Ambient-temperature supercritical drying of transparent silica aerogels

A novel technique to supercritically dry alcogels to transparent silica aerogels at near ambient temperature is described. This supercritical drying occurs at ⩽ 40°C instead of at ≥ 270°C, by substituting liquid CO₂ for the alcohol in the alcogel. The time required for drying is reduced from 2–3 days to 8–10 h. Light scattering, optical and micro-structural properties of aerogels produced by this process and by high-temperature supercritical drying are compared and shown to be similar.