SOLUTIONS OF ALKALI SOAPS AND WATER IN FATTY ACIDS .I. REGION OF EXISTENCE OF SOLUTIONS

A characteristic feature for soap-fatty acid-water systems is the occurence of a large region with isotropic solutions in fatty acid as solvent. In non-aqueous fatty acid the solubility of the soap is rather high and the presence of the soap enhances considerably the solubility of water in the acid. At certain temperatures the solution region extends to a long narrow salient towards the water corner of the system. The solubility of the soap in non-aqueous fatty-acid is interpreted as a sign that there is an interaction between the molecules that leads to formation of a stable acid salt dissolved in the acid. The large solubility of water in these solutions suggests that the water may be bound by the acid soap. The molar ratio of fatty acid-to-soap was found to be about 3:1-2:1 in the narrow salient of all hitherto studied systems and this shows that the acid soap in this part of the solution region has a rather well defined composition. Preliminary X-ray diffraction observations indicate that the acid soap in question may form micelles. Reasons are presented that in these micellar systems the intermicellar solution mainly consists of fatty acid at water contents up to about 40-50 per cent, where the phase equilibria studies indicate a structural change, but that the intermicellar solution at higher water contents mainly may consist of water. © 1969 Dr. Dietrich Steinkopff Verlag.