Physicochemical Studies on the Interfacial and Micellization Behavior of CTAB in Aqueous Polyethylene Glycol Media

Interfacial and micellization behavior of cetyltrimethylammonium bromide (CTAB) have been studied in aqueous polyethylene glycol (PEG) mixed solvent systems of varying concentrations and molar mass. Interfacial behavior of CTAB was investigated by the equilibrium surface tension method. Conductance studies of surfactant solutions under different condition helped in determining the critical micelle concentration (CMC) and degree of dissociation of CTAB micelles. In addition, the limiting molar conductivity of surfactant and micellar species were evaluated from the differential plots. The CMC of CTAB was found to increase with increasing PEG concentration as well as its molar mass, although, the process of interfacial adsorption and micellization was found to be spontaneous, as evidenced by negative free energy change. The viscosity of CTAB micelles in aqueous-PEG mixtures was found to increase with the increase in PEG concentration and molar mass. Dynamic light scattering measurements revealed a size enhancement effect contributed by the PEG oligomers. An increase in the CMC of CTAB and the subsequent presence of a higher number of ionic species in their dissociated form was further established by an overall increase in the zeta potential value in the presence of PEG oligomers. It is proposed that the PEG could wrap around the micelles through their conformational changes. Results also suggest that PEG oligomers could give solvophobic effect which enhances the CMC of CTAB compared to that in pure water.