A novel highly sensitive humidity sensor derived from sulfonated poly(ether ether ketone) with metal salts-ion substitution

Abstract

Sulfonated poly (ether ether ketone) (SPEEK) was successfully synthesized by post-sulfonation. A novel humidity sensor was made of SPEEK and SPEEK with metal salts-ion (Ca2+, Cu2+) substitution and fabricated by spin coating on a ceramic substrate. The effect of different counter-ion forms on the electrical and humidity-sensing properties of SPEEK membranes was investigated. The chemical structure of SPEEK was confirmed using its 1H NMR spectrum. The polymeric materials were detailed characterized, including FTIR spectra, thermogravimetric analysis (TGA), and contact angle measurement. These results indicated there were significant differences in their chemical structure, thermal and transport properties for SPEEK when exchanged with the different metal salts-ions. In addition, comparing with SPEEK, the humidity-sensing properties of SPEEK-Ca2+ exhibited high sensitivity from 33% RH to 97% RH, satisfactory linearity, small hysteresis during the sorption processes, short response/recovery time, excellent repeatability and complex impedance in low and high relative humidity. This means that the water molecules in the SPEEK-Ca2+ membranes interact with the Ca2+ cations more strongly when exchanged with the different metal salts-ions, and in result the diffusion of the water molecules is reduced. These results inditated this novel polymer electrolyte with metal salts-ion would be a promising candidate for humidity sensor applications.