Hierarchical Coupling Mechanisms of Semicrystalline Polyethylene under Nanoindentation: A Multiscale Simulation Study

This study employed all-atom, united-atom, and coarse-grained resolution models to perform a cross-scale correlation analysis of the nanoindentation process in semicrystalline polyethylene, systematically elucidating the multilevel coupling mechanism from intrachain conformation to segmental organization and further to phase structure under indentation conditions. At the intrachain conformation scale, bond lengths and bond angles primarily accommodated recoverable elastic deformation, whereas dihedral angles experienced irreversible conformational transitions induced by the indenter. Such intrachain conformational changes provided both space and driving force for the overall rearrangement at the segmental organization scale, resulting in a decrease in the interchain nonbonded potential energy after unloading that exceeded the increase in the intrachain dihedral potential energy, thereby relaxing the system into a more compact metastable state with lower total potential energy. Finally, the differences in interchain mobility were amplified at the phase structure scale, manifesting as the crystalline regions bearing concentrated loads while the amorphous regions provided extensive buffering; stress underwent nonuniform redistribution at the interface between the two phases, inducing fragmentation of some crystalline regions and relaxation of the entanglement network, yet the density of the amorphous regions and the content of tie chains were thereby increased. The findings provide theoretical support for understanding and rationally designing the surface and interfacial mechanical properties of semi-crystalline polymers.