Facile fabrication of functional silica aerogel with gradient transmittance and refractive indices via slope-rotation method

Functionally gradient silica aerogels have been applied in many areas with their gradient porosity, refractive indices and acoustical impedance. For the purpose of accurately controlling the process of gradient formation, a new approach called slope-rotation method was proposed. Such a method could benignly fabricate gradient density sol by sloping, rotating and mixing the two different density sols in one-step. Gradient density aerogel was obtained after ethanol supercritical drying. The microstructure and density distribution of aerogels were characterized by nitrogen adsorption, scanning electron microscopy, and X-ray phase contrast. The transmittance and refractive index were tested by UV-visible absorption spectrum and a self-built device. The results indicated that the transmittance and refractive index had been gradient changed with the gradient density. This approach was an effective method for the preparation of gradient density silica aerogels and could be suitable for producing gradient density porous materials derived from a sol-gel process.