Dr. Mary Ann Meador, Senior Research Scientist, Glenn Research Center, Cleveland, OH
Mary Ann Meador received a B.S. in Chemistry from Duquesne University in 1979 and a Ph.D. in Organic Chemistry from Michigan State University in 1983. Currently, she is a senior scientist in the Materials Chemistry and Physics Branch of the Materials and Structures Division at NASA Glenn. She is an associate editor for ACS Applied Materials and Interfaces and was recently appointed as Adjunct Professor of Polymer Engineering at the University of Akron.
Dr. Meador guides projects that will synthesize new types of aerogels. Her research has focused on the design and development of new polymers for a variety of applications, including high-temperature composites.
Aerogels are low-density solids with a high degree of porosity: 85-98%. Different than foams, aerogels have extremely small pores, on the nanometer scale. This makes them 2-5 times better insulators than foams, since gas phase heat conduction is very poor. Since they are comprised mostly of air, they also have very low-dielectric constants and hence have application as low-dielectric substrates for devices, such as lightweight antennas. Aerogels also have very large internal surface areas, which means they could also have application as sensor platforms. However, the main application is as insulation for aerospace, housing, and construction, or high-performance clothing.
It's created very similarly to silica aerogels, the most well-studied type of aerogel. We start off with monomers in solution, and we have a cross linker that yields a network structure. When this network forms, it gels. The gel is basically the polymer structure filled with a solvent that was used to make the gel.
Just as silica gels are dried using super-critical fluid extraction with liquid CO2, we do the same thing. The gels are put into a chamber, basically an autoclave. The liquid CO2 is introduced into the chamber, to push out the solvent that's inside the gel. That is carried out about four times to make sure you get rid of all the solvent inside the gel. Then, we take it to the supercritical point of liquid CO2, and the CO2 immediately evolves out of the aerogel as a gas. There's no collapse of the pore structure, which is the issue if you dry the aerogel in a normal way, like ambient drying, which will collapse the pores through capillary forces. So essentially they're made the same as other aerogels.
The issue with aerogels is their fragility. They have a lot of interesting properties. Because of the way that they're made, they have very small pore sizes; that leads to really good insulation qualities, and also very low thermal conductivities, low dielectric, and high surface areas. Because they also have typically been very fragile, it's difficult to put them into use as a monolithic material. With the polyimides, our goal was to improve the mechanical properties so that you would retain all the interesting properties of aerogels, but add the mechanical integrity.
We actually were working on a project to design a flexible insulation for inflatable aerodynamic decelerators for Entry, Descent, and Landing (EDL). These are essentially a large structure that inflates in order to provide drag to slow a spacecraft down, or to slow down another payload to land on the surface of a planet like Mars, or even bring things back to Earth. The challenge was to make the aerogel in a flexible form.
We had been working previously on hybrid aerogels made from silicone polymers—the silica leading to pretty stiff polymers. Our thought was to get rid of the silica altogether and concentrate on a polymer structure. At the same, the insulation has to be able to withstand certain heat of re-entry, so we chose polyimide as a very-high-temperature stable polymer. Making the aerogel structure from the polymer essentially gives us the ability to make thin films of the aerogel. That's what provides the flexible form of the insulation.
If the aerogel has to be molded into a specific shape to provide insulation around something, it's a lot more challenging. But if you can make it in a thin film that can now be wrapped around structures, it's a much more conventional way to deliver an insulation. Thin films could be used to wrap around a cryotank, to wrap around pipes, which are handling cryogenic liquids, or they can be wrapped around things that you want to keep heat in. Essentially, like we're used to using insulation, where we might take flexible fiberglass and wrap it around something.
We are expanding the ability to make polymer aerogels by looking at other polymers. One issue with the polyimides: Since they are a high-temperature polymer, they tend to be a little stiffer than other types of polymer, and it would be nicer to be able to make the aerogel insulation in a thicker form. For the polyimide, they need to be about a half-millimeter thick in order to still be flexible. That means you have to wrap a lot of insulation around something, in order to provide enough insulation, even though they're aerogels and you can get away with a much thinner coating or insulation.
We're working on polyamide aerogels, which are more flexible because they don't have as many bonds in the polymer backbone. The other advantage of polyimides is their cost relative to polyimides, which tend to be more of a "boutique" polymer used in things like aircraft engine applications or other [applications] wherever you need a very high temperature. In a lot of insulation applications, you don't need that high temperature stability. Polyamides is one of the furthest along, but we're also looking at polyethylene and some other polymers as an aerogel form.
I interact with four or five members of our team that are synthesizing new aerogels. We have a couple of research associates and another NASA civil servant working on the project, plus we usually have a number of students at different times of the year. I'm guiding the research projects, helping to find funding for the next project that we're going to work on, and writing journal articles and giving presentations to get the word out.
The most exciting would be taking something that we're doing right here and seeing it enable a future mission to Mars. Nearly as exciting would be to translate it into something that could be useful on Earth as well. If we can introduce a form of the aerogel that's cheap enough to be used in homes and other applications, that would be incredibly exciting as well.
Silica aerogels are currently sold by a number of companies, either as pellets or as composite blankets. Though they are superior insulators, current commercial products suffer from being very dusty (composite blankets) or limited in application (pellets). Polyimide aerogels are much stronger and can be made as thick, stiff panels, or as thin films which are flexible. Neither form is dusty. Thermal conductivity, or insulation capability, is very similar to the composite blankets. We have had over 100 companies with different applications - ranging from consumer electronics, to clothing, to home insulation -inquiring about the technology, so the commercial potential is high.
Since polyimide precursors tend to be a little on the expensive side, the polyimide aerogels may not compete for applications where there is enough space for the proper amount of conventional insulation. Your attic, for instance, probably has room for 12 inches of insulation with an R of 1/inch to give an R of 12, though only 1 inch of aerogel might be needed. If you need an R of 12, where you only have 1-2 inches of space, you need an aerogel - refrigeration, for example.
We think the commercial potential for other types of polymer aerogels would be higher since they may be more cost-competitive with conventional insulation. Hence, we are working on polyamide aerogels as an alternative, lower-cost option.
For more information on the polyimide aerogels, please visit our aerogel feature page.