Interaction, stability, and microenvironmental properties of mixed micelles of Triton X100 and n-alkyltrimethylammonium bromides: Influence of alkyl chain length

Micellar properties of binary surfactant systems of Triton X100 (TX100) wit h three different n-alkyltrimethylammonium bromides (n = 12 (DTAB), 14 (TTA B), and 16 (CTAB)) were investigated by the fluorescence probe technique. T he critical micelle concentration (cmc) values of the corresponding mixture s in the whole range of composition were obtained by the pyrene 1:3 ratio m ethod. In order to estimate the interaction between the surfactants in the mixed micelles, the cmc data were treated by using the conventional regular solution approach for mixed micelles. It was found that whereas the intera ction parameter values (beta(12)) remained fairly constant for the TX100-TT AB and TX100-CTAB systems, the TX100-DTAB system was not well modeled by us ing that theory. However, in all cases the results showed deviation from id eal behavior. The stability of the mixed micelles was also discussed in the light of Maeda's treatment (J. Colloid Interface Sci. 1995, 172, 98), and the observed differences between the three systems were justified on the ba sis of a certain steric factor due mainly to the presence of the phenyl gro up of TX100 in connection with the length of the monomer of the cationic co mponent. The micropolarity of the mixed aggregates was examined by the pyre ne 1:3 ratio index in micellar solutions of concentration well above the cm c. It was observed that the increasing participation of the ionic component induces the formation of more closed micelles with a more dehydrated struc ture. The polarized fluorescence measurements, by using diphenylbutadiene a s a probe, were interpreted by using the wobbling in cone model. It was fou nd that the order parameter decreases as the participation of the cationic surfactant in the micelle increases, indicating the formation of a less ord ered structure than that of pure TX100 micelles. Data obtained in this inve stigation allowed to establish a clear correlation between micellar stabili ty and microenvironmental properties of the mixed aggregates.