Alarcón L M, Frechero M A, Montani R A, Appignanesi G A
Sección Fisicoquímica, INQUISUR-UNS-CONICET and Departamento de Química, Universidad Nacional del Sur, Avenida Alem 1253, 8000 Bahía Blanca, Argentina.
Phys Rev E Stat Nonlin Soft Matter Phys. 2009 Aug;80(2 Pt 2):026127. doi: 10.1103/PhysRevE.80.026127. Epub 2009 Aug 26.
Supercooled liquids have been shown to be dynamically heterogeneous with different regions of the system presenting dynamics that vary from each other even by orders of magnitude. Computer simulations have confirmed such a picture by detecting that the mobile particles in model glass formers are not homogeneously distributed within the system but arranged in clusters. More recently, the dynamics of small systems has been characterized by demonstrating that their structural relaxation is not homogeneous in time, in the sense that it does not evolve gradually but it is signed by rapid bursts of mobility characterized by relative compact clusters of mobile particles. These events (which have been named d clusters) are fast and sparse and trigger the transitions the system experiences between metabasins (MB) of its potential-energy surface. The MB residence times are much larger than the time scales of occurrence of the d clusters, and it has been suggested that the events that occur within them scarcely contribute to the structural relaxation of the system. Thus, the picture of glassy relaxation that emerges would indicate that at any time a supercooled liquid may present different spatial regions, each one characterized by different structural relaxation times. In turn, each of such regions would not relax smoothly or gradually but by means of sporadic sharp relaxation events. Here, we assess for a model glass former the relative relevance of the MB exploration events and of the d clusters both in small systems and within regions of large systems, to show that the structural relaxation at the region level is indeed extremely heterogeneous in time and utterly governed by the latter.
过冷液体已被证明具有动态非均匀性，系统的不同区域呈现出彼此差异甚至达几个数量级的动力学。计算机模拟通过检测模型玻璃形成体中的移动粒子并非在系统内均匀分布而是聚集成簇，证实了这样的图景。最近，小系统的动力学特征表现为其结构弛豫在时间上并非均匀的，即它不是逐渐演化，而是以移动粒子相对紧密的簇为特征的快速迁移突发为标志。这些事件（已被命名为d簇）快速且稀疏，并触发系统在其势能面的亚稳态（MB）之间经历的转变。MB停留时间远大于d簇出现的时间尺度，并且有人提出在MB内发生的事件对系统的结构弛豫贡献甚微。因此，所呈现的玻璃态弛豫图景表明，在任何时刻，过冷液体可能呈现不同的空间区域，每个区域具有不同的结构弛豫时间。反过来，每个这样的区域不会平滑或逐渐弛豫，而是通过零星的急剧弛豫事件弛豫。在这里，我们评估了一个模型玻璃形成体中，MB探索事件和d簇在小系统以及大系统区域内的相对相关性，以表明区域层面的结构弛豫在时间上确实极其不均匀，并且完全由后者主导。
