Small angle neutron scattering characterization of colloidal and fractal aerogels

Extreme length scales of aerogel structures limit the effectiveness of many characterization techniques. With the resolutions commensurate with the le ngth scales found in these materials, small angle neutron scattering measur ements were conducted and interpreted using several models developed for ot her ceramic systems (polydispersed hard-sphere, fractal, and maximum entrop y models). Interference (polydispersed hard-sphere) and maximum entropy mod els indicate that tetraethoxysilane (TEOS) aerogel structure may be compris ed of oblate nanoparticles within oblate mesoparticles. The fractal model w as used to describe the structures of triethoxysilane (TES) and trimethoxys ilane (TMS) aerogels and to quantify their fractal properties. TES aerogels appear to be networks of volume fractals while TMS aerogels contain both v olume and surface fractalelements. (C) 2001 Elsevier Science B.V. All right s reserved.