Multi-physically cross-linked hydrogels simultaneously with MPa level mechanical strengths and high equilibrium water content above 70 %

How to balance the mechanical strengths and water content of synthetic hydrogels, and design and prepare new hydrogel systems simultaneously with mechanical strengths over MPa level and equilibrium water content (EWC) above 70 % remain difficult and challenging tasks. In this work, multi-physically cross-linked poly(acrylamide- co -acrylic acid)/sodium alginate-tamarind gum/ferric ion/tetraborate (P(AM- co -AA x )/SA y -TG y /Fe 3+ /B) hydrogels simultaneously with MPa level mechanical strengths and high EWC above 70 % were successfully synthesized by combining the advantages of SA and TG. TG played a role of increasing hydration of the hydrogels, rendering the high equilibrium water content, while SA was mainly responsible for providing mechanical strengths to the hydrogels via ionic coordination bonds with ferric ions. The optimal P(AM- co -AA 0.175 )/SA 3 -TG 3 /Fe 3+ /B hydrogels exhibited high elastic modulus of ∼5.39 MPa, fracture strength of ∼3.24 MPa, elongation strain at break of 121 %, toughness of ∼2.58 MJ/m 3 , and EWC of ∼71.6 %. The P(AM- co -AA x )/SA y -TG y /Fe 3+ /B hydrogels also exhibited effective energy dissipation mechanisms, excellent self-recovery properties and environmental stabilities in wide temperature range of 0–75 °C and pH range of 3–11. By soaking in 0.9 % NaCl solution, the obtained P(AM- co -AA 0.175 )/SA 3 -TG 3 /Fe 3+ /B/NaCl hydrogels exhibited excellent electrical conductivity and strain sensitivity, which could be used as strain sensors.