Tough and Recoverable Triple-Network Hydrogels Based on Multiple Pairs of Toughing Mechanisms With Excellent Ionic Conductivity as Stable Strain Sensors

The emerging applications of hydrogels in flexible devices require it possess multifunctional properties including stable mechanical and functions under various deformations or external environments. Herein, a multifunctional polyvinyl alcohol/M-alginate/PAM hydrogel with very excellent mechanical properties and sensing functions was fabricated by introducing multiple pairs of toughing mechanisms into triple network (TN). The multiple supramolecular physical networks work as sacrificial networks to toughen the materials when hydrogel deforms. The broken bonds can reform upon unloading endowing the recovery of hydrogels' properties and functions with the assistance of the elastic covalent network. The optimal TN hydrogels are extremely tough (a fracture strength of 512 kPa, a fracture toughness of 3 M J/[m.sup.3]) and recoverable from fatigue damage (~77% toughness recovery after 5 min resting at room temperature). The presence of abundant ionic species endows the tough and recoverable TN hydrogels high ionic conductivity and high sensitivity as strain sensors. Moreover, such TN hydrogels with multi-bond crosslinking in three networks can potentially guarantee stable mechanical and sensor functions under various deformations or external environments compared to the DN candidates. This work provides a simple strategy for fabricating multifunctional hydrogels with high stability to fulfill its flexible devices applications.
INTRODUCTION Ionic conductive hydrogels with polymer networks swollen with electrolyte solutions have been explored for applications in flexible devices, including ionic skin sensors and hydrogel-based electrolytes for energy storage devices [...]