Thermo-Responsive Photonic Hydrogel for Smart Window Applications

In this study, we report a versatile strategy for the fabrication of large-area, structurally colored photonic crystal films and their thermo-responsive hydrogel composites using monodisperse silica nanoparticles. Silica nanoparticles with controlled sizes (100390 nm) were synthesized via the Stber method and characterized by transmission electron microscope and dynamic light scattering, confirming excellent monodispersity and size uniformity. These nanoparticles were self-assembled into highly ordered 3D photonic crystal structures using a vertical deposition method, producing vivid structural colors tunable across the visible spectrum in accordance with Braggs law. To overcome mechanical fragility, the photonic crystals were embedded within a hydrogel scaffold, yielding free-standing, large-area films that preserved structural order while providing thermo-responsive color shifts. Upon heating, the films exhibited reversible blue-shifts due to hydrogel contraction, as confirmed by in situ UVvis spectroscopy, demonstrating robust and repeatable optical responsiveness. The photonic hydrogel are planned to be further explored for potential applications, including temperature indicators and radiative cooling materials, leveraging both optical feedback and passive thermal management. The combination of tunable structural color, mechanical stability, and dynamic response establishes these photonic hydrogels as a promising platform for functional coatings, smart windows, and energy-efficient optical devices.