hydrogels are not a
simply sum of properties of particular components. The synergy effect leading to unique behaviours of
thermo-sensitive gels results from the specific intermolecular interactions. Therefore knowledge on
interactions between polymer and water play a key role in description of hydrogel properties. Thermo-
responsive hydrogels are commonly synthesised from polymers exhibiting the lower critical solution
temperature (LCST) such as for example: (2-(2-methoxyethoxy)ethyl metacrylate. Phase separation
occurring above critical temperature (c.a. 20oC for MEO2MA) is highly interesting problem in all aspects.
Hydrogels obtained by radiational polymerisation from poly(2-(2-methoxyethoxy)ethyl metacrylate
were the objects of presented Raman spectroscopy studies. Intermolecular interactions in the systems
differing on crosslinking as well as swelling degrees have been investigated. Moreover influence of changing
environmental temperature on position of Raman bands and their assignment of vibrational mode will be
discussed. Received results will be compared with data obtained for other thermo-responsive systems.
Acknowledgements. This work was supported by projects from the Ministry of Science and Higher Education of
Poland, No: N N209200738. Presented studies were realised in frame of ECBNT.
References 1. Y. Maeda, T. Kubota and H. Yamauchi, Langmuir 2007, 23, 11259-11265.
2. M. Pastorczak, M. Kozanecki and J. Ulanski, Polymer 2009, 50, 4535-4542.
MORPHOLOGY AND SURFACE PLASMON ENHANCED OPTICAL PROCESSES OF
CATIONIC POLYTHIOPHENE / METAL NANOPARTICLES COMPOSITES SYSTEM AND
ITS APPLICATION TO SERS
Samrana Kazim1, J. Pfleger
1, J. Hromadkova
1, M. Prochazka
2, D. Bondarev
3, J.Vohlidal
3
1Institute of Macromolecular Chemistry, ASCR, Heyrovský Square 2, 162 06 Prague 6, Czech Republic
2 Charles University in Prague, Faculty of Mathematics and Physics, Ke Karlovu 5, Prague 2, CZ
3Charles University in Prague, Faculty of Sciences, Hlavova 2030, Prague 2, Czech Republic
e-mail:[email protected]
Conjugated polyelectrolytes (CPEs) show interesting optical, electrical and redox properties
together with good solubility in water and water-miscible solvents making possible processing of
these polymers from aqueous solutions. This makes them suitable for various biosensor and
optoelectronic applications. Solubility of CPEs in water also substantially simplifies preparation of
their composites with noble-metal nanoparticles (NPs) that can show the effect of local
enhancement of electromagnetic field, which can be evidenced by the surface enhancement of
Raman scattering.1
Recently we have prepared a new conjugated cationic polyelectrolyte with regioregular
poly(alkylthiophene) backbone and ionic-liquid-like side groups: poly{3-[6-(1-methylimidazolium-
3-yl)hexyl]thiophene-2,5-diyl bromide}, PMHT-Br.2 In this work, we report the effect of PMHT-Br
on the morphology and optical properties of Au or Ag metal NPs/PMHT-Br systems formed by
aggregation of metal nanoparticles. Gold (Au) and silver (Ag) hydrosol was prepared by a simple
chemical reduction method using NaBH4 as a reducing agent. Au or Ag NPs/PMHT-Br composite
sol systems were prepared by adding different concentration of PMHT-Br into the Au or Ag
hydrosol.
NN Me
Br
S n
Ag
+
PMHT-Br, regioregularity ca 92 %
12
borate-stabilized Ag NPs
borate anions
+ SERS-activenanocomposites
The PMHT-Br concentration was found to have a strong impact on assembling of metal NPs,
and consequently, on the optical processes in the system. Optimum aggregation is achieved at
components ratios providing a charge balance between metal NPs and PMHT-Br, at which metal
NPs are nearly single-polymer-layer coated, their zeta potential is close to zero and they easily form
aggregates in which their interparticle distances lie in the region enabling occurrence of the desired
plasmonic effect. At higher metal NPs/PMHT-Br ratios, metal NPs do not aggregate since they
preserve their original negative zeta potential (borate-stabilized Au or Ag sol) but effectively
quench fluorescence of PMHT-Br. At lower metal NPs/PMHT-Br ratios, zeta potential of metal
NPs is switched to positive values hence they do not aggregate either. Prevailing resonance
enhancement of Raman scattering is observed for systems of non-balanced compositions.
TEM images of the metal NPs/PMHT-Br systems together with the observed concentration
dependent zeta potential of particles present in the system and Raman spectra and fluorescence
quenching measurements have shown that electrostatic interactions of negatively charged metal
NPs with cationic PMHT-Br chains play key role in the formation of systems showing surface-
enhanced optical effects.
Acknowledgements Financial support of the Czech Science Foundation projects P208/10/0941 and EU NoE project
FlexNet are greatly acknowledged.
References: [1] S. Kazim, J. Pfleger, M. Procházka, D. Bondarev, J. Vohlídal, J. Coll. Interf. Sci. 2011, 354, 611
[2] D. Bondarev, J. Zedník, I. Šloufová, A. Sharf, M. Procházka, J. Pfleger, J. Vohlídal, J. Pol. Sci: A Polym. Chem,
2010,48, 3073.
Ultracentrifuged poly(allylamine hydrochloride)/poly(acrylic acid) polyelectrolyte complexes
Patricia Tiradoa, Andreas Reisch
a, Camille Orthlieb
a, Emilie Roger
a, Fouzia Boulmedais, Jean-Claude
Voegelb, Pierre Schaaf
c, Joseph B. Schlenoff
d, Benoît Frisch
a
aLaboratoire de Conception et Application de Molécules Bioactives, UMR 7199 CNRS/Université de
Strasbourg. Faculté de Pharmacie, 74 route du Rhin, 67401 Illkirch Cedex, France. E-mail :
[email protected] b Institut National de la Santé et de la Recherche Médicale, Unité 595, Faculté de Chirurgie Dentaire, 11
rue Humann, 67085 Strasbourg Cedex, France. c Centre National de la Recherche Scientifique, Unité Propre de Recherche 22, Institut Charles Sadron, rue
du Loess, BP 84047, 67034 Strasbourg Cedex 2, France. d
Department of Chemistry and Biochemistry, The Florida State University, Tallahassee, 32306 Florida,
United States.
