A SANS investigation on absolute scale of a homologous series of base-catalysed silica aerogels

Abstract

Small angle neutron scattering data for a homologous series of base-catalysed silica aerogels are presented. The data are brought on an absolute scale by normalisation with water. Both oxidised and untreated samples are investigated, and it is found that oxidation does not alter the overall aerogel structure, the only effect of oxidation being the removal of surface groups. It is concluded that the samples are best described as consisting of elemental building blocks with a radial size of 20 Å, aggregated into clusters with a density dependent radius, 5–10 times larger than the building block size. The monolithic aerogel is formed by connection of these clusters. The existence of clusters in the aerogel structure is manifested in the data by the presence of cluster-cluster correlation effects. These effects are not observed in SANS spectra reported in the literature for neutrally reacted aerogels.