Category Archives: coatings

Preserving stone and repairing historic Church of the Scalzi in Venice (Italy) with nanotechnology

Since stone wear down and away with time these researchers from China and Italy are trying to find ways to mitigate the damage. (At the end of this piece I have a list of other posts about stone buildings and monuments, preservation, and nanotechnology.)

From an August 23, 2023 news snippet by Echo Xie for the South China Morning Post, Note: Links have been removed,

A team of Chinese and Italian researchers has restored parts of a 300-year-old Catholic church in Venice, Italy, using modern nanotechnology.

The Church of Santa Maria di Nazareth [Church of the Scalzi], which overlooks the Grand Canal and is a prime example of Venetian Baroque architecture, is the beneficiary of a patented method developed to consolidate, or treat, marble stones damaged by time and the elements.The research was funded by the Veneto regional government, the National Natural Science Foundation of China, and the Ministry of Science and Technology’s belt and road foreign expert exchange programme [part of the Belt and Road Initiative?].

There’s a more extended Sept. 6, 2023 snippet about the research on Vuink,

The cutting-edge method could be used to restore landmarks of world-class cultural heritage – including the Pantheon, Trajan’s Column and the Victoria Memorial in London as well as historic sculptures – made from marble similar to the church [Church of Santa Maria di Nazareth]

The research team, led by scientists at China’s Northwestern Polytechnical University in Xian and the CNR [National Research Council of Italy]-Institute of Geosciences and Earth Resources in Florence, Italy, found an “effective and enduring” method to consolidate marble stones after the design and systematic study of nine different treatment methods.

….

Ivana Milanovic’s, ASME [American Society of Mechanical Engineers] Fellow’s Post [undated] on LinkedIn provides more details,

… They [research team] discovered the combination of two commonly used consolidation products – nanosilica and tetraethoxysilane (TEOS) – had the highest consolidating effect among all tested materials.

In the study published in the peer-reviewed journal [Science China Technological Sciences], the authors used a two-step method to consolidate the marble stones. They first applied nanosilica with dimensions less than 10nm to the surface of the stone using a poultice, a paste-like material, to cover the stone. The nanosilica particles could then penetrate as deep as 5cm (2 inches) into the pores of the stone and consolidate it. Then they used the same poultice method and put TEOS on the surface, which could enhance the stone’s hardness or mechanical strength. …

Here’s a link to and a citation for the paper,

Enhanced consolidation efficacy and durability of highly porous calcareous building stones enabled by nanosilica-based treatments by YiJian Cao, Mara Camaiti, Monica Endrizzi, Giorgio Forti, Ernesta Vergani & Ilaria Forti. Science China Technological Sciences volume 66, pages 2197–2212 (2023 Published May 18, 2023

This paper is behind a paywall. However, it is possible to request a PDF copy of the paper from the authors on their Research Gate “Enhanced consolidation efficacy and durability of highly porous calcareous building stones enabled by nanosilica-based treatments” webpage,

My other stone postings:

That should be enough, eh?

A structural colour solution for energy-saving paint (thank the butterflies)

The UCF-developed plasmonic paint uses nanoscale structural arrangement of colorless materials — aluminum and aluminum oxide — instead of pigments to create colors. Here the plasmonic paint is applied to the wings of metal butterflies, the insect that inspired the research. Credit: University of Central Florida

A March 9, 2023 news item on Nanowerk announces research into multicolour energy-saving coating/paint, so, this is a structural colour story, Note: Links have been removed,

University of Central Florida researcher Debashis Chanda, a professor in UCF’s NanoScience Technology Center, has drawn inspiration from butterflies to create the first environmentally friendly, large-scale and multicolor alternative to pigment-based colorants, which can contribute to energy-saving efforts and help reduce global warming.

A March 8, 2023 University of Central Florida (UCF) news release (also on EurekAlert) by Katrina Cabansay, which originated the news item, provides more context and more details,

“The range of colors and hues in the natural world are astonishing — from colorful flowers, birds and butterflies to underwater creatures like fish and cephalopods,” Chanda says. “Structural color serves as the primary color-generating mechanism in several extremely vivid species where geometrical arrangement of typically two colorless materials produces all colors. On the other hand, with manmade pigment, new molecules are needed for every color present.”

Based on such bio-inspirations, Chanda’s research group innovated a plasmonic paint, which utilizes nanoscale structural arrangement of colorless materials — aluminum and aluminum oxide — instead of pigments to create colors.

While pigment colorants control light absorption based on the electronic property of the pigment material and hence every color needs a new molecule, structural colorants control the way light is reflected, scattered or absorbed based purely on the geometrical arrangement of nanostructures.

Such structural colors are environmentally friendly as they only use metals and oxides, unlike present pigment-based colors that use artificially synthesized molecules.

The researchers have combined their structural color flakes with a commercial binder to form long-lasting paints of all colors.

“Normal color fades because pigment loses its ability to absorb photons,” Chanda says. “Here, we’re not limited by that phenomenon. Once we paint something with structural color, it should stay for centuries.”

Additionally, because plasmonic paint reflects the entire infrared spectrum, less heat is absorbed by the paint, resulting in the underneath surface staying 25 to 30 degrees Fahrenheit cooler than it would if it were covered with standard commercial paint, the researcher says.

“Over 10% of total electricity in the U.S. goes toward air conditioner usage,” Chanda says. “The temperature difference plasmonic paint promises would lead to significant energy savings. Using less electricity for cooling would also cut down carbon dioxide emissions, lessening global warming.”

Plasmonic paint is also extremely lightweight, the researcher says.

This is due to the paint’s large area-to-thickness ratio, with full coloration achieved at a paint thickness of only 150 nanometers, making it the lightest paint in the world, Chanda says.

The paint is so lightweight that only about 3 pounds of plasmonic paint could cover a Boeing 747, which normally requires more than 1,000 pounds of conventional paint, he says.

