Hydrophobic silica aerogels derived from polyethoxydisiloxane and perfluoroalkylsilane

Silica aerogels are porous materials with unusual properties such as large internal surface area, small refractive index, low thermal conductivity and high visible transparency, etc. They have been used in a variety of applications. Most of the aerogels are hydrophilic and become wet in the presence of atmospheric moisture and get deteriorated with time. Therefore, one of the most important requirements for long-term use of the aerogels is making them hydrophobic. In this paper, hydrophobic aerogels are synthesized from polyethoxydisiloxane (E-40) and use perfluoroaklysilane (PFAS) as a coprecursor. With the increase of the volume ratio of PFAS/E-40, the gelation time, shrinkage rate and density increase. Fourier transform infrared spectra, relative pore size distribution and thermogravimetric analysis are used to characterize the hydrophobic aerogels. The fluoroaklyl groups are successfully incorporated into the silica aerogels in hydrolysis-condensation reactions. BET shows the surface area of the aerogels is larger than that of the as-prepared pure silica aerogels. And it has the largest surface area when the PFAS/E-40 volume ratio is at 0.6. The weight loss of the aerogels is very small up to 500 °C and the contact angle of water to the surface of the aerogels is about 145°.