Self-aggregation of tetradecyltrimethylammonium bromide (TTAB, [CH3(CH2)13N+(CH3)3Br-]) and polyoxyethylene 23 lauryl ether (Brij-35, [CH3 (CH2)11(OCH2CH2)23OH]) binary surfactant mixture in aqueous medium was studied using tensiometric, conductometric, density, quasielastic light scattering, potentiometric, and fluorometric measurements. The binary surfactant mixture was studied well above the Krafft temperature, which was evaluated by conductance measurements. Rubingh's nonideal solution theory predicted nonideal mixing and attractive interaction between the constituent surfactants in the mixed micelle. Moreover, attractive interaction between the two surfactants in the mixed micelle is explained by assuming that water acts as a bridge between the hydrophilic polar groups of the surfactant molecules. The chain-chain interaction among the surfactant does not seem to be high in this case. The partial specific volume of pure as well as binary surfactant mixtures was also evaluated, and it was inferred that the mixed micelles are more hydrated compared to individual components. The excess Gibbs free energy of mixing was evaluated, and it indicated relatively more stable mixed micelles for this binary combination. Surface tension measurements indicate an existence of a second state of aggregation for the mixed surfactant system, which is supported by the break in conductance−concentration of surfactant profile. The Krafft temperature of TTAB decreases as the nonionic surfactant content increases in the mixed system. Quasielastic light scattering studies suggest an increase in the hydrodynamic radius of the micelle in the mixed surfactant system.

The self-aggregation of Tween 40, Tween 60, and Tween 80 in ethylene glycol-water mixture was investigated using surface tension, density, and fluorescence measurements. The mixtures were observed to appreciably affect the critical micelle concentration (cmc) of the surfactants and their aggregation numbers. In order to evaluate the influence of the solvent mixture, the difference in the Gibbs energy of micellization of Tween 40, Tween 60, and Tween 80 between water and binary mixtures were determined. The ability of ethylene glycol acting as a structure breaker and its interaction with the surfactant hydrophilic group are the controlling factors for the micellization of the surfactants in the mixture. The surface activity of the surfactants decreases with increasing concentration of ethylene glycol in the mixture. Micellar micropolarity was determined using the fluorescence method. The results indicate the participation by ethylene glycol in the micellar solvation layer.

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Mixed surfactants play a promising role in surface chemical applications. In this study, interfacial and bulk behaviors of binary and ternary combinations of tetradecyltrimethylammonium bromide (C(14)TAB), tetradecyltriphenylphosphonium bromide (C(14)TPB), and tetradecylpyridinium bromide (C(14)PB) have been examined in detail using the methods of tensiometry, conductometry, fluorimetry, and microcalorimetry. The state of micellar aggregation, amphiphile composition in the micelle, extent of counterion binding by the micelle, and interaction among the surfactant monomers in the binary and ternary combinations have been quantitatively assessed in the light of the regular solution theories of Rubingh and that of Rubingh and Holland. The monomer packing in the micelles and their expected shapes have also been estimated from topological considerations. Conceptual rationalization of results has been presented together with associated energetics of the interfacial adsorption and self-aggregation in the bulk.