Surface Gold and Silver-PolymerNanocomposite Self-Standing Films

Simona Badilescu, Jai Prakash, and Muthukumaran Packirisamy

ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Surface Nanocomposites Prepared by in Situ Methods and Thermal Convection . . . . . . . . . . . . . . 3Surface Nanocomposites Prepared by Physical Deposition Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

AbstractSurface gold (silver)-polymer nanocomposites are an emerging category of compos-ite materials not studied in a systematic manner until now. It was found that,sometimes, in situ synthesis methods, using a metal precursor, result in nano-composites with gold nanoparticles segregated in a subsurface layer of the polymerand/or at the interfaces with the substrate and the atmosphere. Surface nano-composites have been obtained through completely different approaches, most ofthe time by chance. One can even question whether these materials arenanocomposites, or, simply, nanoparticles layered on the surface of a polymer, orsegregated in a subsurface layer. Their properties, including the sensing capabilities,are completely different from the nanocomposites, having nanoparticles uniformlydispersed in the polymer matrix. The dispersion and organization of nanoparticles inpolymer matrices are important to control the properties of nanocomposites. In spiteof the efforts to achieve nanocomposites with appropriate morphologies andenhanced surface properties, the control of nanoparticles spatial distribution stillremains a challenge. This paper brings together a range of methods that aim to

S. Badilescu (*) · M. PackirisamyOptical Bio-Microsystems Laboratory, Department of Mechanical, Industrial and AerospaceEngineering, Concordia University, Montreal, Qc, Canadae-mail: simonabadilescu0@gmail.com

J. PrakashDepartment of Chemistry, National Institute of Technology Hamirpur, Hamirpur, India

© Springer Nature Switzerland AG 2019C. M. Hussain, S. Thomas (eds.), Handbook of Polymer and Ceramic Nanotechnology,https://doi.org/10.1007/978-3-030-10614-0_11-1

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control the formation, growth, and segregation of nanoparticles in polymer films. Thediversity of procedures that may result in the formation of surface nanocomposites,some from the authors’ own work, is overviewed in this paper.

KeywordsNanocomposites · Gold nanoparticles · Segregation · Sensing

Introduction

Nanoparticle-polymer composites, “where two small worlds meet” (Balazs et al.2006), are advanced functional materials, generally, with nanoparticles integratedinto a polymer matrix. In addition to the characteristics of polymers, nanocompositesmay acquire the outstanding electrical, optical, and magnetic properties of theirmetal nanoparticle components. The properties of the nanocomposite are influencedby the size, shape, and distribution of nanoparticles in the polymer matrix. Potentialapplications of nanocomposites that originate from the properties of nano-sizednoble metals are ultrathin color filters, UV absorbers, optical sensors, plasmonwaveguides, optical strain detectors, and thermochromic materials. Because of thestrong Au and Ag localized surface plasmon resonance (LSPR) bands in the visiblespectrum, stemming from the excitation of plasmons by the incident light and givingrise to characteristic absorption and strong field confinement and enhancement, somegold nanocomposites are particularly appropriate for sensing applications. LSPR hasbeen extensively exploited for sensing and biosensing with enormous progress inrecent years, both in terms of instrumentation and applications. Of the various metalnanoparticles reported in the literature, gold is the most promising candidate, due toits excellent surface properties that can be exploited in biotechnological, optical, andelectrochemical applications. The advantages of the gold nanoparticles include non-toxicity, strong scattering length, bio-conjugation, and long-term stability, charac-teristics essential for a stable and sensitive biosensing platform as well as for otherapplications. In general, the biosensing properties of nanocomposites depend onparameters related to the conditions of their preparation, pivotal for the distributionand the spatial organization of the metal particles in a polymer matrix. Nano-composites can be synthesized through different approaches, principally, either byin situ methods or by incorporating pre-made nanoparticles into a polymer matrix, byusing a common solvent (ex situ). In addition, physical methods such as chemicalvapor deposition, ion implantation, sputtering, gamma and ultraviolet irradiation,and thermal evaporation have been successfully used. Convective assembly of goldnanoparticles on the surface of polymer films results in formation of surface nano-composites (Fanous et al. 2018). It was found that, sometimes, in situ synthesismethods, using a metal precursor, result in nanocomposites having gold nano-particles segregated in a subsurface layer of the polymer. This special class ofnanocomposites is an emerging category of composite materials that were notstudied in a systematic manner until now. They were obtained through very differentapproaches, sometimes almost by chance. Their properties, including their sensing

