Oh and by the way, the coating also helps prevent heat loss out of pipes and tanks, which means that heat (and money) that would otherwise be wasted goes where it’s supposed to go.  Energy literally equals money in a refinery and, believe it or not <20% of all of the pipelines in refineries are insulated due to the cost and hassle associated with installing and maintaining insulation on the pipes.  Additionally, traditional insulation materials can trap moisture underneath them, causing the pipe to rust under the insulation (corrosion under insulation, or “CUI”).  Looks like this stuff would make insulating refineries paint-on easy?

“Cool” stuff, Cabot!  Read the press release here.

On that note, Aerogel.org is getting ready to rev up with some great new content, including long-overdue podcasts and videos!  Stay tuned.

http://www.discovery.com/tell-a-lie

Watch the clip here:

To paraphrase aerogel scientist Dr. Debra Rolison, here’s a way to think about functionalization:

If making an aerogel is like building a house, then functionalization is like painting, decorating, and putting your stuff inside the house so that you can actually live, work, and have fun in it!

Functionalization can:

• Make a water-absorbing material waterproof
• Change the color of a material
• Render a surface antibiotic
• Make chemical sensors (“artificial noses”)
• Make non-magnetic materials magnetic
• Make sophisticated batteries
• …and more!

Flat surfaces such as silicon wafers or glass are commonly functionalized to make useful and interesting materials and devices.  But aerogels, with  ultrahigh surface areas wrapped up inside their porous skeletal frameworks, can also be functionalized to make materials with even more amazing properties than ordinary aerogels!

Aerogels are Three-Dimensional Surfaces

While aerogels are generally three-dimensional materials, they contain a tremendous amount of surface area.  The surface of each and every nanosized strut that makes up the open-porous skeleton of the aerogel can potentially serve as a surface for molecules or particles to be attached to.   And there’s a lot of surface area wrapped inside an aerogel–a typical piece of silica aerogel, say with a density of 0.1 g/cm³, easily has a surface area of 750 m²/g, which means a ice-cube sized piece having 2.2-cm sides (a little less than a cubic inch) has 750 m², about 10% of a soccer (football) field.

Here’s an analogy to understand how aerogels can contain so much surface area in such a small volume.  Imagine taking a piece of thick construction paper and crumpling up into a ball (and imagine further it doesn’t uncrumple itself when you let go).  Now imagine taking a piece of newspaper and crumpling it into a ball.  Certainly, you would be able to crumple the newspaper up into a smaller ball than the construction paper since it’s thinner, which means you would need to crumple up a much larger piece of newspaper to get the same size ball as your crumpled construction paper.  Now imagine your paper was only a few hundred atoms thin.  It would take a very large sheet of this hypothetical, nanoscopically thin paper to get the same size ball as your original ball of construction paper.  Similarly, aerogels, made up of nanoscopically thin struts link together in a three-dimensional network, pack a lot of surface area into a small volume!  The zillions of nooks and crannies carved out by these tiny struts add up to a lot of surface area in a small volume.

Why Aerogels Are Great Things to Functionalize

Usually when you functionalize something, the molecules you’re functionalizing with do something you care about.  They soak stuff up you want to soak up, the light up when something you want to know about touches them, they prevent things from sticking you don’t want to stick, etc.  And generally, the more of those molecules you can cram into a small space, the more powerful, efficient, and effective your material will be at doing what you want it to do.

Aerogels offer lots of advantages in this regard:

• Aerogels pack tremendous surface into a small volume (that is, they have a high surface-to-volume ratio)
• Aerogel backbones can be made of many different substances, providing tremendous chemical flexibility
• Aerogels can frequently made through ambient-temperature bench-top processes
• The open pore network of aerogels enables movement (mass transport) of stuff through the aerogel, providing avenues for getting things you might want to detect or adsorb to the functional groups that will sense or adsorb them

Waterproof Aerogels: An Example of Functionalization

One classic example of functionalization of aerogels is the making of hydrophobic (waterproof) silica aerogels.  Silica aerogels like the kind described in the base-catalyzed recipe using TMOS under the Make section are normally hydrophilic, that is, they readily absorb moisture from the air (which causes them to shrink and become cloudy over time) and wick up liquid water on contact (which causes them to shrivel up and densify).  This is because of surface hydroxyl (-OH) groups that cover the struts of the aerogel’s skeleton–sticky, polar groups to which water can readily stick by hydrogen bonding.   To make a waterproof silica aerogel, we can replace the hydrogen on these sticky -OH groups with a much less sticky, non-polar group called trimethylsilyl (-Si(CH₃)₃).  Transforming just 30% of these -OH groups into -OSi(CH₃)₃ groups is enough to make the struts of the aerogel repel water, allowing the aerogel to float in water indefinitely without wicking water into its pore network (which would cause the aerogel to shrivel up).

You can read more about how silica aerogels are made hydrophobic through functionalization under Learn>Flavors of Aerogel>Silica Aerogel and even how to make hydrophobic aerogels yourself under Make>Aerogel Recipes>Silica Aerogel>Hydrophobic and Subcritically-Dried Silica Aerogel.

How to Functionalize an Aerogel

There are three points in the process of making an aerogel where you can functionalize its surface: during gelation of the precursor gel, after gelation of the precursor gel, and after supercritical drying.

Functionalizing During Gelation

Special reactive monomers are included in the sol-gel process used to produce the gel precursor, resulting in a gel network with special chemical groups poking out of its struts.  Examples include using methyltrimethoxysilane along with TMOS to put hydrophobic methyl (-CH₃) groups onto a silica gel’s backbone so that the resulting aerogel will be hydrophobic.

