We study dipolophoretic (DIP), i.e. the combined induced – charge electrophoretic (ICEP) and dielectrophoretic (DEP) interactions between a pair of identical conducting circular cylindrical particles suspended in an unbounded electrolyte solution and subject to a weak uniform time dependent external field acting in a plane perpendicular to the axes of the cylinders. Within the framework of the thin – Debye – layer limit, we specifically focus on the cases of an AC field acting in a fixed direction in the plane and a constant – magnitude field rotating with frequency, respectively.
Both the ICEP and DEP result in particle mutual attraction when their line – of – centres (LOC) is aligned with the external field and repulsion when it is perpendicular thereto. The nonlinearity inherent in both mechanisms gives rise to opposing effects acting to orient the LOC parallel to the external field (DEP) or perpendicular thereto (ICEP). Thus, at low frequencies, when the latter prevails, particles ultimately move apart in the direction perpendicular to the external field. With increasing frequency, DEP prevails over ICEP in a widening domain of the plane resulting in particles eventually pairing (or chaining in multi-particle suspensions) along field lines.
