Self-Aggregation of Alkyl (C10-, C12-, C14-, and C16-) Triphenyl Phosphonium Bromides and Their 1:1 Molar Mixtures in Aqueous Medium: A Thermodynamic Study

The self-aggregation of alkyl (C 10 -, C 12 -, C 14 -, and C 16 -) triphenyl phosphonium bromide surfactants (ATPBs) and their equimolar binary mixtures in aqueous medium was studied microcalorimetrically and conductometrically at different temperatures. The thermograms of C 10 - and C 12 TPB have shown differences in behavior from those of C 14 - and C 16 TPB. Their binary (1:1 mol/mol) mixtures with C 10 - or C 12 TPB as one of the components have also evidenced differences in behavior. Individually as well as in mixed conditions, the ATPBs have indicated formation of two states of aggregation corroborated by both calorimetric and conductometric measurements. On the basis of the results, the thermodynamic parameters, free energy (Δ G m °), enthalpy (Δ H m °), entropy (Δ S m °), and specific heat (Δ C p m °), of micellization have been evaluated. The specific heat has been found to vary linearly with the carbon number in the ATPB chain. The Δ H m ° and Δ S m ° values for the micellization of the pure ATPBs have nicely compensated each other. The free energy of transfer of a mole of CH 2 from an aqueous environment to a micelle was found to be −2.0 kJ mol -1 .