Tailoring structural and physical properties of polymethylsilsesquioxane aerogels by adjusting NH3 center dot H2O concentration

The polymethylsilsesquioxane (PMSQ) aerogels obtained from the precursor of methyltrimethoxysilane (MTMS) have been a kind of high-performance thermal insulating materials due to its ultra-low thermal conductivity and improved mechanical property. In this paper, a facile way was introduced to control the microstructure of the PMSQ aerogels using a sol-gel system with supercritical ethanol drying. It was found that the skeleton structures changed from the tenuous branched chains to a stronger network of particle aggregates with the increase of NH3 center dot H2O concentration. The pore sizes in the aerogels were controllable and gradually changing from concentrating at similar to 10 nm to 40 nm. The effect of different assembly structures on the physical properties were explored in detail. The aerogels with smaller particles and pore sizes are transparent and have the specific surface area as high as 615.0 m(2)/g, while the particle aggregates and larger pore sizes make the skeleton sturdier, which endow the aerogels with improved resilience ability of 80%. All the aerogels show low thermal conductivity in the range of 20.7-21.4 mW/m . K and hydrophobic property with a contact angle higher than 140 degrees. More importantly, with high ammonia concentration, aerogels obtained by ambient pressure drying have a resilience of 98% and exhibit low thermal conductivity of 22.3 mW/m . K. This extends the range of practical applications for the PMSQ aerogels. (C) 2017 Elsevier Inc. All rights reserved.