Do String-like Cooperative Motions Predict Relaxation Times in Glass-Forming Liquids?,The Journal of Physical Chemistry B

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Do String-like Cooperative Motions Predict Relaxation Times in Glass-Forming Liquids?
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2019-12-30 , DOI: 10.1021/acs.jpcb.9b09468
Jui-Hsiang Hung ₁ , David S Simmons ₂

Affiliation

The Adam-Gibbs theory of glass formation posits that the growth in the activation barrier of fragile liquids on cooling emerges from a loss of configurational entropy and concomitant growth in "cooperatively rearranging regions" (CRRs). A body of literature over 2 decades has suggested that "string-like" cooperatively rearranging clusters observed in molecular simulations may be these CRRs-a scenario that would have profound implications for the understanding of the glass transition. The central element of this postulate is the report of an apparent zero-parameter relationship between the mass of string-like CRRs and the relaxation time. Here, we show, based on molecular dynamics simulations of multiple glass-forming liquids, that this finding is the result of an implicit adjustable parameter-a "replacement distance". This parameter is equivalent to an adjustable exponent within a generalized Adam-Gibbs relation, such that it tunes the entire functional form of the relation. Moreover, we are unable to find any objective criterion, based on the radial distribution function or the cluster fractal dimension, for selecting this replacement distance across multiple systems. We conclude that the present data do not establish that string-like cooperative rearrangements, as presently defined, are predictive of segmental relaxation via an Adam-Gibbs-like physical model.

中文翻译：

弦状的合作运动能预测玻璃形成液体中的弛豫时间吗？

Adam-Gibbs的玻璃形成理论认为，易碎液体在冷却时的激活势垒的增长来自“合作重排区域”（CRRs）中结构熵的丧失和伴随的增长。超过20年的文献资料表明，在分子模拟中观察到的“串状”协作重排簇可能是这些CRR，这种情况对理解玻璃化转变具有深远的意义。该假设的中心要素是关于串状CRR的质量和弛豫时间之间明显的零参数关系的报告。在这里，我们基于多种玻璃形成液体的分子动力学模拟显示，这一发现是隐式可调参数-“置换距离”的结果。此参数等效于广义Adam-Gibbs关系中的可调指数，因此它可以调整关系的整个功能形式。此外，我们无法基于径向分布函数或聚类分形维数找到任何客观标准来选择跨多个系统的替换距离。我们得出的结论是，目前的数据不能确定当前定义的弦状协作重排是通过类似于Adam-Gibbs的物理模型预测节段松弛的。在多个系统上选择此替换距离。我们得出的结论是，目前的数据不能确定当前定义的弦状协作重排是通过类似于Adam-Gibbs的物理模型预测节段松弛的。在多个系统上选择此替换距离。我们得出的结论是，目前的数据不能确定当前定义的弦状协作重排是通过类似于Adam-Gibbs的物理模型预测节段松弛的。

更新日期：2019-12-30

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