Researchers develop new airgels for beam cooling and absorption of electromagnetic waves

Aerogels, known for their porosity and low density, are solid materials that offer versatile functionality—from engulfing fat globules in weight management supplements to facilitating more sustainable metal recycling processes.

Traditionally used to provide thermal insulation in the aerospace industry, scientists from the National University of Singapore (NUS) have taken the material to the next level – harnessing its unique properties to add value to numerous applications in building and construction , environmental remediation, drug distribution. , even clothing and textiles.

In a pioneering effort, a research team led by Associate Professor Duong Hai-Minh from the Department of Mechanical Engineering under the NUS College of Design and Engineering has developed airgel for two new applications: radiative cooling and electromagnetic wave (EMW) absorption. .

Using plastic waste, the team designed thin-film airgels that function as thermal insulators and radiant coolers. These airgels can be applied to any surface, such as building roofs, to reduce indoor temperatures, providing a scalable and sustainable solution for energy-free thermal management. The team’s findings were published in the journal Solar energy on May 15, 2024.

In another study, published in the journal carbon on 10 February 2024 NUS researchers developed a simple and scalable method to produce aerogels that absorb X-band EMW, characteristic of those used in weather monitoring and air traffic control. These lightweight and durable airgels shield against electromagnetic pollution, protecting people and sensitive equipment in our increasingly digital world.

The researchers’ work builds on their previous successes in developing aerogels from a variety of waste materials, from plastics and paper to agricultural byproducts such as pineapple leaves.

Airgel for radiation cooling

Traditional cooling systems, such as air conditioners, have a huge appetite for energy, accounting for about 20% of the electricity used in buildings worldwide. The new aerogels developed by the NUS team present a passive cooling alternative, exploiting the natural process of radiative cooling to dissipate heat into space without consuming energy.

“This process involves the use of specially designed aerogels to emit infrared radiation through the atmospheric ‘sky window,’ effectively cooling surface temperatures below ambient levels,” said Assoc. Prof. Duong. “We are excited to be able to recycle fibers from single-use polyethylene terephthalate (PET) bottles for new purpose-built aerogels to help address the global plastic waste crisis.”

Previously the team had worked with PET fibers to produce airgel, but this latest method is significantly more energy efficient, consuming around 97% less energy and reducing production time by 96%.

When tested in the warm climate of Singapore, conducted in collaboration with Dr. Jaesuk Hwang from the Center for Quantum Technologies at NUS, 0.5 centimeters of the material produced a cooling effect of 2°, achieved by emitting infrared heat into the environment while exhibiting good thermal insulation. , preventing the absorption of heat from the surrounding environment.

“These aerogels can reduce energy consumption in both residential and commercial buildings, especially in tropical climates where cooling is now a must,” added Assoc. Prof. Duong.

Future research will focus on adapting these aerogels to different climatic conditions and expanding their applications beyond building insulation, such as in industrial processes where efficient thermal management of fluid circulation pipes is essential.

Airgel for absorption of electromagnetic waves

Modern electronic devices emit EMW that can disrupt nearby equipment and pose health risks, including DNA damage and cancer. Therefore, it is essential to develop materials that can effectively absorb EMW to protect people and infrastructure from these negative effects. Applications include enhancing the privacy and security of buildings, as well as protecting sensitive medical equipment.

To address this need, Ass. The team of Prof. Duong has developed a scalable and environmentally friendly procedure to produce new aerogels that are effective in absorbing EMW. The process involves mixing three main components – carbon nanotubes, polyvinyl alcohol and carboxymethyl cellulose – followed by freeze drying.

The airgel, with a thickness of about 3 millimeters – roughly the width of 40 human hairs – demonstrated an impressive performance of absorbing 99.99% of EMW energy. Across the X-band (8.2-12.4 GHz) of the electromagnetic spectrum, used primarily for radar systems, weather monitoring and air traffic control, airgel consistently demonstrated its ability to absorb 90% of EMW energy .

“In addition to providing a broad absorption bandwidth of 1.2-2.2 GHz in the X-band, our aerogel is also about 10 times lighter than existing composites used for EMW absorption,” added Assoc. Prof. Duong. “Unlike other ingredients, our airgel does not require mixing with heavy polymer fillers before use.”

Researchers have estimated that producing 1 square meter of airgel, 1 centimeter thick, costs less than $100. This cost is significantly lower than the price of other similar commercial materials, which can range from $180 to over $1,000.

Looking ahead, the team plans to improve the airgel’s mechanical properties, such as flexibility, to expand their applicability in various construction and infrastructure projects. The researchers also aim to conduct real-world tests to fully evaluate the EMW absorption capabilities of the aerogels in practical scenarios.