Studies on self supported film of PMMA, PMMA-PVA and PMMA-(PVAAg) nano composite for highly linear response over wide range of humidity

A novel combination of Poly methyl methacrylate (PMMA) as a self supported film, coated with poly vinyl alcohol (PVA) and (Ex-situ doped Ag particles in PVA) Ag/PVA nanocomposite with optimized thickness of PMMA is fabricated as a Relative Humidity (RH) sensor. A film of PMMA, when tested for relative humidity sensing using direct optical transmission gives response in the range 80–92% RH. To increase the range of response, PVA, higher hydrophilic, was spin coated on PMMA, layer by layer. It was found that with the 4^th layer of PVA over PMMA, wide sensing range (2–92%RH) is covered, with three distinct regions of sensitivity. To achieve linearity over the complete relative humidity sensing range, Ag particles were added in PVA, and coated on PMMA. This resulted in linear response (1.85 mv/%RH), over a wide range of RH (2–95%). The concentration of Ag, having 5∶2 by volume of PVA and Ag gives good linearity (R² > 0.99) with response and recovery time of 15 and 18 sec respectively with 4% hysteresis and good repeatability.(tested over 7cycles.