Cluster size distribution in a Monte Carlo simulation of the micellar phase of an amphiphile and solvent mixture

Abstract

The results of a Monte Carlo simulation of a two-dimensional lattice model of an amphiphile and solvent mixture are presented. The simulation is carried out using multispin coding techniques with 512 three-segment amphiphiles at an effective volume concentration of 9.4 %. The amphiphiles interact through a nearest-neighbour potential which includes a head–solvent and tail–solvent interaction. The cluster size distribution is determined as a function of temperature and head–solvent interaction. No prior assumption is made about the nature of the clusters which are formed at each temperature. When the head–solvent interaction is sufficiently solvophilic, the low-temperature configurations consist of a large number of micelle-like clusters rather than the complete phase separation of two immiscible fluids, which is observed for solvophobic head–solvent interactions. The average cluster size is consistent with that observed experimentally. However, the cluster size distribution shows a significant polydispersity and the micellar clusters are more disordered than is commonly assumed for micelle systems.