American Chemical Society – A major improvement in the world’s lightest solid material and best solid insulating material, described here today, may put more of this space-age wonder into insulated clothing, refrigerators with thinner walls that hold more food, building insulation and other products.
The report, on development of a new flexible “aerogel” ― stuff so light it has been called “solid smoke” ― was part of the 244th National Meeting & Exposition of the American Chemical Society, the world’s largest scientific society.
Mary Ann B. Meador, Ph.D., explained that traditional aerogels, developed decades ago and made from silica, found in beach sand, are brittle, and break and crumble easily. Scientists have improved the strength of aerogels over the years, and Meador described one of these muscled-up materials developed with colleagues at the NASA Glenn Research Center in Cleveland, Ohio.
“The new aerogels are up to 500 times stronger than their silica counterparts,” Meador said. “A thick piece actually can support the weight of a car. And they can be produced in a thin form, a film so flexible that a wide variety of commercial and industrial uses are possible.”
Flexible aerogels, for instance, could be used in a new genre of super-insulating clothing that keeps people warm in the cold with less bulk than traditional “thermal” garments. Tents and sleeping bags would have the same advantages. Home refrigerator and freezer walls insulated with other forms of the material would shrink in thickness, increasing storage capacity. Meador said that the aerogel is 5-10 times more efficient than existing insulation, with a quarter-inch-thick sheet providing as much insulation as 3 inches of fiberglass. And there could be multiple applications in thin-but-high-efficiency insulation for buildings, pipes, water heater tanks and other devices.
NASA envisions one use in an advanced re-entry system for spacecraft returning to Earth from the International Space Station, and perhaps other missions. Re-entry vehicles need a heat shield that keeps them from burning up due to frictional heating from Earth’s atmosphere. Those shields can be bulky and heavy. So NASA is exploring use of a heat shield made from flexible aerogel that inflates like a balloon when spacecraft enter the atmosphere.
Meador said the material also could be used to insulate spacesuits. However, it likely would not be good for firefighting clothing products, which require protection beyond the 575 degrees Fahrenheit limits of the aerogel.
Scientists produced the stronger new aerogels in two ways. One involved making changes in the innermost architecture of traditional silica aerogels. They used a polymer, a plastic-like material, to reinforce the networks of silica that extend throughout an aerogel’s structure. Another involved making aerogels from polyimide, an incredibly strong and heat-resistant polymer, or plastic-like material, and then inserting brace-like cross-links to add further strength to the structure.
Abstract – Polyimide gels are produced by cross-linking anhydride capped polyamic acid oligomers with aromatic triamine in solution and chemically imidizing. The gels are then supercritically dried to form nanoporous polyimide aerogels with densities as low as 0.14 g/cm(3) and surface areas as high as 512 m(2)/g. To understand the effect of the polyimide backbone on properties, aerogels from several combinations of diamine and dianhydride, and formulated oligomer chain length are examined. Formulations made from 2,2′-dimethylbenzidine as the diamine shrink the least but have among the highest compressive modulus. Formulations made using 4,4′-oxydianiline or 2,2’dimethylbenzidine can be fabricated into continuous thin films using a roll to roll casting process. The films are flexible enough to be rolled or folded back on themselves and recover completely without cracking or flaking, and have tensile strengths of 4-9 MPa. Finally, the highest onset of decomposition (above 600 °C) of the polyimide aerogels was obtained using p-phenylene diamine as the backbone diamine with either dianhydride studied. All of the aerogels are suitable candidates for high-temperature insulation with glass transition temperatures ranging from 270-340 °C and onsets of decomposition from 460-610 °C.
The polymer cross-linked aerogels described and referred to above exhibit far greater strength than the corresponding native ceramic aerogels (as much as two orders of magnitude greater strength with only a two- to three-fold increase in density). However, despite their improved strength they still remain relatively inflexible and are subject to brittle failure. Consequently there are numerous applications that could benefit from the insulative and improved mechanical properties of ceramic aerogels as described in the aforementioned publications, but where additional flexibility is necessary or would be desirable. For example, space-suit insulation could benefit significantly from more flexible ceramic aerogels having the insulative properties described above.
* Cross-linked polyimide aerogels are viable approach to higher temperature, flexible insulation for inflatable decelerators
* all-polyimide aerogels are as strong or stronger than polymer reinforced silica aerogels at the same density
* Currently, examining use of carbon nanofiber(Poster 334)and clay nanoparticles to improve performance
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