Researchers have developed a novel strategy to control the shapes of polymeric materials by utilizing photoresponsive molecular switches. This could aid the development of an electrolyte that exhibits photoreversible viscoelastic changes and could be applied to other polymers to produce stimuli-responsive soft materials in, for example, printing and biomedicine.

The researchers reported that thermoresponsive triblock copolymers in a conventional Ionic liquid (IL) containing a small amount of azobenezene-IL (a photoresponsive molecule) showed reversible physical property changes upon light irradiation. Sol and gel states of the mixture were tunable by light. In other words, the gel state was formed under UV light and the sol state was formed under visible light. Photoisomerization of azobenzene in the IL triggered the macroscopic response. The composite also possessed similar ion conductivity as conventional ILs.

Liquid-state salts at room temperature, ILs are high-potential materials in electrochemistry and materials science because of their unique properties such as high chemical and thermal stabilities, negligible volatility and flammability, and suitable ionic conductivity.

"This is the first application of an ionic liquid functioning as a molecular switch," says Masayoshi Watanabe, Professor, Yokohama National University. "The important point in this system is that photo-responsive azobenzene is added to a solvent. Compared to conventional stimuli-responsive polymers, the solubility of the mixture can be controlled by the structural change of the solvent, not that of the polymer."