Monolithic, low-density 3-D assemblies of nanoparticles, known as aerogels, are pursued for unique properties above and beyond those of the individual building blocks. Specifically, since those materials are characterized by large internal voids (mesopores), they demonstrate low thermal conductivity, low dielectric constants and high acoustic impedance. Aerogels, however, are also extremely fragile materials, limiting their application to a few specialized environments, like for example as Cherenkov radiation detectors in certain nuclear reactors, as devices for capture of hypervelocity particles in space (NASA's Stardust Program), and as thermal insulation of electronic boxes aboard planetary vehicles such as the Sojourner Rover on Mars in 1997, and the two Mars Exploration Rovers Spirit and Opportunity in 2004.
The aerogel fragility problem is traced to well-defined weak points in their skeletal framework, the interparticle necks. Using the surface functionality of the inorganic nanoparticles as a focal point, we have directed attachment of a conformal polymer coating over the entire skeletal framework, bridging the nanoparticles and rendering all necks wider (see for example: N. Leventis et al. "Nano-Engineering Strong Silica Aerogels," NanoLetters 2002, 2, 957-960; N. Leventis "Three-Dimensional Core-Shell Superstructures: Mechanically Strong Aerogels," Acc. Chem. Res. 2007, 40, 874-884). Thus, although the bulk density may increase only by a factor of 3 (still an ultra-lightweight material), the mesoporosity (pores in the range 2-50 nm) remains unchanged, while the strength of the material can increase by up to a factor of 300 above the strength of the underlying inorganic framework. In that regard, polymer crosslinked aerogels may combine a multiple of the specific compressive strength of carbon fiber reinforced composite with the thermal conductivity of styrofoam. The crosslinked aerogel technology has been demonstrated with several different polymers such as polyurethanes/polyureas, epoxies and polyolefins, while ~35 different metal and semimetal sol-gel oxides from the periodic table have been crosslinked successfully yielding a combination of structural, magnetic and optical properties. Currently the technology is evaluated for application in thermal/acoustic insulation, ballistics, separation technology, dielectrics and catalysis.
Speaker: Nicholas Leventis
Department of Chemistry, University of Missouri-Rolla, Rolla, MO 65409, U.S.A.
Time: Monday, 5 November 2007, 13:00
NICHOLAS LEVENTIS BIOGRAPHICAL SKETCH
Nicholas Leventis received his B.S. degree in chemistry from the Chemistry Department of the University of Athens in 1980, and his Ph.D. in organic chemistry/photochemistry from Michigan State University with Peter Wagner in 1985. He spent three years as postdoctoral fellow with Mark Wrighton at MIT and he worked for six years in the private sector before coming to the Chemistry Department of the University of Missouri-Rolla as an Assistant Professor in 1994, advancing to Associate Professor in 1999 and to Professor in 2007. Dr. Leventis spent the summer of 1998 at the U.S. Naval Research Laboratory, Washington D.C., as a Senior Faculty Fellow. During an extended leave from UMR (September 2002-February 2006) Dr. Leventis joined as a Civil Servant (GS-14 promoted to GS-15 in June 2005) the Polymers Branch of the NASA Glenn Research Center in Cleveland, OH, where he established and directed research on polymer crosslinked aerogels.
In 1992 Dr. Leventis received the Arthur K. Doolitte Award of the Polymeric Materials Science and Engineering Section of the American Chemical Society for his work on electrochromic polymers. In 2005 Dr. Leventis received the NASA Exceptional Scientific Achievement Medal for "ground breaking research in the development of polymer cross-linked aerogels." This award is granted occasionally by the Agency for a significant, specific accomplishment or substantial improvement in operations, efficiency, service, financial savings, science, or technology, which contributes to the mission of NASA. Dr. Leventis' new aerogel technology has won the Nano 50TM Award twice, in year 2005 for "Reinforced Aerogels" as well as in 2007 for "Mechanically Strong, Polymer Crosslinked Aerogels (X-Aerogels)." Nano 50TM Awards recognize the top 50 technologies, products, and innovators that have significantly impacted - or are expected to impact - the state of the art in nanotechnology.
Besides aerogels, Dr. Leventis interests include physical organic chemistry, electrochemistry, polymers and inorganic materials and has published about 100 papers in all major areas of chemistry.