Direct Observation of Photo‐Induced Reversible Sol–Gel Transition in Block Copolymer Self‐Assembly Containing an Azobenzene Ionic Liquid

• Published in: Macromolecular rapid communications. 2021-05, Vol.42 (10), p.e2100091-n/a
• Main Authors: Mizuno, Haruna, Hashimoto, Kei, Shigenobu, Keisuke, Kokubo, Hisashi, Ueno, Kazuhide, Watanabe, Masayoshi
• Format: Article
• Language: English
• Subjects: Assembly; atomic force microscope; Atomic force microscopy; Azo compounds; block copolymer; Block copolymers; Conductivity; Diffusion rate; Ion currents; ionic liquid; Ionic liquids; Ions; microphase‐separated structure; photoresponsiveness; Rheological properties; Sol-gel processes; sol–gel transition
• ISSN: 1022-1336; 1521-3927
• DOI: 10.1002/marc.202100091

Using atomic force microscopy, the photo‐induced reversible changes in a block copolymer self‐assembly containing an azobenzene ionic liquid, which undergoes sol–gel transition is directly observed. This is the first report on the sol–gel transition of an ABA‐type block copolymer consisting of upper critical solution temperature (UCST)‐type A blocks in a photoresponsive ionic liquid mixture. The sol–gel transition is accompanied by an order‐to‐disorder structural change, which subsequently induces a change in the ionic conductivity. Surprisingly, the photo‐induced ionic conductivity and rheological changes occurs rapidly (≈30 s) despite the dense (≈80 wt%) polymeric system. The rapid structural change is probably attributable to the fast diffusion of the ionic liquid. Using atomic force microscopy, the photo‐induced reversible changes in a block copolymer self‐assembly containing an azobenzene ionic liquid that undergoes sol–gel transition is observed. The sol–gel transition is accompanied by an order‐to‐disorder structural change, leading to an alteration of the ionic conductivity. Surprisingly, the photo‐induced ionic conductivity and rheological changes are rapid (≈30 s).