Ultralow-Bulk-Density Transparent Boehmite Nanofiber Cryogel Monoliths and Their Optical Properties for a Volumetric Three-Dimensional Display

Ultralow-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 the microstructure. We succeeded in fabricating a transparent cryogel with a bulk density of 3.5 mg cm^–3 via vacuum freeze-drying of a monolithic wet gel composed of boehmite nanofibers. In the case of the addition of a functional material into the starting sol, a composite material can be obtained. The composite cryogel with a fluorescent molecule was applied to a volumetric three-dimensional display.