Study On Humidity Sensitive Materials And Sensors For Polymer Nano - Composite Gas

In recent years, polymers and its composites based sensitive materials have been widely employed in the fabrication of gas and humidity sensors, due to their prominent advantages such as simple preparation, facile modification of the sensitive properties, detection of gases/humidity at room temperature, etc. In this thesis, humidity and gas sensitive materials of polyelectrolyte/polyaniline (PANI), polyelectrolyte/reduced graphene oxide (RGO) and nanostructured PANI were prepared, and employed to construct humidity and gas sensors. The composition, structure and morphology of the sensitive materials were characterized by FT-IR, UV-vis, SEM, TEM, AFM, etc. The sensitive properties towards humidity and ammonia of the sensors had been investigated at room temperature. The effects of the composition, deposition sequence of the sensitive layers and preparation techniques of the sensors on their humidity and gas sensitive characteristics were examined, and the sensing mechanisms were explored.Two kinds of bilayer-structured composite humidity sensors were fabricated by depositing the thin films of quaternized and crosslinked poly(4-vinylpyridine) (QC-P4VP) and PANI, or QC-P4VP and RGO onto interdigitated gold electrode in sequence. It was found that introduction of PANI or RGO significantly lowered the impedance of the composite sensors at low humidity levels. The sensor based on QC-P4VP/PANI revealed impedance change of three orders of magnitude from relative humidity (RH) of 1% to 98%, suggesting its capability of detecting full-range humidity with high sensitivity. While the sensor based on QC-P4VP/RGO was featured with the ability to detect ultra-low humidity (0.18%RH) with high sensitivity. A sensing mechanism had been proposed by considering the special configuration of the composite sensor, and the contributions of both sensitive layers to the overall humidity response of the composite sensor.Water-dispersible nanostructured PANI doped with hydrochloric acid, p-toluenesulfonic acid, camphorsulfonic acid, phytic acid or poly(styrene sulfonic acid) (PSSA) was prepared and employed to construct gas sensors. The sensor based on PANI doped with PSSA displayed the best sensitive properties to ammonia. Preparation techniques also had great effect on the ammonia sensitive properties of PANI-PSSA sensor. The optimal molar ratio of PSSA/aniline/ammonium persulfate in polymerization process was 1:1:0.7. Through dip-coating interdigitated gold electrode in 20 mg/mL aqueous dispersion, ammonia sensor featured with high sensitivity (detection limit was 200ppb), good reversiblity and selectivity at room temperature could be constructed.