The purpose of this paper is to! nvestigate the effect of monovalent salts on the thermodynamics of micelle formation in aqueous Ca-lecithin solution, qqae critical micelle concentration (CMC) and mean hydrodynamic radius (RH) of the micelles as functions of amphiphile concentration, temperature, ionic identity, and strength were determined using the laser light scattering technique. Then the standard Gibb's free energy (AGO), enthalpy (AH), and chemical potential (A/Z) of the micelle formation and growth were deduced from the experimental data. It is found that the micellization is a spontaneous process. Compared with the situation in a salt free solution, the reaction of micelle formation in KI added solutions is less exothermic, and the micelles in the solutions are less likely to form, and are smaller and less stable. The reaction of micelle formation in KC! added solutions, however, is more exothermic, and the micelles in the solutions are facile to form, and are larger and more stable. This indicates that monovalent salts affect the micelle formation and growth in the way predicted by the tendency of A/Z to vary with ionic identity and strength of the salts.

The effect of divalent and trivalent salts on the mocelle formation of C8-Lecithir solution was investigated using the technique of static and dynamic light scattering. The Gibbs free energy, enthalpy and entropy of the micellization process are also deduced experienta l data for evaluating the thermodynamics of the micelle formation.

This article reviews both the experimental and theoretical works done on the effect of salts, including monovalent, divalent and trivalent salts, on the aqueous micellar solution of dioctanoyl phosphatidylcholine, a good model system of zwitterionic suffactants for investigation. The experimental methods and results on measuring the solution properties of the surfactant, such as the critical micelle concentration, the behaviors of micelle growth and phase separation, as fimctions of salt identity and concentration are described. The thermodynamic parameters of the micelle formation, the mechanism and theoretical model of the salt effects on the micellar solution of the surfactant are also introduced.

The effect of divalent and trivalent salts (CaCl2, CaBr2, MgCl2, MgBr2, LaCl3, CeCl3, La(NO3)3, and Ce(NO3)3) on the micelle formation in C8-lecithin solutions was investigated using the techniques of static and dynamic light scattering. The critical micelle concentration (cmc), mean hydrodynamic radius (Rh), gyration radius (Rg), and weight-average molecular weight of the micelles were measured as functions of salt identity and concentration, amphiphile concentration, and temperature. It was found that the micelles in solutions of magnesium are less likely to form and less stable; their standard enthalpy is less exothermic as the ionic strength increases. On the contrary, the micelles in solutions of calcium and trivalent salts form easily, and are more stable; their standard enthalpy is also more exothermic as the ionic strength increases. Based on our model of the Gibb's free energy for the salt-added solutions, we obtained the following formula for the effect of salts on cmc: ln(cmc)'=ln(cmc)+k1I1/2+k2I, where (cmc)' and (cmc) are the critical micelle concentrations in salt-added and salt-free solutions, respectively, I is the ionic strength, and k1 and k2 are the salt effect parameters. The agreement between the formula and the experimental data for all the systems under study shows that the formula is more satisfactory than those suggested previously by other authors in describing the effect of salts on the cmc in the micellar solutions of not only zwitterionic but also nonionic surfactants.

We report measurements of the location and shape of the coexistence curve for binary liquid-liquid phase separation in aqueous micellar solutions of Ca-lecithin, as a function of the concentrations of KI, NaI, LiI, KCI, NaCI, and LiCI. The salts containing iodide dramatically lower the critical temperature for phase separation Tc as the salt concentration is increased. The chloride salts, however, first lower and then raise Tc as the salt concentration is increased. The identity of the added cations used has a comparatively minor effect on Te. Potassium ions are more effective in changing Tc than sodium ions, which in turn are more effective than lithium ions. We have used our data to deduce the dependence on salt identity and concentration of the parameters C and Ap, which reflect the strength of intermicellar interactions and the extent of micellar growth, respectively, within a Gibbs free energy model for micellar solutions. The theoretical coexistence curves calculated using the deduced parameters agree well with our experimental findings.