Mei Baicheng, Zhuang Bilin, Lu Yuyuan, An Lijia, Wang Zhen-Gang
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China.
Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.
J Phys Chem Lett. 2022 May 5;13(17):3957-3964. doi: 10.1021/acs.jpclett.2c00072. Epub 2022 Apr 28.
Glass formers exhibit a pronounced slowdown in dynamics, accompanied by progressive heterogeneity as they approach the glass transition. There is intense debate over whether the dramatic slowdown is caused by dynamical heterogeneity and whether the enhanced dynamical heterogeneity originates from structural causes. However, the connection between dynamical heterogeneity and the spatial distribution of the single-particle free volume (a purely static structural quantity) was found to be rather weak, which raises the question of whether dynamic heterogeneity has a purely structural origin. Here, by introducing the concept of local-average free volume, we present numerical evidence that long-time dynamic heterogeneity shows significantly enhanced correlation with the average local free volume over a length scale of a few neighboring shells. Our results resolve the long-standing controversy about whether free volume plays an important role in particle rearrangements associated with the activated hopping relaxation. The concept of "local average" can be applied to other local structural descriptors to better correlate with dynamic heterogeneity in glass-forming liquids.
玻璃形成体在动力学上表现出明显的减慢，随着它们接近玻璃化转变，动力学异质性逐渐增强。关于这种剧烈的减慢是否由动力学异质性引起，以及增强的动力学异质性是否源于结构原因，存在激烈的争论。然而，人们发现动力学异质性与单粒子自由体积的空间分布（一个纯粹的静态结构量）之间的联系相当微弱，这就提出了动力学异质性是否具有纯粹结构起源的问题。在这里，通过引入局部平均自由体积的概念，我们给出了数值证据，表明在几个相邻壳层的长度尺度上，长时间的动力学异质性与平均局部自由体积显示出显著增强的相关性。我们的结果解决了关于自由体积在与活化跳跃弛豫相关的粒子重排中是否起重要作用的长期争议。“局部平均”的概念可以应用于其他局部结构描述符，以更好地与玻璃形成液体中的动力学异质性相关联。
