Effect of Synthesis Conditions on Pore Structure and Physical Properties of Silica Aerogel Dried at Ambient Pressure

In this work, silica aerogel particles were synthesized by TEOS precursor via two-step sol-gel process followed by ambient pressure drying. Effect of synthesis parameters on the pore structure, physical properties and hydrophobicity of silica aerogel particles were investigated. Nitrogen adsorption-desorption, contact angle and FE-SEM images were used to characterize the aerogel particles. Aerogel samples exhibited the porosity of ≥ 76%, specific surface area of ≥714 m2/g and average pore size of 5-22 nm. The results showed that the synthesis conditions intensively affected the pore structure and properties of the silica aerogel. An increase in the amount of catalyst accelerated the hydrolysis and condensation reactions in the sol-gel process of TEOS and lead to the large pore size (22 nm). However, with the decrease in the water and catalyst concentration, the heterogeneous structure with wide pore size distribution near 7 nm was obtained for aerogel particles leading to more shrinkage and higher density. It was found that the porosity and density of aerogel particles were affected by the gelation temperatures. The lower gelation temperature (20 °C) led to smaller clusters with less crosslinking producing a relatively dense structure. Furthermore, synthesis at low temperature influenced the pore size distribution and density of aerogels. Also, the heterogeneous structure with higher density and narrow pore size distributions was obtained due to the low condensation reaction at low temperature. The content of the surface modification agent in the range of 5 to 20%, showed no effects on the physical properties and hydrophobicity of silica aerogels having the water contact angle of 158˚.

Keywords:

Hydrophobicity , Physical Properties , Pore Structure , Silica Aerogel , Synthesis Parameters.