conjugated polymer poly(2-methoxy-5-(3′,7′- dimethyloctyloxy)-1,4-phenylenevinylene)...

Conjugated Polymer Poly(2-methoxy-5-(3′,7′- dimethyloctyloxy)-1,4-phenylenevinylene)Modification on Carbon Nanotubes with Assistance of Supercritical Carbon Dioxide:Chemical Interaction, Solubility, and Light Emission

Zongpeng Li,† Hongtao Guan,† Ning Yu,† Qun Xu,*,† Ichiro Imae,*,‡ and Junyu Wei†

College of Materials Science and Engineering, Zhengzhou UniVersity, Zhengzhou 450052, People’s Republic of China,and Department of Applied Chemistry, Faculty of Engineering, Hiroshima UniVersity, Higashi-Hiroshima739-8527, Japan

ReceiVed: February 12, 2010; ReVised Manuscript ReceiVed: May 3, 2010

In this study, we report a facile and efficient method using supercritical (SC) CO2 to help a p-type conductingpolymer, conjugated polymer MDMO-PPV wrapping on carbon nanotubes (CNTs). One-dimensional CNTswere periodically decorated with the congeries of MDMO-PPV molecular chains forming functional nanohybridstructures. The solubility and light emission of the hybrid MDMO-PPV/CNTs can be controlled by varyingSC CO2 pressure. Using FT-IR, we can observe there exists chemical interaction between MDMO-PPV andCNTs, and the interaction not only bestowed CNTs desired solubility but also added functionality of lightemission to CNTs. The fluorescence spectroscopy of the MDMO-PPV/CNTs shows their light emission isstrongly depend on solvent. For DMSO as the solvent, the higher SC CO2 pressure ensures the excellentdispersion and solubility of MDMO-PPV/CNTs, and accordingly causes the light quenching of the hybrid.For DMAc as the solvent, the enhanced emission light can be observed from the MDMO-PPV/CNTs, especiallyat higher SC CO2 pressure. We anticipate this work opens a gateway for making use of SC CO2 to helpfunctionalize CNTs with conjugated polymer for use in polymer solar cells, light-emitting diodes, and others.

1. Introduction

In recent years, the integration of organic and inorganicbuilding blocks into novel nanohybrid structures has drawn abroad interdisciplinary attention,1,2 as this approach to innovativematerials bears interesting opportunities for the control over fine-tuning desirable functionalities.3,4 Due to their unique structuraland physical properties,5-7 carbon nanotubes (CNTs) are of greatinterest in scientific research and technological innovation.Particularly, their remarkable electronic and optical propertiesmake them promising as nanosensor, nanoelectrode, moleculardiode, and photoelectrochemical devices.8-11 Polymer solar cellshave attracted great attention in developing low-cost, large-area,and mechanically flexible photovoltaic devices.11-13 In thisrespect, the combination of carbon nanotubes with π-conjugatedpolymers is of particular interest because the latter are potentialmaterials for several device applications, such as light-emittingdiodes, field effect transistors, and photovoltaic devices. Toreach a high efficiency, electron-hole dissociation and carriertransport rate play an important role.14-18 Both single-walledcarbon nanotubes (SWCNTs) and multiwalled carbon nanotubes(MWCNTs) have been found to enhance the conductivity ofCNTs/polymer composites by orders of magnitude.19-24 CNTscan act as very good electron acceptors and exciton dissociationcenters by providing high field at the polymer/CNT interfacesand further improve the device efficiency if integrated intopolymeric photovoltaic devices.25,26

The cost per Watt must come down if the photovoltaic devicewants to be in competition with other power sources. One

possible solution is the use of polymer-based semiconductorsthat have the potential to lower costs by utilizing inexpensiveliquid-based processing.27 Conjugated polymers such as PPV[poly(phenylene-vinylene)] and its derivatives (e.g., MEH-PPV,MDMO-PPV, etc.), have been widely studied as photovoltaicmaterials in recent years.28-30 Scheme 1 shows the molecularstructure of MDMO-PPV, its full name is poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene), which is afamous p-type conducting polymer, and it is often used fororganic thin film solar cells. The excellent dispersion of CNTsin MDMO-PPV is very important for the resulting blends.However, because of strong intrinsic van der Waals forces,CNTs tend to hold together as bundles and they have very lowsolubility in solvents, leading to poor dispersion when mixedinto the polymer matrix. Up to now, the most commonly usedapproaches to CNT solubilization have involved chemicalmodification and noncovalent wrapping methods.31 For the

* To whom correspondence should be addressed. Q.X.: e-mail [email protected], phone +86 371 67767827, fax +86 371 67767827. I.I.: [email protected], phone +81 82 4247688, fax +81 82 4245494.

