Depletion Effect during the Synthesis of Conductive Segregated-Network Graphene-Polymer Composites

The in situ growth of crosslinked polymer chains within the confined, nanometer-scale gaps of a graphene network governs the electrical conductivity of graphene-based polymer composites, yet the underlying polymerization behavior remains poorly understood. Here, we investigate the depletion effect that drives graphene sheets in a segregated network to move closer together as the continuous phase polymerizes. By monitoring the electrical resistance and reaction temperature of graphene-stabilized high internal phase emulsions of styrene, methyl methacrylate, and t-butyl acrylate, we provide evidence of the depletion effect, a phenomenon in which high-molecular-weight polymer chains are excluded from confined interfaces, thereby enhancing graphene sheet-to-sheet contact and reducing electrical resistance. Systematic experiments reveal that polymerization parameters, including temperature, initiator presence, and crosslinking, govern conductivity transitions, with the resistance drop tracking the auto-acceleration exotherm and the onset of crosslinker-driven coil growth. Consistent with this interpretation, 4-point probe measurements on graphene films show that opposite-sign Q–e pairs (PMMA-DVB, PS-EGDMA, and PS-TMPTA) yield sheet resistances that are an order of magnitude lower than same-sign pairs (PS-DVB, PMMA-EGDMA, and PMMA-TMPTA), consistent with the predicted ordering due to faster crosslinker incorporation. These findings establish crosslinker reactivity as a kinetic handle on polymer network evolution under confinement and demonstrate electrical resistance as a sensitive in situ reporter of polymer growth.