Thermo-responsive viscoelastic wormlike micelle to elastic hydrogel transition in dual-component systems

In this work, we report a thermo-responsive phase transition from a viscoelastic wormlike micelle solution to an elastic hydrogel in a mixture of an imidazole-type surfactant, 1-hexadecyl-3-methylimidazolium bromide (C16MIMBr), and sodium salicylate (NaSal). Above the critical temperature T-gel, the sample exhibits characteristic wormlike micelle features with strong viscoelastic properties. As the temperature was lowered below the T-gel, the viscoelastic solution transforms into an elastic hydrogel with a remarkable elastic modulus increase. Polarization microscopy, SEM, and XRD were employed to reveal the morphology and molecular arrangement of the organized microstructures in the hydrogel. The unexpected phase transition from viscoelastic solution to hydrogel can be attributed to the crystallization of wormlike micelles, which is related to the strong synergic interaction between the surfactant and hydrotrope.