The Nature of the Surfactant-Block Model of Micelle Structure

Abstract

The molecular packing of surfactants in micellar aggregates in water is unknown. Usually a spherical hydrocarbon core is assumed to be formed with chaotic packing, i. e., with negligible near order, as formalized by mean-field theories. True molecular pictures of a micelle, however, must include not only segmental distribution functions but pair-correlation functions of the segments as well. The surfactant-block model is an attempt to propose on a semiempirical basis a micelle structure with explicit molecular regularity, with a parallel correlation of the hydrocarbon chains up to a width equal to the chain length, with preferential orthogonal assembly of these molecular blocks. Its architecture is based on the features of the liquid-crystalline lipid bilayer modified in a minimal way to account for the well established features of the droplet-like micelle. The implications of the model in its present qualitative issue are not in contradiction with the experimental data. As the model is more detailed than the chaotic model, more detailed experiments are required in order to prove or to disprove it. A quantitative theoretical treatment of the model is to be attained only by a distinct extension of approaches presently available. The concept of block assembly is particularly useful with respect to non-bilayer defects in lipid membranes, leading to the process of membrane fusion.