Multiresponsive Viscoelastic Vesicle Gels of Nonionic C12EO4 and Anionic AzoNa

Viscoelastic vesicle gels were prepared by mixing a nonionic surfactant, tetraethylene glycol monododecyl ether (C₁₂EO₄), and an anionic dye, sodium 4-phenylazobenzoic acid (AzoNa). The gels, which were composed of multilamellar vesicles, were analyzed by cryogenic transmission electron microscopy (cryo-TEM), freeze-fracture transmission electron microscopy (FF-TEM), ²H NMR spectroscopy, and small-angle X-ray scattering (SAXS). The mechanism of vesicle-gel formation is explained by the influence of anionic molecules on the bilayer bending modulus. Interestingly, the vesicle gels were observed to be sensitive to temperature, pH, and light. The viscoelastic vesicle gels respond to heat; they thin at lower temperatures and become thicker at higher temperatures. The vesicle gels are only stable from pH 7 to 11, and the gels become thinner outside of this range. UV light can also trigger a structural phase transition from micelles to multilamellar vesicle gels.