An efficient pure polyimide ammonia sensor

Pyromellitic dianhydride-4,4-oxydianiline (PMDA-ODA), broadly known as Kapton, is investigated for detection and quantification of ammonia (NH3) vapors from ammonia solutions of different molarities. The PMDA-ODA films are made by solution casting on microscope glass slides and cured at 200 °C. Ammonia sensing is performed by measuring the changes in the electric current intensity under ambient conditions of temperature and humidity. The sensor exhibits fast response to ammonia vapors, for aqueous ammonia solutions with molarity as low as 3.5 mM. The adsorption processes of ammonia to the polyimide surface after exposure to ammonia vapors are investigated by FTIR and XPS, revealing that ammonia results in the disruption of imide linkages and the simultaneous creation of amides I and II. Control experiments performed on commercial Kapton adhesive tape show negligible sensitivity of the commercial product to ammonia vapors from different ammonia solution molarities. A device is also presented, demonstrating the real-time detection of ammonia vapors.