Chain movement in crystallization process by molecular dynamics simulation

Abstract

Molecular dynamics simulations on the melting and crystallization processes of a single polymer chain consisting of 300 CH₂ units were performed. Melting point was determined to be 620 K – the temperature at which a chain changed its shape from a folded structure to an unfolded-globular structure. On the crystallization process, simulations were performed at a low temperature (300 K), about half the melting temperature and at a high temperature (600 K), slightly below the melting temperature. At both temperatures, folded structures were obtained and sliding movements of a chain were observed during the crystallization process. At the large supercooling temperature, that is 300 K, the folding length of the crystal varied with each crystallization run and the total potential energies of the structures were found to be trapped in local minima. Refolding to the most stable structure was not observed. At the small supercooling temperature, that is 600 K, the size of folding length again varied with each crystallization run, but its deviation was much less than at 300 K. Total potential energies of the final folded structures at 600 K were all equivalent and assigned to a global minima. During the run at 600 K, refolding events to other folded structures which had a different number of stems and equivalent total potential energy were sometimes observed.