Continuous adjustment of fractal dimension of silica aerogels

In previous study, it was found that the fractal dimension of the silica aerogel could be only controlled by adjusting the catalysts. In this work, we used the aging process investigated by Hæreid et al. to continuously adjust the fractal dimension of silica aerogel. The fractal structure of the silica aerogels were analyzed by small angle x-ray scattering (SAXS). The SAXS measurements show linear increases in the volume fractal dimension (2.32-2.64) of the secondary particles with aging time (0-72 h). This linear behavior is due to the silica precipitated from the aging solution to the secondary particles is at a constant rate. In the meantime, the light transmittances was obtained by ultraviolet-Visible-infrared spectrophotometer, extinction coefficient were obtained by fitting the curve of light transmittances. We developed a new model to build a connection between the extinction coefficient and the fractal dimension of the silica aerogel obtained by SAXS. From new model, it was found it is due to the increases in volume fractal dimension (Df) that result in increases of extinction coefficient and decreases of light transmittances. The optical transparency of silica aerogel is strongly affected by the volume fractal dimension (Df) of the secondary particles of silica aerogel.