Introduction
Polyelectrolyte complexes are physical hydrogels in which the cross-links are formed by ion-pairing
of oppositely charged groups on the polyanions and polycations. They can be obtained by simply mixing
solutions of polyanions and polycations; however, this yields inhomogeneous products that cannot be easily
processed. Recently, the Schlenoff group introduced the ultracentrifugation of complexes of poly(styrene
sulfonate) and poly(diallyldimethyl ammonium) in the presence of high concentrations of salt as a new
processing technique that yields macroscopically homogeneous materials with interesting mechanical
properties and potential for biomedical applications: compact polyelectrolyte complexes1-3
.
In this work we extended this approach to weak polyelectrolytes, poly(acrylic acid) (PAA) and
poly(allylamine hydrochloride) PAH, which yields materials responsive to salt concentration and pH. We
studied the influence of the assembly conditions on structure and properties of these materials
Experimental
Primary complexes were made by mixing aqueous solutions of poly(allylamine hydrochloride) and
poly(acrylic acid). These were compacted and homogenized by ultracentrifugation. Various conditions of
mixing order, mixing speed and concentration of the polyelectrolyte solutions, their NaCl concentrations and
pH were used in order to study their influence on the product. The matrix morphology was studied using
confocal fluorescence microscopy and the ratio of the polyelectrolytes was determined by proton 1H NMR
spectroscopy.
Results
Ultracentrifugation transformed the initial PAA/PAH complexes into macroscopically homogeneous
materials showing excellent mechanical resistance. Mixing order, mixing speed, and pH can be used to vary
the ratio of PAA to PAH in these materials between 0.6 to 1 and 1.4 to 1. This ratio in turn controlled
porosity, pore sizes, and their distribution. The size of the pores changed in response to salt concentration
and pH. These parameters also controlled the mechanical properties of the materials, with those having
stoichiometric amounts of PAA and PAH at neutral pH and low ionic strength being the most rigid.
PAA/PAH : 0.6/1 0.9/1 1/1
Figure 1: Influence of the PAA to PAH ratio on the microstructure of the ultracentrifuged complexes. Fluorescence
microscopy images of slices of complexes prepared in 2.5 M NaCl at pH 7.4 and conditioned in 0.15 M NaCl. Scale
bars are 100 µm
Conclusions
We showed that a new processing method, ultracentrifugation of polyelectrolyte complexes, can be
applied to weak polyelectrolytes such as PAA and PAH, and that this provides interesting materials. Fine
tuning of the assembly conditions allowed control of the composition and porosity. The materials are
responsive to various environmental stimuli. Together those properties make them interesting candidates for
bioactive biomaterials.
Acknowledgements
This work is supported by the Gutenberg Chair project of Prof. Schlenoff awarded from the
University of Strasbourg and a fellowship from the Venezuelan Ministry of Science.
References 1C. H. Porcel, J. B. Schlenoff, Biomacromolecules 2009, 10, 2968.
2 R. S. Shamoun, A. Reisch, J. B. Schlenoff, Advanced Functional Material, in press
3 H. H. Hariri, J. B. Schlenoff, Macromolecules 2010, 43, 8656.
Collective Volume Plasmons in Materials with Nanoscale Phase Separation
Sarychev A.K.a, Boyarintsev S.O.a, Rakhmanov A.L.a, Kugel K.I.a and Sukhorukov Yu.P.b
a Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Izhorskaya Str. 13, Moscow, 125412 Russia; [email protected]
b Institute of Metal Physics, Ural Branch, Russian Academy of Sciences, S. Kovalevskaya Str. 18, Ekaterinburg, 620990 Russia
Nanoscale phase separation is a spontaneous formation of droplets, where the electron density is much larger than in the background, in a chemically homogeneous solid. The droplets of the high conducting phase can be random or regular arranged. The nanoscale phase separation could be observed in high Tc superconductors, in various manganites like La0.7Ca0.3MnO3, and in many other substances that are in a focus of the modern solid state physics. We consider here the optical properties of the manganites. The phase-separated materials can be considered as natural metamaterials since the spatial scale of inhomogeneities is less than the wavelength λ of the incident electromagnetic wave. Among important phenomena found here, we could mention a wide peak in reflection R, transmission T, and absorption A in the infrared range1,2,3 and the enhancement of Raman scattering in the same wavelength range4. These phenomena observed in single crystals and high-quality films are temperature dependent and can be attributed to inhomogeneous structure of the studied samples. We show that the phase separation can provoke such exciting optical phenomena as anomalous absorption, giant field fluctuations, and orders of magnitude enhanced Raman scattering. We study here a 3D metal--insulator nanocomposite. Such a system is usually described in terms of the effective media theory (EMT). However, the EMT is (i) an uncontrollable approach and (ii) it cannot be used for the analysis of a local field distribution in inhomogeneous media. In this paper, we use computer simulations of the nanocomposite. We compute the local electric field distribution, E(r), and find specific excitations, giant fluctuations of E(r) in a characteristic volume including a number of metallic droplets, as it is seen from Fig. 1. The giant fluctuations are of special importance for the description of optical effects sensitive to the local field, like the Raman scattering, optical nonlinearities, etc. We name these excitations collective volume plasmons (CVP). We also compute the dependence of the averaged system permittivity ε on frequency ω and content of the metallic phase p, and calculate reflection and absorption coefficients of the system. It is shown that the phase separation provokes such exciting optical phenomena as anomalous absorption, giant field fluctuations, and orders of magnitude enhanced Raman scattering5. We predict peaks in R(ω) and A(ω) within a wide p range in agreement with experimental results obtained for manganite single crystals and high-quality thin films in the infrared spectral range. References
