Reinforced silica aerogel

The often quoted high strength-to-weight ratio of silica aerogels is somewhat misleading as it is mostly due to their low density, rather than high strength. In fact, silica aerogels are notoriously brittle and can be quite dusty. Most reinforcement strategies result in an increase in strength, but at a high cost in thermal conductivity. In our lab, the reinforcement of silica aerogel could be reached by different strategies: i. Molecular approach: co-gelation of silica with biopolymers (e.g. pectin,[1] chitosan[2]) or synthetic prepolymers [3], and ii. Macroscopic reinforcing approach: impregnate silica into a biopolymer scaffold, e.g. freeze-dried cellulose [4], or fiber reinforced silica aerogel blankets [5-6]. The latter approach has been scaled-up to the pilot scale at Empa using an ambient pressure drying protocol [5]. For both approaches, materials with a dramatic increase in mechanical strength can be produced, without compromising the ultra-low thermal conductivity.
[1] S. Zhao et al. Strong, Thermally Superinsulating Biopolymer–Silica Aerogel Hybrids by Cogelation of Silicic Acid with Pectin, Angew. Chem. Int. Ed. 54 (2015) 14282-14286. [2] S. Zhao et al., Facile One-Pot Synthesis of Mechanically Robust Biopolymer–Silica Nanocomposite Aerogel by Cogelation of Silicic Acid with Chitosan in Aqueous Media, ACS Sustainable Chem. Eng. 4 (2016) 5674-5683. [3] S. Iswar et al., Reinforced and superinsulating silica aerogel through in situ cross-linking with silane terminated prepolymers, Acta Mater. (2018). [4] S. Zhao et al., Multiscale Assembly of Superinsulating Silica Aerogels Within Silylated Nanocellulosic Scaffolds: Improved Mechanical Properties Promoted by Nanoscale Chemical Compatibilization, Adv. Funct. Mater. 25 (2015) 2326-2334. [5] R.G. Martinez et al., Thermal assessment of ambient pressure dried silica aerogel composite boards at laboratory and field scale, Energy and Buildings 128 (2016) 111-118. [6] Iswar, Subramaniam, et al. "Effect of aging on thermal conductivity of fiber-reinforced aerogel composites: An X-ray tomography study." Microporous and Mesoporous Materials 278 (2019): 289-296.

Dr. Shanyu Zhao
Group leader in Functional Aerogel Materials Group

Phone: +41 58 765 4244