Bilayer thin film humidity sensors based on sodium polystyrenesulfonate and substituted polyacetylenes

Bilayer thin film humidity sensors based on sodium polystyrenesulfonate (NaPSS) and substituted polyacetylenes (poly(propiolic acid) (PPA), poly(p-diethynylbenzene) (PDEB) and poly(propiolic acid-co-propargyl alcohol) (PA-co-OHP)) have been prepared, and their humidity sensitive properties have been investigated over a wide range of relative humidity (10–95% RH). The bilayer sensors exhibit different humidity response depending on the sensing properties of the outer layers of polyacetylenes. Of all the bilayer sensors, the sensor based on NaPSS and PA-co-OHP doped with FeCl3 shows the best sensing properties. Its impedance changes linearly with relative humidity for approximately four orders of magnitude in a wide range of 10–85% RH, showing high sensitivity and quick response in both adsorption and desorption processes. In addition, its capacitance shows a highly sensitive and quick response to humidity variation.