Imperviousness of the hydrophobic silica aerogels against various solvents and acids

The experimental results on the imperviousness of the silica aerogels against various organic solvents and acids, are reported. Various types of hydrophobic silica aerogels were prepared using methyltrimethoxysilane (MTMS); tetraethoxysilane (TEOS) with ethyltriethoxysilane (ETES) and phenyltriethoxysilane (PTES) as co-precursors. The organic solvents used were: methanol, ethanol and acetone, and the acids used were: hydrochloric acid (HCl), nitric acid (HNO₃) and sulphuric acid (H₂SO₄). The imperviousness of the aerogels against these solvents and acids were tested with the variation of the percentage of organic solvents and acids in water from 10 to 100% and was characterized by the contact angle measurements. It was observed that in all the cases, the contact angle decreased with an increase in the percentage of solvent in water. While there was no absorption of the solvent up to 20% in water by the ETES and PTES modified aerogels, the MTMS-based aerogels showed the imperviousness up to 60% of the solvent in water. The MTMS aerogels were also impervious against all the three acids up to 100%, while the ETES and PTES modified aerogels could withstand only up to 80% of acids in water.