Synergism in mixtures of n-octyl-β-d-thioglucoside and different n-alkyltrimethylammonium bromides: effect of the alkyl chain length

Abstract

Mixtures of n-octyl-β-D-thioglucoside with three different n-alkyltrimethylammonium bromides (n 012 (DTAB), 14 (TTAB), and 16 (CTAB)) have been studied by using fluorescence spectroscopic techniques. The critical micelle concentration values of pure and mixed systems were determined by the pyrene 1:3 ratio method. The experimental results were treated by using thermodynamic mixing approaches based on the pseudophase separation model. It was found that all the mixed systems show a negative deviation from ideal behavior, more pronounced as the larger the alkyl tail of the co-surfactant. It was also observed that the three mixed systems fulfill the conditions of synergism, this behavior being also dependent on the alkyl chain length. By using the static quenching method, the mean micellar aggregation numbers of mixed micelles were obtained. In all the cases, it was observed that the aggregation number is initially reduced with the participation of the cationic surfactant, remaining almost constant and close to the aggregation number of the pure cationic micelles. The local viscosity of pure and mixed micelles was examined by the photophysical response of the hydrophobic probe coumarin 6 solubilized in the micellar medium. It was found that the participation of the ionic component induces the formation of a less ordered structure than that of pure nonionic micelles. This effect being less pronounced as the chain hydrocarbon length of the co-surfactant increases.

Partition Coefficients of Ionizable Solutes in Mixed Nonionic/Ionic Micellar Systems

“…eq 15 and 17) and the surfactant−surfactant interactions. 4,57,59 The higher values determined by the RSA compared to the ideal composition reveals synergistic micelle formation, which is more dominant for the SDS mixed micelle because of the stronger interaction between Brij 35 and SDS compared to that between Brij 35 and CTAB. 10,46−48 The values determined with the COSMO-RSbased approaches (approaches I and II) are close to the RSA values in the case of SDS mixed micelles.…”

“…In practical applications, such as cosmetics, detergency, and enhanced oil recovery, surfactants are mostly used in mixtures because they have improved characteristics compared to those of single-surfactant solutions. − Thus, in recent years much effort was spent in investigating the dominant effects by means of different experimental setups. , The critical micelle concentration (cmc) is the most studied characteristic in mixed-surfactant systems besides properties such as the micelle size, composition, and aggregation number. On the basis of the experimental data, models for the description of the mixed-surfactant systems were developed. , Out of these, the mass action models (MAMs) and pseudophase separation approximations (PSAs) are the most studied approaches. , In particular, the PSA in combination with the regular solution approximation (RSA) was applied extensively and successfully for the description of intramicellar interactions. , On the basis of experimental cmc data for single surfactants and the mixture, the composition of the micelles and the interaction parameter β are calculated.…”

“…β is an empirical parameter that quantifies the interaction between the surfactants in the micelle, and thus the nonideality of the system is accounted for. On the basis of the interaction parameter, conclusions concerning the contribution of the surfactant headgroups and the length of the alkyl chain were drawn. ,, However, because of its undifferentiated description of the interaction and lack of thermodynamic fundamentals, the RSA is often questioned. ,,, Predictive models based on thermodynamic fundamentals were suggested, which consider different energy contributions. − These models give more detailed information about the different influences, such as the steric, hydrophobic, and electrostatic contributions to the formation of micelles.…”

“…1−3 Thus, in recent years much effort was spent in investigating the dominant effects by means of different experimental setups. 4,5 The critical micelle concentration (cmc) is the most studied characteristic in mixed-surfactant systems besides properties such as the micelle size, composition, and aggregation number. On the basis of the experimental data, models for the description of the mixedsurfactant systems were developed.…”

“…On the basis of the interaction parameter, conclusions concerning the contribution of the surfactant headgroups and the length of the alkyl chain were drawn. 4,9,10 However, because of its undifferentiated description of the interaction and lack of thermodynamic fundamentals, the RSA is often questioned. 2,5,8,11 Predictive models based on thermodynamic fundamentals were suggested, which consider different energy contributions.…”