The effect of the preparation conditions on the optical properties of transparent silica aerogels

Hemispherical and specular transmittance in visible wavelength region and small-angle neutron-scattering of silica aerogels were measured to investigate the effects of supercritical drying media and heat treatment on the optical properties and structure of them. Silica aerogels were prepared by using methanol, ethanol, 2-propanol and carbon dioxide as supercritical drying medium. The analysis of transmission spectra suggested that a reduction of transmittance in visible light can be attributed to Rayleigh scattering, and the scattering intensity depended on the supercritical drying medium. The difference of the scattering intensity among the samples was related to the difference of the cluster size of aerogels from the results of small angle neutron scattering. Heat treatment affected the scattering intensity, but the change of the cluster size was not observed.