Layer-by-layer anchoring of copolymer of methyl methacrylate and [3-(methacrylamino)propyl] trimethyl ammonium chloride to gold surface on flexible substrate for sensing humidity

Novel flexible impedance-type humidity sensors were fabricated by anchoring humidity-sensitive polyelectrolyte to the gold electrode on plastic substrates using a peptide chemical protocol. A pair of comb-like Au electrodes on a polyester (PET) substrate was pretreated with 3-mercaptopropionic acid (MPA) and further reacted with a copolymer of methyl methacrylate (MMA) and [3-(methacrylamino)propyl] trimethyl ammonium chloride (MAPTAC) using N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC) as peptide coupling reagent. The prepared humidity-sensing film was characterized by electrochemical impedance spectroscopy (EIS) and Fourier transform infrared spectroscopy (FTIR). The amount of added EDC influenced the stability of the anchored poly-MMA-MAPTAC onto the MPA/Au surface in water.The flexible impedance-type humidity sensor made of poly-MMA-MAPTAC that was anchored onto the MPA/Au surface using 200 mM added EDC had a wide working range of humidities, a high sensitivity, an acceptable linearity, a small hysteresis, high flexibility, a short response time, a weak dependence on temperature and good long-term stability. The dependence of the impedance on frequency was greater at lower RH.