Chanda says his interest in structural color stems from the vibrancy of butterflies.

“As a kid, I always wanted to build a butterfly,” he says. “Color draws my interest.”

Future Research

Chanda says the next steps of the project include further exploration of the paint’s energy-saving aspects to improve its viability as commercial paint.

“The conventional pigment paint is made in big facilities where they can make hundreds of gallons of paint,” he says. “At this moment, unless we go through the scale-up process, it is still expensive to produce at an academic lab.”

“We need to bring something different like, non-toxicity, cooling effect, ultralight weight, to the table that other conventional paints can’t.” Chanda says.

Licensing Opportunity

For more information about licensing this technology, please visit the Inorganic Paint Pigment for Vivid Plasmonic Color technology sheet.

Researcher’s Credentials

Chanda has joint appointments in UCF’s NanoScience Technology Center, Department of Physics and College of Optics and Photonics. He received his doctorate in photonics from the University of Toronto and worked as a postdoctoral fellow at the University of Illinois at Urbana-Champaign. He joined UCF in Fall 2012.

Here’s a link to and a citation for the paper,

Ultralight plasmonic structural color paint by Pablo Cencillo-Abad, Daniel Franklin, Pamela Mastranzo-Ortega, Javier Sanchez-Mondragon, and Debashis Chanda. Science Advances 8 Mar 2023 Vol 9, Issue 10 DOI: 10.1126/sciadv.adf7207

This paper is open access.

Here’s the researcher with one of ‘his butterflies’ (I may be reading a little too much into this but it looks like he’s uncomfortable having his photo taken but game to do it for work that he’s proud of),

Caption: Debashis Chanda, a professor in UCF’s NanoScience Technology Center, drew inspiration from butterflies to create the innovative new plasmonic paint, shown here applied to metal butterfly wings. Credit: University of Central Florida

Textiles fight back bacteria with electronics

These textiles according to an April 24, 2023 news item on SpaceDaily do a little more than fight off bacteria (as impressive as that is),

Scientists from around the world have developed a simple metallic coating treatment for clothing or wearable textiles which can repair itself, repel dangerous bacteria from the wearer and even monitor a person’s electrocardiogram (ECG) heart signals.

Researchers from North Carolina State University [US], Flinders University [Australia] and South Korea [Sungkyunkwan University (SKKU] say the conductive circuits created by liquid metal (LM) particles can transform wearable electronics and open doors for further development of human-machine interfaces, including soft robotics and health monitoring systems.

An April 25, 2023 Flinders University press release (also on EurekAlert but published April 26, 2023), which originated the news item, provides more technical details about the conductive, self-healing textiles, Note: Links have been removed,

The ‘breathable’ electronic textiles have special connectivity powers to ‘autonomously heal’ itself even when cut, says the US team led by international expert in the field, Professor Michael Dickey.  

When the coated textiles are pressed with significant force, the particles merge into a conductive path, which enables the creation of circuits that can maintain conductivity when stretched, researchers say.   

“The conductive patterns autonomously heal when cut by forming new conductive paths along the edge of the cut, providing a self-healing feature which makes these textiles useful as circuit interconnects, Joule heaters and flexible electrodes to measure ECG signals,” says Flinders University medical biotechnology researcher Dr Khanh Truong, senior co-author in a new article in Advanced Materials Technologies. 

The technique involves dip-coating fabric into a suspension of LM particles at room temperature.  

“Evenly coated textiles remain electrically insulating due to the native oxide that forms on the LM particles. However, the insulating effect can be removed by compressing the textile to rupture the oxide and thereby allow the particles to percolate.  

“This enables the creation of conductive circuits by compressing the textile with a patterned mold. The electrical conductivity of the circuits increases by coating more particles on the textile.”  

As well the LM-coated textiles offer effective antimicrobial protection against Pseudomonas aeruginosa and Staphylococcus aureus.  

This germ repellent ability not only gives the treated fabric protective qualities but prevents the porous material from becoming contaminated if worn for and extended time, or put in contact with other people.    

The particles of gallium-based liquid metals have low melting point, metallic electrical conductivity, high thermal conductivity, effectively zero vapor pressure, low toxicity and antimicrobial properties.  

LMs have both fluidic and metallic properties so show great promise in applications such as microfluidics, soft composites, sensors, thermal switches and microelectronics.  

One of the advantages of LM is that it can be deposited and patterned at room temperature onto surfaces in unconventional ways that are not possible with solid metals. 

Here’s a link to and a citation for the paper,

Liquid Metal Coated Textiles with Autonomous Electrical Healing and Antibacterial Properties (2023) by Jiayi Yang, Praneshnandan Nithyanandam, Shreyas Kanetkar, Ki Yoon Kwon, Jinwoo Ma, Sooik Im, Ji-Hyun Oh, Mohammad Shamsi, Mike Wilkins, Michael Daniele Tae-il Kim, Huu Ngoc Nguyen, Vi Khanh Truong and Michael D Dickey. Advanced Materials Technologies Online Version of Record before inclusion in an issue 2202183 DOI: 10.1002/admt.202202183 First published: 02 April 2023 [2nd DOI:] https://doi.org/10.1002/admt.202202183 

This paper is open access.

Reducing microplastic pollution from when you wash your clothes with a new coating

A January 26, 2023 University of Toronto news release (also found on EurekAlert and here but published on January 30, 2023) by Safa Jinje announced a coating the minimizes the amount of microplastic entering the water when your clothes are washed, Note: Links have been removed,

A team of University of Toronto Engineering researchers, led by Professor Kevin Golovin, have designed a solution to reduce the amount of microplastic fibres that are shed when clothes made of synthetic fabrics are washed.   

In a world swamped by fast fashion — an industry that produces a high-volume of cheaply made clothing at an immense cost to the environment — more than two-thirds of clothes are now made of synthetic fabrics. 

