Electrokinetics in concentrated suspensions of ideally polarizable spheres

Electrokinetics plays an important role in many fields ranging processing techniques for fine particle systems to controlled drug release devices. In many situations, semi-dilute or dense suspensions are used, where hydrodynamic interactions become significant. However, the analysis of the electrokinetics in these suspensions has been poorly understood. In this study, we numerically investigate concentrated suspensions undergoing dielectrophoresis and induced-charge electrophoresis. Large-scale simulations are performed for suspensions at various volume fractions with periodic boundary conditions. Results show an intriguing suspension dynamics at different volume fraction regimes. In a dilute regime, the hydrodynamic diffusivity increases with a volume fraction before reaching a global maximum and then decreases in a semi-dilute regime until it approaches the local minimum at a volume fraction of 30%. Interestingly, the hydrodynamic diffusivity increases again in a concentrated regime until it reaches a local maximum at a volume fraction of 50% and then drastically decreases as it approaches the packing fraction. Further investigations are discussed to better understand this unique behavior in a concentrated regime.