Metallopolymer Organohydrogels with Photo‐Controlled Coordination Crosslinks Work Properly Below 0 °C

• Published in: Advanced materials (Weinheim) 2020-04, Vol.32 (14), p.e1908324-n/a
• Main Authors: Liu, Jiahui, Xie, Chaoming, Kretzschmann, Annika, Koynov, Kaloian, Butt, Hans‐Jürgen, Wu, Si
• Format: Article
• Language: English
• Subjects: anti‐freezing; Coordination; Crosslinking; crosslinks; Freezing; Gels; Glycerol-Water; High temperature; Light irradiation; Materials science; Mechanical properties; metallopolymers; photoresponsive materials; Polymers; Remote control; Room temperature; Sol-gel processes
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201908324

Controlling the structures and functions of gels is important for both fundamental research and technological applications. Introducing photoresponsive units into gels enables remote control of their properties with light. However, existing gels show photoresponsiveness only at room temperature or elevated temperatures. The development of photoresponsive gels that work below 0 °C can expand their usage in cold environments. Here, photoresponsive metallopolymer organohydrogels that function even at −20 °C are reported. The organohydrogels are prepared using photoresponsive Ru–thioether coordination bonds as reversible crosslinks to form polymer networks. A water/glycerol mixture is used as an anti‐freezing solvent. At −20 °C, the Ru–thioether coordination bonds are dissociated under light irradiation and reformed reversibly in the dark, which result in alternating crosslinking densities in the polymer networks. This process enables inducing reversible gel‐to‐sol transitions, healing damaged gels, controlling the mechanical properties and volumes of the gels, and rewriting microstructures on the gels below 0 °C. Metallopolymer organohydrogels, which function even at −20 °C, are prepared using Ru–thioether coordination bonds as photoresponsive crosslinks. At −20 °C, the Ru–thioether bonds are dissociated under light irradiation and re‐form reversibly in the dark. This process enables reversible gel‐to‐sol transitions, the healing of damaged gels, control over the mechanical properties of the gels, and rewriting of microstructures on the gels below 0 °C to be induced.