1. Ch. Hartinger et al., Phys. Rev. B, 73 (2006), 024408.
2. A. Rusydi et al., Phys. Rev. B, 78 (2008), 125110.
3. P. Gao et al., Phys. Rev. B, 78 (2008), 220404.
4. M. Seikh et al., Pramana, J. Phys., 64 (2005), 119.
5. A. K. Sarychev, S. O. Boyarintsev, A. L. Rakhmanov, K. I. Kugel, and Yu. P. Sukhorukov, Phys. Rev. Lett., 107 (2011), 267401
Fig. 1 Intensity of the local electric field I=|E(x,y,z)/E0|2 at a fixed value of z for the system with dimensions x×y×z=50×50×50
ULTRAFAST EXCITATION DYNAMICS IN POLYANILINE
David Rais, Miroslav Menšík, Jiří Pfleger
Institute of Macromolecular Chemistry, AS CR, v.v.i., Heyrovský Sq. 2, 162 06 Prague, Czech Republic
Introduction. Polyaniline is a -conjugated polymer with a relatively flexible backbone, which influences
the dynamics of excited electronic states1. It is known, that the undoped forms of polyaniline support
extremely long-lived photoexcitations2. Their exceptionally long stability was explained by a model
suggested by Ginder and Epstein3 revealed the key role of the ring torsion angle and its coupling to electronic
energy states. In case of emeraldine base they assumed existence of photo-generated charge-transfer exciton,
which has negative charge centered on a quinoid and positive charge +e distributed phenyl rings on either
side of a quinoid. The exciton is expected to exist in excited states EX* and also in a long-lived metastable
states EX† that are stabilized by metastable ring conformations. Those conformations are created by rotation
of the phenyl ring plane out of the plane defined by the nitrogen atoms. In the ground state, the quinoid ring
is rotated by 8°, the adjacent benzenoid rings are both rotated by -43° and the remaining benzenoid ring is
rotated by 16°, cf. ref.4.
Figure 1: Chemical structure of emeraldine
base
Figure 2: A steady state UV-vis optical absorption spectrum of
emeraldine base (red full curve). Spectrum of a laser excitation
pulse (black dotted curve).
Materials and Methods. Emeraldine base was prepared according to the well-established procedure by
reaction of 1.30 g aniline hydrochloride (0.2 M aqueous solution) with 2.86 g of ammonium peroxodisulfate
(0.25 M aqueous solution) at room temperature. For the photoinduced transient absorption measurement, the
emeraldine base was dissolved in dimethylsulfoxide (A.C.S. spectroscopic grade) in concentration 22 ppm.
The diluted solution was vigorously bubbled for about 3 h with dry nitrogen in order to reduce the amount of
O2 and H2O just prior to the experiments. During the transient absorption spectra measurement the solution
was kept in tightly closed quartz cuvette with 1 mm optical length.
We studied dynamics of photo-generated excitations in emeraldine base form of polyaniline (cf. Fig. 1) by
means of pump-probe transient absorption spectroscopy5. The excitation pulse (pump) with duration < 100 fs
was tuned to 700 nm wavelength (cf. Fig. 2, mean energy was 3.8 J) to excite the long-wavelength optical
absorption of the polymer.
Results and Discussion. The UV-vis optical absorption spectrum of the emeraldine base shows two maxima
(cf. Fig. 2), which can be attributed to two chromophores: The short wavelength maximum at 330 nm
corresponds to transition on the phenyl rings; the broad absorption band centered at 623 nm
corresponds to internal charge transfer within the quinoid ring and surrounding benzenoid rings6.
The time-resolved changes in absorption spectra reveal two regions with decreased absorbance and two
regions with increased absorbance (cf. Fig. 3, left). The decrease of the absorbance around 620 nm is
obviously due to depletion of the ground state population. A polaron, which absorbs in long-wavelength part
of the spectrum above 750 nm (cf. ref.6), is formed immediately. Also, the excited state absorption band
(ESA) located around 500 nm appears.
The evolution of this ESA part of the spectrum is interesting, since it reveals the process of exciton
localization. At very short times, when the pump and probe pulses are in almost perfect temporal overlap
(t = 0), the spectrum of ESA shows maximum at 490 nm, which shifts continuously towards 420 nm during
first 0.3 ps. In longer times (up to 6 ns), its position does not change.
In Fig. 3 (right) notice the temporal shift of maxima of various representative kinetic curves obtained for
certain fixed wavelengths selected from the respective regions described above. The origin (t = 0) was
adjusted to maximum of the ground state bleaching process (red circles). Bleaching in region above 350 nm
due to rotation of the phenyl rings reached its maximum with 0.5 ps delay. According to theoretical
calculations by Harigaya7, and experimental measurements the decrease of oscillator strength of the
transition occurs due to the increase in mutual phenyl ring rotation angles in polyaniline chain. Our
observation is in agreement with this predicted behaviour, thus we can assign this feature to the increase of
phenyl ring rotation disorder. The kinetic of such photo-induced reaction is governed by rather large moment
of inertia of rotation of a phenyl group along its in plane axis. Dynamics of this motion was revealed
experimentally by Eigner et. al.8 and ascribed to the chain "wagging" motion with the vibrational response
about 111 cm-1
(0.3 ± 0.1 ps period).
Figure 3: Left: Time-resolved spectra of photoinduced changes in optical absorption in DMSO solution of emeraldine
base . For the sake of for clarity of presentation, the curves were smoothened to cancel random noise and some parts of
spectra around 700 nm (the excitation wavelength region) were corrected for light scattering. Right: Time evolution of
the optical absorbance change A at particular probe wavelengths (as indicated in the legend).
Conclusions. We observed the kinetic of process of charge-transfer exciton localization in the emeraldine
base form of polyaniline. The process takes about 0.5 ps and involves rotation of phenyl rings into new
conformations, some of which are metastable.
Acknowledgements. This work was partially supported by Ministry of Industry and Trade of the Czech Republic,
project No. FR-TI1/144 and by NoE FlexNet Project, EU ICT 247745 (7FP).
References.
