In the natural world, there exist many sources of inspiration for the creation of new high-performance materials. Structural color observed in various creatures, plants, and minerals has received a great amount of attention in recent years because of its eye-catching, non-photobleachable, and energy-saving properties, which are important for developing unprecedented coloring materials. One of the most popular methods to obtain artificial structurally colored materials is the elaboration of periodic dielectric structures on a length scale that is comparable to the wavelength of light in materials and thus causes multiple Bragg reflections. However, the fabrication of such mesoscale structures requires a great amount of time, effort, and, in some cases, cost when using existing top-down or bottom-up approaches. Herein, we demonstrate a facile self-assembly approach to obtain a porous gel exhibiting angle-independent structural color using a principle different from that of traditional dielectric periodically structured materials. The channel-like porous structure in the gel might be self-assembled from the phaseseparated polymers that result from spinodal decomposition and it might be locked in by kinetic arrest, likely through entanglement or cross-linking. The porous swollen gel changes color reversibly with solvent, covering the whole visible region in response to solvent composition and temperature by means of changes in the wavelength dispersions of the refractive indices of the gel portion and the solvent portion in the pore.Structural color is generally defined as coloration caused by complicated and diverse interactions between light and materials, such as interference effects, diffraction grating, light scattering, and dispersion of refractive index, and it essentially does not lose the energy of the light. [1][2][3] For the reason, structural color has been the subject of extensive studies for applications in energy saving mobile devices with a reflective full-color paperlike display. Though structural coloration can be caused by not only periodic dielectric structures but also randomly dispersed particles and a simple prism, recent studies of artificial structurally colored materials have focused mainly on the fabrication of periodical microstructures, such as multilayer films [4][5][6] and photonic crystals. [7][8][9] This trend is in part due to the relative ease to understand the structures, and the simple principle of Bragg diffraction, which generates structural color from periodic dielectric structures. However, to design a reflective full-color paperlike display with a wide viewing angle, the angle dependence of the structural color based on Bragg diffraction becomes a major issue.Recently, we demonstrated for the first time that amorphous arrays with a short-range order prepared from submicrometer spherical colloidal gel particles [10] or silica colloidal particles [11] are capable of displaying angle-independent structural color and can be applied to nonfading color materials and full-color pape...
