MODELING THE INFLUENCE OF SURFACTANT ARCHITECTURE ON THE CRITICAL MICELLE CONCENTRATION OF DOUBLE-HEADED AND GEMINI SURFACTANTS

Abstract

Monte Carlo simulations have been used in the past to investigate a variety of surfactant systems; however, there is little published literature for double-headed and gemini surfactants with asymmetric tails. We perform Larson-type Monte Carlo simulations of double-headed and gemini surfactant systems with asymmetric tails in two- and three-dimensions. The model predicts that the addition of a second head group to form a double-headed surfactant results in an increase in the critical micelle concentration (CMC) compared to a single-headed surfactant, in agreement with experiment. It also indicates that the placement of the second head group has an impact on the final CMC value. We study a series of gemini surfactants with asymmetric tails and find no change in the value of the CMC as the ratio of the lengths of the two tails increases. This is contrary to the only experimental study that found there was a slight decrease in the CMC as the ratio of the lengths of the two tails increases. We examine this difference in terms of the relatively small effect surfactant asymmetry has on value of the CMC and the fact that the model is capable of qualitatively reproducing the known dependence of the CMC on other architectural properties. This initial probe into systems of double-headed and gemini surfactants with asymmetric tails confirms many of the previously published findings and provides avenues for possible future research using Monte Carlo simulations.