Investigation of aggregation behavior of ionic surfactant mixture in crystal violet dye solution at different temperatures and solvent compositions: conductivity and theoretical approach

Abstract The conductometric measurement technique was utilized to have in-depth knowledge on the aggregation behavior of a mixture of two ionic surfactants – sodium dodecyl sulfate (SDS; a common anionic surfactant) and cetyltrimethylammonium bromide (CTAB; a cationic surfactant), in crystal violet (CV) and CV + ethanol (5 and 10% (w/w)) solution media. The related micellar and thermodynamic parameters of the mixed system have been assessed and presented in this paper. The cmc values of pure SDS/CTAB, & their mixture in presence of CV dye, were observed to decrease and thus the insertion of CV favors the micellization of pure and mixed micelle. Also, the cmc values of the mixture of SDS & CTAB undergo a drop with increasing the concentration of CTAB at a specific temperature and these cmc fall in the middle of the detected cmc of SDS & CTAB micelles in all the media studied. The observed values of cmc are lower in magnitude in comparison to the ideal cmc and the numerical values of the interaction parameter (β) are negative, which manifests the existence of attractive interaction between SDS and CTAB surfactants in presence of CV dye. The cmc values are also dependent on the fluctuation of experimental temperature. The micellar mole fraction of component 1 (CTAB) in SDS + CTAB mixture (X1Rub) and the ideal micellar mole fraction () was obtained to be relatively greater than the related stoichiometric mole fraction (α1) of component 1 (CTAB). The activity coefficients (f1Rub and f2Rub) remained below unity in all test cases, suggesting a attractive interaction effect in the mixed micellar system. The obtained thermodynamic parameters demonstrate that the single and mixed micellization phenomena are spontaneous in nature and the main driving forces are hydrophobic and exothermic in nature.