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Aerogel, a literal space-age material, could provide electric motors and devices with crucial shielding to protect neighboring electronic components without the need for heavier metal-based coverings.
New research published in the online journal Advanced Science suggests an alternative to shielding made from thin metal sheets or magnetized foils, which can often be too bulky and heavy for delicate devices. The research team was led by Zhihui Zeng and Gustav Nyström from the Swiss Federal Laboratories for Materials Science and Technology (EMPA),
The use of aerogel , which is one of the lightest solid materials ever manufactured , could provide the closed, conductive shell needed for shielding high-frequency electromagnetic fields while being light, flexible, and durable.
Aerogel is a ‘Wonder Material’
Aerogel was discovered in the 1930s and has a density three times that of air, meaning a block of aerogel the size of the average human would weigh less than a pound. However, the same block would be strong enough to support a small-to-medium-sized car or about half a tonne.
Aerogels are traditionally made from silicas by combining a polymer with a solvent to create a gel. The liquid is then drawn out of the gel and replaced with air. This results in a highly porous, low-density, translucent, solid material that is often referred to as ‘frozen smoke’ due to its cloud-like appearance.
One of the most popular uses of silica aerogels is as insulation for a variety of platforms, including buildings, roofing, gas pipelines, and even personal apparel.
Chemical company Cabot is one of the world’s leading suppliers of silica aerogels, placing them in a wide range of products ranging from paints to personal care items where the material can be used as an anti-caking agent.
In 1999, Aspen Systems provided aerogel to NASA for use in the ‘Stardust’ mission. The material was used to take dust samples from a comet.
Read more: What is Aerogel? Theory, Properties and Applications
For their research, the EMPA team created an aerogel that uses nanofibres of cellulose harvested from wood and suitable for a wide range of chemical alterations. Such cellulose-based aerogels have been a subject of intense study due to their adaptability, lending themselves to the creation of a wide range of microstructures.
Nyström and his team at EMPA are particularly interested in how these structures relate to the properties of the aerogels.
The results in terms of frequency-blocking achieved by the researchers are impressive. The team found that by weaving their cellulose nanofibres with silver nanowires, they could create ultra-light and fine structures with a density of just 1.7 mg per cm³ that could achieve 40 dB shielding in an 8 to 12 GHz frequency range. This suggests that the aerogel blocked virtually all the radiation in that frequency range.
How are Reduced Graphene Oxide Aerogels used in Photovoltaics?
The aerogel is further adaptable as the flux of the electromagnetic radiation that the material allows to pass through can be adjusted by increasing and decreasing the amount of silver nanowire in the mix and by the creation of the pores that run through its structure.
The researchers also point out that its pores are of vital importance to its shielding effects. When falling inside these pores, incident electromagnetic fields bounce back and forward, which creates further electromagnetic fields within the material. These new fields counteract the initial field.
To amplify this effect, the EMPA scientists ensured that the pores were precisely the right shape and size. This meant pouring the aerogel while it was still in its liquid state into specially created molds. As the gel slowly cooled, ice-crystals grew, creating the perfect pore structure for this damping effect.
The process used by the team to ‘freeze in’ these pores also allows the specific orientation of these fields. As a result, the damping effect can be applied in particular directions. For example, if the team allows the material to solidify in the mold from the bottom to the top, the damping effect is weakened in the vertical direction and maximized in the horizontal direction.
The team also tested the aerogels’ durability, assessing the strength of this damping effect after rigorous flexing. They found that structures created were almost as strong after 1000 back and forth ‘flexes’ as they were in their initial state.
The shielding that the material provides can also be boosted by eradicating the silver nanowire and replacing it with nanoplates of titanium carbide created by a unique etching process. These nanoplates are analogous to bricks joined together by a mortar of cellulose fiber. The team says that this titanium carbide nano-cellulose aerogel is by far the lightest electromagnetic shielding material on Earth, and perhaps beyond it.
Aerogel: Out of this World
Aside from EMPA, NASA is one of the most interested parties in the advancement and improvement of aerogels. A famous application of aerogel is in the development of the Mars Rover, which is currently exploring the red planet.
One of the key dilemmas that the team developing the Rover faced was enabling it to keep cool during the Martian day while simultaneously preventing it from freezing at night.
Conditions on the solar system’s fourth planet vary radically from day to night, with temperatures ranging from around 22° Celsius to around -96° Celsius. Therefore, the Rover’s workings, which must remain at operating temperatures between -40° Celsius to 40° Celsius, must be protected from these extremes.
Aerogels on the Rover’s body allow heaters to keep it warm at night, while its porous nature allows the heat to ‘leak’ from it during the day in a way that is analogous to human sweating.
As impressive as the usage is, the insulating properties of aerogel explored and enhanced by the EMPA could have far more significant uses on Mars in the future.
Aerogels could create environmentally sealed terraforming domes that could allow humans to live and work on our nearest planetary neighbor. One of the major hindrances to terraforming Mars is that it is bombarded by more harsh UV radiation than Earth is. However, the insulating properties of aerogels can block out harmful UV radiation while still allowing other frequencies through.
From shielding delicate electronics to exploring other planets, aerogel is a material of the future, and researchers from EMPA and NASA, in addition to companies such as Cabot, stand to be at the forefront of that revolution.
References and Further Reading
Zeng. Z, Wang. C, Siqueira. G, et al,  Nanocellulose-MXene Biomimetic Aerogels with Orientation-Tunable Electromagnetic Interference Shielding Performance. Advanced Science. [https://onlinelibrary.wiley.com/doi/epdf/10.1002/advs.202000979]
Wadsworth. R, Kerber. L, Cockell. C,  Enabling Martian habitability with silica aerogel via the solid-state greenhouse effect. Nature Astronomy, [https://www.nature.com/articles/s41550-019-0813-0]
‘Rover Temperature Controls,’ Mars Exploration Rovers, NASA, [https://mars.nasa.gov/mer/mission/rover/temperature/]