Conductive, sensitivity, flexibility, anti-freezing and anti-drying silica/carbon nanotubes/sodium ions modified sodium alginate hydrogels for wearable strain sensing applications

The biocompatibility and salient gelling feature of alginate via forming the interpenetrating network structure has received extensive interests for different applications. Traditional alginate hydrogels freeze at low temperature and evaporate easily at room temperature, leading to reduced performance. Consequently, it is crucial to develop methods to prevent alginate hydrogel from freezing at subzero temperature and dehydration at normal temperature to maintain the performance stability. Utilizing polyacrylic acid, sodium alginate, and acrylamide-hydroxyethyl methacrylate copolymers as flexible matrix materials, this study develops a wearable silica (SiO₂)/carbon nanotubes (CNT)/sodium ions (SiO₂/CNT/Na⁺) modified sodium alginate hydrogel strain sensor characterized by high sensitivity, flexibility, and anti-freezing and anti-drying properties. The hydrogel doped with NaCl (50 mg), CNT (10 mg) and M-SiO₂ (200 mg) shows excellent mechanical and electrical properties, the tensile strength is 436 KPa, the break elongation is 426 %, the elastic modulus is 99 KPa, and the toughness is 897 kJ/m³. The modified sodium alginate hydrogel used as strain sensor shows fast response time (∼100 ms), high sensitivity factor and excellent stability. The strain sensor exhibits excellent flexibility, ductility, self-adhesion, anti-freezing and anti-drying properties, significantly enhancing its strain sensing application field.