Molecular Dynamics Study on the Crystallization of a Cluster of Polymer Chains Depending on the Initial Entanglement Structure

Abstract

Using a large polymer chain cluster, we have examined entanglement densities of the polymer chains in the bulk and in the surface by molecular dynamics simulation. The entanglement density was measured by the interchain contact fraction (ICF), which was developed as a structural parameter of the entanglement. It was found that the surface location has a lower ICF than the bulk core does. Different entanglement structures then underwent crystallization processes. It resulted in a multidomain system, in which the directors of the order domains are in isotropic distributed. For calculating the crystallinity of the systems, we developed a method, the site order parameter (SOP), which endows local order to every particle in the system; when determining the order for crystalline phase, one can count the crystallinity. SOP enables us to transform a molecular chain picture into an order image, where white stands for the crystalline phase and black for the amorphous. Snapshots of the simulations show evolution of the nucleation and the crystal growth through SOP images. The dynamic effect of the entanglement was observed in the crystallization behaviors. It shows that the entanglement has a higher density in the bulk and a lower density in the surface. The result shows that a shorter induction period of nucleation and a higher crystal growth rate was found in the surface location, since possessing lower ICF.