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Beena Shah ¹, A. K. Rakshit ¹, Surekha Devi ¹

Affiliations
1 Department of Chemistry, Faculty of Science, M.S. University of Baroda, Baroda 390002, IN

Abstract

The kinetics and thermodynamics of adsorption of the indicator dye Brilliant Cresyl Blue onsilica have been studied under varying conditions in aqueous and aqueous surfactant solutions. Both Langmuir and Freundlich isotherms have been found to be applicable. The monolayer capacity was 17.6 ± 0.3 mg·g^-1 of silica. The nonionic surfactant Brij 35 influences the amount of adsorption to some extent but the ionic surfactants CTAB and NaDS do not show any such effect.

Keywords

Brilliant Cresyl Blue, Adsorption, Kinetics, Isotherms.

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A. K. Rakshit ¹, S. Ajith ¹

Affiliations
1 Department of Chemistry, M.S. University of Baroda, Baroda 390002, IN

Abstract

Thermodynamics studies of mixed system of nonionic (Brij 35) and cationic (CTAB) uere performed. The change in cmc values were very high when a small amount of Brij 35 was present in the mixed system but CTAB did not show such an effect. Phase separation model was used in calculating the thermodynamic quantities of micellization. Interaction parameters between surfactant molecules in the mixed micellar state were computed by using Rubingh's model.

Keywords

Mixed Micelle, CTAB-Brij 35, System, Free Energy of Micellization, Molecular Interactions in Micelles.

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S. B. Sulthana ¹, S. G. T. Bhat ², A. K. Rakshit ¹

Affiliations
1 Department of Chemistry, M. S. University of Baroda, Baroda 390 002, IN
2 Research and Development Centre, Indian Petrochemicals Corporation Limited, Baroda 391 346, IN

Abstract

The interfacial and thermodynamic properties of sodium dodecyl benzene sulfonate (SDBS) and polyoxyethylene-10-dodecylether mixed surfactant systems in aqueous solutions were studied. The critical micelle concentration (CMC) and the degree of ionization (α) for all the systems were computed at 35, 40, 45 and 50°C, by both surface tension and conductivity measurements. The standard free energy (ΔG⁰_m), enthalpy (ΔH⁰_m) and entropy (ΔS⁰_m) of micellization were evaluated. An enthalpy-entropy compensation was observed. Gibbs adsorption equation was used to compute surface excess concentration (Γ_max) and hence minimum area per molecule (A_min). Surface pressure at CMC (Π_cMc) was also computed. The thermodynamic quantities of adsorption of the surfactants at the air/water interface were evaluated. Interaction between the surfactant molecules in the mixed monolayers (β^σ) and mixed micelles (β^m) were calculated from the regular solution approach. Viscosities of surfactant solutions were determined and the viscosity activation parameters were calculated.

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