When clothes made from synthetic fabrics, such as nylon, polyester, acrylic and rayon, are washed in washing machines, the friction caused by cleaning cycles produces tiny tears in the fabric. These tears in turn cause microplastic fibres measuring less than 500 micrometres in length to break off and make their way down laundry drains to enter waterways.   

Once microplastics end up in oceans and freshwater lakes and rivers, the particles are difficult to remove and will take decades or more to fully break down. The accumulation of this debris in bodies of water can threaten marine life. It can also become part of the human food chain through its presence in food and tap water, with effects on human health that are not yet clear.  

Governments around the world have been looking for ways to minimize the pollution that comes from washing synthetic fabrics. One example is washing machine filters, which have emerged as a leading fix to stop microplastic fibres from entering waterways. In Ontario, legislative members have introduced a bill that would require filters in new washing machines in the province.  

“And yet, when we look at what governments around the world are doing, there is no trend towards preventing the creation of microplastic fibres in the first place,” says Golovin.  

“Our research is pushing in a different direction, where we actually solve the problem rather than putting a Band-Aid on the issue.”   

Golovin and his team have created a two-layer coating made of polydimethylsiloxane (PDMS) brushes, which are linear, single polymer chains grown from a substrate to form a nanoscale surface layer.  

Experiments conducted by the team showed that this coating can significantly reduce microfibre shedding of nylon clothing after repeated laundering. The researchers share their findings in a new paper published in Nature Sustainability

“My lab has been working with this coating on other surfaces, including glass and metals, for a few years now,” says Golovin. “One of the properties we have observed is that it is quite slippery, meaning it has very low friction.” 

PDMS is a silicon-based organic polymer that is found in many household products. Its presence in shampoos makes hair shiny and slippery. It is also used as a food additive in oils to prevent liquids from foaming when bottled. 

Dr. Sudip Kumar Lahiri, a postdoctoral researcher in Golovin’s lab and lead author of the study, had the idea that if they could reduce the friction that occurs during wash cycles with a PDMS-based fabric finish, then that could stop fibres from rubbing together and breaking off during laundering.  

One of the biggest challenges the researchers faced during their study was ensuring the PDMS brushes stayed on the fabric. Lahiri, who is a textile engineer by trade, developed a molecular primer based on his understanding of fabric dyes.  

Lahiri reasoned that the type of bonding responsible for keeping dyed apparel colourful after repeated washes could work for the PDMS coating as well.  

Neither the primer nor the PDMS brushes work separately to decrease the microplastic-fibre shedding. But together, they created a strong finish that reduced the release of microfibres by more than 90% after nine washes.  

“PDMS brushes are environmentally friendly because they are not derived from petroleum like many polymers used today,” says Golovin, who was awarded a Connaught New Researcher award for this work.  

“With the addition of Sudip’s primer, our coating is robust enough to remain on the garment and continue to reduce micro-fibre shedding over time.”  

Since PDMS is naturally a hydrophobic (water-repellent) material, the researchers are currently working on making the coating hydrophilic, so that coated fabrics will be better able to wick away sweat. The team has also expanded the research to look beyond nylon fabrics, including polyester and synthetic-fabric blends.  

“Many textiles are made of multiple types of fibres,” says Golovin. “We are working to formulate the correct polymer architecture so that our coating can durably adhere to all of those fibres simultaneously.” 

Here’s a link to and a citation for the paper,

Polydimethylsiloxane-coated textiles with minimized microplastic pollution by Sudip Kumar Lahiri, Zahra Azimi Dijvejin & Kevin Golovin. Nature Sustainability (2023) DOI: https://doi.org/10.1038/s41893-022-01059-4 Published: 26 January 2023

This paper is behind a paywall.

Nanoimaging helps unravel mystery of coating used in Stradivarius violins

Caption: A highly precise, nanometer-scale imaging technique revealed a protein-based layer between the wood and the varnish coating of these two Stradivarius violins [images of the San Lorenzo 1718 (left) and the Toscano 1690 (right)]. Credit: Adapted from Analytical Chemistry 2022, DOI: 10.1021/acs.analchem.2c02965

An October 25, 2022 American Chemical Society (ACS) news release (also on EurekAlert) describes how the mystery of the violins was unraveled,

Stradivarius violins produce elegant music with a level of clarity that is unparalleled by modern instruments, according to some musicians. And it’s the finishing touches — mysterious treatments applied hundreds of years ago by Antonio Stradivari — that contribute to their unique look and sound. In a step toward unraveling the secret, researchers in ACS’ Analytical Chemistry report on a nanometer-scale imaging of two of Stradivari’s violins, revealing a protein-based layer between the wood and varnish.

Previous studies have reported that some stringed instruments crafted by Stradivari have a hidden coating underneath the shiny varnish. This coating’s purpose would have been to fill in and smooth out the wood, influencing the wood’s resonance and the sound that’s produced. Knowing the components of this film could be key to replicating the historic instruments in modern times. So, Lisa Vaccari, Marco Malagodi and colleagues wanted to find a technique that would determine the composition of the layer between the wood and varnish of two precious violins — the San Lorenzo 1718 and the Toscano 1690.

Using a technique previously used on historic violins, synchrotron radiation Fourier-transform infrared spectromicroscopy, the team found that both samples had an intermediary layer, but this method couldn’t differentiate the layer’s composition from the adjacent wood. Then they turned to infrared scattering-type scanning near field microscopy (IR s-SNOM) to analyze the samples. The IR s-SNOM apparatus includes a microscope that collects images tens of nanometers wide and measures the infrared light scattered from the coating layer and the wood to collect information about their chemical composition. The results of the new method showed that the layer between the wood and varnish of both instruments contained protein-based compounds, congregating in nano-sized patches. Because IR s-SNOM provided a detailed 3D picture of the types of substances on the violin’s surface, the researchers say that it could be used in future studies to identify compounds in complex multi-layer cultural heritage samples.

