Experimental study of particle electrophoresis in shear-thinning fluids

Electric field is the method of choice in microfluidic devices for precise transport and placement of particles via fluid electroosmosis and particle electrophoresis. However, current studies on particle electrophoresis in microchannels have been focused mainly upon Newtonian fluids though many of the chemical and biological fluids possess non-Newtonian characteristics. Especially lacking is the experimental study of particle electrophoresis in either type of fluids. We report in this work an unprecedented experimental observation that polystyrene particles migrate towards the walls of straight rectangular microchannels in the electroosmotic flow of shear-thinning xanthan gum (XG) solutions. This phenomenon is opposite to the particle focusing along the channel center in our control experiment with the Newtonian base fluid of the XG solutions. It is attributed to a fluid shear thinning-induced lift that overcomes the wall-induced repulsive electrical lift. The parametric effects of the fluid-particle-channel-(electric) field system are systematically investigated. Published under license by AIP Publishing.