Molecular organization in micelles and vesicles

Abstract

The configurations of the hydrocarbon chains in micelles are severely constrained by the space-filling requirements of the chain segments, by the continuity of the chains, and by the micellar geometry. A statistical theory that takes full account of these constraints is developed by using a lattice model. The chain ends are deduced to be nonuniformly distributed, with maximal incidence approximately midway between the center of the micelle and the outer surface. Whereas the chain disorder near the outside of the hydrophobic core may approach that of a liquid, crowding of the chains near the core center imposes a degree of order approaching that in a crystal. These results are at variance with the prevailing view that the micellar interior resembles a “liquid hydrocarbon droplet.” Also discussed are the effects of curvature on the chain configurations in monolayers and bilayers. It is found, for example, that the “disorder gradients” in inner and outer half-bilayers of small vesicles should be substantially different. Implications of these results are discussed.