日本ゼオライト学会　刊行物 Publication of Japan Zeolite Association

Supercritical drying is a method of drying a wet gel through a supercritical phase. As a supercritical phase has no clear interfaces with liquid or gaseous phases, the method can produce an aerogel by substituting solvent inside the gel with air without making any damages on the inner skeletal microstructure. Inorganic oxide aerogels, such as silica and alumina, had long been a major topic in this field, but recently aerogel ingredients have been diversified in various inorganic and organic materials. In this review, the author makes brief introductions of typical supercritical drying and recent topics on chitosan aerogel, one of the biopolymer aerogels invented by author’s group. The chitosan aerogel has a three-dimensional network structure consisting of chitosan nanofibers of 5–30 nm in diameter. This aerogel can be a good candidate for thermal superinsulation applications owing to its transparency, mechanical toughness, and ultralow thermal conductivity. According to recent investigation using small-angle X-ray scattering, unlike conventional silica aerogels, the nanofibrous structure of the chitosan aerogel is constructed during supercritical drying. This result indicates that supercritical drying is not always inactive to the microstructure, and it can be used as an active tool for microstructure fabrication.