Pressure-Dependent Dynamics of Polymer Melts from Arrhenius to Non-Arrhenius: The Cooperative Free Volume Rate Equation Tested against Simulation Data
Pressure-Dependent Dynamics of Polymer Melts from Arrhenius to Non-Arrhenius: The Cooperative Free Volume Rate Equation Tested against Simulation Data
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DOI：
10.1021/acs.macromol.8b00591
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发表时间：
2018-06
期刊：
影响因子：
5.5
通讯作者：
Ronald P White;J. Lipson
中科院分区：
文献类型：
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作者：
Ronald P White;J. Lipson
应用协同自由体积模型分析了分子动力学模拟的20聚聚合物熔体在较宽压力范围内的链段驰豫时间τ(T，V)。20-聚体的热力学表征允许确定硬核体积(VHC)的恒定贡献，然后产生自由体积的预测，VFree=V-VHC。CFV速率模型基于激活自由能，该激活自由能随合作节段的数量n*而增加，其中系统的自由体积VFree是决定n*的因素。该模型预测在等温线上，lnτ与1/VFree与T相关的斜率是线性的。20聚体熔体数据在所有温度下都遵循这种线性行为。假设每个合作链段的活化能是固定的，则得到一个非常简单的解析形式，该形式描述了20聚体熔体的所有高T行为，包括Arrhenius到Non-Arrhenius的转变区域。这种形式反映了气体运动贡献的重要性，以及两者的重要性。
We apply the cooperative free volume (CFV) model to analyze the segmental relaxation times, τ(T,V), of a model 20-mer polymer melt simulated via molecular dynamics over a broad pressure range. Thermodynamic characterization of the 20-mer allows determination of the constant contribution from the hard-core volume (Vhc), which then yields predictions for the free volume, Vfree = V – Vhc. The CFV rate model is based on an activation free energy that increases with the number of cooperating segments, n*, wherein the system’s free volume, Vfree, is what determines n*. The model predicts that on isotherms ln τ vs 1/Vfree is linear with T-dependent slopes. The 20-mer melt data follow this linear behavior at all temperatures. Assuming a fixed activation energy per cooperating segment leads to a very simple analytic form that describes all of the 20-mer melt’s high T behavior, including the Arrhenius to non-Arrhenius transition regime. This form reflects the importance of a gas kinetic contribution as well as both...