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The micellar characteristics of a non-ionic, natural surfactant, saponin obtained from the soapnut tree, Sapindus mukorossi, were studied in aqueous solution. Critical micelle concentration of Sapindus saponin determined using conductivity measurements and UV absorption studies was 0.045 wt%. Increase in temperature and salt concentration led to decrease in the critical micelle concentration of Sapindus saponin. The critical micelle concentration was found to increase with increase in hardness of water and increase in pH. The micellar aggregation number was determined using cyclic voltammetry and was found to be between 13 and 21. The size of the Sapindus saponin micelles was determined using intrinsic viscosity measurements and was found to be independent of saponin concentration for concentrations above the CMC. Solubilisation of two types of crude oils and a vegetable oil was studied using micellar solubilisation technique. At lower concentrations of the surfactant, the micellar solubilisation of crude oils in saponin was better than synthetic surfactants like Triton X100® and SDS where as, the solubilisation of vegetable oil was better in synthetic surfactants.

The dependence on composition of the polarity of H2O+MeCN mixtures has been determined from measurements of the empirical solvent polarity parameter ET. ET has been found to vary with composition in a similar fashion to that which has been reported previously for most other H2O+non-electrolyte mixtures for which ET data are available. The variation of ET with composition is interpreted in terms of the Naberukhin-Rogov structural model for H2O+nonelectrolyte mixtures.

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