Nonantiperiodic Nonlinear Electrophoresis of Colloidal Particles

Presented here is the first synergistic experimental observation and computational prediction of nonantiperiodic nonlinear electrophoresis (NANEP), obtained by imposing a sinusoidal nonantiperiodic voltage on negatively charged colloidal (polystyrene) particles in a microfluidic device. The motion of micrometer-sized polystyrene particles driven by NANEP was experimentally observed and predicted computationally, demonstrating that a net particle drift can be obtained with the application of a (spatially uniform) AC signal without the need of a DC bias. Experiments applying AC voltages with amplitudes of 150 and 500 V while toggling on and off the nonantiperiodic signal were conducted, from which particle position was measured and compared with the predictions from simulations of the full nonlinear electrokinetic equations, obtaining good agreement in the amplitude of the particle position oscillation and its net drift. Further experiments varying the amplitude of the applied voltage signal were used to build a net drift speed profile as a function of the electric field peak-to-peak amplitude. The numerical simulations identified fore-aft spatial symmetry breaking in the period-averaged velocity profile and electric field around the particle as the mechanism for generating nonzero net particle drift.