Department of Physics, North Dakota State University, Fargo, North Dakota 58108-6050, USA.
Phys Rev E. 2017 Dec;96(6-1):062610. doi: 10.1103/PhysRevE.96.062610. Epub 2017 Dec 18.
Interparticle interactions and bulk properties of colloidal suspensions can be substantially modified by the addition of nanoparticles. Extreme asymmetries in size and charge between colloidal particles and nanoparticles present severe computational challenges to molecular-scale modeling of such complex systems. We present a statistical mechanical theory of effective electrostatic interactions that can greatly ease large-scale modeling of charged colloid-nanoparticle mixtures. By applying a sequential coarse-graining procedure, we show that a multicomponent mixture of charged colloids, nanoparticles, counterions, and coions can be mapped first onto a binary mixture of colloids and nanoparticles and then onto a one-component model of colloids alone. In a linear-response approximation, the one-component model is governed by a single effective pair potential and a one-body volume energy, whose parameters depend nontrivially on nanoparticle size, charge, and concentration. To test the theory, we perform molecular dynamics simulations of the two-component and one-component models and compute structural properties. For moderate electrostatic couplings, colloid-colloid radial distribution functions and static structure factors agree closely between the two models, validating the sequential coarse-graining approach. Nanoparticles of sufficient charge and concentration enhance screening of electrostatic interactions, weakening correlations between charged colloids and destabilizing suspensions, consistent with experiments.
通过添加纳米颗粒可以显著改变胶体悬浮液的颗粒间相互作用和整体性质。胶体颗粒和纳米颗粒之间在尺寸和电荷方面的极端不对称性给此类复杂系统的分子尺度建模带来了严峻的计算挑战。我们提出了一种有效的静电相互作用统计力学理论，该理论可以大大简化带电胶体-纳米颗粒混合物的大规模建模。通过应用顺序粗粒化过程，我们表明带电胶体、纳米颗粒、抗衡离子和共离子的多组分混合物可以首先映射到胶体和纳米颗粒的二元混合物上，然后映射到仅胶体的单组分模型上。在线性响应近似下，单组分模型由单个有效对势和单个体积能量控制，其参数与纳米颗粒的尺寸、电荷和浓度有很大关系。为了检验理论，我们对两组件和单组件模型进行了分子动力学模拟并计算了结构性质。对于中等的静电耦合，两种模型之间的胶体-胶体径向分布函数和静态结构因子非常吻合，验证了顺序粗粒化方法的有效性。具有足够电荷和浓度的纳米颗粒增强了静电相互作用的屏蔽，削弱了带电胶体之间的相关性并使悬浮液不稳定，这与实验结果一致。
