Vesicles and Nanofibers with Krafft Transition from Cationic Surfactant-Divalent Azobenzene Dye Salt-Free Complex

An unusual thermo-reversible sol-gel transition was found in the salt-free complex of cetyltrimethylammonium bromide and disodium 4, 4'-azobenzene dicarboxylate around the Krafft temperature. The combined investigation by dynamic light scattering, polarized microscopy, atomic force microscopy, cryogenic transmission electron microscopy, and small angle x-ray scattering revealed that vesicles were formed in the aqueous solution at 50 degrees C, and nanofibers composed of two-dimensional hexagonal array of cylindrical micelles in the gel state at 25 degrees C.