Electrostatic interaction between dissimilar colloids at fluid interfaces

The electrostatic interaction between two non-identical, moderately charged colloids situated in close proximity of each other at a fluid interface is studied. By resorting to a well-justified model system, this problem is analytically solved within the framework of linearized Poisson-Boltzmann (PB) density functional theory (DFT). The resulting interaction comprises a surface and a line part, both of which, as functions of the inter-particle separation, show a rich behavior including monotonic as well as non-monotonic variations. In almost all cases, these variations cannot be captured correctly by using the superposition approximation. Moreover, expressions for the surface tensions, the line tensions and the fluid-fluid interfacial tension, which are all independent of the inter-particle separation, are obtained. Our results are expected to be particularly useful for emulsions stabilized by oppositely charged particles.