State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People's Republic of China.
James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA.
J Chem Phys. 2014 Mar 28;140(12):124502. doi: 10.1063/1.4868987.
We study the point-to-set length scales and dynamics in three-dimensional Kob-Andersen glass-forming liquids with amorphous boundary conditions by using molecular dynamics simulation, where a set of particles in an equilibrium configuration are pinned while other particles move as before. We consider three different geometries, i.e., spherical cavity, cubic cavity, and walls, for the pinning set of particles. We present the growing static and dynamic point-to-set correlation length scales in the temperature range higher than the ideal mode-coupling theory transition temperature of the bulk. Our results reveal that the two-point static spatial correlations are almost the same for these three geometries at the same temperature, which implies weak geometry dependence on the structure of such glass-forming liquids. By analyzing z (the distance from the wall) dependent point-to-set overlaps, we find that the particles in the layers near the pinning wall relax slower than those far away from the wall. Associated with the dynamical slowdown, the static length scale increases modestly while the dynamic length scale increases dramatically as the temperature is lowered. Compared with the two cavities, the "Walls" system relaxes faster at the same temperature and the same distance from the wall and has smaller length scales. Moreover, the relation between time scale and static length scales depends on the degree of supercooling and the type of geometries. We did not see any clear evidence for the one-to-one correspondence between static and dynamic point-to-set length scales, and also for the one-to-one correspondence between static length scales and relaxation time in the deep supercooled regime. Our results provide clues for the existence of multi-relaxation modes in the supercooled regime in three-dimensional Kob-Andersen glass-forming liquids.
我们使用分子动力学模拟研究了具有非晶界条件的三维 Kob-Andersen 玻璃形成液体中的点到集长度标度和动力学，其中一组处于平衡构型的粒子被钉扎，而其他粒子则像以前一样移动。我们考虑了三种不同的几何形状，即球形腔、立方腔和壁，用于钉扎粒子集。我们在高于本体理想模式耦合理论转变温度的温度范围内呈现出静态和动态点到集相关长度标度的增长。我们的结果表明，在相同温度下，这三种几何形状的两点静态空间相关性几乎相同，这意味着弱几何形状对这种玻璃形成液体的结构依赖性。通过分析 z（距壁的距离）依赖的点到集重叠，我们发现靠近钉扎壁的层中的粒子比远离壁的粒子松弛得更慢。与动力学减速相关，静态长度标度适度增加，而动态长度标度随着温度降低而显著增加。与两个腔相比，在相同温度和相同距离处，“壁”系统的弛豫速度更快，长度标度更小。此外，时间标度与静态长度标度之间的关系取决于过冷度和几何形状的类型。我们没有看到静态和动态点到集长度标度之间存在一一对应关系的任何明确证据，也没有看到在过冷深区静态长度标度和弛豫时间之间存在一一对应关系的任何明确证据。我们的结果为三维 Kob-Andersen 玻璃形成液体中超冷区中存在多弛豫模式提供了线索。
