Characterizations of enriched metallic single-walled carbon nanotubes in polymer composite
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Characterizations of enriched metallic single-walled carbon nanotubes in polymer composite
Bin Chen1, Jing Li, Yijiang Lu2, Martin Cinke2, Dyng Au3 NASA Ames Research Center, MS 245-3, Moffett Field, CA 94035 Julie P. Harmon, Patricia Anne O. Muisener, LaNetra Clayton Department of Chemistry, University of South Florida 4202 E. Fowler Avenue, Tampa, Fl 33620 Email: [email protected]
Abstract We characterize the electric properties of single-walled carbon nanotube (SWNT) dispersed in the polymethyl methacrylate (PMMA) composites. In the melt-blended sample, the SWNTs – originally semiconducting – became predominantly metallic. The interaction of the PMMA and SWNT is investigated by the polarized Raman studies. The structure changes in the PMMA and SWNT shows that the anisotropic interactions play important role in SWNT electronic density of states (DOS) changes. The increased metallic SWNT percentage is confirmed by the conductivity and dielectric constant measurements of composite and neat PMMA. 1
SETI Institute ELORET Corp. 3 NASA summer intern from Department of Electrical Engineering, University of California at Santa Cruz 2
Introduction As-grown SWNTs are a mixture of semiconducting and metallic nanotubes in an approximate 2:1 ratio. The separation of the SWNT mixture is complicated by the ropelike hydrophobic aggregates consisting of semiconducting and metallic tubes, which are bundled together due to their high aspect ratio. In order to tailor the isolated SWNT with the desired charility, proper dispersion and self-assembly schemes have become recent focuses1. One of the promising approaches to break the bundles is to disperse them into a polymer matrix or forming a composite. This approach is especially attractive since the polymer processing platform can be readily adapted for many SWNT applications. The PMMA polymer matrix used in this study has good structural stability and flexible processability. They can be good cadidate for passive electronic components and
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electromagnetic shielding materials2. SWNT polymer composites have been proposed as a possible solution to increase their electronic mobility to at least 10-6 S m-1. In this report, we demonstrate that the electronic conductivity is enhanced in the thermally processed composites through anisotropic interaction between PMMA and SWNT. The UV polymerized composites have no such anisotropic effects, resulting in no increase in its electronic properties. Previous resonant Raman studies3 has suggested that the anisotropic interaction between SWNT and PMMA was responsible for the changes in the electronic DOS of the SWNTs in the melt-blended composite. In this work, polarized Raman technique is used to study the anisotropic interactions between PMMA backbone and SWNT sidewall with the Raman scattering paralel or perpendicular to incident light.
Experimental Details SWNTs produced from laser ablation techniques were purified according to the procedure in the literature4. PMMA-SWNT composite films were synthesized by two diff
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