(535f) Microstructure and Pattern Formation in Suspensions of Polarizable Spheres in Electric Fields

We use theory and numerical simulations to investigate the microstructure in suspensions of spherical particles in a viscous electrolyte under a uniform electric field. Dipolar interactions between particles arise from dielectrophoresis (DEP) as a result of the Maxwell stress in the fluid. The dynamics under these interactions are analyzed in the thin Debye layer limit, and the formation of chain-like structures is predicted in the field direction in agreement with previous studies. Interactions between finite-length chains are also analyzed, and are found to be attractive in the near field but repulsive in the far field. Simulations in large-scale suspensions in a thin gap are also performed with periodic boundary conditions in the directions perpendicular to the electric field. Results confirm the rapid formation of finite chains, which is then followed by a slow coarsening process in which chains coalesce into sheets, which eventually rearrange to form mesoscale cellular structures. If the particles are polarizable, they can also acquire an additional non-uniform surface charge, which can result in interactions by induced-charge electrophoresis (ICEP). When both DEP and ICEP take place concurrently, a phenomenon coined dipolophoresis (DIP), ICEP interactions are found to dominate and suppress chain formation. DIP interactions are instead predicted to result in transient particle pairings, which lead to the formation of short-lived clusters surrounded by clarified regions. The effects of DIP on suspension dynamics are also investigated using large-scale simulations with periodic boundary conditions, where the resulting microstructure is characterized using pair distribution functions and particle occupancy statistics.