Theory of Chain Packing in Amphiphilic Aggregates

Amphiphilic molecules in aqueous solutions cluster together into diverse aggregates organized in a variety of macroscopic phases (1-5). Extreme examples are the small globular micelles of surfactant molecules such as sodium-dodecyl-sulfate (sds), and the large bilayers of biological phos­ pholipids such as lecithin. The former are dispersed in an isotropic solution, whereas the latter may be organized into finite vesicles or as ordered macroscopic lamellae. Many other structures and phases have been ob­ served, depending on the nature of the amphiphiles and their concentra­ tion as well as on the temperature and composition (e.g. salinity) of the surrounding solution. A common characteristic of all the aggregates is that they comprise two regions: a hydrophobic core composed of the hydro­ carbon tails (typically alkyl chains) of the amphiphiles, and a hydrophilic mantle containing their polar (ionic, nonionic or zwitter-ionic) heads. Intercst in amphiphile solutions and micellar aggregates is wide and interdisciplinary, involving basic questions in physics, biology, medicine, and chemistry, as well as having practical applications in the oil,