Determining Critical Micelle Concentrations of Surfactants Based on Viscosity Calculations from Coarse-Grained Molecular Dynamics Simulations

Alternative methods for determining the critical micelle concentration (CMC) are proposed using coarse grained molecular dynamics (MD) simulations. In the literature, the CMC value is commonly taken to be the free (unassociated) surfactant concentration in the presence of micellar aggregates given by MD simulations. In the present study, two surfactants with different head groups and the same alkyl tail, n-octyltrimethylammonium bromide (C8TAB) and sodium octyl sulfate (S8S), were used to calculate the CMC value. The CMC of surfactants can be calculated from the variation in the zero-shear-rate viscosity as a function of the surfactant concentration in both the premicellar and micellar regions. Linear slopes were obtained in both regions with increasing surfactant concentrations. The CMC values for C8TAB and S8S were determined from the intersection of the two lines and are in good agreement with experimental values.