Polyelectrolyte / Inorganic Nanocomposite Humidity Sensitive Materials And Humidity Sensors

Polyelectrolytes have been widely used in the preparation of humidity sensors. However, they could not detect very low humidity due to the extremely high impedance at dry atmosphere. In this paper, the humidity sensitive materials of nanocomposites of polyelectrolytes with carbon nanotubes (MWNTs) and Ag nanoparticles were prepared, and characterized by IR,1H-NMR, GPC and SEM. Humidity sensors based on the nanocompsoites were fabricated by dip-coating. Their humidity sensitive properties were investigated. The nanocomposite sensor showed much decreased impedance at low humidity and could thus detect low humidity with good sensitivity. Furthermore, their humidity sensing mechanisms were explored.The composite of crosslinked and quaternized poly(4-vinyl pyridine) and MWNTs was prepared via solution blending and the in-situ cross-linking and quaternization, and characterized by IR,1H-NMR, GPC and SEM. The resistive-type humidity sensors were fabricated based on the nanocomposites, and their humidity sensitive properties were investigated. The effects of the composition of the composites and the additives on the sensing characteristics were explored. The composite sensor exhibited high sensitivity (impedance changes of two orders of magnitude between 10-90%RH), and could detect very low humidity (down to 1%RH). It was put forward that the introduction of MWNTs greatly changed the conductivity of the composites, and facilitated the detection of low humidity.The composite of crosslinked quaternized poly(4-vinyl pyridine) and silver nanoparticles was prepared by gas-phase reduction and crosslinking and quaternization, and characterized. Bilayer humidity sensors based on the composites were fabricated, and their humidity sensitive properties were studied. The effects of the composition of the composites, the method of reduction of silver salt, the polymer additives and the deposition sequence of the sensitive films on the sensing characteristics were all investigated. The composite sensor could detect very low humidity (down to 1%RH) with high sensitivity (impedance change of three orders of magnitude between 10 and 90%RH), and exhibit fast response (response time of 24 s for adsorption time).