Strong light scattering upon capillary condensation in silica aerogels

This chapter elucidates the mechanisms responsible for the strong light scattering upon capillary condensation in silica aerogels. The light scattering as a function of the scattering angle and the wavelength dependence of the direct-hemispherical transmittance of the silica aerogel are presented for various amounts of 2-propanol absorbed. The light scattering data/light were evaluated by a superposition of two “2-phase media” contributions to account for scattering from the bulk (B) and the external surface (S) of the sample. Within the framework of given investigation the directional-hemispherical reflectance and transmittance were measured instead of the corresponding directional–directional quantities because directional-hemispherical data also contain information about the scattering of the incoming radiation. A new temperature controlled set-up is being tested that allows for simultaneous measurements of sorption and light scattering under well controlled conditions.