Samarium hydrate double-network chitosan composite hydrogels with anti-freezing, water retention and fatigue resistance for mechanical strain sensors

Hydrogels are important materials for mechanical sensors of artificial intelligence, and their good electrical conductivity and mechanical properties have broad application space in the field of multifunctional materials. However, it is still a challenge to prepare hydrogels with excellent conductivity and sensing, anti-freezing and water retention, resilience and fatigue resistance. Herein, chitosan/poly(acrylic acid-acrylamide‑sodium p-styrenesulfonate)/glycerol/samarium hydrate (C/P/G/S) double-network (DN) hydrogels were prepared by Interpenetrating Polymer Networks (IPNs) of chitosan (CS) with acrylic acid (AA), acrylamide (AM), sodium p-styrenesulfonate (SSS), glycerol (GL) and samarium hydrate (SH) under ultraviolet (UV) light. The C/P/G/S DN hydrogels have satisfactory mechanical properties, conductivity, mechanical strain sensing performances, water retention and frost resistance capacities. Specially, the compressive stress of hydrogels at 80% compressive strain is up to 1.7 MPa. It also shows preeminent fatigue resistance and resilience in continuous cyclic stretching and cyclic compression (5 and 100 times). The conductivity of the hydrogels can reach 1.9 S/m when the SH is 1.8 g. Meanwhile, mechanical strain sensing tests of the hydrogels at room temperature and low temperature were also performed simultaneously. The hydrogels have stable mechanical strain sensing properties and good electrical conductivity even at −20 °C. More importantly, when C/P/G/S DN hydrogels were placed at room temperature and ventilated for 30 days, the water loss rate of hydrogels was only 13.9%.