Gaussian curvature and the equilibrium among bilayer cylinders, spheres, and discs

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In mixtures of cetyltrimethylammonium bromide (CTAB) and sodium perfluorooctanoate (FC(7)) in aqueous solution, novel bilayer cylinders with hemispherical end caps and open, flat discs coexist with spherical unilamellar vesicles, apparently at equilibrium. Such equilibrium among bilayer cylinders, spheres, and discs is only possible for systems with a spontaneous curvature, R(o), and a positive Gaussian curvature modulus, (kappa) over bar. We have measured the size distributions of the spherical vesicles, cylinders, and discs by using cryo-electron microscopy; a simple analysis of this length distribution allows us to independently determine that the mean curvature modulus, kappa approximate to 5 +/- 1 k(B)T and (kappa) over bar approximate to 2 +/- 1 k(B)T. This is one of the few situations in which R(o), kappa, and (kappa) over bar can be determined from the same experiment. From a similar analysis of the disk size distribution, we find that the edges of the discs are likely stabilized by excess CTAB. The fraction of discs, spherical vesicles, and cylinders depends on the CTAB/FC(7) mole ratio: increasing CTAB favors discs, while decreasing CTAB favors cylinders. This control over aggregate shape with surfactant concentration may be useful for the design of templates for polymerization, mesoporous silicates, etc.
Publisher
NATL ACAD SCIENCES
Issue Date
2002-11
Language
English
Article Type
Article
Keywords

SPONTANEOUS VESICLE FORMATION; PHASE-BEHAVIOR; L-ALPHA; FLUID MEMBRANES; CETYLTRIMETHYLAMMONIUM BROMIDE; SURFACTANT MIXTURES; ELECTRON-MICROSCOPY; ANIONIC SURFACTANT; AQUEOUS MIXTURES; LIPID-BILAYERS

Citation

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, v.99, no.24, pp.15318 - 15322

ISSN
0027-8424
URI
http://hdl.handle.net/10203/24545
Appears in Collection
CBE-Journal Papers(저널논문)
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