AGGREGATION BEHAVIOR AND MICROSTRUCTURE OF CATIONIC TRISILOXANE SURFACTANTS IN AQUEOUS-SOLUTIONS

Aqueous aggregation behavior of a family of novel cationic siloxane surfactants (Me(3)SiO)(2)Si(Me)(CH2N+-Me(2)(CH2)(2)OH X- (denoted as BisX, X = Cl, Br, and I) is reported. At 20 degrees C, BisCl forms micelles between 1.3 and 20 wt %, but both BisBr and BisI assemble into vesicles at surfactant concentrations even below 1 wt %. At the midrange of surfactant concentrations, BisCl and BisBr form a lamellar liquid crystal phase. All of the three BisX surfactants form a solid phase on the surfactant-rich side of the lamellar liquid crystal phase, in which BisX molecules pack in lamellar bilayers. Differences in aqueous aggregation behavior exhibited by the three BisX surfactants are attributed to the variable degrees of halide counterion binding to the quaternary ammonium head group. The correlation between the microstructures of BisX surfactants in dilute concentrations and ''superspreading'' is the same as that found previously in nonionic siloxane surfactant solutions.