Rational design of graphene surface chemistry for high-performance rubber/graphene composites

In a rubber/filler composite, the surface chemistry of the filler is a critical factor in determining the properties of the composite because it affects the dispersion of the filler and the interfacial adhesion between the filler and rubber. In this study, we primarily focus on how graphene surface chemistry affects the dispersion of graphene and interfacial adhesion in butadiene-styrene rubber (SBR)/graphene composites and on the resultant properties of the composites. Composites that contain graphene with tailored surface chemistry are prepared via the chemical reduction of graphene oxide (GO) in situ. Subsequently, the dispersion of the graphene and interfacial adhesion are fully investigated in relation to the graphene surface chemistry. As revealed by dielectric relaxation spectroscopy, the bulk segmental relaxation is independent of the graphene surface chemistry, whereas the interfacial relaxation mode is retarded in the composite with stronger graphene-rubber affinity. The contribution of the graphene surface chemistry to the dispersion of the graphene and interfacial adhesion is quantified by calculating the surface energies. The results indicate that, when the CO_x fraction in the graphene is greater than 0.2, it exerts an increasingly strong effect on the dispersion of the graphene; in contrast, when the CO_x fraction is less than 0.2, it exerts a significant and positive effect on the interfacial interaction. In particular, on the basis of the surface energy analysis, quantitative predictors for the dispersion of graphene and interfacial adhesion are presented; these predictors can be used for the virtual design of graphene surface chemistry to optimize the properties of composites.