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capabilities, are completely different from nanocomposites, having the nanoparticlesuniformly dispersed in the polymer matrix. One can even question whether thesematerials are nanocomposites, or, simply, nanoparticles layered on the surface of apolymer, or segregated in a subsurface layer. For the purpose of this paper, they willbe called surface nanocomposites. It has to be mentioned that ion implantation,thermal evaporation, and sputtering methods all result in nanoparticles on the surfaceof the polymer. The control over the shape, size, and proximity of nanoparticles canbe achieved by controlling the deposition parameters. In spite of the efforts toachieve nanocomposites with appropriate morphologies and enhanced surface prop-erties, the control of nanoparticles spatial distribution still remains a challenge. Thedispersion and organization of nanoparticles in polymer matrices are important tocontrol the properties of nanocomposites. This paper brings together a range of novelmethods that aim to control the formation, growth, and segregation of NPs inpolymer films. The recent achievements in the fabrication of surface nano-composites, some of the characterization methods of the resulting material, andtheir potential applications will be overviewed in this paper.

Surface Nanocomposites Prepared by in Situ Methods andThermal Convection

As shown in the next section, when physical deposition methods are used to preparegold nanocomposites, gold nanoparticles will stay on the surface of the samples.When used for sensing, they have the advantage to be in a direct contact with theanalyte. In the case of in situ (chemical) methods, using gold precursors and variouspolymers, for now, there is no general method that could be used to prepare surfacenanocomposites. In the literature, there are few examples of surface nanocomposites,and they have been prepared by a variety of approaches, in most of the cases, withoutthe express purpose to obtain them. The diversity of procedures that may result in theformation of surface nanocomposites and their properties are briefly describedbelow.

In one example, gold-PDMS surface nanocomposites have been preparedrecently (Bonyár et al. 2017), simply by pipetting a small amount of gold precursorsolution (HAuCl4) on the top of a 5-mm-thick PDMS sample, kept in a hermeticallysealed Petri dish for a given time, at a given temperature (Bonyár et al. 2018).

The authors concluded that the reduction of the precursor at the solution-polymerinterface leads to the formation and growth of gold nanoparticles which sink and arecovered by a polymer layer. When PDMS is used, the reductant of the precursor isthe cross-linker, present in the PDMS composition.

Because of the polymer layer covering the nanoparticles, the nanocompositeprepared in this way had a very low refractive index sensitivity. However, in asubsequent work, the authors found that, in spite of the embedding of nanoparticles,this nanocomposite has been proved to be a highly sensitive SERS substrate (Bonyáret al. 2018) (Fig. 1).

Surface Gold and Silver-Polymer Nanocomposite Self-Standing Films 3

By using a similar method, SadAbadi et al. (2013) prepared surface nano-composites by using microwave irradiation to enhance the reduction of Au3+ at theinterface of the polymer-precursor solution. The fabrication of the nanocompositestarts with dropping 60 μL of the ethanol solution of chloroauric acid (HAuCl4) on aPDMS sample. The solution is spread over the whole area, after keeping it 10 min incontact with the PDMS surface. The samples are then introduced in a commercialmicrowave oven and irradiated for different times. Figure 2 illustrates the procedure,and Fig. 3 shows the increased absorbance of the Au-LSPR band when the goldprecursor concentration is increased.

The sensing ability of nanocomposites prepared through microwave irradiationwas found to be quite low.

