(670e) Polymer Latex/Single-Walled Carbon Nanotube Composites
Single wall nanotubes (SWNTs) were dispersed in water using the surfactant sodium dodecylbenzenesulfonate to facilitate dispersion. (Styrene-isoprene) copolymer (S-I copolymer) and SWNT composites were prepared by emulsion polymerization and miniemulsion polymerization in the presence of SWNTs, as well as mixing the dispersed SWNTs with S-I copolymer latex. In the former method, surfactant was displaced from SWNTs to monomer droplets, resulting in aggregation of SWNTs during the reaction leading to a marked decrease in mechanical properties, and no improvement in electrical conductivity. Mixing dispersed SWNTs with the latex after reaction kept SWNTs in their dispersed state and gave a polymer composite with a percolation threshold of 0.5%. Mechanical properties significantly improved at weight fractions as low as 0.1%. Dynamic mechanical analysis made on film samples in tension showed that the composites had a measurable modulus above the glass transition temperature indicating that entanglements have formed giving mechanical stability to the composite. The value of the modulus as well as the temperature where the modulus was not measurable increased as the nanotube concentration increased. As done with measurements in shear, a mechanical percolation threshold was measured as a function of temperature.