Tuning the Physical Properties of Aerogels by Spatially Selective Modification

Techniques are presented that allow to introduce anisotropy into the structure of aerogels and tune properties such as mechanical strength, thermal conductivity, hydrophobicity, and porosity. These hybrid aerogels can be roughly divided into three classes. The first class is functionally graded aerogels. Functionally graded aerogels can be fabricated by creating density, catalyst, or polymerization gradients within aerogel monoliths. The resulting composites present mechanical strength gradients which have been used, for example, in the Space Dust Project. Functionally graded aerogels also make the materials promising for thermal insulation with enhanced mechanical properties, and aerogels with hydrophobicity gradients are potentially suitable for waste remediation. The second class is aerogels where nanoparticles are synthesized inside the pores to tune optical absorption, emission, and index of refraction. The third class is aerogels where selected regions are reinforced or otherwise modified by photolithographic techniques. For example, photolithographic techniques can be used to reinforce selected aerogel regions by polymer crosslinking. The character of the modification can be adapted, etc.