Other groups (Hasell et al. 2008) have prepared silver nanoparticle impregnatedpolycarbonate substrates for SERS application, by using supercritical CO2(scCO2)as a solvent for the organometallic precursor of Ag. After an impregnation time of24 h, at a pressure of 10.4 MPa, a uniform band of Ag nanoparticles can be seen in

Fig. 1 Surface Au-PDMSsamples prepared underdifferent conditions.(Reproduced with permissionfrom IEEE for Bonyár et al.2017)

Fig. 2 Procedure for thepreparation. The ethanolsolution of the gold salt (1%)is dropped on the PDMSsurface. (Reproduced withkind permission from Wileyfor SadAbadi et al. 2013,2014)

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the TEM image, located along the outermost edge of the cross section, with athickness of around 6.5 μm. The authors call this “depth limited incorporation”due to the time-dependent infusion of the precursor into polycarbonate. By modifi-cation of the time and pressure, the depth and size/concentration can be controlled.

The depth limited incorporation of NPs suggests a time-dependent infusion of theprecursor into the polymer during the impregnation step. The stable data obtained byusing the silver nanoparticle impregnated polycarbonate as SERS substrates are dueto the partial protection of Ag NPs by a thin polymer layer. The results have shownthe possible application of these nanocomposites as SERS substrates. It is interestingto mention that the nanoparticles embedded in the polymer are still effective inRaman enhancement but not for sensing.

Deshmukh and Composto (2007) have prepared Ag-PMMA nanocomposites,containing 5–20% (wt.) of silver, by the thermal decomposition of a silver precursorin PMMA films. An organometallic complex, with silver acetate dissolved in methylisobutyl ketone is used as a source of Ag. PMMA powder is added, and the residualcomplex is removed during the thermal decomposition. After 10 hours of stirring, thesolution was spin-coated on silicon and glass substrates and pre-annealed at 107 �C for24 h, to remove the residual solvent. Ag NPs were formed by further annealing at185 �C for several hours. Depth profiles (Rutherford backscattering) spectra clearlyshowing the strong surface segregation upon annealing are given in Fig. 4.

The authors explained the segregation of Ag at the surface and substrate regionsby the diffusion of the precursor upon annealing, concurrently with nanoparticleformation. High-density NPs are found, located near the surface. In this case, theformation of AgNPs happened during the pre-annealing process. Aggregates of NPsform near the surface, and their diameters are 20–75 nm. The surface-rich Ag layer isfound to be around 60 nm thick. TEM results have shown that the NPs adjacent tothe surface are covered by a polymer layer a few nanometers thick (1–5 nm). The

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Surface Gold and Silver-Polymer Nanocomposite Self-Standing Films 5

precursor migrates to the surface, and, only upon heating, (temperature of decom-position is 185 �C) it is reduced to AgNPs, both at the surface and substrate, creatingan excess of silver at both interfaces. The silver nanoparticles produced by thermaldecomposition are 2–10 nm in diameter and roughly spherical. Controlling the nearsurface morphology can tailor macroscopic properties such as reflectivity andconductivity of the film. Applications of Ag-PMMA nanocomposite for nonlinearoptical limitation, plasmon waveguides, and metal-enhanced fluorescence have beensuggested by the authors.

Several surface nanocomposites have been prepared by depositing ready-madegold nanoparticles on polymer films (PMMA, poly(styrene), poly(vinyl alcohol),PDMS, and (SU-82), spin-coated on glass substrates, by using a thermal convectionmethod (Fanous et al. 2018). A schematic of the thermal convection technique isshown in Fig. 5.

By slightly heating a gold colloidal solution, the gold particles are gradually trans-ferred as ordered multilayers on the polymer substrate. Further, the nanocomposite washeated gradually as shown in Fig. 6, and the material was investigated at different stagesof heat treatment.

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This technique involves the transfer of gold nanoparticles from the colloidalsolution onto the polymer film, through evaporation and assembly. Spherical goldnanoparticles were produced according to Turkevich’s method, employing thereduction of chloroauric acid by sodium citrate (Kimling et al. 2006). The solutionwas prepared from 1 mM of gold(III) chloride trihydrate dissolved in 90 ml of water,which was subsequently boiled. Fifteen milliliters of a sodium citrate solution (2%)was added, and the solution was heated until the color of the solution became red-purple. After that, the solution was further boiled for 15 min and then left to cool toroom temperature. The gold colloidal solution was evaporated onto the slanted(inclined, slightly angled) polymer samples in a beaker, and the gold nanoparticleswere self-assembled through a convective assembly process, as shown in Fig. 6.

