Conformational Transition Behavior of Amorphous Polyethylene across the Glass Transition Temperature

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• 作者：Rongliang Wu ; Xiongfei Zhang ; Qing Ji ; Bin Kong ; Xiaozhen Yang
• 刊名：Journal of Physical Chemistry B
• 出版年：2009
• 出版时间：July 9, 2009
• 年：2009
• 卷：113
• 期：27
• 页码：9077-9083
• 全文大小：303K
• 年卷期：v.113,no.27(July 9, 2009)
• ISSN：1520-5207

文摘

Molecular dynamics simulations have been used to investigate the conformational transition behavior in amorphous polyethylene with different chain lengths across the glass transition temperature (T_g). In the present study, we examined the barrier height of conformational transition rates in different states. It was found that two lines of the logarithmic rates versus inverse temperature in the melt state and in the glass state are evidently different. The two lines have an intersection, which indicates T_g well. The barrier height in the glass state was unexpectedly observed lower than that in the melt state. For gaining better understanding of the transition barrier reduction, we analyzed motion heterogeneity of the systems and found the torsional transition rate distribution becoming gradually heterogeneous when the temperature went down to the glass state. The result indicates that the motion heterogeneity was caused by the torsion transition being “frozen”. The frozen torsions made the system into a nonequilibrium state and possess a novel transition behavior, which accounted for most of the transitions that started at a location close to top of barrier, and also the enhancement of a small magnitude of transition jumps.