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

Aqueous aggregation behavior of a family of novel cationic siloxane su rfactants (Me(3)SiO)(2)Si(Me)(CH2N+-Me(2)(CH2)(2)OH X- (denoted as Bis X, X = Cl, Br, and I) is reported. At 20 degrees C, BisCl forms micell es between 1.3 and 20 wt %, but both BisBr and BisI assemble into vesi cles at surfactant concentrations even below 1 wt %. At the midrange o f surfactant concentrations, BisCl and BisBr form a lamellar liquid cr ystal phase. All of the three BisX surfactants form a solid phase on t he surfactant-rich side of the lamellar liquid crystal phase, in which BisX molecules pack in lamellar bilayers. Differences in aqueous aggr egation behavior exhibited by the three BisX surfactants are attribute d to the variable degrees of halide counterion binding to the quaterna ry ammonium head group. The correlation between the microstructures of BisX surfactants in dilute concentrations and ''superspreading'' is t he same as that found previously in nonionic siloxane surfactant solut ions.