LYOTROPIC LIQUID-CRYSTAL PHASE-BEHAVIOR OF POLYMERIC SILOXANE SURFACTANTS

Optical microscopy, cryo-TEM, and small angle X-ray scattering were us ed to characterize the liquid crystal phase behavior of two ABA and tw o comb-type polymeric siloxane surfactants in water. These polymeric s urfactants follow the usual sequence of LC phases, progressing from la mellar phase to inverse hexagonal phase upon increasing temperature or decreasing the hydrophilic head group size. Bilayer thicknesses are c onsistently shorter than extended molecular lengths, indicating that t he molecules are packed into the bilayer in a relatively coiled and in terdigitated conformation. Polydispersity appears to stabilize vesicle s, allowing the curvature requirements of all species to be met while maintaining zero net curvature. Three of the four surfactants studied form vesicles spontaneously on contact with water. At low concentratio ns we found vesicle dispersions, or vesicle/micelle mixed dispersions. 1 A diverse array of vesicle morphologies were observed, including rou nd and tubular, unilamellar and multilamellar structures, as well as p ossible instances of vesicle fission. The bilayer bending constant is quite small due to the properties of the siloxane hydrophobe and polyd ispersity.