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Fig. 5 Schematic of theconvective assemblyprocedure of deposition ofgold nanoparticles.(Reproduced with permissionfrom Springer Nature forFanous et al. 2018)

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Fig. 6 Schematic depicting the gradual morphological changes through incremental heat treatmentof AuNP-polymer surface nanocomposites. (Reproduced with permission from Springer Nature forFanous et al. 2018)

Surface Gold and Silver-Polymer Nanocomposite Self-Standing Films 7

Once immersed in the solution, the slides were kept in the oven, until the wholeamount of gold was slowly transferred to the substrate, typically a duration of 2 days.

The segregation of gold nanoparticles at the surface of the PVA film is shown inthe schematic seen in Fig. 7 and the SEM image in Fig. 7.

It has been found that the incremental heating of the nanocomposite film resultedin an enhancement of the refractive index sensitivity. Preliminary results have showna large redshift of the Au-LSPR band when some of the surface nanocompositeswere heated incrementally, and to describe this technique, the authors coined theterm “thermal manipulation.” It is thought that the increased sensitivity is due to themorphology changes induced by the incremental heating (Fig. 8).

Gold-PDMS surface nanocomposites have been also prepared in the channel of alab-on-a-chip to be used for plasmonic biosensing (SadAbadi et al. 2013). Theprecursor solution was introduced in the channel and kept for a day, to completethe reduction reaction. Figure 9 illustrates the cross section of the channel, showingthe migration of the reductant molecules to the surface.

Nanoparticles were integrated in a PDMS microfluidic device for plasmonicbiosensing purposes (SadAbadi et al. 2013). The synthesis of the nanocompositein the microchannel resulted in an improvement of the size distribution as shown inFig. 10.

In agreement with the narrower size distribution, the Au-LSPR band (Fig. 10d)appears also much narrower and is situated at a lower wavelength, compared to thenanocomposite prepared in a macro-environment. This results in an improvedperformance of the sensing. Figure 11 shows the steps of the biosensing protocolfor the detection of the bovine growth hormone. The detection limit found thedetection of this hormone was as low as 3.7 ng/mL.

Fig. 7 SEM image of AuNPson the PVA surface at roomtemperature (beforeannealing). (Reproduced withpermission from SpringerNature for Fanous et al. 2018)

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Surface Nanocomposites Prepared by Physical DepositionMethods

Physical deposition methods have been extensively used for producing such surfacenanocomposites for a variety of applications, including optoelectronics and biomedicalapplications. These methods include physical vapor deposition (PVD) of metals using

Fig. 8 Position of the Au plasmon band at different temperatures (80 �C (dark blue), 100 �C (red),125 �C (green), 150 �C (purple), 175 �C (light blue), 200 �C (orange)) with the wavelengthdifference of the first and last bands for a PVA, b PDMS, c SU-82, and d PS. (Reproduced withpermission from Springer Nature for Fanous et al. 2018)

Fig. 9 Illustration of the insitu reaction in the channeland the migration of reducingagent. (Reproduced withpermission from SpringerNature for Fanous et al. 2018,SadAbadi et al. 2013)

Surface Gold and Silver-Polymer Nanocomposite Self-Standing Films 9

sputtering, electron beam evaporation, ion implantation, etc. (Prakash et al. 2016a;Ferreira et al. 2012). The composite layer could be obtained by annealing the metallayer after deposition or by co-sputtering/vapor phase co-evaporation of the metal andpolymer (Giesfeldt et al. 2003, 2005; Avasthi et al. 2007; Mishra et al. 2010).

