Humidity sensing performance of spin coated polyaniline–carboxymethyl cellulose composite at room temperature

Abstract

In the present research, humidity sensing properties of polyaniline–carboxymethyl cellulose (PANI–CMC), a biopolymer composite, have been investigated. PANI and the composite were synthesized separately at room temperature without/with CMC, by simple chemical polymerization method. Improved crystallinity and π-electron delocalization of the composite as compared to PANI were confirmed by X-ray diffraction studies. CMC forming a kind of network on which PANI particles adhered in the composite was confirmed by scanning electron microscopic image. The appearance of band at 3444 cm−1 in the fourier transform infrared spectrum of the composite attributed to hydrogen bonding between dopant ions of PANI and polar molecules of CMC confirmed interaction between PANI and CMC. Humidity sensing response of PANI and the composite at room temperature were tested at a selected frequency of 100 Hz using films of the respective materials deposited on glass substrate by spin coating technique. The study on sensing response of the composite film revealed change in its impedance by about three orders of magnitude, for a change in relative humidity (RH) from 25 to 75 %. The response and recovery time of the composite at 75 % RH were about 10 and 90 s respectively. The maximum humidity hysteresis of the composite was around 5 % at 65 % RH. Humidity sensing stability of the composite for a period of 1 month was also tested.