□□□ ―118―Double-inverse opals for switchable photonic band gaps and structural color □□□□□□□□□□□□□□□□□□□□□□□□ Tom Welling (Creative Interdisciplinary Research Division/Materials & Energy) Crystals made from colloidal particles with a similar size as the wavelength of light show beautiful reflective color known as structural color. They exist in nature and are made from non-toxic, cheap, and sustainable materials, which makes them a promising alternative for existing technologies. However, the colors of such materials often lack high saturation. This year, we improved the color properties of structural color thin films and pigments. First, thin films were made with core-shell particles using a sol-gel assembly method. The space between the particles was filled with the same materials as the shell, which meant incoherent scattering was reduced. As a result, highly reflective and transparent films were obtained [1]. Second, we made a proof-of-concept switchable colloidal crystal from yolk-shell particles [2], which can be reasonably expected to be expanded to double-inverse opals. Third, we started creating structural color pigments with structures known as supraparticles. We expanded on a recent technique to extract water from particle-containing water-in-oil emulsion droplets via osmosis. For low osmotic pressure differences, this technique results in ball-shaped ordered structures. We managed to make colorful paint using these structures by incorporating them in existing paint formulations. Combining the knowledge gained from these projects is crucial to achieve our vision of fast, switchable photonic crystals. References [1] T.A.J. Welling*, K. Kurioka, H. Namigata, K. Suga, D. Nagao, K. Watanabe*, ACS Appl. Nano Mater., in press (2023). [2] H. Namigata, T.A.J. Welling, K. Watanabe, K. Suga, A. Imhof, A. van Blaaderen, D. Nagao, ACS Appl. Opt. Mater., 2, 181 (2023). □□□□□□□□□□□□□□□□□□□□□□□□□□□□□□20223□□□□□□□3□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□ [1]□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□ElevationSpace□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□□[2]□□□□2□□□□[3,4]□□□ □□□□ [1] Yuji Saito et al., IEEE Sensors Journal 23(24) pp. 31006 – 31016, 2023. [2] Yuji Saito et al., Journal of Propulsion and Power, to be published. [3] □□□□□□□□2023-137433 [4] □□□□□□□□2023-137434 □□□□□□□□□□□□□□□□□□□□□□□□□
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