• Advantage: Simplifies processing, reduces number of steps
• Disadvantage: Can be very tricky to develop a gel recipe that incorporates special reactive molecules as they can change pH, gel time, and chemical pathways needed to form the gel, and themselves may react with chemicals and solvents needed to form the gel.

Functionalizing After Gelation

Once a gel has formed, special reactive molecules can be introduced into the gel’s pore network by diffusion.  Once the reactive molecules find their way into the pore network, a chemical reaction between them and the gel backbone can be initiated.  The result is the bonding of the reactive molecule to the gel backbone, covering the backbone with new chemical groups!  Examples include the reaction of trimethylchlorosilane with -OH groups to form -OSi(CH₃)₃ groups on the backbone to render the resulting aerogel hydrophobic.

• Advantage: Ensures proper functionalization of the gel backbone, allows greatest flexibility and control over how functionalization happens
• Disadvantages: Involves diffusion-limited infilitration which is slow and ill-suited for large, low-aspect-ratio monoliths such as cubes and spheres.  May require exchange of pore fluid for a solvent that will not react with functionalization agent.

Functionalizing After Supercritical Drying

Chemically similar to functionalization of a wet gel after gelation as described  for above, except for that the reactive molecules are introduced as a vapor into the pore network of an aerogel (not a wet gel).  The vaporous reactive molecule diffuses its way through the dry pore network and finds its way to a surface group on a strut in the pore network, where a chemical reaction can be initiated result in the formation of special functional groups on the surface of the strut.

• Advantage: Eliminates tedious, slow solvent exchanges needed to functionalize after gelation, does not interfere with gel chemistry
• Disadvantages: Diffusion-limited process ill-suited for thick low-aspect-ratio monoliths, can be tricky to get reactive molecules into the aerogel pore network without invoking capillary collapse (shrinking/shrivelling), may be difficult to get reactive molecule for functionalization into vaporous form, often times more hazardous than liquid-based processing

Cool Stuff You Can Do With Functionalization

We mentioned waterproof silica aerogels as an example of functionalization already, but there’s lots of other things you can do through functionalization, like:

• Make brittle silica and metal oxide aerogels superstrong and tough by functionalizing the surface with polymers
• Make precursors for metallic aerogels by functionalizing metal oxide aerogels with carbon-rich polymers
• Make carbon aerogels into battery-like materials by functionalizing with electrochemical coatings such as manganese dioxide
• Make silica aerogels into oxygen sensors by functionalizing with oxygen-sensitive fluorophores
• Make carbon aerogels into efficient catalysts by functionalizing with precious metals
• Make silica or carbon aerogels into hydrogen storage materials by functionalizing with metals that form hydrides
• Make aerogels that absorb 20x their weight in oil by functionalizing with oleophilic groups
• Make aerogels that filter biomolecules like DNA by functionalizing with the complementary DNA sequence

And lots of other things too!

Functionalize Something!

Hopefully you now have a perspective on why functionalization of aerogels is a powerful way to make new materials and one of the primary reasons why aerogels have such great technological potential.  The fun starts when you think about aerogels as palettes for creating functional, active materials, not only as material destinations themselves.

