Folding Behavior of Polyethylene Chains with Different Topologies: Insights from All-Atom and United-Atom Simulations

Molecular dynamics simulations were employed to investigate the folding behavior of single polyethylene (PE) chain with different topologies. The chain conformations and structural characteristics were analyzed in detail using four different force fields based on all-atom and united-atom models. The results show that the end-to-end distance (Ree) and radius of gyration (Rg) for chains with different topologies vary significantly in the all-atom model, due to its detailed atomic representation. In contrast, the Ree and Rg values in the united-atom model are nearly identical, with differences only emerging during the collapse stages using the TraPPE-UA force field. The crystallinity of linear, single-branched, and double-branched chains is nearly identical across different force fields, except for the OPLS-AA force field. In the all-atom model, the OPLS-AA force field leads to chains folding into ordered stems with a richer trans conformation, while the PCFF-AA force field results in random-coil structures, and the united-atom model yields globular folded structures. Based on the findings, branching primarily affects the local arrangement of intramolecular segments, with minimal impact on the overall folding scale or spatial configuration.