Aggregation of surfactants in aqueous systems

Surfactants form micelles in aqueous solution above the critical micelle concentration (cmc); micelles are dynamic structures. Micellization is driven by the transfer of surfactant chains from water to the micelle core. There is an optimum size (aggregation number) and shape for micelles (dependent on surfactant molecular shape and packing within micelles) for which the standard free energy of micellization, Δ‎micμ‎o, is minimum. Inert electrolyte influences the degree of dissociation (α‎) of ionic micelles and hence micellar shape and aggregation number. Micellization in mixed surfactant solutions, and in mixed polymer + surfactant systems is also discussed. Micelles can dissolve (solubilize) other amphiphilic materials and nonpolar oils, which changes the cmc. If sufficient oil is solubilized, microemulsion droplets result (see Chapter 10). As the concentration of micelles in solution rises, intermicellar interactions lead to the formation of a variety of lyotropic liquid crystalline phases (mesophases).