  Antagonistic salts are composed of hydrophilic and hydrophobic ions. In a
mixture solvent (water-oil) such ion pairs are preferentially attracted to
water or oil, giving rise to a coupling between the charge density and the
composition. First, they form a large electric double layer at a water-oil
interface, reducing the surface tension and producing mesophases. Here, the
cations and anions are loosely bound by the Coulomb attraction across the
interface on the scale of the Debye screening length. Second, on solid
surfaces, hydrophilic (hydrophobic) ions are trapped in a water-rich (oil-rich)
adsorption layer, while those of the other species are expelled from the layer.
This yields a solvation mechanism of local charge separation near a solid. In
particular, near the solvent criticality, disturbances around solid surfaces
can become oscillatory in space. In mesophases, we calculate periodic
structures, which resemble those in experiments.
