Powder Technology, Vol.110, No.1-2, 90-97, 2000
Aggregation of pairs of particles on electrodes during electrophoretic deposition
During electrophoretic deposition (EPD) of colloidal particles, the particles that have been deposited on the electrode surface move laterally along the electrode and form larger clusters. Models based on fluid convection have been advanced to explain this phenomenon. The models fall into two categories: (1) electrokinetic - electroosmotic flow is generated by the interaction between the applied electric field and the charged double layer on the surface of each particle, and (2) polarization - flow is generated by nonuniform 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 model predicts that the rate goes as E-infinity(2) and is independent of the zeta potential. We report experimental data for the dynamics of interactions between two deposited particles in a steady electric field in the range 20-100 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 changed, and two different concentrations of supporting electrolyte were used. The aggregation trajectories of sets of two deposited particles from an initial separation of about a particle diameter were recorded using optical microscopy, and the video frames were analyzed to compute separation vs. time for each set of particles. The data show that the relative velocity between the particles is proportional to the electric field and the zeta potential of the particles, and scale with the particle size as predicted by the electrokinetic theory.