COLL 348 |
| Joseph A. Zasadzinski, Department of Chemical Engineering, Department of Chemical Engineering, University of Califirnia, Santa Barbara, Santa Barbara, CA 93106-5080 |
| The role of spontaneous curvature in determining the products of self-assembly is generally under-appreciated. In the more commonly accepted explanation of vesicle stability, Helfrich undulations insure that the interbilayer potential is always repulsive when the bending constant, K, is of order kBT. However, when K > kBT, unilamellar vesicles can be stabilized by a spontaneous curvature that picks out a particular vesicle radius; other radii are energetically disfavored. We present measurements of the bilayer elastic constant and the spontaneous curvature, Ro, for different systems of equilibrium vesicles by an analysis of the vesicle size distribution determined by cryo-transmission electron microscopy (TEM). For a number of spontaneous vesicle systems analyzed in this way, K < kBT, suggesting that the unilamellar vesicles are stabilized by Helfrich undulation repulsions. However, for perfluorooctanoate containing vesicles, K >> kBT, suggesting stabilization by the energetic costs of deviations from the spontaneous curvature. Adding electrolyte to these vesicles leads to novel structures with two bilayers; the attractive interactions between the bilayers can overcome the cost of small deviations from the spontaneous curvature to form two layer vesicles, but larger deviations to form three and more layer vesicles are prohibited. Vesicles with a discrete numbers of bilayers at equilibrium are only possible for bilayers with a large bending modulus coupled with a spontaneous curvature. In these systems, the spontaneous curvature also influences the corresponding lamellar phases, leading to stable close-packed onions rather than flat lamellae at higher concentrations. We also show that adding low molecular weight polymer-surfactants can alter the spontaneous curvature and bending constant, leading to more monodisperse vesicle populations and stable, close packed onion lamellar phases. |
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Awards Lectures
2:00 PM-4:05 PM, Tuesday, March 30, 2004 Marriott -- Orange County 4, Oral
Division of Colloid and Surface Chemistry |