Fast synthesis of mechanically robust methylsilsesquioxane aerogels: Process parameters optimization based on condensation reactions

Ambient pressure drying is a mainstream alternative to the supercritical drying process for synthesizing aerogels due to its low cost and high safety, but the problems of time-consuming and low mechanical properties of the synthesized aerogels need to be solved. This work tailored the skeleton of methylsilsesquioxane aerogels by ammonia concentration ( c N H 3 · H 2 O ) and revealed their microstructure evolution mechanism affected by the condensation reactions of methyltrimethoxysilane hydrolysates in the subsequent aging and drying process. The effects of process parameters, including the cNH3·H2O, aging temperature and time, drying temperature and time on the gelation time, macroscopic morphologies, microstructures, and compression properties of as-synthesized methylsilsesquioxane aerogels were investigated. A cNH3·H2O of 4.0 mol/L endowed the methylsilsesquioxane aerogels with a compression strength of 0.171 MPa and a maximum compression strain of 59.5 %. The optimal aging conditions were at 50 °C for 3 h which increased the compression strength and maximum compression strain of as-synthesized aerogels to 0.201 MPa, and 66.2 %, respectively. The synthesis time of methylsilsesquioxane aerogels was reduced to 6.5 h through an optimized step drying process, while further increasing their compression strength and maximum compression strain to 0.359 MPa and 73.5 %, respectively. The process parameters optimization method enables the facile synthesis of methylsilsesquioxane aerogels with mechanically robust texture, providing a theoretical basis for developing next-generation scalable production technologies of aerogels.