Mixed micelles of triton X100: interaction, composition, stability and micro-environmental properties of the aggregates

Micellization of aqueous binary mixtures of triton X100 (TX100) in the presence of sodium dodecyl sulphate (SDS), cetyltrimethylammonium bromide (CTAB), and octaoxyethylene monodecyl ether (C12E8) has been investigated by the fluorescence probe technique. The critical micelle concentration values of the three binary combinations (TX100-SDS, TX100-CTAB and TX100-C12E8) in the whole range of compositions, obtained by using the pyrene 1:3 ratio method, were analysed in the light of the conventional regular solution theory for mixed micelles, as well as according to the formulation recently proposed by Maeda (1995, J. Colloid Interface Sci., 172, 98). This last theoretical approach was found to be very appropriate for describing the nature of the interactions involved in the formation and stability of the mixed micelles of TX100. Studies on the micropolarity of the mixed aggregates, as sensed by the probe pyrene. indicated that the incorporation of cosurfactant in the TX100 micelle induces the formation of mixed micelles with a more dehydrated structure. Data obtained from the polarized fluorescence measurements of diphenylbutadiene solubilized in the micellar phase, which were analysed according to the 'wobling-in-cone' model, showed the appearance of a less ordered micro-environment around the probe as cosurfactant proportion in the mixed micelle increased. The results obtained indicate that SDS is the cosurfactant which exerts a more pronounced effect on the micro-environment properties of mixed micelles.