Phenyl-modified silica aerogels with high-temperature hydrophobicity for self-cleaning and thermal insulation under extreme circumstances

Abstract

Silica aerogels tend to be employed as thermal insulating materials, however their properties are inevitable to deteriorate in humid conditions owing to the hydrophilic nature, especially above 200 °C. Herein, phenyl modified silica aerogels with superhydrophobicity, self-cleaning capacity, and ultra thermal insulation are prepared. Phenyltriethoxysilane (PTES) working as the modifier condenses with tetraethyl orthosilicate (TEOS), forming a three-dimension network containing ladder polyphenylsilsesquioxane structure, where the introduction of bulk phenyl groups decreases free energy and fabricates hierarchical regime, leading to distinctive water repellency. The water contact angles are larger than 150° with low hysteresis (less than 2°), rendering droplet bouncing and self-cleaning capacities. As the molar ratio of PTES to TEOS rises to 1, the superhydrophobicity can be preserved at temperatures as high as 500 °C. In addition, hot-steam resistance and excellent thermal insulation are achieved. When subjected to a direct impact of 200 °C steam for 5 h, the hybrid aerogel demonstrates a reversible rise of thermal conductivity around 34%. The maximum back-surface temperature keeps 55.9 °C after exposure to hot steam for 10 min. The modification can broaden the application area of silica aerogels in high-temperature thermal insulation.