The authors acknowledge CERIC-ERIC [Association of European-level Research Infrastructure Facilities] and Elettra Sincrotrone Trieste for access to experimental facilities and financial support.

The American Chemical Society (ACS) is a nonprofit organization chartered by the U.S. Congress. ACS’ mission is to advance the broader chemistry enterprise and its practitioners for the benefit of Earth and all its people. The Society is a global leader in promoting excellence in science education and providing access to chemistry-related information and research through its multiple research solutions, peer-reviewed journals, scientific conferences, eBooks and weekly news periodical Chemical & Engineering News. ACS journals are among the most cited, most trusted and most read within the scientific literature; however, ACS itself does not conduct chemical research. As a leader in scientific information solutions, its CAS division partners with global innovators to accelerate breakthroughs by curating, connecting and analyzing the world’s scientific knowledge. ACS’ main offices are in Washington, D.C., and Columbus, Ohio.

Here’s a link to and a citation for the paper,

A Nanofocused Light on Stradivari Violins: Infrared s-SNOM Reveals New Clues Behind Craftsmanship Mastery by Chiaramaria Stani, Claudia Invernizzi, Giovanni Birarda, Patrizia Davit, Lisa Vaccari, Marco Malagodi, Monica Gulmini, and Giacomo Fiocco. Anal. Chem. 2022, 94, 43, 14815–14819 DOI: https://doi.org/10.1021/acs.analchem.2c02965 Publication Date:October 17, 2022 Copyright © 2022 American Chemical Society

This paper appears to be open access.

Nano4EARTH workshop recordings available online

Announced in October 2022, the US government’s Nano4EARTH is the Biden-Harris {President Joe Biden and Vice President Kamala Harris] Administration’s first national nanotechnology challenge. (You can find out more about the challenge in my November 28, 2022 posting.)

More recently, JD Supra’s February 22, 2023 news item notes Nano4EARTH’s kick-off workshop (Note: Links have been removed),

The kickoff workshop for Nano4EARTH was held January 24-25, 2023. Nano4EARTH will leverage recent investments in understanding and controlling matter at the nanoscale to develop technologies, industries, and training opportunities that address climate change. On January 26, 2023, the White House Office of Science and Technology Policy (OSTP) issued a press release summarizing the workshop. According to OSTP, more than 400 people across sectors, with diverse expertise and perspectives, participated in the workshop. OSTP states that discussions focused on identifying nanotechnologies that will have an impact on climate change in four years or less, in addition to sharing resources to address barriers to entrepreneurship and technology adoption. Workshop participants identified goals and metrics to maintain momentum throughout the challenge. New connections and networks spanning federal agencies, non-federal organizations, and industry were created and several examples of collaborations and events centered on nanotechnology and climate change developed organically between participants.

A January 26, 2023 White House Office of Science and Technology Policy (OSTP) press release, which originated the news item on JD Supra, described some common workshop themes,

  • Battery technology has seen increased adoption in personal vehicles and long-term energy storage solutions, but further advances in Li-ion, as well as new chemistries and architectures, show tremendous and broad potential. It is critical that research directions are well matched with particular use cases.
  • Catalysts leveraging new understandings of nanoscale materials and phenomena could optimize many high-greenhouse gas emitting industrial processes, minimize the need for rare-earth metals, and serve as a precursor for alternative energy sources such as green hydrogen and electrofuels. 
  • Coatings and other material innovations are likely to increase the overall efficiency of nearly any industrial process and lead to more resilient structures and devices, especially in changing and harsh environments. Examples include reflective coatings, corrosion protection, heat management in computing, lubricants and other additives, and membranes for separations. Drop-in solutions would have a more near-term impact.
  • Capture of greenhouse gasses through advanced materials and sorbents (e.g., metal organic frameworks) and nature mimicking processes (e.g., artificial photosynthesis), especially deployed at the point of production, could be impactful but deploying at scale has significant challenges. In the near term, renewable energy production and efficient transmission is worthy of increased attention.

In the months to come, the NNCO will convene a series of roundtable discussions that focus on some of the highest potential nanotechnologies identified at the kick-off workshop. Subject matter experts and federal partners will be asked to match nanotechnology opportunities to urgent climate change needs, with strong consideration of the broader societal needs and impacts. Feedback from the kick-off workshop will also inform additional activities and events to facilitate conversations and collaborations across this growing community.

The US National Nanotechnology Initiative-hosted Nano4EARTH Kick-off Workshop page features the meeting agenda where there are links to video recordings of each session.

Speaking in Color, an AI-powered paint tool

This June 16, 2022 article by Jeff Beer for Fast Company took me in an unexpected direction but first, there’s this from Beer’s story,

If an architect wanted to create a building that matched the color of a New York City summer sunset, they’d have to pore over potentially hundreds of color cards designed for industry to get anything close, and still it’d be a tall order to find that exact match. But a new AI-powered, voice-controlled tool from Sherwin-Williams aims to change that.

The paint brand recently launched Speaking in Color, a tool that allows users to tell it about certain places, objects, or shades in order to arrive at that perfect color. You start with a broad description like, say, “New York City summer sunset,” and then fine tune from there once it responds with photos and other options with more in-depth preferences like “darker red,” “make it moodier,” or “add a sliver of sun,” until it’s done.

Developed with agency Wunderman Thompson, it’s a React web app that uses natural language to find your preferred color using both third-party and proprietary code. The tool’s custom algorithm allows you to tweak colors in a way that translates statements like “make it dimmer,” “add warmth,” or “more like the 1980s” into mathematical adjustments.

