Abstract
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.
Highlights
VP is mainly composed by UV or visible light curable processes in which the light activates the photopolymerization process [1,2]
Similar trend is further observed for the 20 wt.% and 40 wt.% ionic liquid (IL) content samples, the total conversion decreasing to around 88% for the 40 wt.% IL content sample after 4 minutes
In relation to the tmax, a slight decrease is observed with increasing IL content, varying between 8.0 s for the 0 wt.% IL/polyurethane acrylate (PUA) sample to 6.2 s for the sample that contains the highest amount of IL
Summary
VP is mainly composed by UV or visible light curable processes in which the light activates the photopolymerization process [1,2]. Performance, cost, environmental and safety concerns, as well as the processing of materials at industrial scale continues to be a problem for nanocomposites [22] In this sense, hybrid materials based on ionic liquids (ILs) dispersed within a polymer matrix allow the development of advanced materials with improved properties than conventional nanocomposites based on inorganic or organic nanoparticles. Besides the great advantages of the ILs for the development of multifunctional materials and the advantages of UV curable polymers for additive manufacturing and protective and functional coatings [41], no studies concerning thermochromic IL-based UV curable hybrid materials able to change the colour with the temperature and to detect relative humidity variations (humidity sensor) have been reported. UV curable ILs/polymer thermochromic and humidity responsive material are presented in this work, based on polyurethane acrylate (PUA) and bis(1-butyl-3methylimidazolium) tetrachloronickelate ([Bmim]2[NiCl4]) able to be implemented as multifunctional materials or coatings with thermochromic and for humidity sensing capability. In order to obtain the blue (dehydrated) initial state, the sample was kept at 70 oC for 5 minutes, while for the colourless (hydrated) state, the sample was kept under ambient conditions during 24 hours
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