Mixed micellization study of cationic surfactants viz. alkyltrimethylammonium bromides (CnTAB) and alkyltriphenylphosphonium bromides (CnTPPB) with similar hydrophobic groups (C12‐, C14‐, and C16‐) was performed using tensiometry and UV–visible light spectrophotometry techniques. Critical micelle concentration (CMC) values of the single and binary surfactant mixtures were obtained from a plot of surface tension versus the logarithm of surfactant concentration (Cs). The degree of synergy and various mixed micelle parameters like interaction parameter (β), activity coefficients (fm) and interfacial parameters like surface pressure (πCMC), packing parameter (P), surface excess concentration (Гmax), surface tension at the CMC (γCMC), and minimum area per molecule (Amin) were evaluated using the regular solution theory (RST). Thermodynamic parameters were calculated using several proposed models which suggest the mixed micellar system to be more thermodynamically stable than their respective individual components. In addition, a dye solubilization study was performed using a spectrophotometric method to validate the CMC data obtained from tensiometric method. Conductometric measurements were also carried out for the mixture of C12TAB + C12TPPB only as it showed a more negative β, indicating a higher degree of synergism.

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pH and concentration dependent growth of gemini surfactant (12-4-12) micelles in the presence of bile salts.

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The solubilisation of hydrophobic azo dye Orange OT in aqueous/salt solution in several cationic surfactant micelles was studied using UV-vis spectroscopy. An attempt was made to correlate dye solubilising strength with adsorption/micellar characteristics. In our experiments we determined the change in solubilisation of hydrophobic dye when added to an aqueous solution of oppositely charged quaternary-salt-based cationic surfactants (conventional and gemini) and remarked on the probable location of the solubilised dye in the surfactant micelle. Results highlight the onset of dye solubilisation around the critical micelle concentration of each surfactant, which is influenced by the non-polar tail, spacer, and polar headgroup, while no dye could be solubilised at concentrations below the critical micelle concentration.