Drug induced micelle-to-vesicle transition in aqueous solutions of cationic surfactants

The effects of the anti-inflammatory drug diclofenac sodium (DS) on the morphology of aqueous micellar aggregates of two ionic liquid-based surfactants (ILBSs), 1-hexadecyl-3-vinylimidazolium bromide, C(16)VnImBr, 1-hexadecyl-3-methylimidazolium bromide C(16)MeImBr, and (conventional) cetyltrimethylammonium bromide, C(16)Me(3)ABr (Vn, Im, Me, A = vinyl, imidazolium, methyl and ammonium, respectively) were studied at 25 degrees C. To probe the morphology changes of the formed aggregates, we employed turbidity, viscosity, dynamic light scattering, and transmission electron microscopy. Depending on [DS], the transitions observed were from spherical micelles -> worm-like micelles -> vesicles. Viscosity data indicated that the first transition occurred at lower [DS] for C(16)VnImBr compared to C(16)MeImBr and C(16)Me(3)ABr; indicating stronger interaction between (C(16)VnIm)+ and DS-. Light scattering results revealed that the DS/C(16)VnImBr system contained larger vesicles, as compared to DS/C(16)MeImBr and DS/C(16)Me(3)ABr. The changes in morphology agree with the expected effects of DS on the packing parameter of the colloidal aggregates.