Production of Spherical Aerogel Microparticles by Supercritical Extraction of Emulsion

Due to high surface area, low density, open pore structure and excellent insulation properties aerogels were intensively investigated in the past decades for diverse range of applications. The state of the art of aerogel production by supercritical drying is to produce monolithic aerogel, where the sol is aged in molds and dried by extraction with supercritical CO2. Aerogels in form of spherical microparticles would be beneficial for many applications, for instance as a drug carrier in pharmaceutics, where aerodynamic plays an important role in case of inhalation route, or as insulating materials where homogeneity and flowability is an issue. Because of aerogel’s mechanical properties it is difficult, rather impossible to obtain spherical microparticles by milling or crushing of the monolithic or bulk aerogel. This work suggests a new method to produce biocompatible aerogel microparticles using emulsion technique (insitu production). Water in oil emulsion was produced by mixing the sol (dispersed phase) with a vegetable oil (continuous phase) followed by the gelation of the aqueous phase. The size and shape of the gel particles is controlled by the agitation (agitator form and speed). Gel-oil emulsion was subsequently extracted with supercritical CO2. Two examples of this process are given: silica and alginate aerogels. Silica aerogel spherical microparticles with a surface area of 1100 m2/g and different mean particle diameters ranging from 200 μm to few millimeters were produced. In case of alginate aerogel the oil phase was separated before the drying step to convert the hydrogel into alcogel before CO2 supercritical drying. This process result in the highest surface area known for similar alginate aerogels (400 m2/g) with a particle mean diameter of 100 μm.