Wide-range linear viscoelastic hydrogels with high mechanical properties and their applications in quantifiable stress-strain sensors

Wide-range linear viscoelastic materials with high mechanical properties have not been reported yet, despite their bright prospect in diverse applications. Herein, we fabricate a class of physical hydrogels manifesting linear stress-strain relationship up to a strain of 1700%, high tensile stress up to 12.0 MPa and fracture toughness up to 82.1 MJ/m(3), yet the materials are quite soft with Young's modulus from 0.2 to 1.1 MPa. Such physical hydrogels are formed by designing a homogeneous network with multiple coordination interactions of different bonding strength. Under small deformation, the homogeneous network enables affine deformation featured by entropic elasticity with negligible energy dissipation. Further increasing the deformation, the elongated network chains progressively break the weak to strong coordination interactions, which not only leads to a linear increase in stress, but also generates constant growth in energy dissipation. Moreover, the hydrogels show linear relative resistance change-strain-stress behavior, and thus can be used as quantifiable stress-strain sensors to simultaneously monitor deformation and force of soft robotics, wearable devices, flexible electronics, rehabilitation and sport equipments.