]]> http://www.aerogel.org/?feed=rss2&p=1918 0 Aerogel.orgAerogels put the fun in functionalization! Learn how you can install new features into aerogels by attaching molecules to the skeletal surface of the aerogel.Functionalization is the process of adding new functions, features, capabilities, or properties to a material by changing the surface chemistry of the material.  It is a fundamental technique used throughout chemistry, materials science, biological engineering, textile engineering, and nanotechnology. Functionalization is performed by attaching molecules or nanoparticles to the surface of a material, sometimes with a chemical bond but sometimes just through adsorption (that is, the thing you&#039;re trying to attach sticks to the surface without forming a covalent or ionic bond). To paraphrase aerogel scientist Dr. Debra Rolison, here&#039;s a way to think about functionalization: If making an aerogel is like building a house, then functionalization is like painting, decorating, and putting your stuff inside the house so that you can actually live, work, and have fun in it! Functionalization can: Make a water-absorbing material waterproof Change the color of a material Render a surface antibiotic Make chemical sensors (&quot;artificial noses&quot;) Make non-magnetic materials magnetic Make sophisticated batteries ...and more! Flat surfaces such as silicon wafers or glass are commonly functionalized to make useful and interesting materials and devices.  But aerogels, with  ultrahigh surface areas wrapped up inside their porous skeletal frameworks, can also be functionalized to make materials with even more amazing properties than ordinary aerogels! Aerogels are Three-Dimensional Surfaces While aerogels are generally three-dimensional materials, they contain a tremendous amount of surface area.  The surface of each and every nanosized strut that makes up the open-porous skeleton of the aerogel can potentially serve as a surface for molecules or particles to be attached to.   And there&#039;s a lot of surface area wrapped inside an aerogel--a typical piece of silica aerogel, say with a density of 0.1 g/cm3, easily has a surface area of 750 m2/g, which means a ice-cube sized piece having 2.2-cm sides (a little less than a cubic inch) has 750 m2, about 10% of a soccer (football) field. Here&#039;s an analogy to understand how aerogels can contain so much surface area in such a small volume.  Imagine taking a piece of thick construction paper and crumpling up into a ball (and imagine further it doesn&#039;t uncrumple itself when you let go).  Now imagine taking a piece of newspaper and crumpling it into a ball.  Certainly, you would be able to crumple the newspaper up into a smaller ball than the construction paper since it&#039;s thinner, which means you would need to crumple up a much larger piece of newspaper to get the same size ball as your crumpled construction paper.  Now imagine your paper was only a few hundred atoms thin.  It would take a very large sheet of this hypothetical, nanoscopically thin paper to get the same size ball as your original ball of construction paper.  Similarly, aerogels, made up of nanoscopically thin struts link together in a three-dimensional network, pack a lot of surface area into a small volume!  The zillions of nooks and crannies carved out by these tiny struts add up to a lot of surface area in a small volume. Why Aerogels Are Great Things to Functionalize Usually when you functionalize something, the molecules you&#039;re functionalizing with do something you care about.  They soak stuff up you want to soak up, the light up when something you want to know about touches them, they prevent things from sticking you don&#039;t want to stick, etc.  And generally, the more of those molecules you can cram into a small space, the more powerful, efficient, and effective your material will be at doing what you want it to do. Aerogels offer lots of advantages in this regard: Aerogels pack tremendous surface into a small volume (that is, they have a high surface-to-volume ratio) Aerogel backbones can be made of many different substances, providing tremendous chemical flexibility Aerogels can frequently made through ambient-temperature bench-top processes The open pore network of aerogels enables movement (mass transport) of stuff through the aerogel, providing avenues for getting things you might want to detect or adsorb to the functional groups that will sense or adsorb them Waterproof Aerogels: An Example of Functionalization One classic example of functionalization of aerogels is the making of hydrophobic (waterproof) silica aerogels.  Silica aerogels like the kind described in the base-catalyzed recipe using TMOS under the Make section are normally hydrophilic, that is, they readily absorb moisture from the air (which causes them to shrink and become cloudy over time) and wick up liquid water on contact (which causes them to shrivel up and densify).  This is because of surface hydroxyl (-OH) groups that cover the struts of the aerogel&#039;s skeleton--sticky, polar groups to which water can readily stick by hydrogen bonding.   To make a waterproof silica aerogel, we can replace the hydrogen on these sticky -OH groups with a much less sticky, non-polar group called trimethylsilyl (-Si(CH3)3).  Transforming just 30% of these -OH groups into -OSi(CH3)3 groups is enough to make the struts of the aerogel repel water, allowing the aerogel to float in water indefinitely without wicking water into its pore network (which would cause the aerogel to shrivel up). You can read more about how silica aerogels are made hydrophobic through functionalization under Learn&gt;Flavors of Aerogel&gt;Silica Aerogel and even how to make hydrophobic aerogels yourself under Make&gt;Aerogel Recipes&gt;Silica Aerogel&gt;Hydrophobic and Subcritically-Dried Silica Aerogel. How to Functionalize an Aerogel There are three points in the process of making an aerogel where you can functionalize its surface: during gelation of the precursor gel, after gelation of the precursor gel, and after supercritical drying. Functionalizing During Gelation Special reactive monomers are included in the sol-gel process used to produce the gel precursor, resulting in a gel network with special chemical groups poking out of its struts.  Examples include using methyltrimethoxysilane along with TMOS to put hydrophobic methyl (-CH3) groups onto a silica gel&#039;s backbone so that the resulting aerogel will be hydrophobic. Advantage: Simplifies processing, reduces number of steps Disadvantage: Can be very tricky to develop a gel recipe that incorporates special reactive molecules as they can change pH, gel time, and chemical pathways needed to form the gel, and themselves may react with chemicals and solvents needed to form the gel. Functionalizing After Gelation Once a gel has formed, special reactive molecules can be introduced into the gel&#039;s pore network by diffusion.  Once the reactive molecules find their way into the pore network, a chemical reaction between them and the gel backbone can be initiated.  The result is the bonding of the reactive molecule to the gel backbone, covering the backbone with new chemical groups!  Examples include the reaction of trimethylchlorosilane with -OH groups to form -OSi(CH3)3 groups on the backbone to render the resulting aerogel hydrophobic. Advantage: Ensures proper functionalization of the gel backbone, allows greatest flexibility and control over how functionalization happens Disadvantages: Involves diffusion-limited infilitration which is slow and ill-suited for large, low-aspect-ratio monoliths such as cubes and spheres.  May require exchange of pore fluid for a solvent that will not react with functionalization agent. Functionalizing After Supercritical Drying Chemically similar to functionalization of a wet gel after gelation as described  for above, except for that the reactive molecules are introduced as a vapor into the pore network of an aerogel (not a wet gel).  The vaporous reactive molecule diffuses its way through the dry pore network and finds its way to a surface group on a strut in the pore network, where a chemical reaction can be initiated result in the formation of special functional groups on the surface of the strut. Advantage: Eliminates tedious, slow solvent exchanges needed to functionalize after gelation, does not interfere with gel chemistry Disadvantages: Diffusion-limited process ill-suited for thick low-aspect-ratio monoliths, can be tricky to get reactive molecules into the aerogel pore network without invoking capillary collapse (shrinking/shrivelling), may be difficult to get reactive molecule for functionalization into vaporous form, often times more hazardous than liquid-based processing Cool Stuff You Can Do With Functionalization We mentioned waterproof silica aerogels as an example of functionalization already, but there&#039;s lots of other things you can do through functionalization, like: Make brittle silica and metal oxide aerogels superstrong and tough by functionalizing the surface with polymers Make precursors for metallic aerogels by functionalizing metal oxide aerogels with carbon-rich polymers Make carbon aerogels into battery-like materials by functionalizing with electrochemical coatings such as manganese dioxide Make silica aerogels into oxygen sensors by functionalizing with oxygen-sensitive fluorophores Make carbon aerogels into efficient catalysts by functionalizing with precious metals Make silica or carbon aerogels into hydrogen storage materials by functionalizing with metals that form hydrides Make aerogels that absorb 20x their weight in oil by functionalizing with oleophilic groups Make aerogels that filter biomolecules like DNA by functionalizing with the complementary DNA sequence And lots of other things too! Functionalize Something! Hopefully you now have a perspective on why functionalization of aerogels is a powerful way to make new materials and one of the primary reasons why aerogels have such great technological potential.  The fun starts when you think about aerogels as palettes for creating functional, active materials, not only as material destinations themselves. http://www.aerogel.org/?p=1918 http://feedproxy.google.com/~r/aerogel/~3/tjLukCn3xMY/ http://www.aerogel.org/?p=1244#comments Sat, 16 Apr 2011 19:54:50 +0000 ssteiner@aerogel.org (Aerogel.org) http://www.aerogel.org/?p=1244 In documenting aerogels, borrowing a few basic photographic techniques will serve you far better than the standard “point and shoot” method.  Because of its nebulous and often transparent appearance, silica aerogel will often confuse the default settings on consumer and professional grade cameras.  Following a few basic guidelines will result in sharper images, with greater surface detail and texture imaged clearly – much better for communicating the quality of the samples you have to others.

