Designing Heterogeneous Surfaces of Two-Dimensional Nanosheets to Maximize Mechanical Reinforcing of Polymer Nanocomposites via Molecular Dynamics Simulation

The relationship between the chemical heterogeneity of two-dimensional (2D) filler surfaces and the mechanical properties of polymer nanocomposites (PNCs) is investigated using coarse-grained molecular dynamics simulations. It is found that there is an optimal surface heterogeneity that results in the highest tensile stress of the nanocomposite. The relationships between the heterogeneity and the entanglement of the polymer, the conformation of polymer chains, as well as the adsorption amount between the fillers and polymer chains are characterized. The results show that increasing the heterogeneity leads to a nonmonotonic variation in the adsorption amount, which further leads to a nonmonotonic variation in the entanglement between the polymer chains and the filler-polymer-filler bridging, and ultimately affects the tensile stress of the nanocomposites. Besides, the effects of the surface heterogeneity and the dispersion of the fillers on the surrounding chain adsorption capability are investigated, and it is found that these two factors affect the adsorption of the fillers on the polymers by changing the effect of entropy and enthalpy between the polymer chains and fillers together. Among them, the nonmonotonicity adsorption amount of the fillers to the polymers mainly comes from the variation of filler dispersion with the variation of heterogeneity. In general, this work provides a fundamental understanding of the reinforcement mechanism of polymer nanocomposites by 2D fillers, enlightening some rational principles for manipulating the physical properties of PNCs.