Surface properties of fluids of charged platelike colloids

Surface properties of mixtures of charged platelike colloids and salt incontact with a charged planar wall are studied within density functionaltheory. The particles are modeled by hard cuboids with their edges constrainedto be parallel to the Cartesian axes corresponding to the Zwanzig model and thecharges of the particles are concentrated in their centers. The densityfunctional applied is an extension of a recently introduced functional forcharged platelike colloids. Analytically and numerically calculated bulk andsurface phase diagrams exhibit first-order wetting for sufficiently smallmacroion charges and isotropic bulk order as well as first-order drying forsufficiently large macroion charges and nematic bulk order. The asymptoticwetting and drying behavior is investigated by means of effective interfacepotentials which turn out to be asymptotically the same as for a suitableneutral system governed by isotropic nonretarded dispersion forces. Wetting anddrying points as well as predrying lines and the corresponding critical pointshave been located numerically. A crossover from monotonic to non-monotonicelectrostatic potential profiles upon varying the surface charge density hasbeen observed. Due to the presence of both the Coulomb interactions and thehard-core repulsions, the surface potential and the surface charge do notvanish simultaneously, i.e., the point of zero charge and the isoelectric pointof the surface do not coincide.Comment: 14 pages, submitte