PVD allows to control over the composition of the nanocomposites by controllingvarious factors such as filling factor, size, and shape of the metal nanoparticles(Prakash et al. 2016a; Torrisi and Ruffino 2015). Through evaporation, or sputteringdeposition of noble metals, there is the formation of spherical nanoparticles onsubstrates like polymers, due to the higher cohesive energy of the metals. Giesfeldtet al. (2005) demonstrated the tuning of optical properties of gold nanoparticlesdeposited onto the PDMS substrates (0.2 or 1.0 A/s) by PVD. They demonstratedthat PVD deposited gold nanoparticles undergone a rapid diffusion in the subsurface

Fig. 10 SEM images and particle size distribution of annealed material; (a) microchannel andformation of gold NPs on the channel surfaces; at the left side, the channel edge is shown and theinset shows the shape of particles. (b, c) SEM image and the corresponding size distribution of goldNPs prepared by 2% solution of gold precursor for 48 h of incubation for two different (cmicrochannel and d macro-scale) environments. (d) Au-LSPR band of nanocomposites preparedin microchannel and macro-scale environment. (Reproduced with permission from Elsevier forSadAbadi et al. 2013)

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of the PDMS polymer layer, creating a subsurface composite layer with tunableoptical properties (Fig. 12). The optical properties could also be tuned by manipu-lating the rate of deposition/average thickness as shown in Fig. 12 and studied for theSERS sensing of biologically relevant amine- and nitro-based compounds as shownin Fig. 13.

It was demonstrated that the Au-PDMS layer exhibited better SERS sensingproperties, compared to the Au-glass (Au islands on glass) synthesized under similar

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Surface Gold and Silver-Polymer Nanocomposite Self-Standing Films 11

experimental parameters. The SERS signals were more pronounced for Au-PDMSwhich was attributed to the unique advantage of PDMS as a solid-phase extractor asshown in Fig. 13.

Similarly, Lee et al. (2015) studied the Ag-glass and Ag-PDMS systems, bydepositing sputtered Ag films on the PDMS template for SERS applications anddemonstrated that the thickness and roughness of the surface layer effected the SERS

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activity. It was shown experimentally as well as theoretically that both factorsinfluenced the SERS enhancement. Zvátora et al. (2011) studied the Au-Teflonsystem for SERS enhancement of biphenyl-4,40-dithiol by sputtering deposition ofAu layer on a Teflon substrate.

Similarly, polymer nanocomposites embedded with gold or silver synthesized byusing other PVD methods such as co-evaporation or co-sputtering provide a thinlayer with excellent optical properties, with promising applications in variousresearch fields (Torrisi and Ruffino 2015; Rozas et al. 2007) (Fig. 14).

Avasthi and his group (Mishra et al. 2010; Avasthi et al. 2007) have studied theoptical properties of Ag-PET thin films synthesized by co-sputtering and reportedthat the optical properties of these films could be tuned to the infrared region. They

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Surface Gold and Silver-Polymer Nanocomposite Self-Standing Films 13

also reported that such nanocomposite thin films can be used as bandpass filter at320 nm which is very useful for HeCd laser.

Similarly, Grytsenko et al. synthesized Au-Teflon nanocomposite films using theco-deposition method, by varying the metal concentrations, and studied their opticalas well as SERS applications, along with the effect of heating on these properties. Itwas found that the size of gold nanoparticles increased with the concentration, andsimilarly, LSPR was also found to be dependent on the size of the gold nanoparticles.These nanocomposite films showed excellent SERS sensing properties toward theRhodamine 6G dye molecules. Biswas et al. (2009) demonstrated the formation offractal Ag-Teflon nanocomposites using a co-deposition technique which wereshown to exhibit excellent SERS substrates for DNA sensing.

Noble metal ion implantation into polymer surface with 10s of keV to 100 keVallows the formation of a surface nanocomposite layer in the near surface of thepolymeric matrices (Kavetskyy et al. 2018; Stepanov 2004). Other ways of utilizingthe ion beam technique for producing nanocomposite materials are the ion beaminduced mixing of thin metal films deposited over the polymer substrates andembedding of metal nanoparticles supported on the polymer surfaces (Fig. 15).

The synthesized nanocomposite layer modifies not only the chemical propertiesbut also the physical properties, and, mainly, the optical properties are improved, dueto the formation of metal nanoclusters.