† Zhengzhou University.‡ Hiroshima University.

SCHEME 1: The Molecular Structure of MDMO-PPV

J. Phys. Chem. C 2010, 114, 10119–10125 10119

10.1021/jp101342h 2010 American Chemical SocietyPublished on Web 05/18/2010

former, the advantage is that the linkage between the functionalgroups and the surface of the CNTs is permanent and mechani-cally stable, but the primary desirable properties of CNTs canbe altered significantly because the covalent bonds linked toCNTs break the sp2 conformation of the carbon atom and causethe disruption of their tubular shape.32,33 Concerning thenoncovalent wrapping, CNTs are often wrapped by surfactants,oligomers, biomolecules, and polymers.34-37 Although theexcellent properties of CNTs can remain, the interaction betweenthe wrapping molecules and CNTs is rather weak.38 Thus, anideal functionalization process, which combines both merits ofthe above two methods, is further pursued by researchers.

Recently, supercritical fluids (SCFs) technology has madetremendous strides in the field of materials science, such asimpregnation, particle formation, foaming, and blending.39-41

Among SCFs, supercritical CO2 (SC CO2) has been promotedas a most sustainable and potentially superior solvent mediafor the processing of nanoscale particles, wires, and films,because beyond the general excellent transport and interfacialproperties, it is nonflammable, nontoxic, inexpensive, naturallyabundant, and has a readily accessible critical point (Tc ) 31,Pc ) 73.8 bar).42-44 Furthermore, the solubility of SC CO2 inmany organic solvents is very high, which leads to a decreaseof the solvent strength and consequently decreases the solubilityof solute in the organic solvent. This phenomenon is defined asthe SC CO2 antisolvent effect. In our previous study, we foundout that modification of CNTs can be achieved by using SCCO2 as antisolvent to induce polymer epitaxial growth on CNTs(SAIPE method).45-48 And a series of polymer supermolecularstructures have been built on carbon nanotubes (CNT). CNTsare wrapped by strands of nanocrystals as “pear-necklace” inmultihelix patterns, shish-kebab structure, and “muscle fiber”in the case of PEG, PE, and a fluorinated crystal polymer(FLCP), respectively. Accordingly, the modified CNTs haveexcellent dispersion in different organic solvents. It is worth-while to note that for the SAIPE method in our previous study,all the adopted polymers are crystalline polymer. Consideringthe conjugated polymer may confer the desired solubility andnew functionality on CNTs without deteriorating their ownunique properties, the conjugated polymer/carbon nanotubescomposites are very intriguing to us. Thus, in this study, weaim to realize the modification of CNTs with MDMO-PPV via

the SC CO2-assisted method. Further we try to explore the effectof experimental conditions on CNTs’ decoration, in order toachieve the controllable morphology and properties of thecomposite of MDMO-PPV/CNTs. The ultimate purpose is tohelp realize the functional design for these tailored nanohybridarchitectures as a basic component in the field of polymer solarcells. Scheme 2 is the representation of a simple experimentalprocess with the assistance of SC CO2, and the structure of theMDMO-PPV and the hybrid structure of MDMO-PPV/SWCNT.

2. Experimental Section

The single-walled carbon nanotubes (SWCNTs) were suppliedby Carbon Nano Materials R&D Center, Chengdu DesranTechnology Co., Ltd. (China) with a purity of 80 wt %. Theywere purified as follows: Proper quantities of crude CNTs wereadded into a three-necked flask containing sulfuric acid and nitricacid at the ratio of 3:1 by volume. The suspension was sonicatedin an ultrasonic bath for 40 min and then in reflux at 120 °Cfor 3 h. After the treated CNTs were centrifuged and washedwith hot distillated water until a pH of 7.0, they were dried ina vacuum oven at 35 °C for 24 h. MDMO-PPV ((Mn) 123 000g/mol, (Mw) 389 000 g/mol, (PDI) 3.2) was supplied by thegroup of Prof. Ichiro Imae in the University of Hiroshima.

