Ultralow-density transparent porous bulk materials with densities of 5 mg cm-3 or less have only been obtained by supercritical drying. In this work, a simple method is reported for obtaining ultralow-density transparent porous beads with a diameter of several millimeters. In the method, a boehmite nanofiber dispersion (BNF sol) is dripped directly into liquid nitrogen and the beads are vacuum-dried. Normally, porous materials obtained via freeze drying exhibit strong light scattering due to structural nonuniformity and are not transparent. However, using dilute BNF as a skeleton structure suppressed the inhomogeneity due to aggregation during the dispersion medium crystallization. The lowest bulk density of the cryogel was 1.1 mgcm-3, and the visible light transmittance reached 90 %. By dispersing functional materials into the BNF sol before freezing, composite materials were obtained. The facile method can be expected to develop the field of functional porous materials.
- Porous materials
- Sol-gel processes
ASJC Scopus subject areas
- Renewable Energy, Sustainability and the Environment
- Energy Engineering and Power Technology
- Materials Chemistry