Abstract
In this work; resistive moisture sensors were obtained by dip coating sulfonated polycarbonate (SPC) onto silver interdigitated electrodes. Commercial polycarbonate was sulfonated with acetyl sulphate at two different sulfonation degrees corresponding to 9.0 and 18.0 mole %. Impedance spectroscopy was used to investigate the humidity sensing properties at controlled relative humidity (RH%) environments generated from standard saline solutions in the range of 11–90 RH%. For the highest sulfonated sample; in the RH% range investigated (11 to 90%); the sensor impedance changed from 4.7 MΩ to 18 kΩ. Humidity sensors made from sulfonated polycarbonate showed exponential decay behavior of the impedance at constant frequency with the environmental relative humidity. Sample 9SPC presented dielectric relaxation response for environmental humidity between 58 and 90 RH% while sample 18SPC presented dielectric relaxation response for the entire measured range between 11 and 90 RH%. Sulfonated polycarbonate could be a promising material for the fabrication of simple and cheap humidity-sensing sensors for the assessment of relative humidity of the surrounding environment, as suggested by experimental results.
Highlights
Humidity detection and monitoring is important in fields such as weather, agriculture, industrial, household electric appliances, medical field and research [1,2,3]
Resistive humidity sensors measure the change in the electrical resistance of a sensor due to proton conduction and the sensor resistance is inversely proportional to relative humidity
Organic materials that are insoluble in water such as cellulose acetate butyrate and polyimide have been used as humidity sensors [12]
Summary
Humidity detection and monitoring is important in fields such as weather, agriculture, industrial, household electric appliances, medical field and research [1,2,3]. Protons are obtained by electrolysis of the water bound to the ionic hygroscopic groups which increases with relative humidity. Most resistive humidity sensors have LiCl as the sensing element [6], and the operating principle is based on ionic conductivity [7]. This device is very sensitive to temperature; several efforts have been made to improve this device by using the conductance technique [6]. For most of the relative humidity range, these materials do not contribute to enhance sensing properties since they just add an electronic conducting channel in parallel, i.e., a resistor that is parallel to the real proton conducting channel
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