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 c NH3·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 c NH3·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.