Thermally Reversible Ion Gels with Photohealing Properties Based on Triblock Copolymer Self-Assembly

High Resolution Image Download MS PowerPoint Slide We describe a functional soft material that can spontaneously repair damage by straightforward application of light illumination. The composite material is composed of a common ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate ([C 4 mim]PF 6 ), and a well-defined ABA triblock copolymer consisting of the IL-compatible poly(ethylene oxide) (PEO) middle block with thermo- and photosensitive random copolymers combining N -isopropylacrylamide (NIPAm) and 4-phenylazophenyl methacrylate (AzoMA) including azobenzene chromophore as terminal A blocks. The composite shows a sol–gel transition under UV light (366 nm, 8 mW cm –2 ) irradiation at 47 °C, whereas that observed under visible light (437 nm, 4 mW cm –2 ) is 55 °C, due to the difference in photochromic states of the azobenzene unit. The ABA triblock copolymer undergoes a reversible gel–sol–gel transition cycle at the bistable temperature (53 °C), with a reversible association/fragmentation of the polymer network resulting from the photoinduced self-assembly of the ABA triblock copolymer in [C 4 mim]PF 6 . A damaged ABA ion gel shows a remarkable photohealing ability based on drastic changes in the fluidity of the polymer–IL composite triggered by light illumination. The damaged part is successfully repaired by shining UV light resulting in solubilization to fill the crack, followed by gelation to fix the crack triggered by visible light illumination. Tensile tests confirmed the excellent recovery efficiency of the resultant photohealed ABA ion gel, which was as high as 81% fracture energy relative to the original sample. The flexible, self-supported ABA ion gel is designed for various applications to exhibit not only photohealing ability to improve operating lifetime of the material but also specific functionalities imparted by the IL, such as high ion conductivity, thermal stability, and (electro)chemical stability.