Insights into interphase thickness characterization for graphene/epoxy nanocomposites: a molecular dynamics simulation

Abstract

This work presents a molecular dynamics simulation study on the interfacial characterization of graphene/epoxy nanocomposites. In polymeric nanocomposites, the thermo-mechanical properties of a system strongly depend on the characteristics of the interphase region between the matrix and the inclusions. The first step in the characterization of this interphase is to distinguish its border limit (i.e., the interphase thickness). Here, we present a methodology to systematically quantify the interphase thickness based on analyzing the variation of the local mass density profile. To this end, three functions (average accumulated mass density, accumulated standard deviation (ASD) and its first derivative) are successively applied on the local mass density profile. Using this procedure, the interphase limit can be easily detected regardless of the oscillatory nature of the local mass density. The effect of the epoxy crosslinking density and number of graphene layers on the interphase thickness is then investigated, and the results are analyzed by studying the interaction energies, polymer dynamics and distribution quality of reacted and unreacted components, as well as conformational changes of the polymer chains in the interphase region. The results reveal that the crosslinking density is the most influential parameter on the interphase thickness: the higher the crosslinking degree, the thicker the interphase region. To a lower extent, the interaction energy has also an effect on the interphase thickness since there is an inverse relationship between the interaction energy and the crosslinking density in our case study. Overall, the reported findings highlight useful insights into the detection and properties of the interphase region in thermoset composites.