Construction of strong and tough carboxymethyl cellulose-based oriented hydrogels by phase separation.

Anisotropic hydrogels have attracted extensive attention because they are similar to natural hydrogel-like materials and exhibit superiority and new functions that isotropic hydrogels cannot. Here, we fabricated strong and tough carboxymethyl cellulose-based conductive hydrogels with oriented hierarchical structures through pre-stretching, solvent displacement induced phase separation, and subsequent ionic crosslinking immobilization. Solvent displacement made the pre-stretched carboxymethyl cellulose-based polymer network more dense and linear, while the toughness of the hydrogel was further improved under the effect of phase separation. Strong and tough hydrogels were prepared by combining pre-stretching and phase separation; the variation range (tensile strength of 2.24-6.19 MPa and toughness of 19.41-22.92 MJ/m) can be adjusted by the stretching ratio. Compared with traditional carboxymethyl cellulose-based hydrogels, the tensile strength and toughness were increased by 49 times and 15 times, respectively. In addition, the hydrogels had good underwater stability, ion cross-linking made the hydrogels have good conductivity, and the directional stratification structure gave the hydrogels conductive anisotropy. These characteristics give hydrogel sensors broad application prospects in flexible wearable devices, anisotropic sensors, and intelligent underwater devices.