Krekelberg William P, Mittal Jeetain, Ganesan Venkat, Truskett Thomas M
Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, USA.
J Chem Phys. 2007 Jul 28;127(4):044502. doi: 10.1063/1.2753154.
We present molecular simulation data for viscosity, self-diffusivity, and the local structural ordering of (i) a hard-sphere fluid and (ii) a square-well fluid with short-range attractions. The latter fluid exhibits a region of dynamic anomalies in its phase diagram, where its mobility increases upon isochoric cooling, which is found to be a subset of a larger region of structural anomalies, in which its pair correlations strengthen upon isochoric heating. This "cascade of anomalies" qualitatively resembles that found in recent simulations of liquid water. The results for the hard-sphere and square-well systems also show that the breakdown of the Stokes-Einstein relation upon supercooling occurs for conditions where viscosity and self-diffusivity develop different couplings to the degree of pairwise structural ordering of the liquid. We discuss how these couplings reflect dynamic heterogeneities. Finally, we note that the simulation data suggest how repulsive and attractive glasses may generally be characterized by two distinct levels of short-range structural order.
我们展示了关于（i）硬球流体和（ii）具有短程吸引力的方阱流体的粘度、自扩散系数以及局部结构有序性的分子模拟数据。后一种流体在其相图中展现出一个动态异常区域，在该区域中，其流动性在等容冷却时增加，这被发现是一个更大的结构异常区域的子集，在这个更大区域中，其对关联在等容加热时增强。这种“异常级联”在性质上类似于最近对液态水的模拟中所发现的情况。硬球和方阱系统的结果还表明，在过冷时斯托克斯 - 爱因斯坦关系的失效发生在粘度和自扩散系数与液体的成对结构有序程度发展出不同耦合的条件下。我们讨论了这些耦合如何反映动态非均匀性。最后，我们注意到模拟数据表明了排斥性玻璃和吸引性玻璃通常可能如何由两种不同水平的短程结构有序来表征。
