Molecular Dynamics Simulations of Crumpling Polymer-Grafted Graphene Sheets: Implications for Functional Nanocomposites

Polymer-grafted graphene (PgG) sheets are of interest in the development of functional nanocomposite materials for sensing, energy storage, and coatings. Although extensive studies have reported on various physical properties of PgG sheets, our understanding of the fundamental structural behavior of crumpled PgG sheets is still lacking. Here, we perform molecular dynamics (MD) simulations of the crumpling behavior of poly(methyl methacrylate) (PMMA)-grafted graphene (PMMA-g-G) sheets with varying grafting densities based on previously developed coarse-grained (CG) models of PMMA and graphene. The simulation results reveal that the conformation of PMMA-g-G sheets in the initial equilibrium is controlled by the polymer grafting density and can be characterized into three different regimes (i.e., flat, folded, and wrinkled states), where the local distribution of PMMA on the graphene affects the local curvature of the sheet. By analyzing the total potential energy, shape descriptor, and conformation of the system during the crumpling process, it is found that the increase in grafting density reduces the self-adhering and self-folding behaviors of the sheet while making the bending behavior dominate the crumpling process. Moreover, the evaluation of the local curvature, stress distributions, and cross-sectional patterns of crumpled PMMA-g-G sheets further uncovers the reduced degree of mechanical heterogeneity due to the increased grafting density. Our study provides fundamental insights into the conformational behavior of PMMA-g-G sheets in equilibrium and crumpled states in relation to grafting density, which is crucial for establishing the structure–property relationships for leveraging crumpled polymer-grafted sheets in functional nanocomposites.