Krekelberg William P, Ganesan Venkat, Truskett Thomas M
J Phys Chem B. 2006 Mar 23;110(11):5166-9. doi: 10.1021/jp060250n.
Free volume theories for the dynamics of dense fluids commonly assume (i) that diffusivity increases with average free volume per particle and (ii) that the size distribution of free volumes can be approximated by that of an equivalent hard-sphere reference system. We use molecular simulations to demonstrate that these assumptions break down when one considers concentrated suspensions of particles with short-range attractions. In these systems, self-diffusivity shows nonmonotonic dependencies on both average free volume and the strength of the interparticle attraction. Moreover, when interparticle attractions are strong, the shape of the free volume distribution is qualitatively different than that of the corresponding hard-sphere reference fluid. We propose a conceptual revision to the traditional free volume perspective that takes into account both the size distribution and the persistence time of the free volumes, and we demonstrate that it can qualitatively capture the disparate behaviors of a model fluid with short-range attractions and its hard-sphere reference fluid.
（i）扩散系数随每个粒子的平均自由体积增加而增大；（ii）自由体积的尺寸分布可以用等效硬球参考系统的尺寸分布来近似。我们通过分子模拟证明，当考虑具有短程吸引力的粒子的浓悬浮液时，这些假设不再成立。在这些系统中，自扩散系数对平均自由体积和粒子间吸引力强度均呈现非单调依赖性。此外，当粒子间吸引力较强时，自由体积分布的形状与相应硬球参考流体的形状在性质上有所不同。我们对传统的自由体积观点提出了一种概念性修正，该修正同时考虑了自由体积的尺寸分布和持续时间，并证明它能够定性地捕捉具有短程吸引力的模型流体及其硬球参考流体的不同行为。
