title: Flexible bilayers with spontaneous curvature lead to lamellar gels and spontaneous vesicles.
abstract: Mixtures of cetyltrimethylammonium tosylate (CTAT) and sodium dodecylbenzene sulfonate (SDBS) in water form a fluid lamellar phase at < or = 40 wt % water but surprisingly turn into viscous gels at higher water fractions. The gels are characterized by spherulite and other bilayer defects consistent with a low bending elasticity, kappa approximately k(B)T, and a nonzero spontaneous curvature. Caillé analysis of the small-angle x-ray line shape confirms that for 7:3 wt:wt CTAT:SDBS bilayers at 50% water, kappa = 0.62 +/- 0.09 k(B)T and kappa = -0.9 +/- 0.2 k(B)T. For 13:7 wt:wt CTAT:SDBS bilayers, the measured bending elasticity decreases with increasing water dilution in good agreement with predictions based on renormalization theory, giving kappa(o) = 0.28 k(B)T. These results show that surfactant mixing is sufficient to make kappa approximately k(B)T, which promotes strong, Helfrich-type repulsion between bilayers that can dominate the van der Waals attraction. These are necessary conditions for spontaneous vesicles formed at even higher water fractions to be equilibrium structures.
authors.affiliation: Department of Chemical Engineering, University of California, Santa Barbara, CA 93106-5080, USA.
authors.forename: Bret A
authors.initials: BA
authors.lastname: Coldren
authors.forename: Heidi
authors.initials: H
authors.lastname: Warriner
authors.forename: Ryan
authors.initials: R
authors.lastname: van Zanten
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Zasadzinski
authors.forename: Eric B
authors.initials: EB
authors.lastname: Sirota