oa Application of chemically synthesized polyaniline-polystyrene blend as a carbon dioxide gas sensor

The use of conducting polymers as sensing elements in chemical sensors is attracting attention due to their high sensitivity in change of the electrical and optical properties when exposed to different types of gases or liquids. The ease in synthesis of these polymers and sensitivity at room temperature add to the sensors' advantages. This can be of importance particularly considering CO2 sensors that are used in different applications such as industrial process, fertilizers, and environmental pollution monitoring. Polyaniline (PANI) is one of the most attractive materials among the variety of conducting polymers due to its unique electrical properties, environmental stability, easy fabrication process, and intrinsic redox reaction. In our present work we successfully prepare conducting polymer PANI-polystyrene (PS) blends doped with HCl by an in situ dispersion polymerisation method. Keeping the aniline concentration constant, five blends are prepared using different monomer ratios of PS. The PANI-PS sensors are deposited on glass substrates by the dripping method. The obtained sensors are characterized by SEM for morphology study and electrical properties by IV characteristics and four-probe conductivity study. The electrical conductivity of the composite films ranged from 4.3 x10¯5 - 5.2 x10¯² S·m¯¹. There is an increase in conductivity value with the decrease in PS content. This is justified as there is an increase in the number of more conducting species, i.e., PANI in the composite with a lower PS content. The PANI-PS blend sensors show good sensitivity to CO2 gas. In particular, sensors with higher concentrations (above the percolation threshold) of PANI, displayed excellent sensitivity and fast response. Conducting polymer PANI-PS blends are prepared using five different concentrations of PS (i.e., 1 M, 0.9 M, 0.8 M, 0.7 M and 0.6 M), and the films obtained are characterized using SEM. SEM pictures show nanoparticle formation, and as the PS concentration decreases, particles combine to form clusters or chains. The electrical properties are also observed to increase with a decrease in the PS concentration. The I-V characteristics show some non-ohmic behavior. The CO2-sensing behavior is most responsive for the blends containing 0.7 and 0.6 M of PS.