Some of the most common problems I have encountered while photographing samples are outlined in the following sections:

• Focusing
• Establishing Scale
• Stability and lighting
• Capturing blueness

Focus on This

The greatest difficulty often experienced when photographing silica or other transparent aerogels will be obtaining correct focus on your sample.   This is caused by a lack of sharp lines around and within monolith.  With no contrast, your camera has nothing to focus on, which often results in the “wild focusing back and forth” that often frustrates our efforts to capture quickly moving objects like pets or children.

In most instances, with your sample placed under strong lighting, this can be overcome simply by depressing the shutter release halfway while aiming the camera at another “reference” object (not pets or children) at approximately the same distance as the camera.

With the shutter release halfway depressed (thus locking the focal distance), re-aim the camera at your sample and push it in entirely.  This will release your shutter without the focus resetting and record your image in correct focus.

A handy technique I often use is to place a sheet of graph paper underneath my sample and focus immediately to the left or  right of the monolith.  This solves both the focus issue and problem of establishing scale mentioned next.

How Big Is It?: Establishing Scale

Often, small samples are photographed without a point of reference, leaving the viewer confused as to the size of the features they are following.  All-white backgrounds may work well for product shots  and Apple advertising, but will make it difficult to accurately communicate the qualities of your samples.

The easiest method for establishing a sense of scale is to add a ruler in the picture, or graph paper as outlined above.  I would recommend against placing printed words around or behind your monolith as type size is easily manipulated and therefore hard to verify after the fact.  Shots in-hand are beautiful but reduce your ability to slow your shutter speed and may to add to blurriness indoors.

Tripods vs. Light

In indoor settings, most cameras will defer to a slow shutter speed setting, meaning the shutter will stay open for an extended period to let enough light in to properly expose the sensor.  The downfall of this is that indoor shots or shots in dark settings (often times a basement or garage laboratory) will result in blurry “drunk-effect” images.  A general rule of thumb is that 1/30 of a second tends to be the longest a handheld shot will remain in focus – anything longer like 1/15 of a second or more is very hard to keep in focus.

Tripods are a good way to deal with your camera’s natural tendency  to slow down in response to dimmer light without blurring out the picture – This is often essential when photographing in a controlled lighting situation (a room without widows or a situation where moving delicate gels is not a good idea).  Adding more light is helpful, but generally avoid overly spotlights nearby as this creates dark shadows and blown out (white) highlights.  The ideal is to raise the light level evenly across the whole scene you are photographing – rather than placing your sample in a moody spotlight – unless you’re trying to make a dramatic effect.

Getting Deep Blue

One of the most difficult tricky things to achieve (and most desirable) when photographing silica aerogel is to photograph the blue of rayleigh scattering through the material.  This subtle effect can be enhanced through a few easy steps.

First, place your monolith against a black background.  Much like the sky (which is backdropped by the inky awesomeness of SPACE), the blue is most evident when there is little or no backlighting to promote Mie scattering (the orange that this produces tends to wash out the blue.

Second, disable any flash your camera has – against a black background, the flash will blow out the color of the monolith, most often returning an image of a white, indistinct blob.

Finally, try to light your sample from the direction the camera is shooting from – this will cause the maximum amount of light to bounce and scatter blue to your camera.  You be getting the “frozen smoke” appearance in no time!

Discovery of Aerogels

Coherent expanded aerogels and jellies

By Kistler, S. S.

Nature (London, United Kingdom) (1931), 127, 741.

The liquid in a gel can be replaced by a gas with little or no shrinkage. The liquid is displaced successively by liquids that are completely miscible with the preceding and succeeding one (H₂O, EtOH, Et₂O for instance), the last one having a low critical temperature. The jelly is placed in an autoclave with an excess of liquid, and the temperature is raised above the critical point. Upon allowing the gas to escape, an aerogel is obtained. Silica gel of apparent density as low as 0.02 was preared in this manner as a slightly opalescent although quite transparent glassy solid.

First Synthesis of Organic and Metal Oxide Aerogels

Coherent expanded aerogels

By Kistler, S. S.

