Polymer nanocomposite based humidity sensor

Abstract

Controlling and monitoring humidity levels are paramount in industrial and manufacturing processes such as food packaging, electronic and optical device fabrications, quality control in textile industry, and oil & gas industry. It is essential to measure the moisture content to control or remove the unwanted moisture subsequently. Therefore, accurate and reliable monitoring of the water content and its composition is very important. Different types of humidity sensing techniques have been used for humidity sensing applications which include chilled mirror hygrometer, capacitive, resistive and Quartz microbalance (QCM). Capacitive and resistive type sensors are easy to make and can be fabricated using low-cost materials. The operating principles of capacitive humidity sensors are based on the change in dielectric constant of the sensing film with a change in a humidity level. Similarly, in resistive type humidity sensors the conductivity of the sensing film changes with alteration in humidity levels. Despite their significant characteristics, polymer-based capacitive and resistive humidity sensors have critical limitations, including low sensitivity, nonlinear response at higher humidity levels, high hysteresis loss and the known polymeric sensing film deformation with time. Therefore, the electrical response of polymer-based humidity sensors is not stable. This increases the need for developing a humidity sensor that shows higher thermal stability, linear response at higher humidity levels, shorter response and recovery time, and low hysteresis loss. In this dissertation, polymer-based humidity sensors are investigated for humidity sensing applications. We develop both capacitive and impedance-based humidity sensors and investigate different polymeric nanocomposites films to improve sensors' characteristics. We investigated the incorporation of hydrophilic and piezoelectric nanoparticles within the polymer matrix to improve the morphology and sensing characteristics such as linearity, response and recovery time and hysteresis loss. Results show that the optimised capacitive sensor shows 2.5% maximum hysteresis loss and response and recovery achieved is 40 sec and 25 sec. Also, we used the polymer blending technique to improve the resistive humidity sensor's sensitivity. The impedance response of the sensing film showed that as the concentration of SPEEK increases the sensitivity of the sensing film increases at lower humidity levels (10 %RH to 90 %RH). In addition, we have investigated the effect of conducting polymer and inorganic nanoparticle hybridization for impedance humidity sensing applications. Result shows that sensor hysteresis is around 4.5% with response and recovery time optimized to 30 sec and 35 sec, respectively. Moreover, we prepared the graphene quantum dots through graphite waste and evaluated potential applications for resistive humidity measurement. we achieved maximum hysteresis is around 2.2% at 30 %RH. The above results are deemed having valuable scientific merit in the area of humidity sensing and related areas, and hence expected to impact the sensing industry at large.