Polymer Free Volume and Its Connection to the Glass Transition
Polymer Free Volume and Its Connection to the Glass Transition
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DOI：
10.1021/acs.macromol.6b00215
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发表时间：
2016-06-14
期刊：
影响因子：
5.5
通讯作者：
Lipson, Jane E. G.
中科院分区：
文献类型：
--
作者：
White, Ronald P.;Lipson, Jane E. G.
在这一观点中，我们总结了最广泛使用的自由体积的定义，并说明它们之间的差异，包括总自由体积和过量自由体积之间的重要区别。我们讨论了当自由体积的替代估计被插入到连接实验测量的属性的关系中时的影响（例如，粘度）与自由体积的比值，例如Doolittle、Fox和Flory、Simha和Boyer、Cohen和Turnbull以及威廉姆斯、Landel和Ferry提出的那些。转向我们自己的局部相关晶格（LCL）模型的结果，我们证明，通过分析一组超过50种聚合物的数据，我们的计算总自由体积百分比不仅导致与实验玻璃化转变温度的预测关系，而且还允许我们将自由体积的不同定义放置在所提出的贡献所代表的物理图像中。我们发现融化了。达到最小（总）自由体积百分比的“边界”后呈玻璃状，该“边界”与温度大致呈线性关系。我们解释这个边界是接近T-依赖的自由体积与固体状的节段振动运动。由于LCL模型是第一原理热力学理论，我们也能够将我们的自由体积预测与我们在每个理论段的预测熵中发现的类似模式联系起来。我们的结果是一致的图片，其中之间的熵差的熔融（液体）状态和相应的固体状态的玻璃化转变是接近消失。这使我们与亚当斯和吉布斯的工作有了新的联系，他们的模型反映了构型熵的类似消失。最后，我们讨论了为什么最好的玻璃态的方法被视为通过自由体积和温度的相关贡献控制。
In this Perspective we summarize the most-widely used definitions of free volume and illustrate the differences between them, including the important distinction between total free volume and excess free volume. We discuss the implications when alternative estimates for free volume are inserted into relationships that connect experimentally measured properties (e.g., the viscosity) to free volume, such as those proposed by Doolittle, Fox and Flory, Simha and Boyer, Cohen and Turnbull, and Williams, Landel, and Ferry. Turning to the results of our own locally correlated lattice (LCL) model; we demonstrate, by analyzing data for a set of over 50 polymers, that our calculations for total percent free volume not only lead to a predictive relationship with experimental glass transition temperatures but also allow us to place the different definitions of free volume within a physical picture of what the proposed contributions represent. We find that melts go. glassy upon reaching a "boundary" of minimum (total) percent free volume that depends roughly linearly on temperature. We interpret this boundary as being close to the T-dependent free volume associated-with solid-like segmental vibrational motions. Since the LCL model is a first-principles thermodynamic theory, we are also able to link our free volume predictions to similar patterns that we find in the predicted entropy per theoretical segment. Our results are consistent With a picture wherein the difference in entropy between the melt (liquid) state and corresponding solid state vanishes as the glass transition is approached. This leads us to a new connection with the work of Adams and Gibbs, whose model reflects a similar vanishing of the configurational entropy. We conclude by discussing why the approach to the glassy state is best viewed as being controlled via the linked contributions of free volume and temperature.