Robust Aerogels

Synthesizing a silica gel inside a cellulose matrix leads to a lightweight yet sturdy composite aerogel, according to researchers in China and Japan (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201105730). Aerogels are high-surface-area porous solids with ultralow densities—they have a wispy, foglike appearance in some cases. The materials are typically derived from gels by replacing a gel’s liquid phase with a gas. They serve as thermal insulators in various applications, including some for use in space missions. But the scope of the applications is limited because aerogels tend to be brittle and fragile. To reinforce aerogels, Jie Cai of China’s Wuhan University, Shigenori Kuga of the University of Tokyo, and coworkers treated nanofibrous cellulose gels with a silica precursor in various concentrations to form a series of composite cellulose-silica gels. They then dried the gels with supercritical CO₂, thereby forming strong and flexible aerogels. Some of the products, which were formed as ribbons, were sufficiently robust and flexible to be tied into a knot. “These composite aerogels have inherited the cellulose network’s physical integrity and flexibility,” Cai says.