Investigation of the aggregation, clouding and thermodynamics of the mixture of sodium alginate with sodium dodecyl sulfate and triton X-100 in aqueous and aqua-organic mixed solvents media

Abstract

Herein, the aggregation, phase separation and binding behavior of sodium alginate (SA) and surfactants (anionic (SDS) and nonionic (TX-100)) mixture in aqueous and aqua-organic mixed solvents have been investigated applying the conductivity, cloud point, and UV–visible spectroscopic methods. In the current study, the various physico-chemical parameters (critical micelle concentration (CMC), extent of bound counter ions, cloud point (CP), binding constant (Kb), thermodynamic properties, and transfer parameters) were determined. The addition of SA facilitates SDS micellization. The CMC of the SA + SDS mixtures were obtained to be dependent on SA concentration, composition of mixed solvents, and temperature. The CMC of the SA + SDS mixture were found to be greater in magnitude in aqua-organic (dimethyl formamide (DMF), acetonitrile (AN), ethylene glycol (EG), and 1,4-dioxane (DX)) mixed solvents than the values observed in H2O medium. The values of counterion binding were found to be enhanced with the boost of concentration of SA and other organic additives. The Kb values of SA + TX-100 mixtures were computed from the Benesi-Hildebrand (BH) plot and the Kb values were found to be temperature-dependent. The CP values of the SA + TX-100 mixture experienced a lessening with growing contents of SA and got enhanced in diols (EG/ propanediol (PrD)) media. The negative values of free energy changes dictate that the micellization of SA + SDS mixture and binding processes for the SA + TX-100 mixture are spontaneous in nature while the positive free energy changes indicate the non-spontaneity of clouding phenomena of SA + TX-100 mixture. The obtained values of enthalpy and entropy changes recommend the presence of hydrophobic, electrostatic, and ion–dipole interactions amongst SA and SDS while hydrogen bonding, ion–dipole, and van der Walls forces are the proposed forces between SA and TX-100. Excellent enthalpy–entropy compensation was observed in each case.