Dynamic electrophoresis of concentrated droplet dispersions at arbitrary surface potentials

Dynamic electrophoresis of a dispersion of spherical droplets with arbitrary zeta potential and double layer thickness is analyzed in this study, based on Kuwabara's unit cell model. Pseudo-spectral method with Chebyshev polynomials is adopted to solve the corresponding general electrokinetic equations. Similar to the observations of hard spheres, the droplets exhibit non-linear phenomena such as maxima or minima on both mobility magnitude and phase lag with varying frequency of input alternative electric field, as the zeta potential of the droplets become high. Our results presented here add another dimension to the previous corresponding results of hard spheres, with the parameter of viscosity ratio, ηo/ηi, where ηo and ηi refer to the fluid viscosities outside and inside of the droplets, respectively. Consistent qualitative behaviors are observed with ηo/ηi=0 representing the hard spheres situation. No abrupt change is observed associating with the phase change to the droplets. The dynamic mobility is found to be faster in magnitude, as might be expected.