It seems to me Wunderman Thompson needs to rethink its Sherwin Williams Speaking in Color promotional video (it’s embedded with Beer’s June 16, 2022 article or you can find it here; scroll down about 50% of the way). You’ll note, the color prompts are not spoken; they’re in text, e.g., ‘crystal-clear Caribbean ocean’. So much for ‘speaking in color’ but the article aroused my curiosity which is how I found this May 19, 2017 article by Annalee Newitz for Ars Technica highlighting another color/AI project (Note: A link has been removed),

At some point, we’ve all wondered about the incredibly strange names for paint colors. Research scientist and neural network goofball Janelle Shane took the wondering a step further. Shane decided to train a neural network to generate new paint colors, complete with appropriate names. The results are possibly the greatest work of artificial intelligence I’ve seen to date.

Writes Shane on her Tumblr, “For this experiment, I gave the neural network a list of about 7,700 Sherwin-Williams paint colors along with their RGB values. (RGB = red, green, and blue color values.) Could the neural network learn to invent new paint colors and give them attractive names?”

Shane told Ars that she chose a neural network algorithm called char-rnn, which predicts the next character in a sequence. So basically the algorithm was working on two tasks: coming up with sequences of letters to form color names, and coming up with sequences of numbers that map to an RGB value. As she checked in on the algorithm’s progress, she found that it was able to create colors long before it could actually name them reliably.

The longer it processed the dataset, the closer the algorithm got to making legit color names, though they were still mostly surreal: “Soreer Gray” is a kind of greenish color, and “Sane Green” is a purplish blue. When Shane cranked up “creativity” on the algorithm’s output, it gave her a violet color called “Dondarf” and a Kelly green called “Bylfgoam Glosd.” After churning through several more iterations of this process, Shane was able to get the algorithm to recognize some basic colors like red and gray, “though not reliably,” because she also gets a sky blue called “Gray Pubic” and a dark green called “Stoomy Brown.”

Brown has since written a book about artificial intelligence (You Look Like a Thing and I Love You; How Artificial Intelligence Works and Why It’s Making the World a Weirder Place [2019]) and continues her investigations of AI. You can find her website and blog here and her Wikipedia entry here.

Gilding medieaval statues with nanoscale gold sheets

The altar examined is thought to have been made around 1420 in Southern Germany and for a long time stood in a mountain chapel on Alp Leiggern in the Swiss canton of Valais. Today it is on display at the Swiss National Museum (Landesmuseum Zürich). (Photo: Swiss National Museum, Landesmuseum Zürich) [ddownloaded from https://www.psi.ch/en/media/our-research/nanomaterial-from-the-middle-ages]

As amazing as the altar appears, it was hiding some even more amazing secrets. From an October 10, 2022 Paul Scherrer Institute (PSI) press release (also on EurekAlert but published October 11, 2022) by Barbara Vonarburg,

To gild sculptures in the late Middle Ages, artists often applied ultra-thin gold foil supported by a silver base layer. For the first time, scientists at the Paul Scherrer Institute [PSI] have managed to produce nanoscale 3D images of this material, known as Zwischgold. The pictures show this was a highly sophisticated mediaeval production technique and demonstrate why restoring such precious gilded artefacts is so difficult.

The samples examined at the Swiss Light Source SLS using one of the most advanced microscopy methods were unusual even for the highly experienced PSI team: minute samples of materials taken from an altar and wooden statues originating from the fifteenth century. The altar is thought to have been made around 1420 in Southern Germany and stood for a long time in a mountain chapel on Alp Leiggern in the Swiss canton of Valais. Today it is on display at the Swiss National Museum (Landesmuseum Zürich). In the middle you can see Mary cradling Baby Jesus. The material sample was taken from a fold in the Virgin Mary’s robe. The tiny samples from the other two mediaeval structures were supplied by Basel Historical Museum.

The material was used to gild the sacred figures. It is not actually gold leaf, but a special double-sided foil of gold and silver where the gold can be ultra-thin because it is supported by the silver base. This material, known as Zwischgold (part-gold) was significantly cheaper than using pure gold leaf. “Although Zwischgold was frequently used in the Middle Ages, very little was known about this material up to now,” says PSI physicist Benjamin Watts: “So we wanted to investigate the samples using 3D technology which can visualise extremely fine details.” Although other microscopy techniques had been used previously to examine Zwischgold, they only provided a 2D cross-section through the material. In other words, it was only possible to view the surface of the cut segment, rather than looking inside the material.  The scientists were also worried that cutting through it may have changed the structure of the sample. The advanced microscopy imaging method used today, ptychographic tomography, provides a 3D image of Zwischgold’s exact composition for the first time.

X-rays generate a diffraction pattern

The PSI scientists conducted their research using X-rays produced by the Swiss Light Source SLS. These produce tomographs displaying details in the nanoscale range – millionths of a millimetre, in other words. “Ptychography is a fairly sophisticated method, as there is no objective lens that forms an image directly on the detector,” Watts explains. Ptychography actually produces a diffraction pattern of the illuminated area, in other words an image with points of differing intensity. By manipulating the sample in a precisely defined manner, it is possible to generate hundreds of overlapping diffraction patterns. “We can then combine these diffraction patterns like a sort of giant Sudoku puzzle and work out what the original image looked like,” says the physicist. A set of ptychographic images taken from different directions can be combined to create a 3D tomogram.

The advantage of this method is its extremely high resolution. “We knew the thickness of the Zwischgold sample taken from Mary was of the order of hundreds of nanometres,” Watts explains. “So we had to be able to reveal even tinier details.” The scientists achieved this using ptychographic tomography, as they report in their latest article in the journal Nanoscale. “The 3D images clearly show how thinly and evenly the gold layer is over the silver base layer,” says Qing Wu, lead author of the publication. The art historian and conservation scientist completed her PhD at the University of Zurich, in collaboration with PSI and the Swiss National Museum. “Many people had assumed that technology in the Middle Ages was not particularly advanced,” Wu comments. “On the contrary: this was not the Dark Ages, but a period when metallurgy and gilding techniques were incredibly well developed.”

