A Novel Polymer-Salt Complex Based on LiCl Doped SPEEK/Poly(Ether Ether Ketone)-Co-Poly(Ethylene Glycol) for Humidity Sensors

Abstract

A novel humidity sensor based on polymer-salt complexes was developed in this research. Poly(ethylene glycol) (PEG) segmented poly(ether ether ketone) copolymers (PEEK-co-PEG) has been successfully synthesized via condensation polymerization and the structure of this copolymer was confirmed by <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> H NMR. Humidity sensors based on SPEEK/PEEK-co-PEG composites were prepared, and then humidity sensitive characteristics were systematically studied. Comparing with pure SPEEK, PEEK-co-PEG composites can significantly reduce the hysteresis effect of humidity sensors with the proportion of introduced PEG flexible segments increasing. Furthermore, different contents of LiCl were doped into polymer composites and their humidity sensing characteristics were also investigated. The humidity sensor based on SPEEK/PEEK-co-PEG/LiCl with [Li <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ]:[O] ratio of 1:2 had excellent sensitivity, linearity, negligible hysteresis and quick response. Moreover, we proposed that the humidity sensing mechanism of sensors based on polymer-salt complexes is related to the combination of both directional motion of Li <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> on PEG backbone under low RH and ionization (SPEEK polyelectrolyte, Li <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and Cl <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> ) under high RH. On the basis of these humidity sensing characteristics and mechanism, this work provides an approach to integrating polymeric and inorganic complexes as the promising materials for humidity sensors.