Estudo computacional de soluções contendo surfactantes iônicos e sal

Abstract

In this work we have performed Langevin Dynamics to study the micellization process in solutions containing ionic surfactants and electrolytes. Our methodology is based on a coarse grained approach, where the water molecules were not represented and the hydrophobic effect was mapped by a short-ranged effective attraction between the tail monomers that are located on different surfactant molecules. This effective attraction in our model is represented by a Lennard-Jones potential, with an intensity described by an adjustable parameter "H. We have performed extensive simulations using the ESPResSo software package, an open source software for simulations of soft-matter systems, in order to obtain the critical micellar concentration (CMC) of cationic surfactants in terms of the parameter "H, in solution with no salt and containing salts. We also analyzed the effect of the hydrophobic surfactant tail length on the CMC value. Finally, we have studied solutions containing cationic and anionic surfactants, or catanionic mixtures, in order to obtain the CMC behavior. Our results where compared with experimental and computational studies, showing a good agreement for most of the cases analyzed, with exception for catanionic mixtures. Although qualitatively similar, our results have shown quantitative disagreement with the available experimental estimates.