Formulating Nonionic Detergents via the Integrated Free Energy Model

This work explores the optimum detergency conditions of alkyl ethoxylate (CXEOY) surfactants with the integrated free energy model (IFEM). IFEM is a molecular thermodynamic model that calculates the free energy of formation of oil-swollen spherical micelles, with a core solubilization radius Ro, using surfactants from empty (oil-free) micelles and oil molecules from a continuous oil phase. The described geometry allows for rapid calculations, using a personal laptop (3.4 GHz processor), where each solubilization energy profile (free energy vs. Ro curve) can be solved in 5 min or less. While previous work showed quantitative agreement between IFEM predictions and experimental solubilization of alkanes in CXEOY micelles, this work explores the possibility of using IFEM as a tool in surfactant selection. Experimental work has shown that detergency improved when operating near the phase inversion temperature (PIT) of the surfactant-hexadecane system. The IFEM simulations in this work show, for the first time, that IFEM can be used to predict the PIT of surfactant-oil systems, and that the surfactants selected via this method are consistent with the selection guided by experimental observations.