Abstract
Surface physico-chemical and thermodynamic studies of some aqueous surfactant solutions were carried out by employing conductance, surface tension and dye solubilization (UV-Vis absorption spectroscopy) techniques. From conductivity and surface tension measurements, critical micelle concentration (CMC), counter-ion association constant (α), equivalent conductance at infinite dilution (λo), surface exess concentration (Гmax ), minimum area per molecule (Amin), surface pressure at CMC (πCMC), thermodynamic properties of micellization (∆Gomic, ∆Homic, ∆Somic) and adsorption (∆Goads, ∆Hoads, ∆Soads) have been obtained for an anionic (sodium dodecyl sulphate (SDS)), a cationic (hexadecyl trimethyl ammonium bromide (HTAB)) and nonionic (Polyoxyethylene (20) sorbitan mono-oleate (Tween 80)) surfactant solutions. Effect of mixing cosolvents (1,2-Ethanediol or 1,2,3-Propanetriol) on physico- chemical properties of surfactant systems at 298.15, 308.15 and 318.15K has been investigated. Surfactants micellar characteristics and their interactions with cosolvents were also investigated by Uv-vis absorption spectroscopy measurements of solutions using bromothymol blue as a probe. The inclusion of cosolvents caused an increase in CMC and degree of counterion dissociation (β) of surfactant solutions whereas the thermodynamic analysis shows that, although the micellization is less favorable in mixed solvent compared to pure water, the process is spontaneous and exothermic.
Key words: Conductance, dye solubilization, micellization, surface physico-chemical properties.
