Surface-conduction enhanced dielectrophoretic-like particle migration in electric-field driven fluid flow through a straight rectangular microchannel

An electric field has been extensively used to manipulate fluids and particles via electrokinetic flow in microchannels and nanochannels for various lab-on-a-chip applications. Recent studies have demonstrated the action of a dielectrophoretic-like lift force on near-wall particles in an electrokinetic flow due to the particles’ modifications of the field-line structure adjacent to a planar wall. This work presents a fundamental investigation of the lateral migration of dielectric particles in the electrokinetic flow of buffer solutions of varying molar concentrations through a straight rectangular microchannel. We find that the particle migration-induced electrokinetic centerline focusing is significantly enhanced with the decrease of the buffer concentration. This observed phenomenon may be attributed to the increased surface conduction effect in a lower-concentration buffer that yields a larger Dukhin number, Du. It seems qualitatively consistent with a recent theoretical study that predicts a greater wall-induced electrical lift with the increasing value of the Dukhin number for Du ≥ 1.