Polystyrene/carbon nanotube (PS/CNT) nanocomposites having enhanced CNT dispersion were prepared through freeze-drying after mixing PS particles and aqueous CNT suspension, and subsequent compression molding. We employed emulsifier-free emulsion or dispersion polymerization technique to produce monodisperse PS particles. We investigated the rheological and electrical properties of the nanocomposites as a function of various characters, such as CNT content, surfactant (SDS) concentration, CNT type, surface modification and PS particle size.
With an increase in the SDS concentration, the storage modulus and complex viscosity of the nanocomposites showed an increase as a result of increased dispersion of CNTs. When the SDS concentration reached a certain value, both the storage modulus and complex viscosity began to decrease, which is speculated to be caused by the low molecular weight of SDS. We found that optimum conditions to increase the electrical conductivity as well as the storage modulus and complex viscosity exist when the ratio of SDS/CNT is 2. Though single-walled CNT generally shows higher mechanical and electrical properties than multi-walled CNT, the PS/SWCNT nanocomposites displayed lower rheological and electrical properties, probably because of poor dispersion.
As an attempt to improve the dispersibility of CNTs in aqueous solution, CNTs were acid-treated or PVP-wrapped. With the former, we found that the CNT surface was found to be damaged and their length shortened significantly, resulting in lowered rheological and electrical properties. PS/PVP-CNT nanocomposites showed higher rheological and electrical properties. The PS/PVP-CNT nanocomposites exhibited higher rheological properties than the PS/CNT nanocomposites dispersed with SDS while electrical conductivity was lower. We speculate that CNTs wrapped with non-conducting PVPs contributed to this observation.
Various PS particles with differing molecular weight and particle size were prepared by different polymerization techniques. When the CNT content is low, the nanocomposites prepared by small PS particles showed higher electrical conductivity, but the opposite results were obtained when the CNT content is high.