Flexible Bilayers with Spontaneous Curvature Lead to Lamellar Gels and Spontaneous Vesicles
Mixtures of cetyltrimethylammonium tosylate (CTAT) and sodium dodecylbenzene sulfonate (SDBS) in water form a fluid lamellar phase at {le}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} {approx} k{sub B}T, and a nonzero spontaneous curvature. Caill{acute e} 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{sub B}T and {kappa} = -0.9 {+-} 0.2 k{sub 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}{sub 0} = 0.28 k{sub B}T. These results show that surfactant mixing is sufficient to make {kappa} {approx} k{sub 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.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 914105
- Report Number(s):
- BNL-78673-2007-JA; PNASA6; TRN: US200804%%311
- Journal Information:
- Proc Natl Acad Sci USA, Vol. 103, Issue 8; ISSN 0027-8424
- Country of Publication:
- United States
- Language:
- English
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