  Dynamic equations are presented for polar binary mixtures containing ions in
the presence of the preferential solvation. In one-phase states, we calculate
the dynamic structure factor of the composition accounting for the ion motions.
Microphase separation can take place for sufficiently large solvation asymmetry
of the cations and the anions. We show two-dimensional simulation results of
the mesophase formation with an antagonistic salt, where the cations are
hydrophilic and the anions are hydrophobic. The structure factor S(q) in the
resultant mesophase has a sharp peak at an intermediate wave number on the
order of the Debye-Huckel wave number. As the quench depth is increased, the
surface tension nearly vanishes in mesophases due to an electric double layer.
