Self-assembly of ionic surfactants and formation ofmesostructures

Abstract

Self-assembly of ionic surfactants resulting in micelle formation isstudied using off-lattice Monte Carlo simulation in twodimensions (2D). We find that in addition to the Lennard-Jones (LJ)interaction, which acts among all of the particles, ascreened Coulomb interaction, acting only among the surfactant heads,makes the geometric arrangement of micelles very different comparedto that for neutral surfactants at the same density. At lowconcentrations, ionic surfactants produce spherical micelles andexhibit intermicellar ordering arising out of the longer-rangerepulsion of the surfactant head groups. For larger concentrations,they tend to form bi-layers. Motivated by recent experiments onpreparation of mesoporous sieves through surfactant-templatingroutes, we then extend these studies to micellization of ionicsurfactants in the presence of other neutral host particles. Themorphologies of the surfactant-host composites are studied as functions of host particle densities, sizes, and their interactionstrengths. Assuming the presence of micelles as quenched disorder,we obtain a qualitative understanding of the local ordering of thehost particles in terms of a dimensionless density parameter fromthe known liquid-vapour phase diagram in 2D of a LJ fluid.