Light gels by conventional drying

Supercritical drying, the preparation route for aerogels gives high quality materials and very low density; however, the process is high risk and has quite high cost. For a large scale application of aerogels, supercritical drying will most probably not give a cost effective product. A process for preparing xerogels with a low density, i.e., aerogel-like materials without the use of supercritical drying is of interest. Shrinkage during drying of a gel is driven by the capillary pressure and is resisted by the bulk modulus of the gel. Hence, it is of importance to reduce the capillary pressure and increase the stiffness and strength of the wet gel without decreasing the pore size significantly. An enhancement in stiffness and strength of wet gels can be performed by aging the wet gels in solutions of monomers. By this method monolithic xerogels with a porosity up to 90% can be prepared. (C) 1998 Elsevier Science B.V. All rights reserved.