State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People's Republic of China.
University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China.
Phys Rev E. 2017 May;95(5-1):050601. doi: 10.1103/PhysRevE.95.050601. Epub 2017 May 15.
It has been broadly accepted that the behavior of glass-forming liquids, where their relaxation dynamics exhibit a pronounced slowdown as they are cooled toward the glass transition temperature, is caused by the increase in one or more correlation lengths. However, the role of length scales in the dynamics of glass-forming liquids is not clearly established, and past simulation work that suggests a surprising nonmonotonic temperature evolution of spatial dynamical correlations near the mode-coupling crossover temperature has been both questioned and supported by subsequent work. Here, using molecular dynamics simulation, we also show a striking maximum in the dynamic length scale ξ_{c}^{dyn} at a given temperature, but the temperature of this maximum is found to shift as the size of the confined system increases. Furthermore, we find that such a maximum disappears for all geometry sizes considered when a rough wall is replaced with a smooth, hard wall, suggesting that the nature of the nonmonotonic temperature dependence of ξ_{c}^{dyn} does not reflect an intrinsic property of bulk liquids, but originates from wall effects. Our results provide new insights into the dynamics of glass-forming liquids, particularly for quasi-two-dimensional systems.
人们普遍认为，随着向玻璃化转变温度的冷却，玻璃形成液体的弛豫动力学会明显减慢，这是由于一个或多个相关长度的增加所致。然而，长度尺度在玻璃形成液体动力学中的作用尚未明确确定，过去的模拟工作表明，在模式耦合交叉温度附近，空间动态相关性具有惊人的非单调温度演化，这一结果受到了后续工作的质疑和支持。在这里，我们使用分子动力学模拟也表明，在给定温度下，动态长度标度 ξ_{c}^{dyn} 会出现显著的最大值，但发现这个最大值的温度会随着受限系统尺寸的增加而发生变化。此外，我们发现，当用粗糙壁代替光滑硬壁时，对于所有考虑的几何形状大小，这种最大值都会消失，这表明 ξ_{c}^{dyn} 的非单调温度依赖性的性质并不反映体相液体的固有特性，而是源于壁效应。我们的结果为玻璃形成液体的动力学提供了新的见解，特别是对于准二维系统。
