The Effect of Methanol on the Micellar Properties of Dodecyltrimethylammonium Bromide (DTAB) in Aqueous Medium at Different Temperatures

The micellar properties of dodecyltrimethylammonium bromide (DTAB) in water and methanol water mixtures at different temperatures have been studied by conductivity and surface tension measurements. The critical micelle concentrations (CMC), degree of ionization (α), standard Gibbs free energy of micellization (\( \Delta G_{\text{m}}^{\text{o}} \)), standard enthalpy of micellization (\( \Delta H_{\text{m}}^{\text{o}} \)), standard entropy of micellization (\( \Delta S_{\text{m}}^{\text{o}} \)) and free energy of transfer (\( \Delta G_{\text{trans}}^{\text{o}} \)) were evaluated from conductivity data. The CMC, maximum excess surface concentration (\( \varGamma_{ \hbox{max} } \)), area occupied per surfactant molecule (\( A_{ \hbox{min} } \)), surface pressure at the CMC (\( {\pi}_{\text{cmc}} \)), packing parameter (P) and standard free energy interfacial adsorption \( (\Delta G_{\text{ads}}^{\text{o}} \)) were estimated from surface tension measurements. The CMC of DTAB was found to increase with increasing volume fraction of methanol and increasing temperature. Thermodynamic parameters and surface properties revealed that the addition of methanol changes the relevant physicochemical properties which affect the process of micellization.