Dispersion and network formation of graphene platelets in polystyrene composites and the resultant conductive properties

A small quantity of graphene platelets (GNPs) were introduced into polystyrene (PS) to prepare the PS/GNP composites through one-step process (solution compounding, PS/GNP-S) and two-step process (solution compounding and subsequent melt compounding, PS/GNP-SM). The dispersion states and microstructures of GNPs in the composites were comparatively investigated. The results demonstrated that the PS/GNP-S composites exhibited relatively poor dispersion of GNP particles but relatively high ability to form the percolated GNP network compared with the PS/GNP-SM composites. Apparently increased glass transition temperatures were achieved for the PS/GNP-S samples. Conductive properties measurements showed that the PS/GNP-S samples exhibited relatively low volume resistivity. Largely enhanced thermal conductivity was achieved for the PS/GNP-S samples, and the thermal conductivity exhibited nonlinear behavior with increasing GNP content, which was different from the linear behavior of the PS/GNP-SM samples. The conductive mechanisms of the composites were discussed using two different analytic models.