The effect of various solvents on physical properties of the ambient pressure dried silica aerogels

فاقد چكيده

The effect of different alcohols and aprotic solvents on silica aerogels synthesized with ambient pressure dried (ADP) method and water glass as a silica source have been reported. The aerogels were prepared with ammonium hydroxide catalyst and trimethylchlorosilane (TMCS) silylating agent as a surface modifier. The effects of different alcohols such as methanol, ethanol, isopropanol and aprotic solvents such as n-hexane and heptane on synthesized aerogels bulk properties are studied. The percentage of volume shrinkage and density were calculated for all samples. FTIR, contact angle, BET, TG/DTA, transmission spectra in visible region were used for characterization of synthesized aerogels. It has been observed that the percentage of volume shrinkage and density is lowest and the optical transparency is highest in the case of aerogels that were obtained with isopropanol. Also results show that aerogels synthesized with n-hexane have better physical properties than heptanes. For this aerogels the density, percentage of volume shrinkage, surface area, contact angle, thermal stability and mean pore diameter, are in the range of 0.12-0.15 g/cm3, 5%, 580 m2/g, 143°, 380°C, 16 nm. Pore size distribution and total pore volume are measured with BJH method and results show maximum peak at 8 nm and 2.38 cm3/g pore volume. The optical characterization of the silica aerogel from IPA and n-hexane solutions showed the 70% transparency at 700 nm wavelength.