Aggregation of pairs of particles on electrodes during electrophoretic deposition

During electrophoretic deposition (EPD) of colloidal particles, the particl es that have been deposited on the electrode surface move laterally along t he electrode and form larger clusters. Models based on fluid convection hav e been advanced to explain this phenomenon. The models fall into two catego ries: (1) electrokinetic - electroosmotic flow is generated by the interact ion between the applied electric field and the charged double layer on the surface of each particle, and (2) polarization - flow is generated by nonun iform current densities on the electrode. The electrokinetic model predicts that the aggregation rate is proportional to the applied electric field E- infinity and the zeta potential of the particles, while the polarization mo del predicts that the rate goes as E-infinity(2) and is independent of the zeta potential. We report experimental data for the dynamics of interaction s between two deposited particles in a steady electric field in the range 2 0-100 V/m. The particles were polystyrene latex and their size was between 2.5 and 10 mu m diameter. The direction of the electric field was also chan ged, and two different concentrations of supporting electrolyte were used. The aggregation trajectories of sets of two deposited particles from an ini tial separation of about a particle diameter were recorded using optical mi croscopy, and the video frames were analyzed to compute separation vs. time for each set of particles. The data show that the relative velocity betwee n the particles is proportional to the electric field and the zeta potentia l of the particles, and scale with the particle size as predicted by the el ectrokinetic theory. (C) 2000 Elsevier Science S.A. All rights reserved.