Journal of Physical Chemistry (1932), 36, 52-64.

cf. C. A. 25, 3901. Aerogels were made by successive displacements of the liquid in a gel by other liquids, each of which must be completely miscible with the preceding one and the last of which has a low critical temperature so that it may be displaced by a gas. Aerogels of SiO₂, Al₂O₂, WO₃, Fe₂O₂, SnO₂, Ni tartrate, cellulose, nitrocellulose, gelatin, agar and egg aluminum were made by removal of water from the normal gels. Rubber offered some difficulties but it was believed that these might be surmounted. The preparation and properties of these aerogels are briefly described and some discussion of the structure is included.

Identification of the Ultralow Thermal Conductivity of Aerogels

Thermal conductivity of silica aerogel

By Kistler, S. S.; Caldwell, A. G.

Journal of Industrial and Engineering Chemistry (Washington, D. C.) (1934), 26, 658-62.

An application is described for the measurement of heat conductivities of materials under variable mechanical and air pressures. Silica aërogel powders of different sieve analyses possess the lowest heat conductivity at atmospheric pressure of any insulator so far reported. The average value for the aërogel powder is 10% less than that for still air. A 30% decrease in conductivity is obtained when the gel is measured in the presence of CCl₂F₂, while the conductivity in vacuum is only 15% of normal. Mechanical pressure up to 15 lbs. per sq. in. does not greatly increase the conductivity in vacuum. An explanation of the very low conductivity is given, and several suggestions for commercial utilization are offered.

Introduction of Metal Alkoxides for Production of Aerogels

Inorganic oxide aerogels

By Teichner, S. J.; Nicolaon, G. A.; Vicarini, M. A.; Gardes, G. E. E.

Advances in Colloid and Interface Science (1976), 5(3), 245-73.

A method of preparation of aerogels of SiO₂, Al₂O₃, TiO₂, ZrO₂, MgO, and mixed oxides was developed. The corresponding alcoholate, dissolved in an organic solvent, such as alcohol or C₆H₆, is hydrolyzed at room temperature and the solvent is evacuated under hypercritical conditions in an autoclave. This method does not require the purification of the precipitated metal oxide nor the substitution of an organic solvent for water which is necessary when the initial gel is prepared in H₂O. SiO₂ aerogels, having a surface area of 1000 m² g^-1, a pore volume of 18 cm^{3 g-1}, and an apparent density of 0.05 g cm^-3 were obtained. These aerogels are hydrophobic, but can be converted to hydrophilic aerogels and may also be made transparent. The transparent SiO₂ aerogels are used as Cherenkov radiators for ionizing radiations. Aerogels of other oxides also exhibit high values of their textural characteristics in comparison with those of oxide gels prepared in a conventional way (xerogels). Mixed oxide aerogels (ZrO₂-MgO, Al₂O₃-MgO, TiO₂-MgO) exhibit higher surface areas than corresponding pure oxide aerogels. The method is also used to prepared oxide-supported metal or metal oxide aerogels for catalysts.

Introduction of Helium Pycnometry for Measuring the Skeletal Density of Aerogels

Skeletal density of silica aerogels

By Woignier, T.; Phalippou, J.

Journal of Non-Crystalline Solids (1987), 93(1), 17-21.

The skeletal density of silica aerogels, produced by hypercritical drying of gels, is studied by He pycnometry. The bulk and the skeletal densities vary as functions of parameters such as TMOS concentration, pH, and densifying heat treatment. Skeletal densities were slightly lower than that of vitreous silica. The results are compared to values obtained on xerogels.

Development of Resorcinol-Formaldehyde and Carbon Aerogels

Resorcinol-formaldehyde aerogels and their carbonized derivatives

By Pekala, R. W.; Kong, F. M.

Polymer Preprints (American Chemical Society, Division of Polymer Chemistry) (1989), 30(1), 221-3.

The morphology and mechanical properties of HCHO-resorcinol (I) copolymer aerogels and their carbonized derivatives were studied and compared. Both pristine and carbonized aerogels exhibited densities 30-300 mg/cm³, cell/pore sizes <1000 Å, and an open cell structure with continuous porosity. The density and surface area of the aerogels decreased with increasing [I]/[Na₂CO₃ polymn. catalyst] ratio. The carbonized aerogels had superior mechanical properties than the pristine aerogels.

Method for Producing Ultralow Density Silica Aerogels

Transparent ultralow-density silica aerogels prepared by a two-step sol-gel process

By Tillotson, T. M.; Hrubesh, L. W.

Journal of Non-Crystalline Solids (1992), 145(1-3), 44-50.

Interest in lowering aerogel densities for applications involving high-energy charged particle detection via the Cherenkov effect has led to the development of a 2-step sol-gel method for preparing ultralow-density aerogels. The method was used to produce uncracked, transparent aerogel tiles with densities 3-80 kg/m³. Comparative characterization of conventional single-step base-catalyzed aerogels to aerogels prepared by this 2-step approach is presented. Results indicate that the aerogel microstructure for the 2-step approach differs from the bead-like structure proposed for single-step base-catalyzed tetramethoxysilane (TMOS) aerogels. TEM micrographs of aerogels prepared by the 2-step method show an interlinked polymer-chain-like structure with an average chain diameter of 2-3 nm and an average chain length of ∼15 nm. UV-visible spectrophotometry shows the transmittance over the visible spectrum (400-800 nm) to be improved for the 2-step aerogels by ≤30%. Other measurements of the ultralow-density aerogels include BET surface area, and compressive modulus.

