Dielectrophoretic motions of multiple particles under an alternating-current electric field

Abstract

In this paper, we have performed direct numerical simulations on two-dimensional dielectrophoretic (DEP) motions of two or three identical particles in close proximity suspended freely in a viscous fluid under an externally applied alternating-current (AC) electric field with the purpose of further understanding AC DEP particle–particle interactions among multiple particles. For the simulations, we solve the Maxwell’s equation with a large sharp jump in the complex electric permittivity across the particle–fluid interface for the complex electric potential and then integrate the Maxwell stress tensor to compute the time-averaged DEP force acting on each particle, while we solve the continuity and Stokes equations for the flow field. To solve the relevant governing equations, we employ a finite-volume based numerical approach, where a sharp interface method is adopted for the solution of the complex electric potential and a direct-forcing based immersed-boundary method is for that of the flow field. Results show that the AC DEP motion of two particles depends significantly on their signs of the real part of the Clausius–Mossotti (CM) factor. When both particles have the same sign (positive or negative), they revolve and finally get aligned in a line with the electric field. With different signs, on the other hand, they revolve in the opposite direction and finally get aligned in a line perpendicular to the electric field. In addition, three particles with the same sign finally get aligned in a line with the electric field like the case of two particles. With mixed signs, however, they eventually exhibit one of the certain regular arrangements depending on their initial configuration and sign combination.