Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712, USA.
J Chem Phys. 2011 Sep 28;135(12):124513. doi: 10.1063/1.3643118.
Partial pair-correlation functions of colloidal suspensions with continuous polydispersity can be challenging to characterize from optical microscopy or computer simulation data due to inadequate sampling. As a result, it is common to adopt an effective one-component description of the structure that ignores the differences between particle types. Unfortunately, whether this kind of simplified description preserves or averages out information important for understanding the behavior of the fluid depends on the degree of polydispersity and can be difficult to assess, especially when the corresponding multicomponent description of the pair correlations is unavailable for comparison. Here, we present a computer simulation study that examines the implications of adopting an effective one-component structural description of a polydisperse fluid. The square-well model that we investigate mimics key aspects of the experimental behavior of suspended colloids with short-range, polymer-mediated attractions. To characterize the partial pair-correlation functions and thermodynamic excess entropy of this system, we introduce a Monte Carlo sampling strategy appropriate for fluids with a large number of pseudo-components. The data from our simulations at high particle concentrations, as well as exact theoretical results for dilute systems, show how qualitatively different trends between structural order and particle attractions emerge from the multicomponent and effective one-component treatments, even with systems characterized by moderate polydispersity. We examine consequences of these differences for excess-entropy based scalings of shear viscosity, and we discuss how use of the multicomponent treatment reveals similarities between the corresponding dynamic scaling behaviors of attractive colloids and liquid water that the effective one-component analysis does not capture.
具有连续多分散性的胶体悬浮液的部分关联函数很难从光学显微镜或计算机模拟数据中进行特征描述，因为采样不足。因此，通常采用忽略颗粒类型之间差异的有效单组分结构描述。不幸的是，这种简化描述是否保留或平均了理解流体行为的重要信息，这取决于多分散性的程度，并且评估起来可能很困难，尤其是在无法获得相应的多组分对关联描述进行比较时。在这里，我们进行了一项计算机模拟研究，研究了采用多分散流体的有效单组分结构描述的含义。我们研究的方阱模型模拟了具有短程聚合物介导吸引力的悬浮胶体的实验行为的关键方面。为了描述该系统的部分关联函数和热力学过剩熵，我们引入了一种适用于具有大量拟组分的流体的蒙特卡罗采样策略。我们在高粒子浓度下的模拟数据以及稀溶液系统的精确理论结果表明，即使对于具有中等多分散性的系统，结构有序性和粒子吸引力之间的定性不同趋势也会从多组分和有效单组分处理中出现。我们研究了这些差异对基于过剩熵的剪切黏度标度的影响，并讨论了多组分处理如何揭示出有吸引力的胶体和液态水的相应动态标度行为之间的相似性，而有效单组分分析则无法捕捉到这些相似性。
