A robust poly (vinyl alcohol) hydrogel prepared by amphiphilic macromolecules for flexible sensors

Hydrogels prepared from polyvinyl alcohol by freeze-thaw method have high mechanical strength and poor toughness due to high crystallinity, which severely limits the application of polyvinyl alcohol hydrogels. Usually, the toughness of hydrogels is often improved by sacrificing their mechanical strength. However, only a few hydrogels can improve their toughness by relying on only one single component to keep the mechanical strength unchanged. More similar hydrogels need to be developed. Herein, PVA/O20AC/EG ion-conducting hydrogels were prepared by dissolving poly (vinyl alcohol) (PVA), poly (oxyethylene 20 oleyl ether acrylate) (O20AC), and sodium chloride (NaCl) in ethylene glycol (EG)/water binary solvent. The longer hydrophobic chains of O20AC can form hydrophobic association micelles that act through hydrogen bonding in the crystalline microdomains between the polyvinyl alcohol chains. The dynamic micelles can effectively achieve energy dissipation in the hydrogel, allowing the hydrogel to improve its toughness without sacrificing mechanical strength. At the same time, the hydrogels have excellent anti-swelling properties. Additionally, a significant number of hydrogen bonds are formed in this system, enhancing the mechanical properties of the hydrogel, with a tensile strength of 1155.94 kPa and elongation at break of 722.49%, and its mechanical properties remain relatively unchanged after three cycles of processing. It can be processed into various desired shapes. The binary solvent strategy provides the hydrogel with good anti-freezing (−33.7 °C) and water retention (the weight of the PVA/O20AC/EG hydrogel remained 89.3% of the original after 7 days under conditions of 20 °C and 50 RH%). Furthermore, the presence of Na+ and Cl− enables the hydrogel to exhibit highly sensitive conductivity changes with deformation (GF = 4.73). Therefore, the construction of poly (vinyl alcohol)-based hydrogels by amphiphilic O20AC, forming hydrophobic micelles and a large number of hydrogen bonds, provides a new idea for the development of multifunctional hydrogel sensing materials.