Thermodynamic investigation of surfactant aggregation in 2-pyrrolidinone

The partial molal volume (Vφ,s) of several surfactants viz. sodium dodecylsulphate (SDS) and sodium tetradecylsulfate (STS), tetraethylammonium bromide (Tea-Br), Span-80, 60, 40, 20 in 2-pyrrolidinone have been determined at concentration below 0.80 mol kg−1 at 30 and 40 °C. The partial molal isentropic compressibility (Kφ,s) of micellar solutions of surfactants SDS, STS, Span-80, 60, 40, 20 have been calculated from ultrasonic velocity measurements at 30 °C. The infinite dilution values of Vφ,s and Kφ,s of the solubilizates in 2-pyrrolidinone are also estimated. The critical micellization concentration (cmc) values for the systems are taken at a concentration where a clear and well defined break is observed in the concentration dependence of the ultrasonic velocity. The cmc data has been utilized to compute standard free energy of micellization (ΔGmo). The results have been interpreted in terms of transfer of surfactant monomer from dispersed to aggregated state. Limiting parameters have been used to explain the solvation of surfactant molecules.