Highly Sensitive Humidity Sensor Based on Ionic Liquid-Polymer Composites

Polymer composites comprising the ionic liquid (IL) [Bmim]-[FeCl4] and poly(vinylidene fluoride) (PVDF) have been developed for humidity sensing applications. Different IL contents (5, 10, and 20 wt %) were incorporated into the PVDF matrix and the morphological, physical-chemical and electrical properties of the composites evaluated, together with their humidity sensitivity response. Higher IL contents (20 wt %) induce a porous morphology in the composites. Further, IL incorporation leads to the crystallization of PVDF in the electroactive beta phase, which content increases with the incorporation of IL into the polymer. The thermal stability of the composites decreases with increasing IL content. The humidity sensing response of the composites was evaluated with relative humidity variations from 35 to 90%. It is shown that all composites exhibit a linear resistance variation with the relative humidity, the sensitivity to humidity variations increasing linearly with the IL content. The developed materials show a strong potentiality for printable humidity sensors.