Functionalized SWNT/polymer nanocomposites for dramatic property improvement

In this paper, we present results for polymer nanocomposites of poly-(methyl methacrylate) (PMMA) and amide-functionalized SWNTs. The results demonstrate that even at very low loadings, 1 wt% (0.5 vol%), the mechanical and electrical properties are significantly improved. The improvement over PMMA properties exceeds the theoretical bounds for composites with the same volume fraction loading of randomly oriented, straight, individually dispersed nanotubes. The modeling and experimental results thus suggest that the nanotube bundles are well dispersed in the polymer matrix, that the functionalization significantly improves interaction with polymer, and that the interphase formed has improved mechanical properties over that of the matrix material. Loss modulus results indicate a significant difference between functionalized and nonfunctionalized tubes in the composite. Functionalized tubes result in a composite in which relaxation mechanisms are shifted by 3°C from that of the matrix material, indicating extensive interphase regions and absence of PMMA with bulk properties. Unfunctionalized composites demonstrate a broadening of relaxation modes, but still retain the signature of bulk PMMA properties. These data suggest a morphological difference with a discrete interphase layer in unfunctionalized composites and a fully transformed matrix in the case of functionalization. This difference is consistent with electrical and mechanical property data.