A thermodynamic assessment of micellization for a mixture of sodium dodecyl benzene sulfonate and Tween 80 surfactants for ultralow interfacial tension

• Synergism of mixture of Tween 80 and DBSNa surfactants in terms lowest IFT with crude oil has been studied.
• Experimental observations have been interpreted thermodynamically through the analysis of regular solution theory.
• Micellization of the mixed surfactant has been studied thermodynamically in terms of free energy calculations.
• The shape of the micelle has been found to be spherical and mole fraction of surfactants in micelle has been calculated.
• Physical delineation of the micelle has been done by DLS interpretation.

Mixing of a non-ionic surfactant Tween 80 and an anionic surfactant sodium dodecyl benzene sulfonate (DBSNa) has been studied to observe their synergism. Induced by its application in IFT reduction with crude oil for a potential enhanced oil recovery, its characterisation has been done to understand the insight of micellization. The CMC for blend of Tween 80 and DBSNa was found to be 0.020 ± 0.0059 mM. Interfacially adsorbed excess concentration Γexcess and surface tension σ reduction has been studied from the tensiometry analysis. Conductivity study has shown relevance to the CMC obtained from tensiometry and provides the binding parameters. Thermodynamic interpretation has been done to quantify the experimental observations through the analysis of regular solution theory. Thermodynamic coefficients and constants have quantified the physical phenomena and ΔH, ΔS, ΔG featured spontaneity of micellization. Cyclic voltammetry study contributes the concepts of electrochemistry and redox potential for mixture. Physical delineation of the micelle has been done by DLS interpretation. Thermodynamic state functions, viz. free energy of micellization (ΔGmicelle) and adsorption (ΔGads) have been calculated to find out the packing parameter P, which indicates a probable spherical or globular micelle of the mixed surfactant.

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