Facile Fabrication of Ultralow-Density Transparent Boehmite Nanofiber Cryogel Monoliths and Their Application in Volumetric Three-Dimensional Displays

Low bulk density transparent porous monoliths have unique optical properties such as low refractive index and usually can be obtained via supercritical drying to prevent deformation and collapse of pore structure. We succeeded in fabricating a transparent cryogel with a bulk density of 3.5 mg cm<sup>−3</sup> by vacuum freeze drying of a monolithic wet gel composed of boehmite nanofibers. In the case of adding a functional material into the starting sol of the gel, a composite material can be obtained. We analyzed the optical properties of transparent cryogels using image processing (direct-global separation) and applied the composite with a fluorescent molecule to volumetric three-dimensional (3D) displays.