Properties of low-density SiO2 aerogels prepared based on the phase separation method

Abstract

To solve the problems of frequent solvent substitution and the high cost of modifiers in the process of aerogel preparation, this study proposed a modification method based on the combination of one-pot technology and phase separation technology, using polyoxydisiloxane (PEDS) as a precursor, with a small amount of n-hexane and Hexamethyldisiloxane(HMDSO) added in-situ, and n-hexane as the aging solution, followed by the addition of trimethylchlorosilane (TMCS), and trimethylethoxysilane (TMES) mixed in one pot for modification, after the end of modification to the mixed solution to the silicon ratio of 2.1 of water, water molecules were weakened by the role of the mutual solubility between ethanol and n-hexane, breaking the ternary phase equilibrium. The upward migration of hexane droplets was observed by microscopy, which led to the precipitation of ethanol from the system. Finally, a low-density SiO₂ aerogel powder was prepared by drying at atmospheric pressure and room temperature. Therefore, the phase separation method can be used to dry the gel under atmospheric pressure, avoiding the need for multiple solvent substitutions and hydrophobic modification in the traditional method. Under the most economical conditions for the use of pharmaceuticals, the silica aerogel powder synthesised by TMCS and TMES at a molar ratio of 1:2 can have a density as low as 0.0785g/cm³, a thermal conductivity as low as 0.0223 W/(m∙K), and a specific surface area as high as 837m²/g. Therefore, the phase separation method opens up a new pathway for the high-efficiency synthesis of silica aerogel powders, which makes aerogel products play a greater role in the field of thermal insulation.