VESICLE FORMATION IN ELECTROLYTE-SOLUTIONS OF A NEW CATIONIC SILOXANE SURFACTANT

The addition of the salts NaX [X = F, Cl, Br, 1, salicylate (Sal), dodecylsulfate (DS)] to 0. 1 3 M (5 wt %) micellar, aqueous solutions of the novel, cationic siloxane surfactant (Me3SiO)2Si(Me)-(CH2)3+NMe2-(CH2)2OHCl- (BisCl) results in spontaneous formation of uni- and multilamellar vesicles. This is the first report of vesicle formation by a siloxane surfactant. The sizes of the vesicles range from 1 0 nm to 10 mum, and they are stable for at least several weeks at room temperature. For the sodium halides, the relative concentrations of salts required to induce vesicle formation follow the anion trend I < Br < Cl. Vesicles do not form in concentrated NaF solutions. This suggests that the vesicle formation is induced by strong anion binding to the cationic micelles. Excess addition of SDS to these vesicular solutions results in the formation of a cubic liquid crystal phase. The critical micelle concentration (cmc) of the aqueous solution of the 1:1 mixture of BisCl and SDS yielded a beta, or interaction, parameter value of -10.3, suggesting strong, attractive interactions between Bis cation and DS anion in the mixed surfactant layer.