1. Stejskal, J.; Kratochvíl, P. & Radhakrishnan, N., Synthetic Metals 1993, 61, 225.
2. Kim, K.; Blatchford, J.; Gustafson, T.; MacDiarmid, A. & Epstein, A., Synthetic Metals 1995, 69, 247.
3. Ginder, J. M. & Epstein, A. J., Physical Review B 1990, 41, 10674.
4. Barta, P.; Kugler, T.; Salaneck, W.; Monkman, A.; Libert, J.; Lazzaroni, R. & Brédas, J., Synthetic Metals 1998, 93,
83.
5. Megerle, U.; Pugliesi, I.; Schriever, C.; Sailer, C. & Riedle, E., Applied Physics B: Lasers and Optics 2009, 96, 215.
6. Ginder, J.; Epstein, A. & MacDiarmid, A., Synthetic Metals 1989, 29, 395.
7. Harigaya, K., Chemical Physics Letters 1997, 281, 319.
8. Eigner, A. A.; Jones, B. H.; Koprucki, B. W. & Massari, A. M., Journal of Physical Chemistry B 2011, 115, 4583.
INTERPENETRATING NETWORK HYDROGELS
Zhansaya K. Sadakbayeva, Miroslava Dušková-Smrčková, Karel Dušek
Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovsky Sq. 2, 162 06 Prague 6, Czech Republic ([email protected])
Hydrogels often suffer from poor mechanical properties and several ways have
been explored to improve them. These methods include preparation of double networks, sliding-ring networks, nanocomposites based on exfoliated clays, conetworks with transient hydrophobic interactions. Making interpenetrating polymer networks (IPNs) is one of the possible ways of improvement of mechanical properties, but sometimes the properties may get worse. We have prepared a series of such IPNs by sequential radical polymerization of more or less hydrophilic monomers in the presence of water and investigated their swelling and rheological properties.
Here, we report on studies when the hydrophilic cross-linked poly(2-hydroxyethyl methacrylate), PHEMA, prepared by radical copolymerization of HEMA in the presence of water was used as Network I. Depending on the amount of water in the reaction mixture, Network I hydrogel was non-porous, homogeneous or porous. The second network
(Network II) was obtained by swelling of Network I with various monomers 2-hydroxyethyl methacrylate, 2-ethoxyethyl methacrylate, and glycerol monomethacrylate
(HEMA, EOEMA, GMMA) followed by their UV-polymerization. In homogeneous PHEMA networks, as a result of swelling the network chain dimensions are altered: if the degree of swelling of Network I in the monomer of Network II is higher than corresponds to the amount of water present during preparation of Network I, the chains get stretched relative to the original state and the state of chains of Network II and vice versa. Stretching is characteristic of HEMA and GMMA Networks II, a strong decrease of the degree of swelling and chain contraction occurs when EOEMA is used for preparation of the second network. In all cases, the IPN gels remain transparent and apparently homogeneous. Alternatively, when the macroporous Network I is swollen in the monomer, the pore walls get stretched or they are stretched or contract depending on the interaction of the respective monomer with PHEMA. These effects can be amplified with respect to the homogeneous IPNs depending on the morphology of the matrix phase.
Combination of morphologies of Network I PHEMA with hydrophility or hydrophobity of Network II makes possible a variation of swelling and mechanical properties. The net effect of stretching of chains by swelling in the monomer of Network II always results in a decrease of the degree of swelling of IPN, but the more hydrophilic Network 2 tends to increase the degree of swelling. When Network I is macroporous, the degree of swelling of the IPN always decreases, but the network is reinforced. For instance, the combination of macroporous Network I with GMMA Network II gives rise to an IPN approximately of the same low-frequency storage modulus G’ as the parent homogeneous PHEMA gel but of much larger degree of swelling. Similarly, the PHEMA-PHEMA combination gives rise to an IPN gel approximately of the same degree of swelling compared to the parent PHEMA gel but of a substantially higher G’.
Acknowledgement: This work was supported by the EU FP7 People NANOPOLY project
PITN-GA-2009-238700.
Enhanced Thermal Conductivity Of An Epoxy-Matrix Composite Using AlN and BN fillers. Marianne Poirota, Raphaël Brunela a Université de Lyon, INSA de Lyon, IMP@INSA, CNRS UMR 5223, F-69621 Villeurbanne, France INTRODUCTION A thermal conductive and electric insulating resin was developed in order to meet the requirements of an electric motor currently in design for the TRAX project. The aim is, thanks to this material, evacuate the heat outward to improve the efficiency of this motor while meeting the specifications. Excellent electrical insulation properties have made epoxy resins the basis of rather ideal molding compounds. Current trends in encapsulating heat-dissipating electronic components with epoxy resins have stimulate interest in the thermal conductivity of filled epoxy resins. Epoxy has a low thermal conductivity but it can be enhanced by the addition of inorganic particles with high thermal conductivity such as AlN and BN fillers 1-4. Accordingly, this work aimed to develop highly thermal conductive composite materials using AlN and BN fillers and the improvement of interface between the filler and the matrix by surface treatment by a coupling agent. EXPERIMENTAL Raw Materials As filler, both AlN and BN were provided by Sigma-Aldrich. The average particles size of AlN is about 5-10 µm and 1 µm for the BN. The value of their intrinsic thermal conductivity is respectively around 200 W/mK and 280 W/mK. The epoxy used in this study was DGEBA LY556 from Huntsman. The curing agent 4-Aminophenyl sulfone is provided by Sigma-Aldrich. The coupling agent was 3-Aminopropyl (diethoxy)methylsilane purchased from Sigma-Aldrich. Surface treatment was made only for AlN fillers. The surface treatment of AlN with a silane coupling agent is to mix silane in 30mL of THF and about 5mL of NaOH (0.1M) (pH=10) and stir for 2h using a magnetic stirrer at room temperature; add AlN particules into this solution, stir for 12h, rinse with acetone by filtration and drying at 110°C for 12h. Preparation The composite was obtained by firstly mix DGEBA LY556 with the curing agent in a reactor. Then fillers were weighted at increasing percentages, 0, 10, 20, 30, 40 vol% in the case of AlN and 0, 10, 20, 30 vol% in the case of BN. Then the fillers were mixed and heated at 130°C during 30min in a vacuum. The uniformly formed mixtures were cast in a mold and cured at 150°C for 2h and 220°C for 3h.
