  We theoretically and experimentally investigate colloid-oil-water-interface
interactions of charged, sterically stabilized, poly(methyl-methacrylate)
colloidal particles dispersed in a low-polar oil (dielectric constant
$\epsilon=5-10$) that is in contact with an adjacent water phase. In this model
system, the colloidal particles cannot penetrate the oil-water interface due to
repulsive van der Waals forces with the interface whereas the multiple salts
that are dissolved in the oil are free to partition into the water phase. The
sign and magnitude of the Donnan potential and/or the particle charge is
affected by these salt concentrations such that the effective interaction
potential can be highly tuned. Both the equilibrium effective colloid-interface
interactions and the ion dynamics are explored within a Poisson-Nernst-Planck
theory, and compared to experimental observations.
