Flexible conductive Ag nanowire/cellulose nanofibril hybrid nanopaper for strain and temperature sensing applications

Abstract Flexible and biodegradable sensors are in urgent need with the rapid development of smart wearable devices. In this study, “green” electrically conductive Ag nanowire (AgNW)/cellulose nanofiber (CNF) hybrid nanopaper was fabricated for flexible sensors using the facial solution blending and vacuum filtration technique. The amphiphilic property of cellulose is beneficial for the homogeneous dispersion of AgNW, constructing effective electrically conductive network. First, two different types of strain sensors were designed to study their application in strain sensing. One is the tensile strain sensor where the hybrid nanopaper was sandwiched between two thermoplastic polyurethane (TPU) film through hot compression, and special micro-crack structure was constructed through the pre-strain process to enhance the sensitivity. Interesting, typical pre-strain dependent strain sensing behavior was observed due to different crack density constructed under different pre-strains. As a result, it exhibits an ultralow detection limit as low as 0.2%, good reproducibility under different strains and excellent stability and durability during 500 cycles (1% strain, 0.5 mm/min). The other is the bending strain sensor where the hybrid nanopaper was adhered onto TPU film, showing stable and recoverable linearly sensing behavior towards two different bending modes (tension and compression). Importantly, the bending sensor displays great potential for human motion and physiological signal detection. Furthermore, the hybrid nanopaper also exhibits stable and reproducible negative temperature sensing behavior when it was served as a temperature sensor. This study provides a guideline for fabricating flexible and biodegradable multifunctional sensors.