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.