Secret recipe revealed

Unfortunately there are no records of how Zwischgold was produced at the time. “We reckon the artisans kept their recipe secret,” says Wu. Based on nanoscale images and documents from later epochs, however, the art historian now knows the method used in the 15th century: first the gold and the silver were hammered separately to produce thin foils, whereby the gold film had to be much thinner than the silver. Then the two metal foils were worked on together. Wu describes the process: “This required special beating tools and pouches with various inserts made of different materials into which the foils were inserted,” Wu explains. This was a fairly complicated procedure that required highly skilled specialists.

“Our investigations of Zwischgold samples showed the average thickness of the gold layer to be around 30 nanometres, while gold leaf produced in the same period and region was approximately 140 nanometres thick,” Wu explains. “This method saved on gold, which was much more expensive”. At the same time, there was also a very strict hierarchy of materials: gold leaf was used to make the halo of one figure, for example, while Zwischgold was used for the robe. Because this material has less of a sheen, the artists often used it to colour the hair or beards of their statues. “It is incredible how someone with only hand tools was able to craft such nanoscale material,” Watts says. Mediaeval artisans also benefited from a unique property of gold and silver crystals when pressed together: their morphology is preserved across the entire metal film. “A lucky coincidence of nature that ensures this technique works,” says the physicist.

Golden surface turns black

The 3D images do bring to light one drawback of using Zwischgold, however: the silver can push through the gold layer and cover it. The silver moves surprisingly quickly – even at room temperature. Within days, a thin silver coating covers the gold completely. At the surface the silver comes into contact with water and sulphur in the air, and corrodes. “This makes the gold surface of the Zwischgold turn black over time,” Watts explains. “The only thing you can do about this is to seal the surface with a varnish so the sulphur does not attack the silver and form silver sulphide.” The artisans using Zwischgold were aware of this problem from the start. They used resin, glue or other organic substances as a varnish. “But over hundreds of years this protective layer has decomposed, allowing corrosion to continue,” Wu explains.

The corrosion also encourages more and more silver to migrate to the surface, creating a gap below the Zwischgold. “We were surprised how clearly this gap under the metal layer could be seen,” says Watts. Especially in the sample taken from Mary’s robe, the Zwischgold had clearly come away from the base layer. “This gap can cause mechanical instability, and we expect that in some cases it is only the protective coating over the Zwischgold that is holding the metal foil in place,” Wu warns. This is a massive problem for the restoration of historical artefacts, as the silver sulphide has become embedded in the varnish layer or even further down. “If we remove the unsightly products of corrosion, the varnish layer will also fall away and we will lose everything,” says Wu. She hopes it will be possible in future to develop a special material that can be used to fill the gap and keep the Zwischgold attached. “Using ptychographic tomography, we could check how well such a consolidation material would perform its task,” says the art historian.

About PSI

The Paul Scherrer Institute PSI develops, builds and operates large, complex research facilities and makes them available to the national and international research community. The institute’s own key research priorities are in the fields of matter and materials, energy and environment and human health. PSI is committed to the training of future generations. Therefore about one quarter of our staff are post-docs, post-graduates or apprentices. Altogether PSI employs 2100 people, thus being the largest research institute in Switzerland. The annual budget amounts to approximately CHF 400 million. PSI is part of the ETH Domain, with the other members being the two Swiss Federal Institutes of Technology, ETH Zurich and EPFL Lausanne, as well as Eawag (Swiss Federal Institute of Aquatic Science and Technology), Empa (Swiss Federal Laboratories for Materials Science and Technology) and WSL (Swiss Federal Institute for Forest, Snow and Landscape Research). Insight into the exciting research of the PSI with changing focal points is provided 3 times a year in the publication 5232 – The Magazine of the Paul Scherrer Institute.

Here’s a link to and a citation for the paper,

A modern look at a medieval bilayer metal leaf: nanotomography of Zwischgold by
Qing Wu, Karolina Soppa, Elisabeth Müller, Julian Müller, Michal Odstrcil, Esther Hsiao Rho Tsai, Andreas Späth, Mirko Holler, Manuel Guizar-Sicairos, Benjamin Butz, Rainer H. Fink, and Benjamin Watts. Nanoscale DOI: https://doi.org/10.1039/D2NR03367D First published: 10 Oct 2022

This paper is open access.

Whimsy and nanoscienists

Mohsen Hosseini and William Ducker’s contest-winning image, titled “Lotus on Anti-SARS-CoV-2 Coating.” [downloaded from https://vtx.vt.edu/articles/2021/12/nnci-image-contest.html]

Not everything is as it seems in this image according to a January 5, 2022 news item on phys.org (Note: Links have been removed),

At extremely small scales, looks can be deceiving. While at first glance you might see lily pads floating on a tranquil pond, this image is actually a clever adaptation of a snapshot taken on a scanning electron microscope.

In reality, the green spots are only a few micrometers across—smaller than width of a human hair. They make up a surface coating that was developed to limit the transmission of SARS-CoV-2, the virus that causes COVID-19. The coating is composed of a silver-based material applied to a glass surface. The lotus flower, though, was some added artistic flair courtesy of image-editing software.

A January 4, 2022 Virginia Tech news release, which originated the news item, provides more details about the ‘whimsical’ researchers, the image contest, and the research that led to their entry,

Mohsen Hosseini, Ph.D. candidate in chemical engineering, and William Ducker, professor of chemical engineering, recently won an award in the National Nanotechnology Coordinated Infrastructure (NNCI) image contest with this image. Both Hosseini and Ducker are affiliated with the Macromolecules Innovation Institute (MII).

Their win was in the category “most whimsical.”

