Humidity sensing; using polyaniline/Mn3O4 composite doped with organic/inorganic acids

The polyaniline/Mn3O4 composite doped with perchloric acid, sulphuric acid, ortho-phosphoric acid, acetic acid and acrylic acid have been characterized as sensing materials to determine relative humidity in the range of 20–90%. Each composite sample has been used in the form of pellet. Relative humidity measurement has been related with the change in resistance of doped composite samples. Each acid doped polyaniline/Mn3O4 showed an increase in resistance as relative humidity increases, however the sensitivity is found to dependent on the type of dopant anions. The response of each composite is found to be almost linear with the humidity but the composites doped with organic acids have found to be more sensitive than those with inorganic dopants. However polyaniline samples doped with these acids under similar conditions showed reverse behaviour that is the resistance decreases with the increase in relative humidity but with lower sensitivity. The anomalous behaviour of the acid doped composite samples may be due to lowering of p-type nature of the polymer chains in the composites with an increase of humidity. Due to the linear increase in resistance of composites doped with organic acids can act as humidity sensor.