Structural characteristics of a cooperatively rearranging region during the glass transition of a polymer system

Abstract

The correlations between local ordered structures and cooperative motion were investigated by dynamic Monte Carlo (MC) simulation. The fraction of trans-conformation increases with the decrease of temperature, indicating the occurrence of a conformational transition from gauche- to trans-conformations. Due to the relatively high degree of close-packing, the trans-conformations are inclined to form local order. Furthermore, all the segments in the polymer system can be divided into two types: the ordered and the disordered ones. Compared with the ordered segments, the disordered segments have more neighboring vacancy sites, and thus move faster and randomly. Correspondingly, the segments in the local order have fewer neighboring vacancy sites, and exhibit lower mobility, which could only move cooperatively along the parallel direction. Those findings suggest that the cooperatively rearranging regions proposed by Adam and Gibbs contain more local ordered structures.