MDMO-PPV decorated on CNTs was achieved by thesupercritical CO2-assisted method. Dimethyl sulfoxide (DMSO)and N,N-dimethylacetamide (DMAc) were used as the solvent,respectively, and they were purchased from Sinopharm Chemi-cal Reagent Co., Ltd. (China). A certain amount of SWCNTswas dispersed in 4 g of DMSO and sonicated for 1 h beforebeing added to a definite concentration of MDMO-PPV/DMSOand MDMO-PPV/DMAc solution. The concentration of modi-fied CNTs is 0.002 wt % and PPV is 0.006 wt %. The mixturewas then quickly transferred into the SC CO2 apparatus to reachthe determined experimental conditions and the experimentaltime was controlled to be 3 h. Transmission electron microscopy(FEI Tecnai G2 20) experiments were conducted with anaccelerating voltage of 120 kV to characterize the morphologyof the polymer-functionalized CNTs. IR spectra were collectedon a TENSOR 27 FTIR spectrometer (Bruker) in absorptionmode with 32 scans at a resolution of 2 cm-1 intervals.Fluorescence spectra were collected on a FluoroMax-P fluo-

SCHEME 2: Sketch of the Supercritical CO2-Assisted Process, and Illustration of the Structure of the MDMO-PPV andthe Hybrid of MDMO-PPV/SWCNT

10120 J. Phys. Chem. C, Vol. 114, No. 22, 2010 Li et al.

rescence spectrometer (HORIBA Jobin Yvon). And 0.15 mLof the solution was dropped onto quartz plate and the samplewas diluted in 5 mL of the corresponding pure solvent.

3. Results and Discussion

Interaction Analysis between SWCNTs and MDMO-PPVby FTIR. The nature of the chemical groups of MDMO-PPVand MDMO-PPV/CNTs is investigated by FTIR spectra inFigure 1. MDMO-PPV shows two absorption bands at 3452and 3057 cm-1 associating with O-H stretching and C-Hstretching in the benzene ring, respectively. Another strong bandat 1204 cm-1 is assigned to the C-O stretching in ether groups.The MDMO-PPV molecule does not contain a hydroxyl group,so the peak of O-H stretching is probably induced by themolecular internal hydrogen bonding. The MDMO-PPV/CNTsexhibits a peak at 3419 cm-1 due to O-H stretching. The surfaceof the carbon nanotubes exhibits hydrogen, which is inducedby the carboxyl attached to CNTs when purified in refluxingH2SO4/HNO3 (3:1 by volume) solvent. Compared to formingmolecular internal hydrogen bonding, the hydrogen atoms fromthe carboxyl groups more easily form intermolecular hydrogenbonding with the oxygen atom on the MDMO-PPV molecule.This is indicated by the O-H stretching band shifting from 3452to 3419 cm-1 and becoming wide.

Two other notable changes can be observed from Figure 1.One is that C-H stretching in the benzene ring at 3057 cm-1

does not exhibit an obvious absorption peak in the endcomposite product. This is due to the major interaction, formingπ-π stacking between the rigid backbone of MDMO-PPV andCNT. Another feature is that the peak at 1204 cm-1 associatingwith the C-O stretching has moved to 1124 cm-1, which isdue to C-O shear vibration in ether groups. We assume thatthere is a kind of hydrophobic interaction between the alkylchains of MDMO-PPV and the wall of CNT. This interactionthat makes the C-O stretching move to shear vibrationinfluences the vibronic structure of the C-O. And this indicatesagain that there are some bonds between MDMO-PPV andCNTs. It is the intense interactions between the polymer andCNTs that provide a channel for energy and electrical transmis-sion, as illustrated in the hybrid structure of MDMO-PPV/SWCNT in Scheme 2.

