In-situ observation of electrophoretic deposition using patterned microelectrodes

A system of platinum microelectrodes was fabricated on a sapphire substrate by lithographic patterning and used to manipulate micron scale silica particles in-plane. The use of a digital video system allowed the motion of particles far from the electrodes and their deposition onto the working electrode to be observed directly during application of a DC field. Particles were also seen to adhere to the substrate before reaching the electrode. The zeta potential of the particles and substrate was measured, and the differing surface chemistry of the two systems was used to explain the adhesion in terms of a local reduction in pH due to the production of hydrogen ion at the anode. The role of electrode reversibility was also investigated.