Monolithic poly(methylsilsesquioxane) aerogels with glasslike transparency: from sol-gel synthesis to ambient pressure drying

Practical aspects of the successful preparation of monolithic poly(methylsilsesquioxane) (PMSQ) aerogels with glasslike transparency via ambient pressure drying (APD) are discussed in detail. Two-step acid-base process starting from methyltrimethoxysilane (MTMS) in the presence of nonionic poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) surfactant and the use of strong base as polycondensation catalyst resulted in fine mesoporous structure, showing low bulk density (0.148 g cm⁻³) and glasslike transparency (95% at 10 mm thickness). Cracking and irreversible shrinkage during APD have been prevented by optimized aging and drying processes. In particular, aging in an aqueous alcohol solution containing a low concentration of MTMS under controlled temperature has been found to be crucial in obtaining PMSQ aerogels with crack-free, low-density, glasslike transparency, and monolithic nature. A large-area APD aerogel in 93 × 93 × 6 mm³, with thermal conductivity of 15.6 mW m⁻¹ K⁻¹, has successfully been obtained due to optimizations of aging and drying conditions. Similar APD aerogels have also been obtained when alkali metal hydroxides, especially lithium hydroxide, are employed as base catalysts. These findings are expected to play important roles in designing industrial productions of monolithic aerogels for thermal superinsulation and other applications.

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