Chapter 1 Solvation effects of ions and ionic surfactants in polar fluids

A Ginzburg-Landau theory is presented on polar binary mixtures con-taining ions. It takes account of electrostatic, solvation, image, and amphiphilic interactions among the ions and the solvent molecules. The ion distributions and the electric potential are calculated around an in-terface with finite thickness in equilibrium. The surface tension is in-creased for hydrophilic ion pairs, but is decreased for hydrophilic and hydrophobic ion pairs. Introducing the amphiphilic interaction, we also treat ionic surfactants, which aggregate at an interface and reduce the surface tension. A mesophase with periodic composition and ion mod-ulations emerges for sufficiently large asymmetry between the cationic and anionic solvation strengths. Also, among ions, there arise long-range attractive interactions in the Ornstein-Zernike form, which are mediated by the composition fluctuations. Under strong solvation conditions, they can dominate over the Coulomb interaction in the range shorter than the correlation length. In the presence of three ion species, the ion distribu