Tackling Humidity with Designer Ionic Liquid-Based Gas Sensing Soft Materials.

Relative humidity (RH) is simultaneously a desired sensing target and an undesired contaminant for gas and volatile organic compound (VOC) sensing systems. Existing gas and VOC sensors are sensitive to water and thus strategies to control humidity interference before or after the sensing materials are required. An unmet challenge is the creation of gas sensitive materials where the response to humidity is controlled by the material itself. Here, humidity effects are controlled through the design of gelatin formulations in ionic liquids without (ionomaterials) and with liquid crystal (hybrid materials) as electrical and optical sensors, respectively. In this design, the anions [DCA]- and [Cl]- of room temperature ionic liquids from the 1-butyl-3-methylimidazolium family tailor the response to humidity and subsequently the possibility to sense VOCs in dry and humid conditions. Due to the combined effect of the materials formulations and sensing mechanisms, changing the anion from [DCA]- to the much more hygroscopic [Cl]- , leads to stronger electrical responses and much weaker optical responses to humidity. Thus, we obtain either humidity sensors or humidity-tolerant VOC sensors that do not require sample pre-conditioning or signal processing for correction of humidity impact. With the widespread of 3 and 4D-printing and intelligent devices, the possibility to monitor and tune humidity in sustainable bio-based materials offers excellent opportunities in e-nose sensing arrays and wearable devices compatible with operation at room conditions. This article is protected by copyright. All rights reserved.