A new class of strong, lightweight, porous materials has been invented as an outgrowth of an effort to develop reinforced silica aerogels. The new material, called X-Aerogel is less hygroscopic, but no less porous and of similar density to the corresponding unmodified aerogels. However, the property that sets XAerogels apart is their mechanical strength, which can be as much as two and a half orders of magnitude stronger that the unmodified aerogels. X-Aerogels are envisioned to be useful for making extremely lightweight, thermally insulating, structural components, but they may also have applications as electrical insulators, components of laminates, catalyst supports, templates for electrode materials, fuel-cell components, and filter membranes.
In broad terms, X-Aerogels are formed by chemical reaction of a cross-linking agent with the surfaces of the nanoporous network of the native aerogel. The crosslinking agent may be a monomeric or an oligomeric precursor of a polymer that forms a conformal coating on the nanoparticles, reinforcing the underlying structure while preserving the mesoporosity. The nanoporous network itself may consist of silica, alumina, titania, vanadia, or other metal oxide aerogels. Research with various other oxide nanoparticle skeletal frameworks has led to X-Aerogels based on approximately 35 different metals from the Periodic Table.
The nanoparticles that comprise the aerogels can be cross-linked in their native form through the hydroxyl groups, which are found naturally on their surface. Thus, the first class of XAerogels utilizes isocyanates for crosslinking, which react both with the surface hydroxyl groups and any water adsorbed on the surfaces of the nanoparticles. This limits polymer accumulation only on the internal surfaces of the aerogel, leaving the mesopores empty. The result is a greatly reinforced structure at a minimal increase in density.
While the isocyanate cross-linked aerogels show great improvements in properties, relying on the native hydroxyl group functionally of aerogels for cross-linking limits the variety of possible precursors that can react with the mesoporous surfaces. This issue has been addressed by chemical modification of the aerogel itself. The mesoporous surface of silica has been modified with amines and olefins, and the resulting particles have been crosslinked with epoxides and with polystyrene. Many other combinations of surface functional groups and cross linkers can be envisioned, which would impart additional desired properties to the X-Aerogels.
This work was done by Nicholas Leventis, Mary Ann B. Meador, and James C. Johnston of Glenn Research Center and Eve F. Fabrizio and Ulvi Ilhan of Ohio Aerospace Institute.
Inquiries concerning rights for the commercial use of this invention should be addressed to:
NASA Glenn Research Center
Innovative Partnerships Office
Attn: Steve Fedor
Mail Stop 4–8
21000 Brookpark Road
Cleveland, Ohio 44135.
Refer to LEW-17685-1.