شهریار عصفوری

In this study a thermodynamic segment-based model was proposed for calculating activity coefficient of non-ionic surfactants. This model was used in prediction of critical concentration of micelle formation. In order to do that, the NRTL-NRF model provided by Haghtalab and Vera for calculation of short-range interactions in electrolyte solutions was developed for systems containing surfactants. The development of this model was performed by assuming the molecules as a chain of segments. The implementation of concepts of NRTL-NRF model on segments is the root of development. In solutions containing surfactants, Gibbs free energy of the system and activity coefficients are composed of two parts (residual and combinatorial). In this thesis, the developed model and Flory-Huggins expression were used for the residual part and the combinatorial one, respectively. To calculate the critical micellar concentration of a system, a pseudophase model and the equilibrium between surfactant monomers in the aqueous phase and surfactants in micelles were applied. To assess the accuracy of model, critical micellar concentration of systems containing poly-oxy-ethylene alcohols was calculated using the model and compared with experimental data. According to obtained percentage relative error, the results showed an improvement in predicted concentrations, despite the less adjustable parameters of the model.