(791g) Direct-Graphene Nanocomposites By Shear Milling and Ionic Liquid Chemistry

Graphite/graphene nanoplatelets (GNPs) combine high modulus and electrical conductivity with a platelet structure that provides superior mechanical reinforcement with electrical conductivity and decreased composite vapor permeation in composites. Additionally, graphite is a plentiful natural resource, and could provide a low-cost alternative to fillers with high-complexity synthesis regimes. However, dispersing GNPs into polymers is complicated by a high aspect ratio, the strong pi-pi interactions within the graphite stack, and a lack of effective direct dispersants. The two primary methods for chemical exfoliation of graphite for nanocomposites are the reduction of graphite oxide, which produces single-layer, chemically altered graphene sheets (rGO) and acid intercalation, which produces few-layer stacks of still-pristine expanded graphite (EG). These chemically modified nanosheets are then dispersed via a combination of miscible solvent and physical processing.

An alternative to dispersing nanoparticles with harsh functionalization chemistries is presented by room temperature ionic liquids (RTILs). Researchers have used an imidazolium-based ionic liquid to electrochemically exfoliate graphene directly from graphite, using electrostatic interactions. Theoretical and spectroscopic studies have suggested cation-pi stacking and electrostatic shielding between graphitic particles by the RTIL solvent as reasons for the superior interactions. Additionally, our recent work has demonstrated that well-chosen ionic liquids can initiate an epoxy cure reaction, in addition to dispersing graphite sheets. This results in materials with potentially unique interphase properties resulting from interactions among the nanoparticle surface, ionic liquid, and thermoset matrix.

Here, we present the synthesis of this RTIL-graphene-epoxy thermoset nanocomposite. Particular attention is paid to the degree of graphite exfoliation during processing, the nanofiller network formation, and the physical interpretation of shear graphite exfoliation. Additionally, electrical and mechanical properties are described and contrasted with other nanocomposite synthesis methods.