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

Various carbon nanotube-paper composites (CPC) have been studied to measure relative humidity. This study presents a tissue paper-based CPC coated with polyacrylic acid (PAA) for sensing humidity and moisture. When a CPC is exposed to humidity, the electrical resistance is changed by the electrostatic interaction with water molecules and by the swelling effect of cellulose fibers. The enhanced swelling effects on CPC coated with PAA, acid and Nafion are studied in terms of resistance change. The hysteresis of a CPC sensor in a cyclic humidity change is characterized for both the CPC region and the interfacial region between carbon nanotubes and a silver electrode. Based on an empirical equation, the humidity sensor is attempted to measure moisture on a simulated sweat model. The CPC sweat sensor provides low-cost, highly sensitive, light-weight flexible platform potentially beneficial for sweat monitoring.