COLL 27 |
| Mixtures of cetyltrimethylammonium tosylate (CTAT) and sodium dodecylbenzene sulfonate (SDBS) in water form a fluid lamellar phase at ≤ 40 wt% water, but turn into viscous gels at higher water fractions. The gels are characterized by spherulite defects consistent with a low bending elasticity, kappa ~ kBT, and a non-zero 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 kBT and kappabar = -.9 ± 0.2 kBT. 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 = 0.28 kBT. These results show that surfactant mixing is sufficient to make kappa ~ kBT, 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 higher water fractions to be equilibrium structures. |
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Surfactant Self-Assembly
9:00 AM-12:15 PM, Sunday, August 19, 2007 BCEC -- 153B, Oral
Division of Colloid & Surface Chemistry |