Photocurable temperature activated humidity hybrid sensing materials for multifunctional coatings

Photocurable thermochromic and humidity responsive materials based on polyurethane acrylated (PUA) and bis(1-butyl-3-methylimidazolium) tetrachloronickelate ([Bmim]2[NiCl4]) ionic liquid (IL) have been prepared with varying IL content up to 40 wt% within the polymer matrix. The influence of IL content on the photopolymerization process, morphology, Young modulus and electrical conductivity of the materials was evaluated. All materials present a total polymer conversion of at least 88%. The presence of the IL influences the morphology of PUA, being observed a porous network structure upon IL incorporation into the PUA matrix. All samples show a Tg around room temperature, which is independent of the IL content and a Young modulus that decreases with the IL content. All composites exhibit humidity dependent thermochromism from colourless to blue. Further, the influence of the relative humidity in the colour change was accessed for the sample containing 20 wt% [Bmim]2[NiCl4], being observed that the colour variation is thermally activated and humidity governed, being 55% the minimum value of the relative humidity for colour change to occur.FCT (Fundação para a Ciência e Tecnologia) for financial support under the framework of Strategic Funding grants UID/FIS/04650/2020, UID/EEA/04436/2020 and UID/QUI/0686/2020 and project no. PTDC/FIS-MAC/28157/2017. The authors thank funding by the Spanish State Research Agency (AEI) and the European Regional Development Fund (ERFD) through the project PID2019-106099RB-C43/AEI/10.13039/501100011033 and under the Operational Programme “Competitiveness and Internationalization” - Research and Development (R&D) and Innovation to SMEs – R&D Individuals Projects, grant agreement number 038397. M. S. also acknowledge the National Research grant “Juan de la Cierva” FJCI-2017-31761. Financial support from the Basque Government Industry and Education Departments under the ELKARTEK, HAZITEK and PIBA programs is also acknowledged. LCF and DCM also thank the grant SFRH/BD/145345/2019 and SFRH/BPD/121526/2016, respectively. Technical and human support provided by SGIker (UPV/EHU, MICINN, GV/EJ, EGEF and ESF) is gratefully acknowledge