Abstract
Herein, we have shown the mixed micelle formation between anionic benzene sulphonate (viz., sodium 4,4′-(16,25-dioxo-15,17,24,26-tetraaza-hexatriacontane15,26-diyl) dibenzenesulphonate [BSC14-C6-14CSB] and sodium 4,4′-(18,27-dioxo-17,19,26,28-tetraaza-tetracontane15,26-diyl) dibenzenesulphonate [BSC16-C6-16CSB]) with conventional anionic surfactant (sodium dodecyl sulphate [SDS]) by conductivity and fluorometry methods. The conductivity measurements were done over a range of mole fractions of SDS at different temperatures to study the mixed micellization and thermodynamic parameters, while fluorescence measurements were performed over entire range of mole fraction of SDS in order to observe the aggregation and micro-polarity. The conductometric study confirms the synergism in all mole fractions of SDS with [BSC14-C6-14CSB] and [BSC16-C6-16CSB] at all temperatures. The Rubinghs regular solution theory (RST) was employed to evaluate micellar mole fraction, X1, ideal micellar mole fraction, Xideal, interaction parameter (β), activity coefficients (f1, and f2) for both mixed micelles systems and Gibbs excess free energy (GE). The GE values are negative for entire mole fraction range suggesting the formation of stable mixed micelles. In addition to this, other thermodynamic parameters like Gibbs free energy change of micellization (ΔGmic), enthalpy change of micellization (ΔHmic) and entropy change of micellization (ΔSmic) were evaluated. Also, the aggregation number (Nagg) in micelles was calculated using pyrene probe fluorescence measurement. The binding constant, dielectric constant and micropolarity of mixed systems of SDS + [BSC14-C6-14CSB] and SDS + [BSC16-C6-16CSB] binary mixtures were obtained from the ratio of peak strength (I1/I3) from the pyrene probe fluorescence emission spectra.
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•Mixed micellization behaviour of SDS–[BSC14-6-14CSB]/[BSC16-6-16CSB]•The synergistic interaction was observed.•The process of micellization is entropy driven.