Polyaniline thin film gas sensors

We have investigated the use of spin-coated thin films of polyaniline (PANI) doped with an organic acid in conductometric gas sensors operating at room temperature. Its advantages are discussed with respect to other organic conductors and inorganic metal oxides operating at much higher temperature. PAni has been also added to matrices of various insulating non conductive polymer such as polystyrene and polyammide (Nylon6). The added polymers have been used to obtain different responses to different gaseous species and vapours. They also greatly improve processability by spin-coating and wettability on glass substrates and on metal and ITO electrodes. Good adhesion and uniformity have been obtained. In addition to sensitivity to alcohol and water vapours, we report a very strong increase in the resistivity as response, in seconds to minutes time scale, to gas pollutants such as ammonia and nitrogen oxides in the ppm concentration range or lower. This variation appears to be reversible even at room temperature and can be significantly sped up by heating the sample to 40-50 °C.