Characterisation The thermal conductivity was given by the product of the thermal diffusivity, specific heat and density. The thermal diffusivity is measured by the flash method. And specific heat of composites was measured by SETARAM C80 II. The surface treatment of the AlN fillers is analysed by TGA and EDX. The Tg was measured with an ARES thermal mechanical analyser. The temperature range of the experiment was from 30°C to 300°C and the heating rate was 3°C/min. Mechanical properties at break were found using a tensile bench MTS 2/M for the three-point bending experiments at a speed of 2mm/min and values of energy using a Charpy. RESULTS AND DISCUSSION Figure 1 shows the thermal conductivity as a function of the volume fraction of BN and AlN fillers. The thermal conductivity increase for all the composites due to the high intrinsic thermal conductivity of the AlN and BN fillers compare to epoxy. By comparing the thermal conductivity between AlN and BN-filled composites, it is found that the thermal conductivity of BN-filled composite is higher than that of AlN-filled composites. This is due to the intrinsic conductivity of BN fillers which is greater than the AlN fillers and it is also related to the filler shape and size. The interface between particles and the matrix is not optimal which is a barrier to the thermal diffusion. The surface treatment of the particles with a silane coupling agent improved the interface between the particles and the matrix in order to increase thermal diffusion. Tg is not influenced by the addition of particles in the matrix. There is not a plasticizing effect. The addition of particles in the epoxy resin increase flexural moduli which makes the composite more fragile.
0
0,20,40,60,8
1
1,21,4
1,6
0 10 20 30 40 50
Filler content (vol%)
Th
erm
al C
on
du
ctiv
ity
(W/m
K)
Epoxy - AlN
Epoxy - BN
Figure 1: Thermal conductivity as a function of the filler content (vol%)
REFERENCES 1. Procter, P.;Solc, J. IEEE Trans Compon Hybrids Manuf Technol 1991, 14, 708. 2. Wong, C. P.; Bollampally, R. S. J Appl Polym Sci 1999, 74, 3396. 3. Wong, C. P.; Bollampally, R. S. IEEE Trans Adv Packag 1999, 22, 54. 4. Kim, W.; Bae, J. W.; Choi, I. D.; Kim, Y. S. Polym Eng Sci 1999, 39, 756.
Modelling of Formation of Branch-Upon-Branch type of Hyperbranched
Polymers
Maciej Krawczyk and Karel Dušek
Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic
162 06 Prague, [email protected]
The branch-upon-branch radical polymerization is a controlled radical polymerization in
which vinyl monomers polymerize in the presence a special transfer agent under formation of
macromonomers and the formed macromonomers take part in the polymerization process.
The kinetic model includes the initiation, propagation and disproportionation (transformation
of free-radical end into a double bond coupled with regeneration of initiator), and termination
reactions.The process is described by sets of kinetic differential equations based on Scheme 1.
By applying the formalism of probability generating functions, the infinite system of kinetic
equations is transformed into a finite system of differential equations describing the time
evolution of the statistical moments (zero-th, first and second) of the degree-of-
polymerization distributions. The dependences of the degree-of-polymerization averages and
non-uniformity on the values of kinetic constants and initial concentration of monomer and
initiator are examined.
Results
The structural evolution of the system is always described as a function of conversion.
Number- and weight-average degrees of polymerization ( nP and wP ) depend on all kinetic
constants and on initial concentration of the initiator *
0 0c . The dependence on initiation
kinetic rate constant Ik is very weak. Also the influence of the propagation kinetic constant is
weak, if the initial concentration of initiator is relatively small (which is common practice).
The disproportionation kinetic rate constant Dk and the *
0 0c have much larger influence
on nP and
wP and also on the polydispersity index. In the first stage of investigation,
compatibility of the investigated model (for the case of 0Dk ) with the model described in
the Polym. Bull. 13, 313-319 (1985) was checked. The compatibility was confirmed. In the
next stage the influence of the Dk on the molecular parameters , ,n w mP P D was investigated.
The main results (for *
0 0 0,01;c 1;Pk 5Ik ) are shown in Fig. 1
* * tk D
i j i jM M M
Scheme 1
Figure 1
The polydispersity index first increases because only a few chains are grafted by other
macromonomers. At higher conversions, the polydispersity increases again because some
branched molecules grow bigger than the other. At conversion equal to 100% the
polydispersity reaches a limiting value dependent of the intensity of the disproportionation
reaction.
ITC STUDY OF THERMORESPONSIVE TRIBLOCK COPOLYMER F127 AND
THERMORESPONSIVE POLY-OXAZOLINES WITH HYDROPHOBIC MOIETIES
Anna Bogomolova
a , Sergey Filippov
a , Jiri Panek
a , Martin Hruby
b , Petr Stepank
a
a Supramolecular Structures, Institute of Macromolecular Chemistry AS CR, v.v.i, Prague, Czech Republic,
[email protected]; b Biomedical Polymers Department, Institute of Macromolecular Chemistry AS CR, v.v.i, Prague, Czech
Republic
By means of isothermal titration calorimetry(ITC) the interactions between thermoresponsive triblock
copolymer F127 and two thermoresponsive statistical poly-oxazolines with hydrophobic moieties have been
studied. The poly-oxazolines copolymers were different in content of hydrophobic groups, presented in a
polymer chain. Hydrohobic thermoresponsive poly-oxazolines could be used for creation of nanoparticules.
The properties of such nanoparticules could be tuned by variation of hydrophobic group number and
different additives. It was shown that the presence of thermosensitive F127 triblock copolymer reduces
nanoparticule size and polydispersity. The detailed mechanism that is responsible for such behavior was
unknown. The aim of this study was to characterize intermolecular interactions between a poly-oxazoline
and polymeric surfactant F127 prior to nanoparticules formation. Complex formation have been investigated
in broad temperatures and concentration ranges. We have proved that both poly-oxazolines make a complex
with F127. For low temperatures and c(F127)<cmc, we have observed complex formation between
individual molecules of F127 and poly-oxazolines that exist in a coil conformation. At temperatures that
closed to precipitation of the poly-oxazolines, a complex is formed between individual molecules F127 and
poly-oxazoline but in globular state. At concentrations of F127 above cmc, the formation mechanism is
different. ITC data show that the complex formation happens through F127 micelles disintegration initiated
by poly-oxazolines titration. From obtained data we concluded that size and polydispersity of formed
nanoparticules is controlled by F127 mainly. Hydrohobicity of thermoresponsive poly-oxazolines has minor
importance for nanoparticules.
