Synthesis of silica aerogels and their application as drug delivery system
This chapter examines the synthesis of silica aerogels and their application as a drug delivery system. The common two-step procedure was modified by the addition of supercritical carbon dioxide (CO2) during the second step. CO2 is commonly used in aerogel production for solvent extraction, but its influence on the gelation process itself has not yet been reported. It has been found that the addition of supercritical CO2 during the sol-gel process enhances gel formation. The enhancement factor depends on the aerogel target density and varies from 5 to 100. The CO2 concentration in the liquid phase generally reaches 30 wt% at the gel point. It was evident that the amount of CO2 required-realizing such a rapid gelation process-strongly depends on the experimental conditions. The reaction enhancement takes place only if CO2 is combined with both the catalysts used in the common two-step process; and if one or both catalysts are not used, CO2 addition leads to the rapid precipitation of colloidal particles.