Carbon aerogels as broadband non-reflective materials

We report the reflectance properties over a wide spectral range of five carbon aerogels prepared by different synthetic routes. Carbon aerogels that were prepared by the conventional base-catalyzed hydration and polymerization of a resorcinol–formaldehyde (RF) solution followed by pyrolysis in an inert atmosphere have the lowest reflectance among all the aerogels investigated. The directional hemispherical reflectance (DHR) of the low density 0.07 g/cm3 conventional carbon aerogel studied is on the order of 0.3% across the entire 40,000–700 cm−1 (0.25–14.3 μm) region. The other carbon aerogels studied all have DHR values below ∼6% in the infrared and below 2.5% in the ultraviolet. Increasing the incidence angle from 8° to 30° leads to an increase of ∼0.2% in the DHR of each material. The low reflectivity of carbon aerogels is attributed to high absorption by carbon along with the rough internal and external surfaces of the aerogel structure.