Shear- and Temperature-Induced Graphene Network Evolution in Graphene/Polystyrene Nanoconnposites and Its Influence on Rheological, Electrical, and Morphological Properties

Herein we report on the characterization of rheological, morphological, and electrical properties of graphene/polystyrene nanocomposites as a function of graphene functionalization. Hydrophobic modified graphite oxide was grafted with polystyrene chains (PS-g-FG), thus enabling a high degree of compatibility with the polystyrene matrix. While nongrafted and noncompatibilized graphene showed a particle network in accordance with the timetemperature superposition principle, the grafted PS-g-FG revealed a structural development with time, which is the consequence of superior but unstable dispersion of the latter. This results in an increasing elasticity of the graphene network as well as in an enhanced electrical conductivity of the composite material. Kinetic investigations showed a multistep process being the basis of this structural evolution. While extensive shear (large amplitude oscillatory shear, LAOS) led to a destruction of the network, small shear impact (small amplitude oscillatory shear; SAOS) in combination with elevated temperature was crucial for an effective buildup of the graphene particle network. In addition, the rheological and electrical percolation threshold was determined simultaneously by a combined rheodielectric setup. The structure development was successfully monitored by electron microscopy, showing an increase in number and size of interconnected graphene domains, accompanied by an exfoliation of aggregated graphene stacks. Thus, the present investigation is a rare example of comparing compatibilization of graphene with detailed characterization of melt rheology, electrical properties, and computer-aided morphological analysis.