Nanocomposite Thin Films Prepared by Layer-by-Layer Technique on Low-Humidity Sensing

In the current work, layer-by-layer self-assembled mica and cationic polyelectrolyte (poly(allylamine hydrochloride)) (PAH) or poly(diallyldimethylammonium chloride) (PDDA) were synthesized on a quartz-crystal microbalance (QCM) for low-humidity sensing applications. The surface characteristics of the thin films were studied for various assembly conditions. The thin films were characterized using QCM and by atomic force microscopy (AFM). The surface roughness and thick-ness of the mica/PDDA thin film both exceeded that of the mica/PAH thin film. The effects of the polycations type, polycations concentration and the number of layers on the low-humidity sensing properties (sensitivity) of the sensors were investigated. Additionally, other low-humidity sensing properties such as sensing linearity, response and recovery times and reproducibility were studied. The mica/PDDA multilayered thin film had the highest sensitivity (0.930–Hz/ppmv at 42.9 ppmv and linearity and a short response time (12 s at 92.2 ppmv