Polyacrylic acid coated carbon nanotube-paper composites for humidity and moisture sensing

Various carbon nanotube-paper composites (CPCs) have been studied to measure relative humidity. This study presents a tissue paper-based CPC coated with polyacrylic acid (PAA) for sensing humidity and surface moisture. When the CPC is exposed to humidity, its electrical resistance changes due to its electrostatic interaction with water molecules and the swelling of cellulose fibers and PAA. The enhancement of sensor response due to the swelling of CPCs coated with PAA, acid, and Nafion is studied in terms of resistance change. The hysteresis of a CPC sensor response to a cyclic humidity change is characterized for both the CPC region and the interfacial region between carbon nanotubes and a silver electrode. Based on the empirical relationship, the humidity sensor is applied for the measurement of surface moisture in a simulated sweat model. The CPC surface moisture sensor provides a low-cost, highly sensitive, light-weight flexible platform potentially beneficial for health, food, agricultural and environmental applications.