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

Abstract

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, C₁₆VnImBr, 1-hexadecyl-3-methylimidazolium bromide C₁₆MeImBr, and (conventional) cetyltrimethylammonium bromide, C₁₆Me₃ABr (Vn, Im, Me, A = vinyl, imidazolium, methyl and ammonium, respectively) were studied at 25 °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 C₁₆VnImBr compared to C₁₆MeImBr and C₁₆Me₃ABr; indicating stronger interaction between (C₁₆VnIm)⁺ and DS⁻. Light scattering results revealed that the DS/C₁₆VnImBr system contained larger vesicles, as compared to DS/C₁₆MeImBr and DS/C₁₆Me₃ABr. The changes in morphology agree with the expected effects of DS on the packing parameter of the colloidal aggregates.