Ionic-liquid-based printable materials for thermochromic and thermoresistive applications

Smart materials exhibiting thermochromic and themoresistive properties based on the electroactive polymer poly(vinylidene fluoride) (PVDF) and the ionic liquid (IL) bis(1-butyl-3-methylimidazolium) tetrachloronickelate ([Bmim](2)[NiCl4]) have been developed with different contents of [Bmim](2)[NiCl4] (10, 20, and 40 wt %) within the polymer matrix. The morphology of the composites is studied, and the thermochromic and thermoresistive properties are evaluated. Independently of the IL content, the PVDF/[Bmim](2)[NiCl4] composites present a porous morphology and thermochromic response, revealed by the color change of the composites from transparent to dark blue, attributed to the tetrahedral complex NiCl42- formed after a dehydration process. Further, the electrical conductivity increases with increasing IL content and decreases with increasing temperature. It is also shown that the incorporation of the IL into the PVDF matrix leads to an increase in the electroactive beta phase and a decrease in the degree of crystallinity and thermal stability with increasing [Bmim](2)[NiCl4] content. The printability and applicability of the developed materials as sensors are also demonstrated.The authors acknowledge the FCT-Fundacao para a Ciencia e Tecnologia-for financial support under the framework of the Strategic Funding UID/FIS/04650/2013, the Associated Laboratory Research Unit for Green Chemistry, Technologies and Clean Processes, LAQV (financed by national funds from FCT/MEC, UID/QUI/50006/2013, and ERDF under the PT2020, POCI-01-0145-FEDER-007265), and project PTDC/EEI-SII/5582/2014 by FEDER funds through the COMPETE 2020-Programa Operational Competitividade e Internacionalizacao (POCI) with the reference project POCI-01-0145-FEDER-006941. Funds provided by FCT in the framework of EuroNanoMed 2016 call, Project LungChek ENMed/0049/2016, are also gratefully acknowledged. D.M.C., N.P., and J.M.S.S.E. also acknowledge the grant/contract SFRH/BPD/121526/2016, SFRH/BD/131729/2017, and IF/00355/2012, respectively. The authors acknowledge funding by the Spanish Ministry of Economy and Competitiveness (MINECO) through the project MAT2016-76039-C4-3-R (AEI/FEDER, UE) and from the Basque Government Industry and Education Departments under the ELKARTEK, HAZITEK, and PIBA (PIBA-2018-06) programs, respectively