Measurement of electroosmotic and electrophoretic velocities using pulsed and sinusoidal electric fields

Abstract

In this work, we explore two methods to simultaneously measure the electroosmoticmobility in microchannels and the electrophoretic mobility of micron-sized tracer particles.The first method is based on imposing a pulsed electric field, which allows to isolateelectrophoresis and electroosmosis at the startup and shutdown of the pulse, respectively.In the second method, a sinusoidal electric field is generated and the mobilities are found byminimizing the difference between the measured velocity of tracer particles and the velocitycomputed from an analytical expression. Both methods produced consistent results usingpolydimethylsiloxane microchannels and polystyrene micro-particles, provided that thetemporal resolution of the particle tracking velocimetry technique used to compute thevelocity of the tracer particles is fast enough to resolve the diffusion time-scale based on thecharacteristic channel length scale. Additionally, we present results with the pulse methodfor viscoelastic fluids, which show a more complex transient response with significantvelocity overshoots and undershoots after the start and the end of the applied electricpulse, respectively.