Quantitative relationship between surface chemistry of graphene and compatibility with rubbers established by two-dimensional solubility parameters

Abstract

Hildebrand (δ_T) and Hansen (δ_D, δ_P, δ_H) solubility parameters are important indexes to predict the compatibility of components intuitively. Currently, almost all the experiments only measured the solubility parameters of the pristine graphene. Therefore, there is a lack of quantitative relationship between the surface chemistry of graphene and solubility parameters, resulting in no theoretical guidance for the surface modification of graphene. In this work, three-dimensional Hansen solubility parameters are converted to two-dimensional solubility parameters. Hildebrand and two-dimensional solubility parameters of six functionalized graphene as a function of grafting ratio are calculated by molecular dynamics (MD) simulation. Interestingly, if the functional group is at the edge of graphene, the δ_T decreases with the increase of the grafting ratio, whereas if the functional group is in the plane of graphene, the δ_T decreases first and then increases with grafting ratio. Two-dimensional solubility parameters are proved to be a good predictor of the compatibility between functionalized graphene and rubbers. The quantitative relationship between the surface chemistry of graphene and compatibility with rubbers based on two-dimensional solubility parameters is constructed. The optimum grafting ratio corresponding to the best compatibility is given. Finally, the effect of temperature on the compatibility behaviors of graphene/rubber mixtures is elucidated.