Worm-like micelles constructed by “pseudo” tetrameric surfactants containing azobenzene groups

Abstract

A tetrameric monomer containing an azobenzene group (abbreviated as tetra-N(AZO)-Br) was synthesized in this paper, and a “pseudo” oligomeric surfactant was constructed using tetra-N(AZO)-Br and a traditional surfactant, sodium oleate (SO), by non-covalent bonded interaction. The synthesized tetra-N(AZO)-Br was characterized by 1H NMR and UV–Vis spectra. The viscoelasticity and the difference in nuclear magnetic resonance (NMR) and ultraviolet (UV) absorption of the SO/tetra-N(AZO)-Br “quasi” tetrameric surfactant solution at different concentrations were investigated. The SO/tetra-N(AZO)-Br “pseudo” tetrameric surfactant could form highly viscoelastic worm-like micelles in solution, and the zero-shear viscosity of the system increased with increasing concentration. The viscoelastic properties of SO/tetra-N(AZO)-Br “pseudo” tetrameric surfactant had no obvious change after UV light irradiation. Since the combination of SO and tetra-N(AZO)-Br molecules was in dynamic equilibrium through the attraction of positive and negative charges, as much as 30% of the trans-tetra-N(AZO)-Br molecules in worm-like aggregates were transformed to their cis- structure. The un-transformed trans-tetra-N(AZO)-Br molecule could move in the aggregate and help maintain the structure of the aggregates, so that the viscosity had no obvious change.