Lüders Anton, Zander Ellen, Nielaba Peter
Statistical and Computational Physics, Department of Physics, University of Konstanz, 78464 Konstanz, Germany.
J Chem Phys. 2021 Sep 14;155(10):104113. doi: 10.1063/5.0060063.
We explore the diffusion properties of colloidal particles with dumbbell and spherocylinder shapes using a hydrodynamic bead-shell approach and additional Brownian dynamics (BD) simulations. By applying the bead-shell method, we determine empirical formulas for the microscopic diffusion coefficients. A comparison of these formulas and established experimental and theoretical results shows remarkable agreement. For example, the maximum relative discrepancy found for dumbbells is less than 5%. As an application example of the empirical formulas, we perform two-dimensional (2D) BD simulations based on a single dumbbell or spherocylinder in a suspension of spheres and calculate the resulting effective long-time diffusion coefficients. The performed BD simulations can be compared to quasi-2D systems such as colloids confined at the interface of two fluids. We find that the effective diffusion coefficient of translation mostly depends on the sphere area fraction ϕ, while the effective diffusion coefficient of rotation is influenced by the aspect ratio and ϕ. Furthermore, the effective rotational diffusion constant seems to depend on the particle shape with the corresponding implementation of the interactions. In the resolution limit of our methods, the shape-dependent differences of the microscopic diffusion coefficients and the long-time diffusion constant of translation are negligible in the first approximation. The determined empirical formulas for the microscopic diffusion coefficients add to the knowledge of the diffusion of anisotropic particles, and they can be used in countless future studies.
我们使用流体动力学珠壳方法和额外的布朗动力学（BD）模拟，探究了哑铃形和球柱形胶体颗粒的扩散特性。通过应用珠壳方法，我们确定了微观扩散系数的经验公式。将这些公式与已有的实验和理论结果进行比较，结果显示出显著的一致性。例如，哑铃形颗粒的最大相对差异小于5%。作为经验公式的一个应用实例，我们基于单个哑铃形或球柱形颗粒在球体悬浮液中的情况进行了二维（2D）BD模拟，并计算了由此产生的有效长时间扩散系数。所进行的BD模拟可以与准二维系统进行比较，例如限制在两种流体界面处的胶体。我们发现，平移的有效扩散系数主要取决于球体面积分数ϕ，而旋转的有效扩散系数则受纵横比和ϕ的影响。此外，有效旋转扩散常数似乎取决于颗粒形状以及相应的相互作用。在我们方法的分辨率极限内，微观扩散系数和长时间平移扩散常数的形状依赖性差异在一阶近似中可以忽略不计。所确定的微观扩散系数的经验公式增加了我们对各向异性颗粒扩散的认识，并且可用于无数未来的研究中。
