Regulating the hydrophobicity and pore structure of silica aerogel for thermal insulation under humid and high temperature conditions

Abstract

This study aims to develop a hydrophobic silica aerogel with high specific surface area and pore volume for thermal insulation under humid and high temperature conditions. Silica aerogels are synthesized through the co-condensation of methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS). The effect of MTES/TEOS ratio on chemical structure, hydrophobicity, and pore structure is investigated. The silica aerogel with a MTES/TEOS molar ratio of 1.4 (MT1.4) exhibits the highest water contact angle of 134°, in addition to a surface area of 1052 m²/g and a pore volume of 3.17 cm³/g. Excessive MTES results in a slight decrease in water contact angle as well as a significant reduction in specific surface area and pore volume. MT1.4 retains a water contact angle of 101° at 300 °C and a specific surface area of 695 m²/g at 500 °C. The thermal conductivity of MT1.4 is as low as 0.0182 W/(m·K) at 25 °C. In the long term up to 42 d, the liquid water and moisture sorption capacities of MT1.4 are as low as 1.9 wt% and 4.7 wt%, respectively. The thermal conductivity hardly changes after water soaking and hygrothermal aging for 42 d. Compared to its state-of-the-art counterparts, MT1.4 offers significant advantages in term of pore structure, thermal stability, thermal insulation, and water resistance, and thus shows great promise for thermal insulation under humid and high temperature conditions.