(464a) Electrophoresis in Dense Colloidal Suspensions: Role of Particle Concentration and Debye Layer Thickness

The electrophoretic mobility of colloidal particles is a property that controls their kinetics of self-assembly in an external electric field. To assemble a colloidal crystal, the applied field induces a phase transition by driving particle densification in the vicinity of the electrode with opposite polarity. The deposition results in a spatially varying particle volume fraction in the direction of the applied field. Therefore, the electrophoretic velocity, which is a decreasing function of the colloid volume fraction, also varies along an axis perpendicular to the electrode surface, and this retardation can significantly affect crystallization rates. To better understand the impact of particle concentration on the electrophoretic velocity, we have studied the electrophoresis phenomenon in suspensions of sterically stabilized poly(methyl methacrylate) colloids in a nonpolar solvent at different volume fractions using confocal laser scanning microscopy. A number of complex phenomena are observed, including significant effects of device geometry and electrolyte concentration. These measurements show that the spatiotemporal evolution of the electrophoretic deposition velocity in response to the changing colloid concentration in the device can yield mobilities that vary by as much as a factor of ten. These results are compared to available theory of the volume fraction dependent electrophoretic mobility. The work furthermore sheds light on the complexity of electrophoretic colloidal deposition under concentrated conditions, a situation that approximates a number of important processes in the coatings industry.