Strong, tough, conductive cellulose/PAA gel enabled by in-situ esterification and noncovalent crosslinking for adaptive sensor

Abstract

Cellulose-based gels with flexibility, structural tunability and biocompatibility are applied in advanced fields. However, most of cellulose-based gels are still limited in insufficient mechanical strength and tedious preparation process. We have developed a tough and flexible cellulose/polyacrylic acid (cellulose/PAA) gel through a simple process involving in-situ esterification and photopolymerization within a polymerizable deep eutectic solvent (PDES: ZnCl₂/acrylic acid/H₂O). In this process, cellulose undergoes highly efficient dissolution (>7 ​wt% within 30 ​min) while simultaneously capturing acrylic acid (AA) in PDES by in situ esterification, endowing cellulose/PAA gel with a double-network structure through synergistic ester covalent crosslinking and dense hydrogen bond interaction. The hydrogen donor-acceptor capability of PDES, coupled with ester bond formation, induce a delocalization effect in AA, enabling spontaneous radical generation for photopolymerization without requiring external initiator and crosslinker. The resulting cellulose/PAA gel exhibit exceptional tensile strength (12.6 ​MPa) and toughness (4.24 ​MJ/m³), which is about 17.67 times than that of the pure cellulose gel. Furthermore, the synergistic presence of carboxyl groups and Zn²⁺ ions within cellulose/PAA gel impart high electric conductivity (4.7 ​mS/cm), enabling real-time detection of diverse physiological motions. The simple and effective method we present provides a pathway for the preparation of high-performance conductive gel from renewable biopolymer for flexible sensors applications.