Influence of an anionic hydrotrope on thermophysical properties of an anionic surfactant sodium dodecyl sulfate

Highlights: • The CMC values of mixed systems decrease with increase in hydrotrope concentration. • Interactions between surfactant and hydrotrope are synergistic in nature. • The CMC values of mixed systems increase with the increase in temperature. • The mixed micellization process was found to be spontaneous. • Non-covalent interactions between surfactant & hydrotrope confirmed by NMR & FT-IR. Herein we report micellization behavior of anionic surfactant, sodium dodecyl sulfate (SDS) in presence and absence of anionic hydrotrope (1,3-Benzenedisulfonic acid disodium salt (BDS)) in aqueous medium. Critical micelle concentrations (CMC) of mixed surfactant-hydrotrope systems were determined by conductometric technique. CMC values of surfactant-hydrotrope decrease with increasing hydrotrope concentration. Interactions between hydrotrope and surfactant are synergistic in nature. We also deduced thermodynamic parameters of micellization (viz., ΔG°_m, ΔH°_m, and ΔS°_m). The effect of hydrotrope and temperature on different thermophysical properties have been discussed. Experimental techniques like FT-IR and NMR were employed to reveal the non-covalent interactions of mixed surfactant-hydrotrope systems.