“As part of the rigor involved in scientific research, I am always careful to maintain the accuracy of my original results,” said Hosseini. “However, this competition was very freeing. It gave me a chance to take my scanning electron microscopy results and legitimately alter it in any way that I chose. It was liberating and fun to express my artistic style. The result isn’t a Monet, but I am glad people liked it.”

The image contest, titled “Plenty of Beauty at the Bottom,” is hosted annually by NNCI in celebration of National Nano Day, which occurred on Oct. 9, 2021. Funded by the National Science Foundation, the NNCI is a network of 16 sites around the country that are dedicated to supporting nanoscience and nanotechnology research and development. Virginia Tech’s NanoEarth center is part of that network, working to advance earth and environmental nanotechnology infrastructure. This image was captured using a scanning electron microscope (SEM) that is part of the Nanoscale Characterization and Fabrication Laboratory (NCFL) in the Virginia Tech Corporate Research Center. This SEM is the latest addition to the instrument suite at the NCFL, which is an initiative of the Institute for Critical Technology and Applied Science. The NCFL gives researchers across the University access to advanced instrumentation including state-of-the-art electron microscopes, optical microscopes, and several spectroscopic techniques.

The development of the protective surface coating began more than a year ago, when the coronavirus pandemic was in its early stages. Working on a team that included another doctoral student, Saeed Behzadinasab, the researchers’ goal was to find a way to prevent the spread of COVID-19 via contaminated surfaces. The coating they produced can successfully inactivate the virus (SARS-CoV-2) when it lands on a solid surface, so that when a person later touches the surface, the virus is unable to infect them.

In studying how their surface coating behaves and performs, the researchers captured images of it at the micro scale. Hosseini explained, “The NNCI contest invitation motivated me to select one of the scanning electron microscope images of my coatings, and edit it according to the contest’s criteria. My brain was filled with ideas since I had recently designed a front cover that was awarded to our paper published in ACS Biomaterials Science & Engineering. I came up with a lotus idea in minutes and that worked very well.”

Interestingly, the researchers had originally developed a brown coating that showed a great deal of promise. However, after conducting tests with consumers, it became clear that the public would be more likely to use a coating that was clear, instead of brown. Ducker’s research group was inspired to produce another coating, which this time would be transparent. As Hosseini put it, “It’s ironic that the invisible coating ended up being the subject of visual art, and even got an award for it.”

Ducker and Hosseini teamed up with Joseph Falkinham and Myra Williams from the Department of Biological Sciences to test the coating on a variety of other illness-causing microorganisms. It proved particularly effective against several bacteria including MRSA, a troublesome antibiotic-resistant bacterium that plagues hospitals.

With its transparent appearance and its broad antimicrobial effectiveness, the coating is now a strong candidate for commercialization. Indeed, Ducker has founded a company dedicated to pursuing the production of this surface coating on a larger scale.

Hosseini and Ducker are proud to have their image shared with the national nanoscience community. The recognition shows an appreciation for their hard work, in addition to their whimsical perspective. According to NanoEarth assistant director Tonya Pruitt, “Virginia Tech has had some excellent submissions to the NNCI image contest over the years, but this is the first year we’ve had a winner!”

Here’s a link to and a citation for the paper,

Reduction of Infectivity of SARS-CoV-2 by Zinc Oxide Coatings by Mohsen Hosseini, Saeed Behzadinasab, Alex W.H. Chin, Leo L.M. Poon, and William A. Ducker. ACS Biomater. Sci. Eng. 2021, 7, 11, 5022–5027 DOI: https://doi.org/10.1021/acsbiomaterials.1c01076 Publication Date:October 6, 2021 Copyright © 2021 American Chemical Society

This paper is behind a paywall.

You can find the other winners and honorable mentions of the NNCI Image Contest 2021 here. The contest is also known as “Plenty of Beauty at the Bottom” in honour of Richard Feynman and his 1959 lecture, “There’s plenty of room at the bottom.”

The NNCI website can be found here.

Windows and roofs ‘self-adapt’ to heating and cooling conditions

I have two items about thermochromic coatings. It’s a little confusing since the American Association for the Advancement of Science (AAAS), which publishes the journal featuring both papers has issued a news release that seemingly refers to both papers as a single piece of research.

Onto, the press/new releases from the research institutions to be followed by the AAAS news release.

Nanyang Technological University (NTU) does windows

A December 16, 2021 news item on Nanowerk announced work on energy-saving glass,

An international research team led by scientists from Nanyang Technological University, Singapore (NTU Singapore) has developed a material that, when coated on a glass window panel, can effectively self-adapt to heat or cool rooms across different climate zones in the world, helping to cut energy usage.

Developed by NTU researchers and reported in the journal Science (“Scalable thermochromic smart windows with passive radiative cooling regulation”), the first-of-its-kind glass automatically responds to changing temperatures by switching between heating and cooling.

The self-adaptive glass is developed using layers of vanadium dioxide nanoparticles composite, Poly(methyl methacrylate) (PMMA), and low-emissivity coating to form a unique structure which could modulate heating and cooling simultaneously.

A December 17, 2021 NTU press release (PDF), also on EurekAlert but published December 16, 2021, which originated the news item, delves further into the research (Note: A link has been removed),

The newly developed glass, which has no electrical components, works by exploiting the spectrums of light responsible for heating and cooling.

During summer, the glass suppresses solar heating (near infrared light), while boosting radiative cooling (long-wave infrared) – a natural phenomenon where heat emits through surfaces towards the cold universe – to cool the room. In the winter, it does the opposite to warm up the room.

In lab tests using an infrared camera to visualise results, the glass allowed a controlled amount of heat to emit in various conditions (room temperature – above 70°C), proving its ability to react dynamically to changing weather conditions.