Development of Subcritical Drying

Preparation of low-density aerogels at ambient pressure for thermal insulation

By Smith, Douglas M.; Deshpande, Ravindra; Brinker, C. Jeffrey

Ceramic Transactions (1993), 31(Porous Materials), 71-80.

Low density ceramic aerogels have numerous properties which suggest a number of applications such as ultrahigh-efficiency thermal insulation. However, the commercial viability of these materials has been limited by their high cost associated with drying at supercritical pressures, low stability to water vapor, and low mechanical strength. Normally, critical point drying is employed to lower the surface tension and hence, capillary pressure, of the pore fluid to essentially zero before drying. A process is presented to control capillary pressure and gel matrix strength by employing a series of aging and pore chemical modification steps such that the gel shrinkage is minimal during rapid drying at ambient pressure. The total processing time from gelation to the final dried product is less than 48 h. The properties (density, surface area, pore size, SAXS) of aerogel monoliths prepared from base-catalyzed silica gels using this technique, CO₂ critical point drying, and supercritical ethanol drying are compared. An additional advantage of this approach is that the final gels are hydrophobic. Densities in the range of 0.15 to 0.3 g/cm³ with pore sizes less than 100 nm are routinely made. Thermal conductivity is on the order of 0.02 W/mK at room temperature and atmospheric pressure.

Reintroduction of Epoxide-Assisted Gelation for Preparing Metal Oxide Aerogels

Synthesis of lanthanide and lanthanide-silicate aerogels

By Tillotson, T.M.; Sunderland, W.E.; Thomas, I.M.; Hrubesh, L.W.

Journal of Sol-Gel Science and Technology (1994), 1(3), 241-9.

The preparation of lanthanide oxide and mixed lanthanide-silicate aerogels from the chlorides of erbium, praseodymium, and neodymium was investigated. A two-step sol-gel method is described for preparing the mixed aerogels by using a sub-stoichiometric amount of water in the first step to prepare a partially condensed silica-lanthanide precursor. The lanthanide oxide aerogels were prepared directly from the chlorides by using propylene oxide as a scavenger for reaction generated hydrochloric acid. The aerogel microstructures vary from colloidal for the lanthanide oxide and high weight percent lanthanide-silicate aerogels to polymeric for the low weight percent lanthanide-silicate aerogels. This change in microstructure is also indicated by BET analyses, which show that the surface area decreases with increasing lanthanide concentration. In general, a decrease in lanthanide content occurred during the supercritical drying step due to insufficient linking and subsequent washing out of the lanthanide from the gels. Also, the retention efficiency for the lanthanide increases with increasing silica concentration and makes quantitative doping by this method practical only for the lower lanthanide concentrations.

First Demonstration of a Supercapacitor Using Carbon Aerogel

The Aerocapacitor: An electrochemical double-layer energy-storage device

By Mayer, S. T.; Pekala, R. W.; Kaschmitter, J. L.

Journal of the Electrochemical Society (1993), 140(2), 446-51.

Unique types of carbon foams, developed at Lawrence Livermore National Laboratory, were used to make an “Aerocapacitor.”. The aerocapacitor is a high power-density, high energy-density, electrochemical double-layer capacitor which uses carbon aerogels as electrodes. These electrodes possess very high surface area per unit volume and are electrically continuous in both the carbon and electrolyte phase on a 10 nm scale. Aerogel surface areas range from 100 to 700 m²/cm³ (as measured by BET analysis), with bulk densities of 0.3-1.0 g/cm³. This morphology permits stored energy to be released rapidly, resulting in high power densities (7.5 kW/kg). Materials parameterization was performed, and device capacitances of several tens of Farads per g and per cm³ of aerogel were achieved.

Refinement of Epoxide-Assisted Gelation for Preparing Metal Oxide Aerogels

New sol-gel synthetic route to transition and main-group metal oxide aerogels using inorganic salt precursors

By Gash, A. E.; Tillotson, T. M.; Satcher, J. H., Jr.; Hrubesh, L. W.; Simpson, R. L.

Journal of Non-Crystalline Solids (2001), 285(1-3), 22-28.

We have developed a new sol-gel route to synthesize several different transition and main-group metal oxide aerogels. The approach is straightforward, inexpensive, versatile, and it produces monolithic microporous materials with high surface areas. Specifically, we report the use of epoxides as gelation agents for the sol-gel synthesis of chromia aerogels and xerogels from simple Cr(III) inorganic salts. The dependence of both gel formation and its rate was studied by varying the solvent used, the Cr(III) precursor salt, the epoxide/Cr(III) ratio, as well as the type of epoxide employed. All of these variables were shown to affect the rate of gel formation and provide a convenient control of this parameter. Dried chromia aerogels were characterized by high-resolution TEM (HRTEM) and nitrogen adsorption/desorption analyses, results of which will be presented. The results presented here show that rigid monolithic metal oxide aerogels can be prepared from solutions of their respective metal ion salts (Fe³⁺, Al³⁺, In³⁺, Ga³⁺, Zr⁴⁺, Hf⁴⁺, Ta⁵⁺, Nb⁵⁺, and W⁶⁺), provided the formal oxidation state of the metal ion is ≥ +3. Conversely, when di-valent transition metal salts are used precipitated solids are the products.

Invention of Mechanically Robust X-Aerogels

Nanoengineering strong silica aerogels

By Leventis, Nicholas; Sotiriou-Leventis, Chariklia; Zhang, Guohui; Rawashdeh, Abdel-Monem M.

