Molecular Thermodynamic Modeling of Surfactants: Analysis and Optimization

Understanding the stability of emulsions is crucial in various processes and products. Surfactant molecules naturally present in oil or added during oil production play a fundamental role in reducing interfacial tension and maintaining the stability of these emulsions. The considerable number of variables in the formulation of emulsions makes experimental studies difficult and encourages the use of modeling and simulation to relate the emulsion stability with molecular properties. Research on microemulsions is essential for improving emulsion stability, as the principles involved in their formation and stability can be used to optimize emulsion performance. Molecular thermodynamic models enable the calculation of microemulsion thermodynamic properties based on Gibbs free energy minimization. This predictive approach takes information from the physicochemical properties of the system and the molecular properties of surfactants to predict the structural and compositional characteristics of microemulsions. This type of modeling allows obtaining crucial information, such as the critical micellar concentration (CMC) of the surfactant, through nonlinear estimation using a regularization function that describes the inflection point of the curve relating the number of free surfactants to the total number of surfactants in the system. The comparison with experimental data on CMC for simple surfactant solutions confirms the predictive ability of this model. Calculated results showed that this model accurately predicts outcomes for ionic surfactants with linear alkyl tails at room temperature but shows significant deviations from experimental data for low temperatures and non-ionic surfactants. The results also indicated that a better description of the model terms related to solubility and interfacial tension could be a way to improve the model in this regard. This improvement can be done by incorporating additional information from experimental data and molecular dynamics simulations, making the model more reliable for studying the stability involving these surfactants.