An Ionically Crosslinked Hyperelastic Hydrogel With Extreme Environmental Tolerance and Self-Strengthening Capability.
Hyperelastic hydrogels have broad application prospects in coatings and flexible sensors. However, these flexible polymer networks often suffer from severe water loss and performance degradation under long-term use and extreme environmental conditions. Here, ionic interactions were used to fabricate a superelastic hydrogel with long-term stability. By modulating the calcium chloride (CaCl2)-chitosan (CTS) ionic cross-linking network, the formation of a "pearl necklace" structure in methacryloyloxyethyltrimethylammonium chloride (DMC) was promoted. Grazing incidence small-angle x-ray scattering (GISAXS) and atomic force microscopy (AFM) confirmed the formation of this structure. Acrylamide provides anchoring sites for the chloride salts, which enhance the ion adhesion and hygroscopic-moisture balance of the hydrogel network. This mechanophysical interaction confers excellent stability to the hydrogel through self-strengthening. The non-oriented hyperelastic network allows the hydrogel to recover quickly after stretching to an areal strain greater than 12 000% and to remain flexible at temperature extremes from -50°C to 120°C. Differential Scanning Calorimetry (DSC) shows that more than 90% of the water in the hydrogel does not undergo a phase transition during this process. Our work provides new insights into the fabrication of flexible hydrogels that can be stably used under extreme conditions.