Synthesis and humidity sensing properties of conducting poly(N-methyl aniline) doped with different acids

Poly(N-methyl aniline) (PNMA), doped with different acids (viz. HCl, HClO4, H3PO4, H3BO3 and acetic acid) was synthesized by a chemical polymerization method using ammonium persulphate as an oxidizing agent. This is a single step polymerization process to synthesize directly the conducting emeraldine salt phase of the polymer. The synthesized polymers were characterized by UV–vis, TGA/SDTA and conductivity measurements. These polymers were then successfully utilized as humidity sensors. The change in resistance with respect to % relative humidity (% RH) was observed, when pressed pellets of the polymers were exposed to a broad range of humidity (20–100% RH). Among the different acids used for the doping purpose of the polymer, the H3PO4-doped polymer showed the best sensing response and was found to be the best candidate for a humidity sensor.