Modeling Induced-Charge Electroosmosis using a meso-scale approach

Electrokinetic flows are important in many applications such as microfluidic pumping and desalination. We recently developed a meso-scale fluid model, the Discrete-Ion Stochastic Continuum Overdamped Solvent (DISCOS) algorithm, to study non-linear electrokinetic effect such as induced-charge electroosmosis (ICEO). ICEO is specifically interesting because it can generate steady flow in an AC field. Electrokinetic effect is inherently related to the development of the electric double layers due to fluctuations of ions in an electrolyte solution, where molecular-scale physics that cannot be captured by a continuum model are still important. While molecular dynamics can also model the double layer, it is computationally expensive and is challenging to scale the problem size to real applications. To overcome these challenges, we simulate ICEO over a metallic plate in DISCOS, where solvent is modeled under the fluctuating hydrodynamics framework, and the ions are treated by the immersed boundary method. We compare our results to experiments and theories with electric field generating ζ-potentials on the order of the thermal voltage, and we obtain qualitative agreement. We also extend electric fields beyond this parameter space, and several interesting remarks are made in this regime.