Different ion beam methodologies have been used for the implantation of metalnanoparticles in the near surface region of the polymers. The various processes

Fig. 14 Schematic of co-sputtering and co-evaporation methods for the fabrication of metal NPsembedded in a matrix. (Reproduced with permission from Taylor & Francis for Prakash et al.2016a)

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involved in the ion implantation have been shown in Fig. 16, along with theformation of metal nanoparticles. For example, Kavetskyy et al. (2018) demon-strated the formation of a near surface region of PMMA substrate as Ag-PMMAnanocomposites, using low-energy Ag ion implantation of 30 keV, and discussed thedetailed mechanism behind. Similarly, Stepanov (2004) reported that polymer sub-surface layers could be embedded with Ag nanoparticles by 30 keV Ag+ ion

Fig. 15 Schematic of ion beam synthesis techniques of embedded metal NPs in a substrate.(Reproduced with permission from Prakash et al. 2016a)

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Fig. 16 Basic physical stages of nanoparticle synthesis by ion implantation vs. ion dose.(Reproduced with permission from Springer Nature for Stepanov 2004)

Surface Gold and Silver-Polymer Nanocomposite Self-Standing Films 15

implantation at varying doses, from 3.1 � 1015 to 7.5 � 1016 cm�2. They examinedthe implanted samples with various spectroscopic and microscopic techniques whichexhibited LSPR and formation of Ag nanoparticles in the near surface of the polymer(Fig. 17). LSPR could be tuned by varying the ion doses. It was also found that theAg implanted layers in polymer became more carbonized due to evolution ofhydrocarbon from the polymers.

Prakash et al. (2011, 2014, 2016a) have demonstrated the formation of a nano-composite layer on PET polymer embedded with gold nanoparticle by low-energyAr ion irradiation. Thin layers of gold film were first deposited over the PET surfaceby evaporation of gold metal in vacuum and then irradiation with 150 keVAr ions.The thin gold layer first dewetted from the polymer surface with subsequentsputtering of a gold film that finally provided gold nanostructures on the surfacewhich on further irradiation got embedded in the polymer surface forming a surfacenanocomposite (Fig. 18).

These gold nanostructures formed on the surface of PET polymer and embed-ded within the surface showed excellent LSPR properties. These gold nano-structures formed on the surface and embedded in the surface also exhibitedenhanced Raman signals for dye molecules at very low concentrations. SERSanalyses showed a unique SERS behavior of these gold nanostructures: dyemolecules were adsorbed parallel and perpendicular on the gold surface whengold nanostructures were existing on the surface and embedded in the surface,respectively (Fig. 19).

Fig. 17 Micrograph of silvernanoparticles produced byAg+ implantation into PMMAat a dose of 5 � 1016 cm�2.(Reproduced with permissionfrom Springer Nature forStepanov 2004)

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Fig. 18 SEM (left) and X-TEM (right) images of Au/PET system (a) pristine with EDAX spectrumand after irradiation at fluency of (b) 5� 1015, (c) 1� 1016, and (d) 5� 1016 ions/cm2 (θ cont is theaverage contact angle of AuNPs with the PET surface for the calculation of interfacial energy and toshow the dewetting of the films from the surface in terms of contact angle). (Reproduced withpermission from Elsevier for Prakash et al. 2011, 2014)

Surface Gold and Silver-Polymer Nanocomposite Self-Standing Films 17

Conclusion

As shown in this chapter, it is the localization of nanoparticles in/on the polymermatrix that will decide on the properties and, consequently, the applications of thisclass of polymer materials. Nanocomposites with the nanoparticles grown throughan in situ reduction reaction will, immediately, sink in a subsurface layer of thepolymer, and, when in this position, covered by a polymer layer, they will not becapable to “feel” the surrounding environment, and the composite will have a lowrefraction index sensitivity and will not be adequate for LSPR sensing applications.It is thought that the formation of the subsurface structure in a thin nanocompositefilm is accounted for by the weak Au-polymer interfacial interactions, permitting thegold to sink under the surface and embed in the polymer.

