Inorganic-Organic Hybrid Aerogels

Abstract

ABSTRACTOrganically modified silica aerogels were prepared by NH4OH-catalyzed hydrolysis and condensation of RSi(OMe)3 / Si(OMe)4 mixtures, followed by supercritical drying of the alcogels with methanol or CO2. Terminal alkyl or aryl groups, bridging groups or functional organic (methacryloxypropyl or glycidoxypropyl) groups were employed for R. By the proper choice of the organic groups, the RSi(OMe)3 / Si(OMe)4 ratio and the drying conditions, hydrophobic aerogels, being insensitive towards moisture, were obtained with no residual Si-OH or Si-OMe groups left. The transparency and porosity of the organically modified aerogels was only slightly diminished relative to unmodified silica aerogels. The elastic constant of the aerogels was significantly influenced by the kind of organic groups. By pyrolysis of the phenyl-substituted aerogels, nanometer-sized carbon structures were generated. They partly coat the primary aerogel particles and provide a very high mass specific extinction in the wavelengths interval critical for thermal radiative transport.