Wireless wearable multifunctional sensor based on carboxylated cellulose nanofibers/silver nanowires for ultra-sensitive, fast humidity response and body temperature monitoring

Humidity and temperature sensors are considered as hotspots for the next generation of wearable multifunctional electronics. However, it is still a notable challenge to realize multifunctional sensors with high-performance humidity response, excellent mechanical properties, and accurate temperature monitoring capability. In this work, a hydrogen-bond cross-linked hybrid network was constructed between carboxystyrene-butadiene rubber (XSBR) and hydrophilic carboxylated cellulose nanofibers (CNF) noncovalently modified silver nanowires (AgNWs). The abundant hydroxyl and carboxyl groups of CNF chains have excellent affinity for water, and the apparent distinction in thermal expansion coefficient between the XSBR matrix and AgNWs has an outstanding response to instantaneous temperature change. The material exhibits a humidity sensitivity up to 22.15 and a humidity response time as low as 390 ms, yet with excellent tensile strength of 4.10 MPa and stretchability of 342 %. In addition, the as-prepared multifunctional sensor possesses an excellent thermal response of 0.5625 %/°C. Based on the superior performance, the sensor has been applied to recognize and monitor different respiration rates in the human body, locate moist objects in close proximity, and also accurately record and respond to the changes in skin surface temperature.