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/cm(2) conventional carbon aerogel studied is on the order of 0.3% across the entire 40,000-700 cm(-1) (0.25-14.3 mum) region. The other carbon aerogels studied all have DHR values below similar to6% in the infrared and below 2.5% in the ultraviolet. Increasing the incidence angle from 8 degrees to 30 degrees leads to an increase of similar to0.2% 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. (C) 2001 Elsevier Science B.V. All rights reserved.