Polymer/Graphene Composites via Spinodal Decomposition of Miscible Polymer Blends

Conductive polymer composites (CPCs) enjoy broad industrial applications such as electrostatic discharge (ESD) protection. Herein, we constructed CPCs by first solution blending graphene nanoplatelets (GNPs) into a miscible blend of poly(methyl methacrylate) (PMMA) and poly(styrene-co-acrylonitrile) (SAN) and then inducing PMMA/SAN spinodal decomposition by annealing well above the lower critical solution temperature. The resulting composite showed spatially regular, co-continuous polymer domains, in which GNPs preferentially localized within the SAN-rich phase and formed a conductive network. We found that GNPs induced local nucleation of SAN into surface layers of ∼4R_g in thickness. Small PMMA domains formed next to these SAN layers and were stable against long annealing times. As a result, GNPs created local blend morphologies that were different from the bulk morphology arising from spinodal decomposition alone. During annealing, GNPs suppressed domain coarsening and preserved the co-continuous morphology, while their connectivity in the polymer matrix was improved. Additionally, inducing PMMA/SAN phase separation significantly increased the ternary blend's electrical conductivity by over 5 orders of magnitude. Compared to the conventional approach of CPC manufacture of compounding carbon black into a homopolymer matrix, our approach achieved bulk electrical conductivity of ∼10^-8 S/cm at 1 wt % GNP loading, rendering this system suitable for ESD protection.