Silica aerogels with enhanced durability, 30-nm mean pore-size, and improved immersibility in liquids

The pore structures and mechanical properties of silica aerogels obtained by traditional base-catalyzed sol–gel synthesis can be modified by curing in neat methanol. The curing process produces gels with a larger mean pore-size and more cumulative pore volume than their uncured (standard) counterparts both before and after heat-treatment steps. Cured silica aerogels that are densified by heat-treating in air to 900 °C for 30 min retain a mean pore-size of ∼30 nm, comparable to a standard/as-dried silica aerogel. Heating the standard silica aerogel to 900 °C for 30 min markedly decreases the mean pore-size to 16 nm. Nanoindentation studies show that the modulus (E) and hardness (H) values for the standard and cured aerogels vary depending on the heat-treatment. The as-dried standard and cured silica aerogels respond comparably to nanoindentation. After heating in air to 900 °C, the modulus and hardness values for both the standard and cured gels increase dramatically, with the standard/900 °C (30 min) aerogels having significantly higher modulus (3.8 GPa) and hardness (0.42 GPa) values than the cured/900 °C (30 min) aerogels (E = 1.2 GPa, H = 0.17 GPa). The increased modulus and hardness of the standard/900 °C gels does not, however, translate into an increased ability to endure the wetting stresses imposed by immersion into liquid. The less dense, cured/900 °C gels are better able to withstand immersion stresses producing a more rugged material and one more amenable to post-processing chemical and physical modification to create multifunctional platforms.