Non-contact percolation of unstable graphene networks in poly(styrene-co-acrylonitrile) nanocomposites: Electrical and rheological properties

Abstract

Poly (styrene-co-acrylonitrile) (SAN)/chemically reduced graphene oxide (CRG) nanocomposites were prepared using a coagulation method. Due to the presence of SAN molecules that prevented CRG sheets from aggregation during reduction, CRG sheets were dispersed homogeneously in SAN. The electrical and rheological properties of the nanocomposites were systematically investigated to elucidate the structure of CRG electrical and rheological networks. With the incorporation of CRG sheets, both the electrical and rheological properties of the nanocomposites were remarkably changed. At higher CRG concentrations, the nanocomposites became electrically conductive and exhibited solid-like behaviors. According to the scaling power law, the electrical networks were constructed at a percolation threshold of 0.17 vol % compared to the rheological networks at 0.10 vol %. This discordance is attributed to the intrinsic difference in the network structure. Though both electrical and rheological networks were constructed through a non-contact mode, the rheological networks required SAN chains as bridges, while electrical networks did not. The CRG networks showed instabilities in both physical and chemical structure. Upon thermal annealing at 190 °C, the networks underwent self-improvement through disordering and thermal reduction of CRG sheets.