Self-assembly of ionic surfactants and formation of mesostructures

Self-assembly of ionic surfactants resulting in micelle formation is studie d using off-lattice Monte Carlo simulation in two dimensions (2D). We find that in addition to the Lennard-Jones (LJ) interaction, which acts among al l of the particles, a screened Coulomb interaction, acting only among the s urfactant heads, makes the geometric arrangement of micelles very different compared to that for neutral surfactants at the same density. At low conce ntrations, ionic surfactants produce spherical micelles and exhibit intermi cellar ordering arising out of the longer-range repulsion of the surfactant head groups. For larger concentrations, they tend to form bi-layers. Motiv ated by recent experiments on preparation of mesoporous sieves through surf actant-templating routes, we then extend these studies to micellization of ionic surfactants in the presence of other neutral host particles. The morp hologies of the surfactant-host composites are studied as functions of host particle densities, sizes, and their interaction strengths. Assuming the p resence of micelles as quenched disorder, we obtain a qualitative understan ding of the local ordering of the host particles in terms of a dimensionles s density parameter from the known liquid-vapour phase diagram in 2D of a L J fluid.