Three Dimensional Core-Shell Superstructures: Mechanically Strong Aerogels
Dr. Nicholas Leventis, Department of Chemistry,
University of Missouri-Rolla, Rolla, MO 65409, U.S.A.
Wednesday, February 13, 2008
Manning Hall room 201
Refreshments served at 2:30pm in Manning Hall room 222
*please note earlier start time to this seminar*
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
Currently the technology is evaluated for application in thermal/acoustic insulation,
ballistics, separation technology, dielectrics and catalysis.