SHAPE MEMORY EFFECT ON TRI BLOCK PCL-PLLA POLYURETHANES
Iván Navarro-Baenaa,b
, Laura Peponib, Ángel Marcos-Fernández
b and José M. Kenny
a,b
a University of Perugia, Strada di Pentima 4, 05100 Terni (Italy);
[email protected] b Institute of Polymer Science and Technology (C.S.I.C.) Spain
Introduction. Stimuli responsive polymers are gaining attention in materials engineering due to their high versatility in
different applications as biomedical, mechatronic or aerospace industries. These materials change its shape
and its properties in presence of certain stimuli such as temperature, pH or electrical fields among others1. In
this paper we report the synthesis and characterization of shape memory polyurethanes, based on synthesized
poly(L-lactic acid) (PLLA) and poly(-caprolactone) (PCL) tri block-copolymers. In recent years the interest
on these polymers for the biomedical sector has increased because. In particular, PLLA is a rigid polymer
with melt temperature around 170 ºC while PCL has a glass transition below room temperature, so, it is
rubber in normal conditions2. The combination of these two materials can produce a material with shape
memory behaviour. In fact, it is possible to obtain a formulation where two different phases co-exist
together, the fixed and the switching one3. The first phase is responsible to remember the original shape. On
the other hand the switching bonds, which are formed below the transition temperature (Ttrans) and are
destroyed above it, permit to fix a temporary shape.
In general, in order to verify the shape memory behaviour of a material it is necessary to heat the sample
above the corresponding Ttrans and to strain the sample. Then, the material is cooled maintaining the
deformation; so, once the applied stress is removed, the recovery of original shape occurs when re-heating
the sample above the Ttrans. Two parameters can be calculated from this experiment to evaluate the shape
memory behaviour, namely the strain fixity and the strain recovery. The first one indicates the ability of a
polymer to fix the temporary shape and the second one evaluates the capacity of the material to recover the
original shape.
In this work, the synthesis of polyurethanes based on the reaction of a diisocyanate with tri block PLLA-PCL
polymers is reported as well as their thermal and mechanical characterization. Moreover, the shape memory
behaviour of these materials has been verified. In these polyurethanes, the PLLA crystals will act as fixed
phase whilst PCL crystals are considering as the switching bonds. Therefore, in our case, the Ttrans will be the
melting temperature of the PCL block.
Materials and methods.
The synthesis of the polyurethanes was performed in two steps. In the first one, tri-block copolymers (PLLA-
b-PCL-b-PLLA) were synthesized by ring opening polymerization of lactic acid induced by PCL-diol, using
Sn(Oct)2 as catalyst. Three commercial PCL-diols with different molecular weights (2000, 4000 and 8000
g/mol, respectively) have been used. The reaction took place in a round bottom flask, with a magnetic stirrer,
in an oil bath, at 180 ºC for 3 h, without solvent. When the reaction finished, the mixture was dissolved in
chloroform and precipitated in cold methanol. After that, the polymer was filtered off and dried in vacuum
for 24 h. Varying the amount of lactic acid as well as of PCL-diol, 12 different PCL-middle-block tri-blocks
were synthesized. In the second step, one of the tri-block copolymers was reacted with hexamethylene
diisocyanate (HDI), (1:1 in mol) in dichloromethane. The reaction took place by stirring the materials with
Sn(Oct)2 as catalyst, in an oil bath at 80 ºC for 5 h. The resulting polymer was precipitated on a glass dish
and dried in vacuum for 24 in order to remove the solvent. The determination of the structure and the
molecular weight of the tri-block copolymers were obtained by 1H-NMR in a Varian Mercury 400 apparatus
at 400 MHz, using CDCl3 as solvent. To study the crystalline structure of each block, differential scanning
calorimetry (DSC) was performed in a Mettler Toledo 800 and Small Angle X-ray Scattering (SAXS)
measurements were taken at beamline BM16 at the European Synchrotron Radiation Facility (Grenoble,
France). Mechanical properties and shape memory characterization was carried out using an Instron,
Universal Testing Machine. Dog-bone specimens of the polyurethanes were cut for the mechanical
characterization, while in order to realize the shape memory characterization, samples were cut in
rectangular specimens of 5.2 mm in width, 15 mm in length and 0.5 mm in thickness.
Result and discussion.First, the synthesis of 12 different (PLLA-b-PCL-b-PLLA) tri-block copolymers was
performed by using 3 different PCL-diols (with different molecular weights of about 2000, 4000 and 8000
g/mol, respectively) and varying both the length of the block of each block and the block correlation. With
1H NMR spectroscopy we observed the presence of PLLA-end groups and the absence of PCL-end groups,
thus confirming the expected PCL-middle-block tri-block structure. Moreover the molecular weight of the
tri-blocks was calculated from this technique4. Based on this experimental value, the required amount of HDI
to synthesize the PCL-PLLA polyurethanes was calculated. 12 different polyurethanes have been obtained
thus varying the ratio between the blocks. In figure 1a, the 1st DSC heating scan and the long period
calculated from SAXS analysis for one of the synthesized polyurethane (U11) is reported. In particular, the
DSC thermogram reveals two broad endothermic peaks. The first peak at about 50 ºC, corresponds to the
melting of PCL crystals and the other one, at about 150 ºC, corresponds to the melting of PLLA crystals.
