This paper reports a combination of self-supported, 80-μm-thick polymeric substrates of poly(dimethyl siloxane), poly(methyl methacrylate), poly(vinyl alcohol) (PVA), and poly(N-vinylpyridine) (PVP) and nanocomposites, silver nanoparticle (nAg)/ 0.1% PVP (S1) and nAg/0.1% PVA (S2), for use in optical-transmission-type humidity sensors. Composites are synthesized by a chemical reduction method at optimum conditions, giving particle sizes of 5-10 nm and 10-20 nm, respectively, for nAg/0.1% PVP and nAg/ 0.1% PVA. Composite formation is confirmed using Fourier transform infrared spectroscopy (FTIR). The role of polymers in obtaining a smaller Ag particle size is studied using ultraviolet-visible spectroscopy and transmission electron microscopy. The nanocomposite is coated onto substrates either on a single side or on both sides by dip coating. The humidity response of nAg/0.1% PVP-0.1% PVP-nAg/0.1% PVP (S1-PVP-S1) sensors, measured using the direct optical transmission method, exhibits an enhancement in sensitivity [0.88 AE 0.04 (/% RH)] for the humidity range 6-94% RH and response (6 s) and recovery (8 s) times compared to nAg/0.1% PVP-PVP S1-PVP sensors and a linear response (R 2 ≥ 0.99). An attempt is made to explain the sensing process with the help of FTIR spectra in dry and humid environments.

No abstract

No abstract

Cobalt (Co) nanoparticles (with different loadings, 1 and 2 wt %, of Co) were synthesized in situ in a poly(vinyl alcohol) (PVA) matrix with and without metanitroaniline (m-NA) as a dopant (2.5 wt %). The obtained nanocomposite films were characterized with various physicochemical techniques, including ultraviolet-visible spectrophotometry, X-ray diffraction analysis, scanning electron microscopy, and Fourier transform infrared analysis. To study the effect of the humidity, the nanocomposite solutions were coated on planar glass substrates. The beam of an He-Ne laser was incident normal to the film surface and was subjected to variable relative humidities (RHs; 4-93%); the transmitted intensity was measured on a photovoltaic diode. Variations in the intensity of light caused by the changes in RH within the range 3-93% were recorded. We optimized the response by varying the film thickness by coating the solution layer by layer. We generated the RH (4-100%) by passing wet water vapors. The neat PVA film of similar thickness gave humidity sensing in the range 78-93% RH. The sensors with m-NA-doped Co/PVA gave better sensitivity (6.4 mV/% RH) than the undoped samples (1.78-2.45 mV/% RH), exhibiting a fast response of 3 s (2-93% RH) and a recovery of 10 s (93 to 2% RH). These samples also showed reversible behavior and long-term stability (for nearly a year) with a good sensitivity and a large dynamic range (2-95% RH). An attempt was made to explain the results on the basis of a bulk mechanism.

No abstract