LAUSR

Abstract Conductometric measurements have been employed to gain a detailed insight into the interactions between two cationic surfactants, tetradecyltrimethylammonium bromide (TTAB) and dodecyltrimethylammonium chloride (DTAC), in water and in an aqueous solution of sodium chloride. The experimental data were analyzed according to Rubingh’s model within the framework of the pseudophase separation model. The evaluated values of critical micelle concentration (cmc) were found to be lower than their corresponding cmcid values, signifying attractive interactions involving both components in the solutions. The micellar mole fractions ($$ X_{1}^{\text{Rub}} $$X1Rub) of TTAB evaluated by Rubingh’s model were always larger than the ideal values ($$ X_{1}^{\text{id}} $$X1id), signifying the higher involvement of TTAB in mixed micelles of TTAB and DTAC. Activity coefficients ($$ f_{ 1}^{\text{Rub}} $$f1Rub and $$ f_{ 2}^{\text{Rub}} $$f2Rub) were always below one in all cases signifying synergism in the mixed micelles. All the outcomes point to synergism and attractive interactions in the mixed systems. Values of excess Gibbs energy were evaluated by employing Rubingh’s model ($$ \Delta G_{\text{ex}}^{\text{Rub}} $$ΔGexRub) and the $$ \Delta G_{\text{ex}}^{\text{Rub}} $$ΔGexRub values obtained are negative. The values of $$ \Delta H_{\text{m}}^{\text{o}} $$ΔHmo and $$ \Delta S_{\text{m}}^{\text{o}} $$ΔSmo reveal that hydrophobic interaction is expected to be the binding force between TTAB and DTAC in aqueous media at lower temperatures, while both hydrophobic interactions as well as exothermic interactions are involved at higher temperatures. The interaction forces between the surfactants were found to be enhanced in the presence of NaCl.