Effect of SC CO2 Pressure on MDMO-PPV DecoratedCNTs. As a characteristic soft matter, MDMO-PPV should besusceptive to environmental change or peripheral effects. Forsupercritical fluid, experimental pressure has an important effecton the solvent power, thus the variation of experimental pressurecan be regarded as a typical outside effect. We fix the MDMO-PPV concentration at 0.006 wt %, CNTs concentration at 0.002

wt %, and temperature at 90 °C, and change the experimentalpressure of SC CO2 from 14 to 15 MPa. The obtained resultsare shown in Figure 2.We can observe a clear tendency thatthe modified effect becomes better from 14 to 15 MPa. At 14MPa, it can be observed that the CNTs are not wrapped totally.By increasing the SC CO2 pressure to 15 MPa, the CNTs canbe wrapped perfectly. Figure 3 is the digital photograph of thetwo products dispersed in DMSO solutions. Apparently thedispersion of the sample treated at 15 MPa is better than that at14 MPa. This indicates that the perfect modification on CNTscan help the excellent dispersion of CNTs.

The interaction between polymer and CNTs bestowed CNTswith not only desired solubility but also added functionality.MDMO-PPV is a famous luminophore and we further studytheir fluorescence spectroscopy at the excitation wavelength of380 nm. The obtained results are shown in Figure 4. Uponphotoexcitation, the spectrum of the MDMO-PPV/DMSOsolution was dominated by the excimer emission at 418 nm.CNTs are not emissive but their hybrids with MDMO-PPV areluminescent. It can be found out that the peak intensity ofMDMO-PPV/CNTs is obviously lower than that of the pureMDMO-PPV. This observed quenching indicates that theexcitons generated in MDMO-PPV are diminished before theradiative recombination due to the presence of the CNTs.50-52

The mechanism about the observed quenching arises not onlyfrom the absorption and scattering affected by the existence of

Figure 1. FTIR spectra of the MDMO-PPV decorated SWCNTs andthe pure MDMO-PPV.

Figure 2. TEM images of the MDMO-PPV-nanocrystals decoratedSWCNTs produced at the same temperature (90 °C) but with differentexperimental pressures: (a) 14 and (b) 15 MPa.

Figure 3. Digital photograph of the MDMO-PPV decorated SWCNTsproduced at the same temperature (90 °C) but with different experi-mental pressures: (a) 14 and (b) 15 MPa.

Conjugated Polymer Modification on Carbon Nanotubes J. Phys. Chem. C, Vol. 114, No. 22, 2010 10121

CNTs, but also from the energy transfer.51 Further it isconsidered as a consequence of electronic interaction betweenPPV and CNTs.49 We also found a slight blue-shift for thefluorescence spectrum of the composite, which signifies thatthe effective π-conjugation length of MDMO-PPV is shortenedin the composite. So for the MDMO-PPV functionalized CNTs,the intrachain in the local structure may be considered moredisordered.

Since adjusting SC CO2 pressure is an efficient way to helpdecorate CNTs, it is necessary to study the effect of pressure atanother experimental condition. Fixing the MDMO-PPV andCNTs concentration, we increase the temperature from 90 to100 °C, and study the effect of SC CO2 pressure on MDMO-PPV decoration on CNTs. Three different SC CO2 pressures of13, 14, and 15 MPa are chosen. The experimental results areshown in Figure 5. At the lower pressure of 13 MPa, thedispersion of CNTs is still not so ideal, shown in Figure 5a.When the SC CO2 pressure increases to 14 MPa, apparentlythe dispersion of the modified CNTs is better. When theexperimental pressure continues to increase and reaches 15 MPa,nearly every CNT is wrapped perfectly and some black dotsoccur on the surface of CNTs. In our previous study aboutpoly(vinyl alcohol) (PVA) modification on CNTs, we alsoobserved the black dots.47 Considering PVA is the crystallinepolymer, we called the black dots nanocrystals. For MDMO-PPV, it is not crystalline polymer, but amorphous polymer, sowe cannot call them nanocrystals. We would like to think theyare the congeries of molecular chains due to the antisolventeffect of SC CO2 on them.

We attribute this effect of SC CO2 pressure to the followingreasons: On the one hand, as the experimental pressure rises,the viscosity of the medium decreases for dissolving more CO2,and thus it facilitates MDMO-PPV chains wrapping on CNTs.On the other hand, due to the antisolvent effect of SC CO2,there is a transition of conformation of polymer chains withdifferent polymer-solvent interactions. When the experimentalpressure is comparatively low, the antisolvent effect is not strongenough, the PPV chains could remain in a loosely elongatedstate. At this period, random wrapping is predominant, whichallows high surface area coverage with low backbone strain froma thermodynamic way. When the pressure reaches 14 MPa, oreven 15 MPa, the solvent strength decreases due to solution of

more CO2. The polymer chains would like to undergo transitionfrom a loose coil to a dense globule so as to minimizepolymer-solvent interactions in the poorer solvent. Figure 6 isthe digital photographs of the three products dispersed in DMSOsolutions. It can be observed that the solubility of the sampleprocessed at 14 and 15 MPa is indeed better than that of 13MPa. So this indicates again that the perfect decoration ofMDMO-PPV on CNTs contributes to their excellent dispersion.

