Molecular simulations of fragility of linear and ring polymers

Abstract

Nowadays, investigation on fragility in glass-forming liquids is a hot topic in the field of condensed matter physics, since the understanding of its microscopic mechanism is useful to uncover the underlying mechanism of the glass transition. In the present paper, we performed dynamic Monte Carlo simulations to explore the correlations between fragility index and conformational changes in linear and ring polymer chains. Compared with ring chains, linear chains exhibit a higher fragility index. In addition, for both ring and linear chains, during approaching the glass transition temperature (Tg), the fraction of segments with trans-conformation increased significantly. To reveal the effect of conformational changes on segmental dynamics during relaxation, a new parameter, the aggregation region of segments with trans-conformation (ARST), is proposed. The maximum ARST has the lowest mobility, which determines the relaxation time of polymers. The fragility index has a strong relationship with the maximum ARST. For linear chains, during approaching Tg, the maximum ARST grew more abruptly, resulting in the larger fragility index.