Gradient composition sol-gel materials

The STARDUST Mission, which launched in February of 1999, plans to fly through the coma of Comet 81P/Wild2, capture some of the material ejected by the comet, and return the samples to Earth in 2006. The capture media for the encounter is silica aerogel. In the course of the capture media development the aerogel evolved from single density, to discontiuous (layered) density changes, to a continuous (gradient) density change. Since various physical properties such as the index of refraction, the porosity, the dielectric constant, etc., are directly related to the density of these materials, they too vary in a gradient manner. Employing the method developed for the production of the STARDUST media, samples have been produced which exhibit order of magnitude density changes and refractive index gradients of up to 0.1. Other samples have been made which include compositional gradients such as varying dopant(s) concentration and oxide composition. The method has been used to form samples that display linear, planar, and cylindrical gradients. Sol-gel materials have been produced of not only gradient aerogel, but also gradient xerogel, as well as, gradient hybrid aerogel/xerogel materials.