We further study their fluorescence spectroscopy at theexcitation wavelength of 380 nm. The obtained results are shownin Figure 7. From Figure 7, we can also observe the quenchingof the fluorescence spectrum for the composite of MDMO-PPVmodified on CNTs. Obviously the peak intensity of thecomposite of MDMO-PPV/CNTs is lower than that of the pureMDMO-PPV. Especially, when the experimental pressurereaches 15 MPa, the quenching degree is apparently higher than

Figure 4. Room temperature fluorescence emission spectra of MDMO-PPV in DMSO and MDMO-PPV/CNTs composite in DMSO. Thecomposites are obtained at 90 °C and different pressures: 14 and 15MPa. The excitation wavelength is 385 nm.

Figure 5. TEM images of the MDMO-PPV-nanocrystals decoratedSWCNTs produced at the same temperature (100 °C) but with differentexperimental pressures: (a) 13, (b) 14, and (c) 15 MPa.

Figure 6. Digital photograph of the MDMO-PPV-nanocrystals deco-rated SWCNTs produced at the same temperature (100 °C) but withdifferent experimental pressures: (a) 13, (b) 14, and (c) 15 MPa.


that of 13 and 14 MPa. The emission quenching is caused bythe electron or energy transfer between MDMO-PPV and CNTs.

Effect of the Experimental Temperature on MDMO-PPVDecorated CNTs. Besides the effect of experimental pressure,experimental temperature should be another key factor for theMDMO-PPV to functionalize on CNTs. Accordingly we observetheir fluorescence emission spectra, and the experimental resultsare shown in Figure 8. This indicates that the emissionquenching of the product obtained at 100 °C is slightly higherthan that of 90 °C. The experimental results can be reflectedfrom their TEM results (Figures 2b and 5c) that both of themappear perfect modification on CNTs. This shows that on thecondition of perfect decoration of MDMO-PPV on CNTs, theemission quenching will happen. We have to stress thisconclusion has its limited precondition because it is well-knownthat the light-emitting properties of polymers depend on thedifferent organic solvent. Especially the different polarity andviscosity of varying solvents have a determined effect on thephotophysical properties. In our SC CO2-assisted process ofMDMO-PPV modification on CNTs, the polarity and viscosityof solvent are closely related to the solution of CO2 in them.So in the following study, we change dimethyl sulfoxide

(DMSO) to N,N-dimethylacetamide (DMAc) as solvent forMDMO-PPV to study the emission spectra of the obtainedMDMO-PPV/CNTs hybrid in DMAc. The volume expansionof the two solvents of DMSO and DMAc in CO2 as a functionof pressure is presented as Figure S1 in the SupportingInformation.

Modification of CNTs with MDMO-PPV with DMAc asSolvents. In addition to the driving force for changing solventfor MDMO-PPV to study the emission spectra, considering thevariation of solvent is another type of peripheral effect for thepolymer to modify CNTs,46 we are very interested in studyingother solvents such as DMAc for MDMO-PPV. The solubilityparameters of MDMO-PPV and two solvents are shown in theSupporting Information (Table S1). And their room temperaturefluorescence emission spectra of pure MDMO-PPV in DMSOand DMAc are shown in Figures S2 and S3 in the SupportingInformation. TEM characterization of the modification ofMDMO-PPV on CNTs is shown in Figure 9. Obviously, CNTsare wrapped by MDMO-PPV. We further study the fluorescencespectroscopy of composite at the excitation wavelength of 396nm. The obtained experimental results are shown in Figure 10.Upon photoexcitation, the spectrum of the MDMO-PPV/DMAcsolution was dominated by the excimer emission at 550 nm.Here we can observe an intriguing phenomenon, which is totallydifferent from that discussed above about MDMO-PPV/DMSOsolution, i.e., the light emission of the MDMO-PPV/CNTshybrid is enhanced by CNTs. As can be observed from Figure10, when SC CO2 pressure reaches 15 MPa, the photolumines-cence intensity of MDMO-PPV/CNTs hybrid is >2-fold higherthan that of pure MDMO-PPV. It is well-known that CNTsquench light emission of conjugated polymer as we observedin DMSO solution and others report. The enhancing effect isvery fascinating. However, the experimental result is not theonly one up to now; in the study of Tang’s group, they havealso observed this phenomenon with their synthesized pyrene-containing poly(phenylacetylene)s (PPAs) to wrap CNTs.25 TheSEM photographs further confirm the wrapping of polymerlayers on the surface of CNTs as shown in Figure 11. Throughcomparing the effect of different solvents for MDMO-PPVduring the supercritical CO2-assisted process, and the further

