Glass Transition in Single Poly(ethylene oxide) Chain: A Molecular Dynamics Simulation Study

Local dynamics of single poly(ethylene oxide) chain in various environments (bulk, film, and isolated systems) has been characterized by the reorientation functions of various backbone bond vectors. Within any observation time, the variations of these reorientation functions with the temperature can be well described by the Kohlrausch-Williams-Watts (KWW) like equation, in which the fitted temperature parameter is identified as the glass transition temperature (T-g). The so-obtained T-g for that polymer faithfully reveals the effects of the observation time, chain flexibility and vector range on the local dynamics. Furthermore, it is found that the KWW like relation is also applicable to the temperature-dependence of the fraction of frozen atoms or torsions defined by the trajectory radii of gyration or the conformational transitions. Consequently, different motions lead to different values of T-g for the same system. Despite all, the consistent trend can be yielded, namely, T-g (bulk) > T-g (film)> T-g (isolated), which captures the effects of free surfaces on enhanced dynamics. In addition, dynamics heterogeneity in the systems can be quantitatively revealed. The newly proposed method holds a bright promise to predict the T-g values of complex polymers especially for comparisons. (C) 2016 Wiley Periodicals, Inc.