Multiresponsive viscoelastic vesicle gels of nonionic C<inf>12</inf>EO <inf>4</inf> and anionic AzoNa

Abstract

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. Shape shifters: Viscoelastic vesicle gels were prepared by mixing tetraethylene glycol monododecyl ether (C12EO4) and 4-phenylbenzoic acid (AzoNa). The vesicle gels were found to be sensitive to temperature, pH, and light. The vesicle gels thicken when heated and thin when cooled and are stable from pH 7 to 11. Outside of this range, the gels become thinner. UV irradiation can also trigger a transition from a micelle solution to multilamellar vesicle gels (see figure). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.