Physicochemical studies on the catanionics of alkyltrimethylammonium bromides and bile salts in aqueous media

Phase manifestation and aggregation behavior of long chain alkyltrimethylammonium bromides (C_nTABr, n=12, 14 and 16) in combination with sodium cholate (NaC) and sodium deoxycholate (NaDC), were studied in aqueous medium. C_nTABr-NaDC mixed systems exhibited different phases, viz., micelles, vesicles and precipitates while only clear isotropic phase was formed with NaC. With increasing chain length of C_nTABr, both the area under precipitate and viscous zones increased. Micellization behavior of mixed surfactant systems at different compositions were studied by conductance, viscosity, fluorescence spectroscopy, dynamic light scattering, zeta potential and small angle X-Ray scattering measurements. Mixed micelles, at all combinations, were basically comprised of larger proportion (∼50-60%) of cationic surfactant, which were independent of the bulk composition. Interaction parameter, activity coefficient and micellar composition were evaluated in the light of Rubinigh's model for Regular Solution Theory (RST). Strong synergistic interaction occurred between C_nTABr and bile salts where NaC behaved differently from NaDC due to its higher hydrophilicity. Complexity of the different systems increased with the increasing chain length of C_nTABr. Such catanionic systems are considered to have prospects in drug delivery systems, nanoparticle synthesis, etc.