Humidity sensing properties of the composite of electrospun crosslinked polyelectrolyte nanofibers decorated with Ag nanoparticles

Crosslinked and quaternized poly(4-vinylpyridine) (QC-P4VP) nanofibers have been fabricated via electro-spinning followed by reaction with 1-4-dibromobutane. Subsequent decoration of the nanofibers with Ag nanoparticles by in-situ reduction obtained a nanostructured composite humidity sensing material. The nanofibers and the composites were characterized by FT-IR and scanning electron microscopy. It was found that the morphology and humidity sensing properties of the nanofibers could be greatly modified by adding poly(vinyl butyral) into the electrospinning solution. Moreover, the decoration with Ag nanoparticles effectively reduced the impedance of the composite under dry atmosphere, and facilitated the measurement of low humidity. Under optimized conditions, the composite presented high response magnitude to humidity, fast response (t(90%) of 16 s an 26 s for response and recovery, respectively), small hysteresis (similar to 2.8%RH), good sensing repeatability and the capability of detecting very low humidity (similar to 3.6%RH), representing much improvement over QC-P4VP nano fibers alone. The complex impedance spectra of the composites under different humidity levels were measured, and the sensing mechanism was explored. It is proposed that the highly desirable humidity sensing properties of the composite result from its balanced hydrophilicity and the distinct nanostructure.