Predicting Critical Micelle Concentrations from Short Time Scale Simulations

The determination of surfactant critical micelle concentrations (CMCs) using molecular simulations is by now a well-established procedure. The approach typically utilizes the equilibrium free surfactant concentration (i.e., those surfactants not in micelles). However, equilibration can be a slow process, particularly for surfactants with low CMC values, requiring large amounts of compute resource even when coarse grained approaches are adopted. We here explore the possibility of using incompletely equilibrated short time scale runs to predict surfactant CMCs using dissipative particle dynamics (DPD) simulations. We ground the methodology in the Aniansson-Wall stepwise association model of micelle kinetics, and apply it to a selection of uncharged (nonionic and zwitterionic) and charged (ionic) surfactants. We find the approach to be useful for predicting the CMC of both charged and uncharged surfactants.