The effect of phenol on the critical micelle concentration and the enthalpy of micellisation of cationic dimeric surfactants in aqueous solutions

The effect of phenol addition to the aqueous phase on the critical micelle concentration and molar enthalpy of micellisation of alkanediyl-alpha,omega-bis(dodecyldimethy-lammonium bromide) Geminis (referred to as C12CSC12, where S is the spacer length) has been studied at 298 K. For C12C2C12, specific conductivities of aqueous surfactant solutions were measured over concentration ranges about the respective critical micelle concentrations at three selected phenol contents. UV absorbances of phenol, taken at a wavelength of 269.5 nm, were compared for different phenol and C12C2C12 concentrations. Titration calorimetry was used to determine the molar dilution enthalpy of a micellar stock solution, in pure water and in a 1.5 mmol kg(-1) solution of phenol in water, as a function of the equilibrium surfactant concentration for three Geminis, C12C2C12, C12C6C12 and C12C12C12. Depression of the critical micelle concentration and the enhanced thermal effect of micellisation in the presence of phenol were inferred from the experimental results. The location of polarisable phenol molecules in the outer portion of the surfactant micelles is postulated.