Molecular dynamics simulations of single polyethylene chain folding during fast quenching using all-atom and united-atom models

Molecular dynamics simulations have been employed to investigate the folding behavior of a single linear polyethylene (PE) chain containing 1000 backbone carbon atoms under fast quenching based on all-atom and united-atom models. The single-chain folding characteristics were studied in detail for six different force fields by analyzing the evolution of chain conformations, folded structure characterisation, free energy and crystallisation. The results show that the all-trans chain undergoes a similar two-stage chain collapse mechanism during isothermal relaxation at T = 500 K, transitioning from local collapse to global collapse into a molten globule state under different force fields. During fast quenching at 100 K ns⁻¹, the molten globule of all-atom model transitions into a folded, significantly anisotropic ordered structure under AMBER-AA or OPLS-AA force fields, while that of the united-atom model remains unchanged in its globular structure. The chain crystallization evolution indicates that the single chain folds into ordered lamellar structures with higher crystallinity under AMBER-AA and OPLS-AA force fields. In contrast, under the other four force fields, the single chain remains in a stable amorphous state.