Saltzman Erica J, Schweizer Kenneth S
Department of Materials Science & Engineering, University of Illinois, Urbana, Illinois 61801, USA.
J Chem Phys. 2004 Jul 22;121(4):2001-9. doi: 10.1063/1.1756856.
Our theory of dynamic barriers, slow relaxation, and the glass transition of polymers melts is numerically applied using parameters relevant to real materials. The numerical results are found to be in qualitative agreement with all the approximate analytic expressions previously derived with quantitative differences on the order of approximately 20-30% or much less. The analytic prediction of a universal temperature dependence of the alpha relaxation time, and its intimate connection with the idea of a nearly universal crossover time, is established. Inter-relations between the breadth of the deeply supercooled regime, two definitions of the dynamic fragility, and the magnitude of the fast local Arrhenius process at the glass transition temperature are demonstrated and system-specific limitations identified. A quantitative application to segmental relaxation over 16 orders of magnitude in a polyvinylacetate melt yields encouraging results regarding the accuracy of the theory. The theoretical relaxation time results are well fit by multiple empirical forms (generally containing an assumed singular aspect) using parameters consistent with experimental studies. No physical significance is ascribed to this finding, but it does provide additional support for the temperature dependence of the alpha relaxation process predicted by the theory.
我们关于聚合物熔体的动态屏障、缓慢松弛和玻璃化转变的理论，通过使用与实际材料相关的参数进行了数值应用。发现数值结果与先前推导的所有近似解析表达式在定性上一致，定量差异约为20% - 30%或更小。确立了α弛豫时间的通用温度依赖性的解析预测及其与近乎通用的交叉时间概念的紧密联系。展示了深度过冷区域的宽度、动态脆性的两种定义以及玻璃化转变温度下快速局部阿仑尼乌斯过程的大小之间的相互关系，并确定了特定系统的局限性。对聚醋酸乙烯酯熔体中跨越16个数量级的链段松弛进行定量应用，得到了关于该理论准确性的令人鼓舞的结果。理论弛豫时间结果通过多种经验形式（通常包含一个假定的奇异方面），使用与实验研究一致的参数得到了很好的拟合。虽然没有赋予这一发现任何物理意义，但它确实为该理论预测的α弛豫过程的温度依赖性提供了额外支持。