Taking into account the enthalpy of fusion of each block it is possible to calculate the crystallinity degree for
each block in the synthesized polyurethanes. Moreover, the SAXS experiment confirms the crystalline
structure of the polymers. In particular, the scattering spectrum reported in figure 1b, shows a broad peak due
to the presence of polymer crystals. SAXS patterns were taken at different temperatures. It can be note a
displacement of the SAXS peak is observed when increasing the temperature, thus indicating the presence of
different kinds of crystals in the polymer. As it is known, for lamellar structure this peak can be related with
the long period through the Bragg equation5. In figure 1a the variation of the long period with the
temperature is reported. Two variations in the curve trend indicate the crystal melting of the two different
blocks. By comparing the two graphs reported on Figure 1a, it can be noted that the melting temperatures
obtained by the SAXS experiments are in good agreement with the DSC results.
Figure 1: a) Long period and DSC and b) Iq
2 vs q curves at different temperatures from the SAXS experiment for U11
As it is known, PLLA has a Tg above room temperature and presents high elastic modulus but it is brittle,
while PCL is a rubber-like polymer with temperature Tg at about -60 ºC. Thus, the synthesized polyurethanes
present a wide range of mechanical properties as a function of their composition and the length of each
block, in terms of elastic modulus, (20 to 229 MPa), tensile strength (8 to 50 MPa) and maximum elongation
at break (10 to 2000 %), showing a good correlation with the composition of the polyurethanes studied.
The shape memory experiments were designed taking into account the melting temperature of the PCL-block
obtained by DSC measurements. In order to characterize the shape memory behavior of these polyurethanes
a range of strains was evaluated and five cycles were performed on the same specimen.
Conclusion.
Bio-polyurethanes based on PCL and PLLA blocks have been synthesized in two steps. They are physico-
chemically characterized by 1H NMR, DSC and SAXS analysis. The mechanical properties are also
analyzed, and correlate with their structure. Moreover, their shape memory behavior has been investigated
and correlated with their structure.
Acknowledgements.
We are indebted to the Ministry of Science and Innovation (MICINN) in Spain for their economic support of the work
(MAT2010-21494-C03-03; MAT 2011-25513) and the access to the synchrotron radiation source (experiment 16-2-87)
in the ESRF (France). LP acknowledges also, the support of Juan de la Cierva grant from MICINN (MICINN-JDC).
References
1. M. Behl, M. Y. Razzaq, A. Lendlein, Advanced Materials 2010, 22, 3388.
2. R. V. Castillo, A. J. Muller, J. M. Raquez, P. Dubois, Macromolecules 2010, 43, 4149.
3. A. Lendlein, S. Kelch, Angewandte-Chemie international edition 2002, 41, 2034.
4. M. Bero, J. Kasperczyk, G. Adamus. Macromolecular Chemistry and Physics 1993, 194, 907.
5. J. K. Kim Kim, D. J. Park, M. S. Lee, K. J. Ihn, Polymer 2001, 42, 7429.
POLY(9,9'-DIHEXADECYLFLUORENE-CO-BITHIOPHENE): SYNTHESIS AND
PHOTOPHYSICAL PROPERTIES
Vagif Dzhabarov, Drahomir Vyprachticky, Ivan Kminek, and Vera Cimrova
Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovský Sq. 2, 162 06
Prague 6, Czech Republic (www.imc.cas.cz)
Introduction. Microwave-assisted synthesis is one of the most prominent way how to reduce the reaction
time of Pd-catalyzed cross-coupling polymerization reactions like Suzuki coupling1. In such reactions aryl
halides and aryl-boronic esters can be utilized2. It is also well known that aryl chlorides like chlorobenzene
are relatively inert to Suzuki cross-coupling3 but have an ability to solubilize rigid-rod polymers and can be
used as solvent. In this work four conjugated alternating copolymers of fluorene and bithiophene
(abbreviated F16T2) were synthesized by microwave assisted Suzuki coupling in different solvents
(chlorobenzene and xylene) by 2 possible ways (fig.1). Products were characterized by elemental analysis,
size exclusion chromatography, UV-Vis and PL spectroscopy, HOMO and LUMO levels were determined
by cyclic voltammetry measurements.
Br Br
C16H33 C16H33
S SBB
O
O
O
O
B B
O
O
O
O
C16H33 C16H33
S SBrBr
S S
C16H33 C16H33
n
1
2
Figure 1. Scheme of possible synthetic routes for poly(9,9-dihexadecylfluorene-2,7-diyl-alt-2,2’-bithiophene-5,5’-diyl)
F16T2.
Experimental.
2,7-dibromo-9,9-dihexadecyluorene, 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-2-yl)-9,9-
dioctylfluorene were synthesized according to ref.4 and ref.5 respectively. The synthesis of polymers was
carried out using palladium-catalyzed Suzuki cross-coupling reaction and all the procedures were performed
under an argon atmosphere.
Poly(9,9-dihexadecylfluorene-2,7-diyl-alt-2,2’-bithiophene-5,5’-diyl) (basic polymerization technique). In
microwave-assisted synthesis monomers 2,7-dibromo-9,9-dihexadecylfluorene (400 mg, 0,518 mmol), 5,5'-
bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,2'-bithiophene (216,44 mg, 0,518 mmol) and catalizer (12
mg of Pd(PPh3)4 – 1% mol) were dissolved in mixture of 8 ml of solvent (chlorobenzene or xylene) with 8
ml of 15% aqueous NaHCO3. Then 3 drops (0,04 g) of Aliquat@336 were added and mixture after bubling
with argon for 10 minutes was putted into microwave reactor for 40 min. After procedure mixture was
separated on two layers and nonpolar layer was poured into 100 ml of methanol. Precipitated product then
was dissolved in CHCl3, filtered and precipitated in methanol again. The solid material was washed for 24 h
in a Soxhlet apparatus using acetone to remove oligomers. The resulting polymers were soluble in
chloroform, THF, DCB.
Results and discussion.
To assess the impact of monomers nature we synthesized four alternating copolymers by microwave-assisted
Suzuki cross-coupling by 2 different ways. Time of reaction was 40 minutes and solvent (chlorobenzene or
xylene) were changed. Solvents were chosen due to high boiling points and relatively high dielectric
constants with ability to dissolve monomers and products. Dielectric constants for chlorobenzene is 5,62 and
for o-xylene is 2,67. Conditions of synthesis (temperature and solvent), molecular weights of synthesized
polymers and other characteristics of polymers presented in table 1.
