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

Abstract

The self-aggregation of alkyl (C10-, C12-, C14-, and C16-) triphenyl phosphonium bromide surfactants (ATPBs) and their equimolar binary mixtures in aqueous medium was studied microcalorimetrically and conductometrically at different temperatures. The thermograms of C10- and C12TPB have shown differences in behavior from those of C14- and C16TPB. Their binary (1:1 mol/mol) mixtures with C10- or C12TPB 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 (ΔGm°), enthalpy (ΔHm°), entropy (ΔSm°), and specific heat (ΔCpm°), of micellization have been evaluated. The specific heat has been found to vary linearly with the carbon number in the ATPB chain. The ΔHm° and ΔSm° values for the micellization of the pure ATPBs have nicely compensated each other. The free energy of transfer of a mole of CH2 from an aqueous environment to a micelle was found to be −2.0 kJ mol-1.