Static and dynamic equilibrium states driven by induced-charge electrophoresis in two-dimensional suspensions*

The external field-driven assembly of colloidal suspensions has gained growing attention since it can be programmed as advanced materials in many applications, such as photonics, displays, and electronic devices. An efficient way for precise and rapid manipulation of particles in a suspension is to apply an electric field. Here, we focus on a two-dimensional suspension of conductive particles in an electric field, which is known to be powered by induced-charge electrophoresis (ICEP). Large-scale simulations are conducted using the Stokesian dynamics simulation method to account for electric and hydrodynamic interactions due to ICEP. As expected, the suspension dynamics get hindered as an area fraction is increased. Interestingly, at an area fraction of 50%, an almost static equilibrium state is observed for a long time, during which a suspension appears nearly frozen. Surprisingly, above this concentration, the suspension dynamics get enhanced, reaching a dynamic equilibrium state at 60% before approaching a static equilibrium state again at random close packing. These equilibrium states will be rationalized by examining the velocity fluctuations and suspension microstructure.