Carbon aerogels as broadband non-reflective materials

We report the reflectance properties over a wide spectral range of five car bon aerogels prepared by different synthetic routes. Carbon aerogels that w ere prepared by the conventional base-catalyzed hydration and polymerizatio n of a resorcinol-formaldehyde (RF) solution followed by pyrolysis in an in ert atmosphere have the lowest reflectance among all the aerogels investiga ted. The directional hemispherical reflectance (DHR) of the low density 0.0 7 g/cm(2) conventional carbon aerogel studied is on the order of 0.3% acros s the entire 40,000-700 cm(-1) (0.25-14.3 mum) region. The other carbon aer ogels studied all have DHR values below similar to6% in the infrared and be low 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 mat erial. The low reflectivity of carbon aerogels is attributed to high absorp tion by carbon along with the rough internal and external surfaces of the a erogel structure. (C) 2001 Elsevier Science B.V. All rights reserved.