  We review our recent studies on selective solvation effects in phase
separation in polar binary mixtures with a small amount of solutes. Such
hydrophilic or hydrophobic particles are preferentially attracted to one of the
solvent components. We discuss the role of antagonistic salt composed of
hydrophilic and hydrophobic ions, which undergo microphase separation at
water-oil interfaces leading to mesophases. We then discuss phase separation
induced by a strong selective solvent above a critical solute density np, which
occurs far from the solvent coexistence curve. We also give theories of ionic
surfactant systems and weakly ionized polyelectrolytes including solvation
among charged particles and polar molecules. We point out that the Gibbs
formula for the surface tension needs to include an electrostatic contribution
in the presence of an electric double layer.
