PH and light dual-stimuli responsive wormlike micelles based on azophenyl surfactant and Sodium oleate

Abstract

Herein, pH and light dual-stimuli responsive wormlike micelles (WLMs) were prepared with (4-butylphenyl)-2-(4-trimethylammoniumhexyloxyphen-yl) diazene (C4AzoC6N) and sodium oleate (NaOA). The viscoelasticity of the system was tested by steady state and dynamic rheology. In the alkaline condition, the binary system is a viscoelastic gel-like liquid with a viscosity of up to 230 Pa·s as the presence of the carboxylate group in NaOA, which promotes the formation of WLMs. After the pH of the solution was changed from alkaline to acidic, NaOA was gradually converted into oleic acid, which precipitated out of the system and the viscoelastic system was turned into a cloudy, low-viscosity flowing liquid. On the other hand, the viscosity of the solution could be repeatedly and reversibly switched more than three times without any deterioration upon light trigger due to the cis-trans isomerization of C4AzoC6N. Compared with other surfactants, NaOA is one of cheap and commercially available compounds, which avoids complex organic synthesis or purification processes. Furthermore, the WLMs can be precisely controlled by pH and UV light dual-stimuli, which will have a wide range of applications in large-scale processes, such as in functional materials and fluid drag reducers.