Along with the chemical methods, various physical methods have also beenreported for the formation of thin polymer nanocomposite layers embedded withAg/Au nanoparticles. These physical methods allow to tune the LSPR properties ofthe nanoparticles deposited under vacuum conditions which allow the formation ofimpurity-free nanocomposites. The thickness and the LSPR properties of the com-posites can be tuned by varying the experimental conditions.

References

Avasthi DK, Mishra YK, Kabiraj D, Lalla NP, Pivin JC (2007) Synthesis of metal–polymernanocomposite for optical applications. Nanotechnology 18(12):125604. https://doi.org/10.1088/0957-4484/18/12/125604

Balazs AC, Emrick T, Russell TP (2006) Nanoparticle polymer composites: where two small worldsmeet. Science 314(5802):1107–1110. https://doi.org/10.1126/science.1130557

Fig. 19 Different adsorption orientations of methyl orange dye molecules on an Au-polymer SERSsubstrate (a) when AuNPS are on the surface and (b) when AuNPs are embedded within the matrix(Prakash et al. 2016a)

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Biswas A, Bayer IS, Dahanayaka DH, Bumm LA, Li Z, Watanabe F, Sharma R, Xu Y, Biris AS,Norton MG, Suhir E (2009) Tailored polymer–metal fractal nanocomposites: an approach tohighly active surface enhanced Raman scattering substrates. Nanotechnology 20(32):325705.https://doi.org/10.1088/0957-4484/20/32/325705

Bonyár A, Izsold Z, Himics L, Veres M, Csarnovics I (2017) Investigation of PDMS-goldnanoparticle composite films for plasmonic sensors. Paper read at 2017 IEEE 23rd internationalsymposium for design and technology in electronic packaging (SIITME), 26–29 Oct 2017

Bonyár A, Izsold Z, Borók A, Csarnovics I, Himics L, Veres M, Harsányi G (2018) PDMS-Au/Agnanocomposite films as highly sensitive SERS substrates. PRO 2(13):1060

Deshmukh RD, Composto RJ (2007) Surface segregation and formation of silver nanoparticlescreated in situ in poly(methyl methacrylate) films. Chem Mater 19(4):745–754. https://doi.org/10.1021/cm062030s

Fanous M, Badilescu S, Packirisamy M (2018) Thermal manipulation of gold nanocomposites formicrofluidic platform optimization. Plasmonics 13(1):305–313. https://doi.org/10.1007/s11468-017-0515-3

Ferreira J, Teixeira FS, Zanatta AR, Salvadori MC, Gordon R, Oliveira ON (2012) Tailored SERSsubstrates obtained with cathodic arc plasma ion implantation of gold nanoparticles into a polymermatrix. Phys Chem Chem Phys 14(6):2050–2055. https://doi.org/10.1039/C2CP23287A

Giesfeldt KS, Connatser RM, De Jesús MA, Lavrik NV, Dutta P, Sepaniak MJ (2003) Studies of theoptical properties of metal-pliable polymer composite materials. Appl Spectrosc 57(11):1346–1352. https://doi.org/10.1366/000370203322554491

Giesfeldt KS, Connatser RM, De Jesús MA, Dutta P, Sepaniak MJ (2005) Gold-polymer nano-composites: studies of their optical properties and their potential as SERS substrates. J RamanSpectrosc 36(12):1134–1142. https://doi.org/10.1002/jrs.1418

Hasell T, Lagonigro L, Peacock AC, Yoda S, Brown PD, Sazio PJA, Howdle SM (2008) Silvernanoparticle impregnated polycarbonate substrates for surface enhanced Raman spectroscopy.Adv Funct Mater 18(8):1265–1271. https://doi.org/10.1002/adfm.200701429

Kavetskyy TS, et al. (2018) Polymer nanocomposites with silver nanoparticles formed bylow-energy ion implantation: Slow positron beam spectroscopy studies. In: Bonča J., KruchininS. (eds) Nanostructured materials for the detection of CBRN. NATO Science for Peace andSecurity Series A: Chemistry and Biology. Springer, Dordrecht

