Multiple hydrogen bonds enable high strength and anti-swelling cellulose-based ionic conductive hydrogels for flexible sensors

Although ionic conductive hydrogels (ICHs) have been widely utilized to fabricate excellent flexible sensors, traditional ICHs are generally easy to swell, resulting in the inevitable failure of flexible sensors. Herein, a facile and effective strategy is employed to impart ICHs with excellent mechanical properties, satisfying anti-swelling property, favorable anti-freezing property, and high ion-conductivity simultaneously, that is to construct multiple hydrogen bonds (H-bonds) through directly dissolving cellulose in salt solutions, avoiding the tedious preparation process of traditional ICHs as well. Notably, the cellulose is directly dissolved in the solution containing zinc ions (Zn2+) and aluminum ions (Al3+), and then acrylic acid (AA) and acrylamide (AAm) are copolymerized in it. Multiple H-bonds are formed among the abundant - OH groups, -NH2 groups, and - COOH groups belonging to cellulose, AAm, and AA, respectively. As a result, the improved anti-swelling ability (88.03 %) and compressive performance (24.11 MPa) of the resultant Ion-C-P(AA-co-AAm) hydrogel are achieved. Besides, excellent conductivity (48.39 mS/cm) and frost resistance are provided by generous Zn2+ and Al3+. Moreover, Ion-C-P(AA-co-AAm) hydrogel exhibits favorable sensitivity in monitoring human activities and can output stable electrical signals in a low-temperature environment, showing a great potential application for flexible sensors.