Presentation on Aerogels - their properties, features, and applications

1. AEROGELS
(A special nanomaterial)
(Paper IV- Nanomaterials)
- Jaiswal Priyanka Balister
- M.Sc. II (Inorganic)
- Semester IV
- Mithibai College (2015-16)

2.  Introduction
• Aerogel was first created by Samuel Stephens
Kistler in 1931.
• Aerogels are the world's lightest solid materials,
composed of up to 99.98% air by volume.
• Highly porous and almost wispy in appearance,
aerogels produced from such materials as silica,
alumina, or zirconia can have densities as low as
just three times that of air.
• They appear as “foam like” translucent substance
referred to as “FROZEN SMOKE”.
• These interesting features make aerogels an ideal
material for industrial and commercial
applications.

3.  What are Aerogels made of…???
• The term aerogel does not refer to a particular substance, but rather to a geometry which a
substance can take on.
• Aerogels can be made of a wide variety of substances, including:
1. Silica
2. Most of the transition metal oxide (for example, iron oxide)
3. Most of the lanthanide and actinide metal oxides (for example, praseodymium oxide)
4. Several main group metal oxides (for example, tin oxide)
5. Organic polymers (such as resorcinol-formaldehyde, phenol-formaldehyde, polyacrylates,
polystyrenes, polyurethanes, and epoxies)
6. Biological polymers (such as gelatin, pectin, and agar agar)
7. Semiconductor Nanostructures (such as cadmium selenide quantum dots)
8. Carbon
9. Carbon Nanotubes
10. Metals (such as copper and gold)

4.  Aerogel Production
• Aerogels are produced by a chemical preparation technique known as the sol-gel
process
• It is followed by either supercritical extraction or modified ambient drying method.
• The sol-gel production process offers the ability to tailor the material properties for
specific applications.
• By adjusting the reaction conditions, such as pressure, temperature, and
stoichiometry, properties of the resulting aerogel (such as density, surface area,
porosity and pore size) can be adjusted and optimized for the intended application.
• During the gelation process dopants can be integrated into the sol and covalently
attached to the silica backbone, thus imparting functionality to the resulting
product.
• By adjusting the viscosity of the sol, we can prepare spin-coated thin films, fibres,
microspheres, or coatings.

5.  Silica Aerogel
• Silica aerogels, the most common form, are prepared as shown below.
• Starting with a solution of partially polymerized silica, water, alcohol, and a catalyst,
condensation and polymerization initiates and continues until the solid silica matrix
spans the container.

6.  Silica Aerogel Production- Reactions
• Hydrolysis
• Condensation
a. Water condensation:
b. Alcohol condensation:
where R = Vinyl, Alkyl, or Aryl groups.

7.  Properties
• Aerogel is a transparent material with interesting optical properties, such as high
light and solar transmittance.
• Aerogels are the lightest materials man has ever synthesized with a pore diameter of
few tens of nanometers.
• It typically has a density between 0.0011 to 0.5 g cm-3, with a typical average of
around 0.020 g cm-3. This means that aerogel is usually only 15 times heavier than
air, and has been produced at a density of only 3 times that of air.
• It is possible to have very high porosity (80-90% or even higher), very low density
and high surface area (500-1500 m2/g) for these aerogels.
• They have very low index of refraction (1-1.05) and very low speed of sound through
them.
• Very low value of thermal conductivity (0.003w/m.K) which is low than most
commonly used insulators makes them best available thermal insulator.

8.  Applications of Aerogels
• As aerogel has diverse chemical and physical properties, it has a wide range of
applications.
• Aerogel is starting to become a must-have material in the insulation industry and has
been used for several years in cavity injected wall insulation and insulating boards.
• Chemical Adaptation of Aerogels for Optical Applications: Silica aerogels are extremely
porous materials which can be made transparent. Optical applications depend on their
homogeneity. A second type of application is that silica aerogels can entrap all kinds of
molecules or dopants with special fluorescent properties.
• Luminescent Aerogels : Photoluminescent materials based on silica aerogels can be
made by encapsulation of various photoluminescent dopants during the gelation
process.
• Aerogel particles can be used as filler for other materials, to provide them with some
hardness, resistance to wear, or some thickening characteristics.
• Aerogels can be used as carriers of diverse components, for instance pigments.

