Highly conductive and anti-freezing cellulose hydrogel for flexible sensors

Ionic conducting hydrogels (ICHs) are emerging materials for multi-functional sensors in the fields of healthcare monitoring and flexible electronics. However, there is a long-standing dilemma between ionic conductivity and mechanical properties of the ICHs. In this work, ionic conductive, flexible, transparent, and anti-freezing hydrogels are fabricated by dissolving cotton linter pulp in ZnCl₂/CaCl₂ solution and cross-linking with epichlorohydrin (ECH). The presence of inorganic salt imparts the hydrogel with high ionic conductivity and low-temperature tolerance. While the introduction of ECH as the second network gives the hydrogel with desirable mechanical performance. By tailoring the ECH addition, the tensile strength, compressive strength, elongation at break, and conductivity of the hydrogel could reach 0.82 MPa, 2.80 MPa, 260 %, and 5.48 S m^-1, respectively. The prepared ICHs are fabricated into sensors for detecting full-range human body motions, and they demonstrate fast response and durable sensitivity to both tensile strain and compressive deformation. Moreover, flexible sensors can work at subzero temperatures. This work provides a new idea for the preparation of cellulose-based hydrogels with good ionic conductivity and mechanical properties under extreme conditions.