The physicochemical properties of CTAB solutions in the presence of α-tocopherol

The electrolytic conductivity, electrophoretic mobility and zeta potential (LDV - laser Doppler velocimetry method) as well as the particles size distribution (DLS - dynamic light scattering method) were determined in the cetyltrimethylammonium bromide (CTAB) solutions (0.25-25.00 mM) at different concentrations of α-tocopherol (0-11.6 mM). The measurements were made at 25 °C and 30 °C. It was found that α-tocopherol (vitamin E) modifies the physicochemical properties of CTAB micellar solutions - the potential carrier of bioactive substances. The electrolytic conductivity of CTAB solutions was lowered by the addition of α-tocopherol. Particularly, the effect was observed in the concentration range 0.25-2.5 mM, i.e. in the vicinity of CMC. The critical micelle concentration (CMC) of CTAB solutions determined from the conductivity data decreased with the increasing vitamin E content due to the mixed aggregates formation. At the same time the electrophoretic mobility and zeta potential increased as a result of higher degree of the mixed aggregates dissociation. This effect was observed for all surfactant concentrations at both temperatures. The hydrodynamic diameter of mixed CTAB/α-tocopherol particles increased from 7-8 nm for the CTAB solutions to 50-60 nm for those containing vitamin E. The information about the aggregates size and their electrokinetic properties can be useful in predicting the encapsulation of biomolecules in the surfactant micelles and their transport by different membranes.