Ferric Salt-Mediated Tough Zwitterionic Hydrogel
Yuming Deng, Jiahui Zhou, Mengjie Si, Gaopeng Wang, Yueman Tang, Zhen-Guo Zhang, Jiayu Hu, Yan Jie Wang, Jintao Yang, Si Yu Zheng
Abstract
Polyzwitterionic gels possess a high density of ionic groups and present great potential in ionotronics. However, zwitterionic chains are easy to be highly hydrated, leading to weak interchain interactions and a poor mechanical performance. Although metal ions like Fe 3+ show great effectiveness in toughening hydrogels, they usually weaken the zwitterionic gel inversely due to the anti-polyelectrolyte effect. Herein, a special co-ion effect of Fe(ClO 4 ) 3 is found, which is adopted to toughen the zwitterionic hydrogel. In contrast to the weak effect of Fe(NO 3 ) 3, FeBr 3, and FeCl 3 salts on gel toughness, Fe(ClO 4 ) 3 can toughen the imidazolium-based polyzwitterion (pVBIPS) effectively. The Fe(ClO 4 ) 3 -treated pVBIPS gel exhibits a high ultimate tensile stress of 1.34 MPa, a Young’s modulus of 1.2 MPa, and tensile work of 2.29 MJ/m 3, surpassing many existing pure zwitterionic hydrogels. It is found that the ClO 4 – ions can effectively bind to the imidazolium moiety of pVBIPS and promote the formation of SO 3 – –Fe 3+ interactions; the trivalent Fe 3+ ions can then bridge multiple sulfonate groups to impart the strength. This work should offer a new strategy for developing tough zwitterionic hydrogels.