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

• Published in: Journal of non-crystalline solids Vol. 350; no. Complete; pp. 244 - 252
• Main Authors: Lucas, Erik M., Doescher, Michael S., Ebenstein, Donna M., Wahl, Kathryn J., Rolison, Debra R.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 15-12-2004; Elsevier
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Physical and chemical studies. Granulometry. Electrokinetic phenomena; A120; 62.20.Qp; 81.05.Rm; M120; 81.20.Fw; P300; 62.25.+g; 81.70.Bt; S160; Pore size; Catalytic reaction; Heat treatment; Aerogel; Sol gel process; Nanoindentation; Mechanical properties; Durability; Silica gel; Hardness; Inorganic compound
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/j.jnoncrysol.2004.07.074

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 30min retain a mean pore-size of ∼30nm, comparable to a standard/as-dried silica aerogel. Heating the standard silica aerogel to 900°C for 30min markedly decreases the mean pore-size to 16nm. 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 (30min) aerogels having significantly higher modulus (3.8GPa) and hardness (0.42GPa) values than the cured/900°C (30min) aerogels (E=1.2GPa, H=0.17GPa). 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.