Table 1. Abbreviation, yields, molecular weights (Mn, Mw), index of polydispersity (PDI),
absorbance maximum in THF solutions, quantum yield in toluene solutions, band gaps (optical and measured
by CV) of the synthesized polymers.
Monomers and
conditions Yield M
n M
w PDI
Absorbance
maximum,
nm
Quantum
yield
Optical
band gap,
eV
Band
gap, eV
F16T2-CB1, 131 °C,
chlorobenzene 63 % 2716 4253 1,5 431 0.31 2.50 2.84
F16T2-X1, 140 °C,
xylene 60% 8390 14110 1,7 446 0.27 2.41 2.82
F16T2-CB2, 131 °C,
chlorobenzen 38 % 4155 6460 1,6 444 0.29 2.38 2.72
F16T2-X2, 140 °C,
xylene 95 % 16000 28240 1,8 449 0.26 2.37 2.83
It was found that chlorobenzene may be used as a solvent in Suzuki coupling with ability to obtain
rather low molar mass polymers. In both solvents polymers with relatively high molar masses can be
synthesized using the 2nd
route (fig. 1). Due to increasing of conjugation length absorbance maximum was
red-shifted up to 449 nm. PL emission of F16T2 polymer lies in green region and PL spectra presents in
figure 2. The related to quinine sulfate quantum yields of photoluminescence are presented in the table 1. It
was found that polymer F16T2-X1 has HOMO = 5,4 eV and LUMO = 2,6 eV levels and due to these values
polymer light emitting devices with configuration of ITO/PEDOT:PSS/F16T2-X1/CaAl was made by spin
coating of 1% weight toluene solution of polymer. Voltage-current curve is presented on figure 2. It was
found that photoluminescence has minor difference from electroluminescence for F16T2-X polymer. Highest
luminescence values obtained were around 300 cd/m2
for device with structure ITO/PEDOT:PSS/F16T2-
X1/CaAl which is comparable with literature for devices with the same configuration.
0 5 10 15 20 25 300,01
0,1
1
10
100
Lum
ina
nce
(cd
/m2)
Voltage (V)
Figure 2. Emission spectra (PL), electroluminescence (EL) and luminance characteristic of light emitting
device with structure ITO/PEDOT:PSS/F16T2-X1/CaAl
Conclusions.
New alternating fluorene-bithiophene copolymers with different molar masses up to 28000 (polystyrene
standard) were synthesized by microwave-assisted Suzuki coupling with short reaction time of only 40 min.
Chlorobenzene as a solvent can be used in such type of polymerization reactions. Polymers, prepared by 2nd
route (fig. 1) showed higher molar masses.
References 1. F. Galbrecht, T. W. Bunnagel, U. Scherf, T. Farrell. Macromol. Rapid Commun., 2007, 28, 387.
2. B. Nehls, U. Asawapirom, S. Füldner, E. Preis, T. Farrell, U. Scherf, Adv. Funct. Mater., 2004, 14, 352.
3. N. Miyaura and A. Suzuki. Chem. Rev. 1995, 95,2457.
4. G. Saikia, P. K. Iyer. J. Org. Chem. 2010, 75, 2714.
5. M. Ranger, D. Rondeau, M. Leclerc. Macromolecules, 1997, 30, 7686.
400 600 800
0,0
0,2
0,4
0,6
0,8
1,0
EL (
rel.un.)
Wavelength (nm)
EL
PL
PENTACENE DERIVATIVES FOR FIELD-EFFECT TRANSISTORS
Veronika Slunečkováa, Hecham Aboubakrb, Samrana Kazima, Olivier Sirib, Jiří Pflegera
aInstitute of Macromolecular Chemistry AS CR, v.v.i., Heyrovského nám. 2, 162 06 Praha 6 Czech Republic; [email protected]
bCNRS Unité No UPR3118, Campus de Luminy, case 913, 13288 Marseille Cedex 09, France
Introduction. Pentacenes are well-known materials for their superior charge carrier mobility, suitable for electronic applications. However, their poor stability against oxidation in air limits their exploitation. The electronic properties of the pentacene molecule should be improved without disturbing the molecular skeleton, in order to maintain strong intermolecular interactions and stability of the solid state intermolecular arrangement. Replacing some of carbon atoms of the pentacene skeleton with heteroatoms could be the desired alternative. Experimental. Pentacene derivatives were prepared by condensation reaction of 2,5-dihydroxy-1,4-benzo-quinone with different compounds. Reactants were mixed well and ground together with a mortar and pestle, the reaction run in water or in acidic conditions, usually at higher temperature. Alkylated tetraazapentacenes where prepared by alkylation of pure tetraazapentacene at room temperature in inert atmosphere. Homogeneous films of alkylated tetraazapentacenes where prepared by dip-coating from chlorobenzene solutions. The films where deposited on n-doped Si/SiO2 substrates with Au source and drain electrodes (bottom contact, bottom gate FET configuration, Fraunhofer IPMS substrates). Thickness of the film was about 10 nm. The output characteristics of the field-effect transistors were measured in the interval +10V to -40V.
Results. Several derivatives of tetraaza-pentacene where synthesized containing methyl-, octyl- and pentadecyl- side-groups, respectively. Non-alkylated derivatives have low solubility in all common solvents suitable for film deposition from solutions. Derivatives containing sulphur were found to be sensitive to light and air exposure. Unsubstituted tetraazapentacenes are pH-sensitive but stable in air. Only methyl-substituted tetraazapentacene 5,14-dimethyl-5,14-dihydro-5,7,12,14-tetraazapentacene showed the field-effect transistor behavior, however due to a limited solubility and hence low thickness of the active channel the source-drain current was very low. Acknowledgements. This work was supported by the Ministry of Education, Youth and Sports of the CZech Republic (MEB021148 – Barrande) and of partially by the NoE FlexNet Project, EU ICT 247745 (7FP)
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