Micellization in a solution containing ionic surfactants: a Langevin Dynamics study

Langevin Dynamics (LD) simulation is used to study the micellization process of systems containing ionic surfactants and electrolyte suspensions. In our model system we use a coarse-grained methodology, with no water molecules, where the hydrophobic effect produced by the hydrocarbon surfactant tail monomers is described by a short-range attraction between the neutral tail monomers that are located at different surfactant molecules. This effective short-range attraction is represented through a Lennard-Jones (LJ) potential, with the LJ well depth $\varepsilon$ taken as an adjustable parameter. Extensive LD simulations were implemented in the ESPResSo package, a free open-source software for soft matter systems, in order to obtain the critical micelle concentration (CMC) of cationic and anionic surfactants and also for a catanionic mixture, a solution containing both types of ionic surfactants. We use the parameter $\varepsilon$ in our simulation model to obtain our CMC estimate, as suggested recently by a Monte Carlo study, in the absence of salt and also when different types of salts are included in the solution. For the catanionic mixtures we are interested to characterize the catanionic micelles that are formed, specially their effective electronic charge and size distribution. We compare our results with the experiments and previous Monte Carlo simulations.