Abstract
Mixed-micelle formation in the binary mixtures of dodecyltrimethylammonium bromide (DTABr) and cetyltrimethylammonium bromide (CTABr) surfactants in water-ethanolamine mixed solvent systems has been studied by conductometric method in the temperature range of 298.1 to 313.1 K at 5 K intervals. It was observed that the presence of ethanolamine forced the formation of mixed micelle to lower total surfactant concentration than in water only. The synergistic interaction was quantitatively investigated using the theoretical models of Clint and Rubingh. The interaction parameter β12 was negative at all the mole fractions of DTABr in the surfactant mixtures indicating a strong synergistic interaction, with the presence of ethanolamine in the solvent system resulting in a more enhanced synergism in micelle formation than in water only. The free energy of micellization ΔGM values was more negative in water-ethanolamine mixed solvent system than in pure water indicating more spontaneity in mixed micelle formation in the presence of ethanolamine than in pure water.
Highlights
Mixed micelles are widely recognized and employed in numerous fields ranging from biological systems to technical applications such as in detergency, cosmetic, pharmaceuticals, enhanced oil recovery, and as flotation agents
Similar observations are reported in the literature and in most cases have been addressed by either carrying out a nonlinear fit of the raw conductivity-surfactant data or by the analysis of the plots of differential conductivity. This latter approach is adopted in this work, which is based on the assumption that the first derivative of the specific conductivity-concentration curve is well-described by the Boltzmann-type decreasing sigmoid given by [29]
(1) The observed Critical Micelle Concentration (CMC) values of dodecyltrimethylammonium bromide (DTABr)-cetyltrimethylammonium bromide (CTABr) mixture obtained by Rubingh model are lower than those predicted from Clint’s model, indicating the presence of nonideality in the mixed micelle formation
Summary
Mixed micelles are widely recognized and employed in numerous fields ranging from biological systems to technical applications such as in detergency, cosmetic, pharmaceuticals, enhanced oil recovery, and as flotation agents. The effects of different kinds of additives including glycols, hydrazine, adn formamide on the micellization of single surfactants have been widely studied [20,21,22,23]. These solvents are known to have high cohesive energies and considerable hydrogen bonding ability which favor aggregation of surfactant monomers to form micelle. Results of the conductometric study of the physicochemical properties such as micellar composition, counterion binding, interaction parameter, thermodynamic parameters of mixed micelle formation of mixed cationic surfactants in ethanolamine-water binary system using dodecyltrimethyl ammonium bromide (DTABr) and cetyltrimethyl ammonium bromide (CTABr) are presented. It may be mentioned that comprehensive studies on binary mixtures of cationic surfactants are reported in the literature, fundamental investigations on the effect of ethanolamine on micellization have not been mentioned
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