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

This paper reports a combination of self-supported, 80-mu m-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. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47035.