Chameleons are attractive animals, which can change their colors because of unique layered skin structures. Inspired by this natural design, we explored a layer-by-layer assembly technique to create thermochromic films that can attain reversible and multiple-colors change. Briefly, inorganic pigments and two kinds of thermochromic microcapsules having different responsive temperatures were assembled sequentially onto a piece of filter paper using extraction filtration before epoxy resin was used to seal the whole structure. Different functions including colorful patterns and luminescent letters can be integrated into the system using this versatile approach. More importantly, arrays of thermochromic films were used with a detector and a heating-control circuit to trigger complicated color change by varying detected colors. We believe that this cost-efficient and convenient approach can be used in multiple applications such as camouflage, anti-counterfeiting, smart constructions and buildings, etc.
Transparent-to-colored electrochromic devices exhibit promising application prospects and have gained popularity. Herein, two triphenylamine derivatives TPA-OCH3 and TPA-CN with styryl moieties and different donor or acceptor units were designed and synthesized to further prepare solvent-resistant thermally cross-linking polymer P(TPA-OCH3) and P(TPA-CN) without any additional initiator. P(TPA-OCH3) and P(TPA-CN) possess two pairs of redox peaks, and P(TPA-OCH3) shows a lower onset oxidation potential compared to P(TPA-CN) because of the pendent donor unit. Correspondingly, both polymers exhibit multicolored changes from the neutral colorless state to noticeable oxidized colors under different potentials. Furthermore, the thermally cross-linking copolymer P(TPA-OCH3-co-TPA-CN) was obtained by TPA-OCH3 and TPA-CN (the molar ratio is 2:1) and presents outstanding electrochromism with four color changes (colorless–orange–blue–purple) due to the multistep redox process of TPA-OCH3 and TPA-CN units. It is more intriguing that the electrochromic device based on the copolymer films possesses a high optical contrast of 57.8% at 680 nm, fast switching time (0.52 and 0.66 s), and robust cyclic stability over 30 000 cycles with very little decay. Therefore, the thermally cross-linking copolymer is a promising candidate material for high-performance transmittive electrochromic devices, such as smart windows, sunglasses, and E-papers.
V 2 O 5 is a promising electrochromic material for adaptive camouflage or electronic display. However, it is still challenging to enable fast response time, multicolor change and good cyclic stability. In this paper, we successfully synthesized different cation (NH 4 + , K + and Na + ) pre-inserted vanadium oxide nanobelt films (NVO, KVO and NaVO) by stirring impregnation method. All nanobelts are composed of V 3 O 8 layers with hydrated cations acting as pillars in the interlayer, exhibiting excellent electrochromic properties and remarkable multicolor changes. Among them, the NVO nanobelt films have the highest transmittance modulation (ΔT = 54 % at 510 nm and ΔT = 56 % at 950 nm), fastest response time (4.4 s for coloration time, 5.5 s for bleaching time at 422 nm and 6.8 s for coloration time and 7.7 s for bleaching time at 950 nm) and best stability (3000 cycles). Impressively, the NVO film is highly reversible between five colors: orange-red, orange, yellow, green and blue-grey, showing great breakthrough in adaptive camouflage application.
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