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Σεμινάριο Τμήματος Επιστήμης των Υλικών

  • Στοιχεία επικοινωνίαςΒασίλης Γιαννόπαπας, Λέκτοραςemail:vyannop AT upatras.gr

08.11.2007, Αίθουσα Σεμιναρίων Τμήματος Επιστήμης των Υλικών

Την Πέμπτη 8 Νοεμβρίου και ώρα 5.00 μ.μ. στην αίθουσα σεμιναρίων του Τμήματος Επιστήμης των Υλικών ο Prof. Nicolas Leventis, Department of Chemistry, University of Missouri-Rolla, Rolla, U.S.A., θα δώσει διάλεξη με θέμα:

« Three Dimensional Core-Shell Superstructures: Mechanically Strong Aerogels»

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.

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