Particle and Fluid Motion in Microchannels under Transverse Oscillatory Fields

Asymmetric rectified electric fields (AREFs) have recently been established to induce a steady electric field in response to an applied oscillatory electric field, provided the ions present have unequal mobilities. Here we examine the behavior of colloidal particles suspended in a thin flat microchannel between parallel electrodes. For unimodal fields, we demonstrate that the pseudo-steady particle distribution is consistent with AREFs acting upon both the particles and the channel surfaces. Theoretical calculations of the 2D fluid flow field inside the channel with an electroosmotic slip boundary condition induced by the AREF provides predictions for the net drag forces acting upon the particles that accord with experimentally observed particle distributions. These findings point to application of oscillatory fields for tunable particle manipulation and micron-scale assembly processes.