Department of Chemical Engineering, Queen's University, Kingston, ON, Canada.
Langmuir. 2012 Mar 6;28(9):4586-97. doi: 10.1021/la2049019. Epub 2012 Feb 27.
The use of spatially nonuniform electric fields for the contact-free colloidal particle assembly into ordered structures of various length scales is a research area of great interest. In the present work, numerical simulations are undertaken in order to advance our understanding of the physical mechanisms that govern this colloidal assembly process and their relation to the electric field characteristics and colloidal system properties. More specifically, the electric-field driven assembly of colloidal silica (d(p) = 0.32 and 2 μm) in DMSO, a near index matching fluid, is studied numerically over a range of voltages and concentration by means of a continuum thermodynamic approach. The equilibrium (u(f) = 0) and nonequilibrium (u(f) ≠ 0) cases were compared to determine whether fluid motion had an effect on the shape and size of assemblies. It was found that the nonequilibrium case was substantially different versus the equilibrium case, in both size and shape of the assembled structure. This dependence was related to the relative magnitudes of the electric-field driven convective motion of particles versus the fluid velocity. Fluid velocity magnitudes on the order of mm/s were predicted for 0.32 μm particles at 1% initial solids content, and the induced fluid velocity was found to be larger at the same voltage/initial volume fraction as the particle size decreased, owing to a larger contribution from entropic forces.
使用非均匀空间电场将胶体粒子无接触组装成各种长度尺度的有序结构是一个非常有趣的研究领域。在目前的工作中，进行了数值模拟，以深入了解控制这种胶体组装过程的物理机制及其与电场特性和胶体系统特性的关系。更具体地说，通过连续热力学方法，在 DMSO 中（一种接近折射率匹配的流体）对胶体二氧化硅（d(p) = 0.32 和 2 μm）在电压和浓度范围内进行了数值研究。比较了平衡（u(f) = 0）和非平衡（u(f) ≠ 0）情况，以确定流体运动是否对组装结构的形状和大小有影响。结果发现，与平衡情况相比，非平衡情况在组装结构的大小和形状上有很大的不同。这种依赖性与电场驱动的粒子对流运动与流体速度的相对大小有关。对于初始固体含量为 1%的 0.32 μm 颗粒，预测的流体速度约为 mm/s，并且随着粒径的减小，由于熵力的贡献更大，在相同的电压/初始体积分数下，诱导的流体速度也更大。
