Innovators at NASA's Glenn Research Center have expanded their growing portfolio of aerogels to include a new optically transparent polyimide aerogel. Aerogels — low-density, highly porous, ultralight materials derived from gels — can be fabricated to achieve specific desirable traits including various ranges of optical transparency. In the past, high optical clarity was most commonly produced in silica aerogels, which shed dust particles and are notoriously fragile and brittle. In contrast, polyimide aerogels possess remarkable strength and flexibility. They are often used in aerospace applications due to their ability to retain their physical and mechanical properties in thermally and chemically demanding environments.
Glenn has devised a new method for harnessing the high transmission and clarity associated with optical glasses in a robust polyimide aerogel. This process uses sol-gel synthesis technology with aromatic dianhydrides and diamines as the precursors, and a trifunctional tri-acid chloride that arranges itself into a three-dimensional (3D) matrix with a low refractive index. The liquid portion of the gel is then removed by supercritical fluid extraction in order to produce the polyimide aerogel and maintain the desired 3D structure without pore collapse. The result is a cross-linked polyimide aerogel that allows for light-wave transmittance while retaining low thermal conductivity.
This unique material can be made into thin blocks or highly flexible films as thin as 0.5 mm. While some embodiments have a yellow color, other embodiments may be nearly colorless. When compared to high-opacity polyimide aerogels, they have much greater surface area (up to 880 m 2/g) and a very homogenous pore size (10 to 20 nm) with only a minor penalty in density (0.15 g/cc vs 0.10 g/cc). These strong, optically transparent aerogels incorporate a number of unique properties with applicability to a host of potential new applications, making this innovation a game-changer in the global aerogel market.