Micellization of ionic surfactants: calculations based on a self-consistent field lattice model

Abstract

The equilibrium structure of micelles formed in aqueous solutions of ionic surfactants is studied by using the self-consistent field lattice approach of Scheutjens, Fleer, and Leermarkers. Equilibrium volume fractions profiles of micelles are obtained, and it appears that the surfactant head groups have a rather wide distribution. The boundary between the hydrocarbon core of the micelle and the solution is rather sharp and does not vary with salt concentration. An electrostatic potential develops, which causes accumulation of indifferent counterions in between the head groups and, consequently, leads to partial neutralization of the charges. The remaining net charge in the head group region is independent of the salt concentration. The calculated effects of chain length, salt concentration, and branching on the cmc and the aggregation numbers show a good agreement with experimental data. By use of lattices of different geometry, transitions from small spherical micelles to large rodlike aggregates can be predicted.