Flexible humidity sensor based on TiO2 nanoparticles-polypyrrole-poly-[3-(methacrylamino)propyl] trimethyl ammonium chloride composite materials

A novel flexible resistive-type humidity sensor was fabricated by the in situ photopolymerization of TiO2 nanoparticles/polypyrrole (TiO2 NPs/PPy) and TiO2 nanoparticles/polypyrrole/poly-[3-(methacrylamino)propyl] trimethyl ammonium chloride (TiO2 NPs/PPy/PMAPTAC) composite thin films on a polyester (PET) substrate. The effect of the TiO2 NPs concentration on the electrical and humidity sensing properties of the TiO2 NPs/PPy composite thin films on a PET substrate was investigated. PMAPTAC was incorporated into the TiO2 NPs/PPy composite thin films to increase the flexibility and sensitivity of the composite films for practical use. Characterizations of the thin films were performed by Fourier transform infrared spectroscopy (FTIR). The flexible humidity sensors based on the TiO2 NPs/PPy/PMAPTAC composite thin films had the best flexibility, highest sensitivity, least hysteresis and greatest linearity. Other sensing properties such as the effects of applied frequency and ambient temperature, response and recovery times, and long-term stability were also studied.