Departamento de Física, CINVESTAV-IPN, Av. Instituto Politécnico Nacional 2508, 07360 Ciudad de México, Mexico.
Soft Matter. 2018 Feb 21;14(8):1355-1364. doi: 10.1039/c7sm02220d.
In this paper we study the structure and phase behavior of binary mixtures of charged particles at low ionic strength. Due to the large size asymmetry between both species, light scattering measurements give us access only to the partial static structure factor that corresponds to the big particles. We observe that the addition of small charged colloids produces a decrease of the main peak of the measured static structure factor and a shift to larger scattering vector values. This finding is in agreement with theory based on integral equations with the Hypernetted-Chain Closure (HNC) relation. The effective interaction between two big particles due to the presence of small particles is obtained by a HNC inversion scheme and used in numerical simulations that adequately reproduce the experiments. We find that the presence of small particles induces an electrostatic depletion screening among the big colloids, creating around them an exclusion zone for the small charged colloids greater than that caused in the case of neutral small colloids, which in turn augments the depletion effect.
本文研究了低离子强度下带电粒子二元混合物的结构和相行为。由于两种物质的尺寸不对称性很大，光散射测量仅能提供对应于大颗粒的部分静态结构因子。我们观察到，添加小带电胶体后，测量的静态结构因子的主峰会降低，并且向较大的散射矢量值移动。这一发现与基于超网链闭（HNC）关系的积分方程理论相符。通过 HNC 反演方案获得了由于小颗粒的存在而导致的两个大颗粒之间的有效相互作用，并将其用于数值模拟，这些模拟很好地再现了实验结果。我们发现，小颗粒的存在会在大胶体之间诱导静电耗尽屏蔽，在它们周围形成一个排斥区，对于小带电胶体而言，该排斥区大于对于中性小胶体的情况，这反过来又增强了耗尽效应。
