Hierarchically porous and highly transparent polymethylsilsesquioxane aerogels with an ultrahigh specific surface area using an organic alkali as a catalyst, surfactant, and template

Abstract

A hierarchically porous aerogel with an ultrahigh specific surface area, high visible light transmittance, excellent mechanical properties, and cubic shell-shaped pores was obtained using a supercritical drying process. Ethanol and methyltriethoxysilane (MTES) were used as a solvent and silicon source, respectively, whereas tetramethylammonium hydroxide (TMAOH) acted as a basic catalyst, surfactant, and template. The phase separation during gelation was finely adjusted by changing the ethanol-to-water ratio to control the gel skeleton structure, the number of crystallization templates, and the light transmittance of the aerogel. The hierarchical porous aerogels exhibited a uniform three-dimensional network. Notably, the specific surface area of the aerogels was 909 m2/g, the visible light transmittance was 58.1%, the hydrophobic angle was 166.5°, the thermal conductivity was 18.2 mW/(m·K), and the stress was 0.301 MPa at 50% compressive strain. The unique structure and excellent performance of the hierarchical porous aerogels make them promising for thermal and sound insulation applications. Moreover, the innovative use of TMAOH as a surfactant and template can be inspiring for the preparation of polymer-reinforced or highly crosslinked aerogels.