Nano Letters (2002), 2(9), 957-960.

In the quest for strong lightwt. materials, silica aerogels would be very attractive, if they were not so fragile. The strength of silica aerogel monoliths has been improved by a factor of >100 through crosslinking the nanoparticle building blocks of preformed silica hydrogels with poly(hexamethylene diisocyanate). Composite monoliths are much less hygroscopic than native silica, and they do not collapse when in contact with liqs.

Synthetic Pathway for Producing Semiconducting Metal Chalcogenide Aerogels

Porous Semiconductor Chalcogenide Aerogels

By Mohanan, Jaya L.; Arachchige, Indika U.; Brock, Stephanie L.

Science (2005), 307(5708), 397-400.

Chalcogenide aerogels based entirely on semiconducting II-VI or IV-VI frameworks have been prepd. from a general strategy that involves oxidative aggregation of metal chalcogenide nanoparticle building blocks followed by supercrit. solvent removal. The resultant materials are mesoporous, exhibit high surface areas, can be prepd. as monoliths, and demonstrate the characteristic quantum-confined optical properties of their nanoparticle components. These materials can be synthesized from a variety of building blocks by chem. or photochem. oxidn., and the properties can be further tuned by heat treatment. Aerogel formation represents a powerful yet facile method for metal chalcogenide nanoparticle assembly and the creation of mesoporous semiconductors.

Discovery of Metal Nanofoams

Ultralow-Density Nanostructured Metal Foams: Combustion Synthesis, Morphology, and Composition

By B.C. Tappan, M.H. Huynh, M.A. Hiskey, D.E. Chavez, E.P. Luther, J.T. Mang, S.F. Son,

Journal of the American Chemical Society (2006), 128(20), 6589-6594.

The synthesis of low-density, nanoporous materials has been an active area of study in chemistry and materials science dating back to the initial synthesis of aerogels. These materials, however, are most often limited to metal oxides, e.g., silica and alumina, and organic aerogels, e.g., resorcinol/formaldehyde, or carbon aerogels, produced from the pyrolysis of organic aerogels. The ability to form monolithic metallic nanocellular porous materials is difficult and sometimes elusive using conventional methodology. Here we report a relatively simple method to access unprecedented ultralow-density, nanostructured, monolithic, transition-metal foams, utilizing self-propagating combustion synthesis of novel transition-metal complexes containing high nitrogen energetic ligands. During the investigation of the decomposition behavior of the high-nitrogen transition metal complexes, it was discovered that nanostructured metal monolithic foams were formed in a post flame-front dynamic assembly having remarkably low densities down to 0.011 g cm^-3 and extremely high surface areas as high as 270 m² g^-1. We have produced monolithic nanoporous metal foams via this method of iron, cobalt, copper, and silver metals. We expect to be able to apply this to many other metals and to be able to tailor the resulting structure significantly.

Synthetic Pathway for Producing Carbon Nanotube Aerogels

Carbon nanotube aerogels

By Bryning, Mateusz B.; Milkie, Daniel E.; Islam, Mohammad F.; Hough, Lawrence A.; Kikkawa, James M.; Yodh, Arjun G.

Advanced Materials (2007), 19(5), 661-664.

The creation of carbon nanotube aerogels from aq.-gel precursors by crit.-point-drying and freeze-drying is reported. The aerogels are strong and elec. conducting and are a potential improvement over current technologies for applications such as sensors, electrodes, and thermoelec. devices. The aerogels can be reinforced by small amts. of polyvinyl alc. and can support 8000 times their own wt.

Synthetic Pathway for Producing Metal Aerogels

Smelting in the age of nano: Iron aerogels

By Leventis, Nicholas; Chandrasekaran, Naveen; Sotiriou-Leventis, Chariklia; Mumtaz, Arif

Journal of Materials Chemistry (2009), 19(1), 63-65.

Porous pig iron was produced by smelting interpenetrating resorcinol-formaldehyde and iron oxide xerogels. Crosslinking alters the thermolytic behavior leading to macropores, but most importantly by melting it mixes intimately the skeletal resorcinol-formaldehyde and iron oxide nanoparticles and depresses their reaction temp. by ≤400°. This is explored further with other interpenetrating networks of nanoparticles.

Researchers lead by Dr. Lei Zhai at the University of Central Florida have fabricated a multiwalled carbon nanotube (MWNT) aerogel with an astonishing density of just four milligrams per cubic centimeter!

The work was recently published in ACS Nano and you can view the full manuscript here.

This material is particularly interesting because it is composed of a dispersion of MWNTs which leave a honeycomb structure with controllable porosity.  More-so, the aerogel has a large surface area and conducts electricity very well, but is a thermal insulator.  This is an ideal characteristic for electronics.

Notably this is not the first aerogel made from carbon nanotubes (or CNTs for short if you’re hip to the materials crowd), nor is it the first CNT-based aerogel to exhibit amazing elastic properties.  But it’s a new pathway to making CNT-based aerogels and the resulting materials are pretty cool.

Hype alert: There is a statement being circulated on the Internet that one of the MWNT aerogels these researchers made is the lowest-density aerogel (and thus solid) ever produced.  Unfortunately, this is not the case:  scientists at Lawrence Livermore National Laboratory have previously produced a silica aerogel with a density of only 1.1 mg/cc, these ones here are 4 mg/cc.

