Combination of polymeric substrates and metal–polymer nanocomposites for optical humidity sensors

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 ± 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. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136 , 47035.