Transparent, elastic and crack-free polymethylsilsesquioxane aerogels prepared by controllable shrinkage of the hydrogels in the aging process

Abstract

Polymethylsilsesquioxane (PMSQ) aerogels have gained extensive attention owing to their improved mechanical properties, good optical transparency and low thermal conductivity. However, the aerogels with high densities prepared by the conventional sol-gel method are fragile and opaque due to the increase in the particles size and the decrease in the uniformity of pore structure. In this research, transparent PMSQ aerogels over a wide range of densities from 0.15 g/cm3 to 0.25 g/cm3 are prepared by controllable shrinkage of the hydrogels in the aging process. Resulted PMSQ aerogels have smaller particle and pore size than that prepared by the conventional method. Surprisingly, the light transmittance of the aerogels with the density of 0.25 g/cm3 at 550 nm wavelength is up to 70%. Meanwhile, the Young's modulus of the aerogel is up to 4.33 MPa. The strength and resilience compressed to 50% can be 3.57 MPa and 99%, respectively. The thermal conductivities of the aerogels prepared by the novel method increase from 18.7 mW m−1 K−1 to 32.9 mW m−1 K−1, with the density increasing from 0.15 g/cm3 to 0.25 g/cm3. These results would extend the range of practical applications for the high density PMSQ aerogels such as the transparent insulators.