'Seeded' growth of silica aerogel by tetraethoxysilane and trimethylchlorosilane co-precursor method

Silica aerogels were successfully synthesized by tetraethoxysilane (TEOS) and trimethylchlorosilane (TMCS) co-precursor method. Silica gels were prepared in two steps. For the introduction of the hydrophobic group Si(CH ₃)₃ and its presence at the growth front, the degrees of the condensation and the crosslinking of the samples should be affected. Depending on the NH₄OH-catalyzed reactions at different temperatures in the second step, 'seeded' growth and direct growth with different mechanisms were observed and investigated. For the sample obtained from 'seeded' growth, first gelation results in the dense gel with good hydrophobic behavior, relative low specific surface area. After the second gelation, the final aerogel was found to have the increased specific surface area and the decrease in the hydrophobicity. The experimental results show little difference between the final aerogel product from seeded growth and the sample from direct growth, but different growth mechanisms were revealed.