9.  Recent Research Activity –
1. In NASA
• Since the 1960’s, aerogel has been used as the insulating material in spacesuits of
NASA astronauts as, it is extremely strong and can survive take off conditions easily.
• In the early 21st century, aerogel was employed in a very special role by NASA- to
capture space dust.
• Aerogel is being used in conjunction with the ‘Stardust’ mission, which aims to
bring back particles from space from beyond the Moon for the first time. This dust
is being primarily collected from the comet ‘Wild 2’.
• Aerogel is being used to capture this comet dust, as it will be able to trap the small
particles without physically altering them. When the particle hits the aerogel, it will
be travelling at speed of up to 6 times that of a rifle bullet, which means most
substances would not be able to slow the dust down without heating and thus
alteration taking place. With aerogel however, the dust buries itself into the porous
material and is gradually brought to a stop as it loses momentum.

10.  Recent Research Activity –
2. New Vehicle For Drug Delivery
• One provocative suggested use for
aerogels comes from pharmaceutical
researchers, who are investigating
aerogels for drug delivery.
• In this application, pharmaceutically
active compounds fill the aerogel’s
many pores.
• The drug-containing aerogel can then
be functionalized to seek specific
disease cells and release the drug.
Ligands on a drug-loaded aerogel particle target the
particle to disease cells, where it releases its
therapeutic contents

11.  Example for Drug Delivery
• For example, in a 2011 patent application (U.S. Patent Application
No. 20110086100), researchers describe a drug delivery mechanism that uses
polyethylene glycol (PEG) aerogel particles rather than the more traditional silica-
based aerogels.
• The researchers begin with highly porous PEG aerogel particles with an average
diameter of 2 µm, which are then coated with a protein called epidermal growth
factor.
• Because cancer cells overexpress receptors that recognize this protein, the coated
aerogel particles home in on cancer cells.
• The coating helps the aerogel get its drug cargo to intended cancer sites rather
than indiscriminately delivering it to cells.
• PEG aerogels are nontoxic and biocompatible, making them attractive drug delivery
vehicles.
• The chemotherapeutic substances that are poorly soluble in water are readily
incorporated in high concentration in PEG aerogels.

12.  Recent Research Activity –
3. Soaking Up Oil Spills
• In 2002, researchers at Lawrence Livermore National Laboratory(LLNL) filed a
patent for a method to recover oil from spills using hydrophobic sol-gels and
aerogels.
• The hydrophobic aerogels, synthesized from tetramethylorthosilicate and (3,3,3-
trifluoropropyl) trimethoxysilane, could absorb significant amounts of oil from
mixtures of oil and salt water.
• The CF3-functionalized aerogel absorbed oil from mixtures of crude oil and saltwater
in ratios as high as 237 parts oil to 1 part aerogel.
• The same researchers claim that fluorinated silica aerogels are an alternative to the
standard granulated activated carbon methods for extracting organic liquids from
aqueous solutions.
• The researchers show that the water-shedding properties of the hydrophobic silica
aerogels provide a more efficient separation of organic materials from water.

13.  Recent Research Activity –
4. Composite Fibers Provide Protection
• Given their lightweight and insulating properties, aerogels are an obvious choice for
use in fabrics and clothing meant for extreme environments.
• Inventors from the University of Science & Technology of China created a clothing
material with a thermal insulation layer manufactured from an aerogel composite
containing DuPont’s Nomex fiber.
• The aerogel composite layer has a thermal conductivity of just 0.021 watts per meter
kelvin. They received a Chinese patent on this work in 2011 (CN 202514650).
• This flame-retardant, chemical-corrosion-resistant, and air-permeable material has in
every sq.cm. of fabric 7,000 pores, each with an average diameter of 1,000 nm. The
patented material can be used for manufacturing fire- or cold-weather-proof suits, as
well as hot- and cold-temperature-resistant gloves, helmets, and linings to protect
fire responders, trade workers, and adventurers alike.

14.  References
1. NANOTECHNOLOGY : PRINCIPLES AND PRACTICES, 3rd edition, Sulabha K. Kulkarni
2. L. W. Hrubesh, “Aerogels: the world's lightest solids,” Chemistry and Industry, no. 24,
pp. 824–827, 1990.
3. http://cen.acs.org/articles/92/i4/Composite-Fibers-Provide-Protection.html
4. http://cen.acs.org/articles/92/i4/Soaking-Oil-Spills.html
5. http://cen.acs.org/articles/92/i4/New-Vehicle-Drug-Delivery.html