AC Electrokinetic Templating of Colloidal Particle Assemblies: Effect of Electrohydrodynamic Flows

摘要

The use of spatially nonuniform electric fields for the contact-freencolloidal particle assembly into ordered structures of various length scales is anresearch area of great interest. In the present work, numerical simulations arenundertaken in order to advance our understanding of the physical mechanisms thatngovern this colloidal assembly process and their relation to the electric fieldncharacteristics and colloidal system properties. More specifically, the electric-fieldndriven assembly of colloidal silica (dp = 0.32 and 2 μm) in DMSO, a near indexnmatching fluid, is studied numerically over a range of voltages and concentrationnby means of a continuum thermodynamic approach. The equilibrium (u⃗fn= 0)nand nonequilibrium (u⃗f ≠ 0) cases were compared to determine whether fluidnmotion had an effect on the shape and size of assemblies. It was found that thennonequilibrium case was substantially different versus the equilibrium case, in bothnsize and shape of the assembled structure. This dependence was related to thenrelative magnitudes of the electric-field driven convective motion of particles versusnthe fluid velocity. Fluid velocity magnitudes on the order of mm/s were predicted for 0.32 μm particles at 1% initial solidsncontent, and the induced fluid velocity was found to be larger at the same voltage/initial volume fraction as the particle sizendecreased, owing to a larger contribution from entropic forces.