Liquid, Transparent, and Antideformable Thermochromic Photonic Crystals for Displays

The conventional thermochromic photonic crystal (TPC) gels based on thermally responsive poly(N‐isopropyl acrylamides) can switch their reflection signals at different temperatures by changing their lattice distances or order degree. However, these TPC gels exhibit a poor sensing range of temperature (ΔT < 30 °C) and poor antideformation properties, significantly limiting their applications. Here, a new type of liquid and transparent TPC is fabricated through assembling silica particles into the mixture of ethanol and poly(ethylene glycol) diacrylate. Different from the conventional TPCs, these liquid TPCs can reversibly alter their reflectance and brightness by temperatures based on the variation of the refractive index contrast (Δn). The liquid TPCs show 1) the unique “off/on” characteristics, 2) outstanding shapeable and antideformable properties, and 3) a large ΔT (80 °C), high sensitivity (reflectance: 0.46% °C−1), fast responsive speed (reflectance: ≈4.75% s−1), and good reversibility (>30 times). It is shown that these TPCs are ideal candidates for visual hot warning labels and temperature‐based display units. This work opens a new avenue for developing advanced stimulus‐responsive photonic materials and upgrades the basic understanding of the color tuning mechanisms.