Theoretical Soft Matter and Biophysics, Institute for Advanced Simulation and Institute of Complex Systems, Forschungszentrum Jülich, 52425 Jülich, Germany.
Soft Matter. 2017 Dec 20;14(1):92-103. doi: 10.1039/c7sm02019h.
Dispersions of particles with short-range attractive and long-range repulsive interactions exhibit rich equilibrium microstructures and a complex phase behavior. We present theoretical and simulation results for structural and, in particular, short-time diffusion properties of a colloidal model system with such interactions, both in the dispersed-fluid and equilibrium-cluster phase regions. The particle interactions are described by a generalized Lennard-Jones-Yukawa pair potential. For the theoretical-analytical description, we apply the hybrid Beenakker-Mazur pairwise additivity (BM-PA) scheme. The static structure factor input to this scheme is calculated self-consistently using the Zerah-Hansen integral equation theory approach. In the simulations, a hybrid simulation method is adopted, combing molecular dynamics simulations of colloids with the multiparticle collision dynamics approach for the fluid, which fully captures hydrodynamic interactions. The comparison of our theoretical and simulation results confirms the high accuracy of the BM-PA scheme for dispersed-fluid phase systems. For particle attraction strengths exceeding a critical value, our simulations yield an equilibrium cluster phase. Calculations of the mean lifetime of the appearing clusters and the comparison with the analytical prediction of the dissociation time of an isolated particle pair reveal quantitative differences pointing to the importance of many-particle hydrodynamic interactions for the cluster dynamics. The cluster lifetime in the equilibrium-cluster phase increases far stronger with increasing attraction strength than that in the dispersed-fluid phase. Moreover, significant changes in the cluster shapes are observed in the course of time. Hence, an equilibrium-cluster dispersion cannot be treated dynamically as a system of permanent rigid bodies.
具有短程吸引力和长程斥力相互作用的颗粒分散体表现出丰富的平衡微观结构和复杂的相行为。我们介绍了具有这种相互作用的胶体模型系统的结构，特别是短时间扩散特性的理论和模拟结果，包括分散流体相区和平衡团簇相区。粒子相互作用由广义 Lennard-Jones-Yukawa 对势描述。对于理论分析，我们应用混合 Beenakker-Mazur 加和性（BM-PA）方案。该方案的静态结构因子输入是使用 Zerah-Hansen 积分方程理论方法自洽计算的。在模拟中，采用了混合模拟方法，将胶体的分子动力学模拟与流体的多粒子碰撞动力学方法相结合，从而完全捕捉到了流体的动力学相互作用。我们的理论和模拟结果的比较证实了 BM-PA 方案对分散流体相系统的高精度。对于吸引强度超过临界值的粒子，我们的模拟产生了平衡团簇相。计算出现的团簇的平均寿命，并与孤立粒子对的离解时间的分析预测进行比较，揭示了定量差异，表明了多粒子流体动力学相互作用对团簇动力学的重要性。平衡团簇相中团簇的寿命随吸引力强度的增加而增加的速度远大于分散流体相中的速度。此外，在时间过程中观察到团簇形状的显著变化。因此，不能将平衡团簇分散体动态地视为永久刚性体系统。