Kimling J, Maier M, Okenve B, Kotaidis V, Ballot H, Plech A (2006) Turkevich method for goldnanoparticle synthesis revisited. J Phys Chem B 110(32):15700–15707. https://doi.org/10.1021/jp061667w

Lee C, Robertson CS, Nguyen AH, Kahraman M, Wachsmann-Hogiu S (2015) Thickness of a metallicfilm, in addition to its roughness, plays a significant role in SERS activity. Sci Rep 5:11644. https://doi.org/10.1038/srep11644. https://www.nature.com/articles/srep11644#supplementary-information

Mishra YK, Mohapatra S, Chakravadhanula VSK, Lalla NP, Zaporojtchenko V, Avasthi DK, FaupelF (2010) Synthesis and characterization of ag-polymer nanocomposites. J Nanosci Nanotechnol10(4):2833–2837. https://doi.org/10.1166/jnn.2010.1449

Prakash J, Tripathi A, Rigato V, Pivin JC, Tripathi J, Chae KH, Gautam S, Kumar P, Asokan K,Avasthi DK (2011) Synthesis of Au nanoparticles at the surface and embedded in carbonaceousmatrix by 150 keV Ar ion irradiation. J Phys D Appl Phys 44(12):125302. https://doi.org/10.1088/0022-3727/44/12/125302

Prakash J, Tripathi A, Sanjeev G, Chae KH, Jonghan S, Rigato V, Tripathi J, Asokan K (2014)Phenomenological understanding of dewetting and embedding of noble metal nanoparticles inthin films induced by ion irradiation. Mater Chem Phys 147(3):920–924. https://doi.org/10.1016/j.matchemphys.2014.06.038

Prakash J, Harris RA, Swart HC (2016a) Embedded plasmonic nanostructures: synthesis, funda-mental aspects and their surface enhanced Raman scattering applications. Int Rev Phys Chem 35(3):353–398. https://doi.org/10.1080/0144235X.2016.1187006

Prakash J, Kumar V, Kroon RE, Asokan K, Rigato V, Chae KH, Gautam S, Swart HC (2016b)Optical and surface enhanced Raman scattering properties of Au nanoparticles embedded in andlocated on a carbonaceous matrix. Phys Chem Chem Phys 18(4):2468–2480. https://doi.org/10.1039/C5CP06134B

Surface Gold and Silver-Polymer Nanocomposite Self-Standing Films 19

Rozas R, Lümmen N, Kraska T (2007) Structure formation of metallic nano-particles in the vapourphase and in disperse materials. Eur Phys J Spec Top 149(1):57–70. https://doi.org/10.1140/epjst/e2007-00244-2

SadAbadi H, Badilescu S, Packirisamy M, Wüthrich R (2013) Integration of gold nanoparticles inPDMS microfluidics for lab-on-a-chip plasmonic biosensing of growth hormones. BiosensBioelectron 44:77–84. https://doi.org/10.1016/j.bios.2013.01.016

SadAbadi H, Badilescu S, Packirisamy M, Wuthrich R (2014) In-situ microwave-assisted fabrica-tion of polymeric nanocomposites. In: Nicolais L, Carotenuto G (eds) Nanocomposites: in situsynthesis of polymer-embedded nanostructures, 1st edn. Wiley, Hoboken

Stepanov AL (2004) Optical properties of metal nanoparticles synthesized in a polymer by ionimplantation: a review. Tech Phys 49(2):143–153. https://doi.org/10.1134/1.1648948

Torrisi V, Ruffino F (2015) Metal-polymer nanocomposites: (co-)evaporation/(co)sputteringapproaches and electrical properties. Coatings 5(3):378–424

Zvátora P, Rezanka P, Prokopec V, Siegel J, Svorčík V, Král V (2011) Polytetrafluorethylene-Au asa substrate for surface-enhanced Raman spectroscopy. Nanoscale Res Lett 6(1):366–366.https://doi.org/10.1186/1556-276X-6-366

20 S. Badilescu et al.