Figure 7. Room temperature fluorescence emission spectra of MDMO-PPV in DMSO solution and MDMO-PPV/CNTs composite in DMSOsolution with reaction conditions at 100 °C and at different pressures:13, 14, and 15 MPa. The excitation wavelength is 385 nm.

Figure 8. Room temperature fluorescence emission spectra of MDMO-PPV in DMSO solution and MDMO-PPV/CNTs composite in DMSOsolution with reaction conditions at 15 MPa and at different temper-atures: 90 and 100 °C. The excitation wavelength is 385 nm.

Figure 9. TEM images of the MDMO-PPV decorated on SWCNTsat the same temperature (100 °C) but with different experimentalpressures: (a) 13 and (b) 15 MPa in DMAC solution.


study on their fluorescence spectroscopy, we found that thechoice of solvent is very necessary, not only for the modificationof CNTs, but also for the variation of electronic transfer betweenpolymer and CNTs, which is the key factor for the emittinglight of the product.

4. Conclusion

In our study, we have further developed the supercritical CO2

antisolvent method to help a kind of amorphous polymer, whileit is a famous p-type conducting polymer, to precipitate anddecorate on CNTs and to fabricate the functional nanohybridof the MDMO-PPV/CNTs. Our experimental results indicatethere exists chemical interaction between MDMO-PPV andCNTs, and the interaction not only bestowed CNTs desiredsolubility but also added functionality such as light emission toCNTs, considering MDMO-PPV is a famous luminophore. Thefluorescence spectroscopy of the MDMO-PPV/CNTs showstheir solubility and light emission is strongly depend on solventand SC CO2 pressure. For DMSO as the solvent, the higher SCCO2 pressure ensures the excellent dispersion and solubility ofMDMO-PPV/CNTs, and accordingly causes the light quenchingof the hybrid. For DMAc as the solvent, the enhanced emissionlight can be observed from the MDMO-PPV/CNTs and thisspecial phenomenon is being investigated. So this work not onlyprovides the possibilities of fabricating π-conjugated polymers/CNTs hybrid with the assistance of SC CO2, but it also can beanticipated to open a gateway for making use of the differentorganic solvents and the peculiar properties of SC CO2 to helpfunctionalize CNTs depending on the practical application, suchas organic photovoltaic cells, light-emitting diodes, etc.

Acknowledgment. We are grateful for the National NaturalScience Foundation of China (Nos. 20974102 and 50955010)and the financial support from the Program for New CenturyExcellent Talents in University (NCET). We thank ProfessorShijun Zheng at Zhengzhou University for valuable discussions.

Supporting Information Available: Table of solubilityparameters of MDMO-PPV, dimethyl sulfoxide (DMSO), and N,N-dimethylacetamide (DMAc); volume expansion of DMSO andDMAc in CO2 as a function of pressure; fluorescence emissionspectra of pure MDMO-PPV in DMSO; and fluorescence emissionspectra of pure MDMO-PPV in DMAc. This material is availablefree of charge via the Internet at http://pubs.acs.org.

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Figure 10. Room temperature fluorescence emission spectra ofMDMO-PPV in DMAC solution and MDMO-PPV/CNTs compositein DMAC solution with reaction conditions at 100 °C and at differentpressures: 13 and 15 MPa. The excitation wavelength is 396 nm.

Figure 11. SEM images of the MDMO-PPV-nanocrystals decoratedSWCNTs produced at 100 °C and 15 MPa in DMAC solution.


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