So how are they made?  Here’s the gist.  Pristine MWNTs are dispersed as individual tubes in chloroform with a compound called poly(3-hexylthiophene)-b-PTMSPMA (P3HT-b-PTMSPMA) by sonicating for 13 min.  This anchors a molecule called PTMSPMA on the surface of the nanotubes. The dispersion of MWNTs then gels in several minutes to several hours depending on the concentration of MWNTs. The resulting gel is aged for 12 h at room temperature and then solvent exchanged into methanol to remove chloroform. An aqueous ammonia solution is then added to crosslink the gel for 12 h by hydrolysis and condensation of the PTMSPMA, during which time the gel shrinks a bit.  Finally methanol and ammonia are removed by exchanging the gel  into water and the gel is freeze-dried to obtain MWNT aerogels.  Note the use of freeze drying here instead of supercritical drying is possible thanks to the improved mechanical properties of the gels which make them more resistant to cracking during solvent removal.

The MWNT aerogels are impressively strong in compression and extremely elastic (squishable) exhibiting a rapid rebound.  According to the paper, these properties, along with a high degree of porosity make the material a promising candidate for chemical and pressure sensing.

http://www.youtube.com/watch?v=jH8jOVSv-Mg

]]> http://www.aerogel.org/?feed=rss2&p=1878 0 Aerogel.orgResearchers at the University of Central Florida have fabricated a multi-walled carbon nanotube (MWNT) aerogel with an astonishing density of just four milligrams per cubic centimeter! Researchers lead by Dr. Lei Zhai at the University of Central Florida have fabricated a multiwalled carbon nanotube (MWNT) aerogel with an astonishing density of just four milligrams per cubic centimeter! The work was recently published in ACS Nano and you can view the full manuscript here. This material is particularly interesting because it is composed of a dispersion of MWNTs which leave a honeycomb structure with controllable porosity.  More-so, the aerogel has a large surface area and conducts electricity very well, but is a thermal insulator.  This is an ideal characteristic for electronics. Notably this is not the first aerogel made from carbon nanotubes (or CNTs for short if you&#039;re hip to the materials crowd), nor is it the first CNT-based aerogel to exhibit amazing elastic properties.  But it&#039;s a new pathway to making CNT-based aerogels and the resulting materials are pretty cool. Hype alert: There is a statement being circulated on the Internet that one of the MWNT aerogels these researchers made is the lowest-density aerogel (and thus solid) ever produced.  Unfortunately, this is not the case:  scientists at Lawrence Livermore National Laboratory have previously produced a silica aerogel with a density of only 1.1 mg/cc, these ones here are 4 mg/cc. So how are they made?  Here&#039;s the gist.  Pristine MWNTs are dispersed as individual tubes in chloroform with a compound called poly(3-hexylthiophene)-b-PTMSPMA (P3HT-b-PTMSPMA) by sonicating for 13 min.  This anchors a molecule called PTMSPMA on the surface of the nanotubes. The dispersion of MWNTs then gels in several minutes to several hours depending on the concentration of MWNTs. The resulting gel is aged for 12 h at room temperature and then solvent exchanged into methanol to remove chloroform. An aqueous ammonia solution is then added to crosslink the gel for 12 h by hydrolysis and condensation of the PTMSPMA, during which time the gel shrinks a bit.  Finally methanol and ammonia are removed by exchanging the gel  into water and the gel is freeze-dried to obtain MWNT aerogels.  Note the use of freeze drying here instead of supercritical drying is possible thanks to the improved mechanical properties of the gels which make them more resistant to cracking during solvent removal. The MWNT aerogels are impressively strong in compression and extremely elastic (squishable) exhibiting a rapid rebound.  According to the paper, these properties, along with a high degree of porosity make the material a promising candidate for chemical and pressure sensing. httpv://www.youtube.com/watch?v=jH8jOVSv-Mg http://www.aerogel.org/?p=1878 http://feedproxy.google.com/~r/aerogel/~3/itvhGgePyMA/ http://www.aerogel.org/?p=1517#comments Sun, 11 Apr 2010 01:47:24 +0000 ssteiner@aerogel.org (Aerogel.org) http://www.aerogel.org/?p=1517 Private astronaut Richard Garriott (also known as “Lord British”, the creator of the Ultima series) received the first-ever Spirit of Yuri’s Night Award in recognition of embodying the Yuri’s Night mission of using space and art to contribute to the future of humanity, both in space and on Earth.  Yuri’s Night is an annual worldwide celebration to commemorate the first human spaceflight made by Russian cosmonaut Yuri Gagarin on April 12, 1961.

Read the press release here.

Designed by artist and Aerogel.org co-founder Will Walker, this year’s Yuri is the fist-ever award to incorporate aerogels. The plaque component of the award was custom laser-machined for Yuri’s Night by aerospace engineers Shannon Dong and Thomas Coffee at MIT. Engraved into the plaque is the same trademark, stylized likeness of Yuri Gagarin that serves as the logo for Yuri’s Night worldwide. Illuminated by diffused ambient light, Gagarin’s image glows with a subtle orange-gold hue. Accenting Gagarin’s image is a rosette of five flawless classic silica aerogel discs, the same material used to

insulate the Mars exploration rovers and used to capture comet dust on the Stardust probe. Their characteristic sky-blue cast is contrasted against the black background of the plaque, reminiscent of the contrast of our own spaceship Earth against the blackness of outer space. The particular aerogels used in the award are comprised of 96% air by volume and were produced by Aerogel Technologies, LLC using a robotic high pressure autoclave.

Production of the award was co-sponsored by BuyAerogel.com and Aerogel.org.