Endowing cationic surfactant micellar solution with pH, light and temperature triple-response characteristics by introducing 4-(phenylazo)-benzoic acid

Abstract

A practical and smart micelle system with pH, light and temperature responses, prepared using the cationic surfactant 3-hexadecyloxy-2-hydroxypropyl trimethyl ammonium bromide and 4-(phenylazo)-benzoic acid (ACA) (in its salt form), was developed as a highly promising fluid for applications in different fields. With increasing the trans-ACA concentration, η0 of the solution increases first and decreases subsequently, and the maximum was at 17 mM, the micellar structure transform from spherical to wormlike micelles, and then to rod morphology. The solution viscosity could be reversibly regulated at pH 4–12 due to the transition of aggregate morphology of self-assembling structure. UV/vis irradiation resulted in a trans to cis photoisomerization of the ACA molecule, and induced the conversion of corresponding wormlike structures into the rodlike micelles. With temperature increase the η0 of solution peaks at 28.6 °C and it doesn't follow an Arrhenius law, micellar contour length profile also varies between wormlike and rodlike. The regulatory mechanism of the micellar solution under the three stimuli is discussed based on the obtained data. This novel smart system may provide a new theoretical basis for future applications, opening a new avenue for synthesizing multifunctional aggregates to adapt to various environmental changes.