New glass regulates both heating and cooling

Windows are one of the key components in a building’s design, but they are also the least energy-efficient and most complicated part. In the United States alone, window-associated energy consumption (heating and cooling) in buildings accounts for approximately four per cent of their total primary energy usage each year according to an estimation based on data available from the Department of Energy in US.[1]

While scientists elsewhere have developed sustainable innovations to ease this energy demand – such as using low emissivity coatings to prevent heat transfer and electrochromic glass that regulate solar transmission from entering the room by becoming tinted – none of the solutions have been able to modulate both heating and cooling at the same time, until now.

The principal investigator of the study, Dr Long Yi of the NTU School of Materials Science and Engineering (MSE) said, “Most energy-saving windows today tackle the part of solar heat gain caused by visible and near infrared sunlight. However, researchers often overlook the radiative cooling in the long wavelength infrared. While innovations focusing on radiative cooling have been used on walls and roofs, this function becomes undesirable during winter. Our team has demonstrated for the first time a glass that can respond favourably to both wavelengths, meaning that it can continuously self-tune to react to a changing temperature across all seasons.”

As a result of these features, the NTU research team believes their innovation offers a convenient way to conserve energy in buildings since it does not rely on any moving components, electrical mechanisms, or blocking views, to function.

To improve the performance of windows, the simultaneous modulation of both solar transmission and radiative cooling are crucial, said co-authors Professor Gang Tan from The University of Wyoming, USA, and Professor Ronggui Yang from the Huazhong University of Science and Technology, Wuhan, China, who led the building energy saving simulation.

“This innovation fills the missing gap between traditional smart windows and radiative cooling by paving a new research direction to minimise energy consumption,” said Prof Gang Tan.

The study is an example of groundbreaking research that supports the NTU 2025 strategic plan, which seeks to address humanity’s grand challenges on sustainability, and accelerate the translation of research discoveries into innovations that mitigate human impact on the environment.

Innovation useful for a wide range of climate types

As a proof of concept, the scientists tested the energy-saving performance of their invention using simulations of climate data covering all populated parts of the globe (seven climate zones).

The team found the glass they developed showed energy savings in both warm and cool seasons, with an overall energy saving performance of up to 9.5%, or ~330,000 kWh per year (estimated energy required to power 60 household in Singapore for a year) less than commercially available low emissivity glass in a simulated medium sized office building.

First author of the study Wang Shancheng, who is Research Fellow and former PhD student of Dr Long Yi, said, “The results prove the viability of applying our glass in all types of climates as it is able to help cut energy use regardless of hot and cold seasonal temperature fluctuations. This sets our invention apart from current energy-saving windows which tend to find limited use in regions with less seasonal variations.”

Moreover, the heating and cooling performance of their glass can be customised to suit the needs of the market and region for which it is intended.

“We can do so by simply adjusting the structure and composition of special nanocomposite coating layered onto the glass panel, allowing our innovation to be potentially used across a wide range of heat regulating applications, and not limited to windows,” Dr Long Yi said.

Providing an independent view, Professor Liangbing Hu, Herbert Rabin Distinguished Professor, Director of the Center for Materials Innovation at the University of Maryland, USA, said, “Long and co-workers made the original development of smart windows that can regulate the near-infrared sunlight and the long-wave infrared heat. The use of this smart window could be highly important for building energy-saving and decarbonization.”  

A Singapore patent has been filed for the innovation. As the next steps, the research team is aiming to achieve even higher energy-saving performance by working on the design of their nanocomposite coating.

The international research team also includes scientists from Nanjing Tech University, China. The study is supported by the Singapore-HUJ Alliance for Research and Enterprise (SHARE), under the Campus for Research Excellence and Technological Enterprise (CREATE) programme, Minster of Education Research Fund Tier 1, and the Sino-Singapore International Joint Research Institute.

Here’s a link to and a citation for the paper,

Scalable thermochromic smart windows with passive radiative cooling regulation by Shancheng Wang, Tengyao Jiang, Yun Meng, Ronggui Yang, Gang Tan, and Yi Long. Science • 16 Dec 2021 • Vol 374, Issue 6574 • pp. 1501-1504 • DOI: 10.1126/science.abg0291

This paper is behind a paywall.

Lawrence Berkeley National Laboratory (Berkeley Lab; LBNL) does roofs

A December 16, 2021 Lawrence Berkeley National Laboratory news release (also on EurekAlert) announces an energy-saving coating for roofs (Note: Links have been removed),

Scientists have developed an all-season smart-roof coating that keeps homes warm during the winter and cool during the summer without consuming natural gas or electricity. Research findings reported in the journal Science point to a groundbreaking technology that outperforms commercial cool-roof systems in energy savings.

“Our all-season roof coating automatically switches from keeping you cool to warm, depending on outdoor air temperature. This is energy-free, emission-free air conditioning and heating, all in one device,” said Junqiao Wu, a faculty scientist in Berkeley Lab’s Materials Sciences Division and a UC Berkeley professor of materials science and engineering who led the study.

Today’s cool roof systems, such as reflective coatings, membranes, shingles, or tiles, have light-colored or darker “cool-colored” surfaces that cool homes by reflecting sunlight. These systems also emit some of the absorbed solar heat as thermal-infrared radiation; in this natural process known as radiative cooling, thermal-infrared light is radiated away from the surface.

The problem with many cool-roof systems currently on the market is that they continue to radiate heat in the winter, which drives up heating costs, Wu explained.

“Our new material – called a temperature-adaptive radiative coating or TARC – can enable energy savings by automatically turning off the radiative cooling in the winter, overcoming the problem of overcooling,” he said.

A roof for all seasons

Metals are typically good conductors of electricity and heat. In 2017, Wu and his research team discovered that electrons in vanadium dioxide behave like a metal to electricity but an insulator to heat – in other words, they conduct electricity well without conducting much heat. “This behavior contrasts with most other metals where electrons conduct heat and electricity proportionally,” Wu explained.

Vanadium dioxide below about 67 degrees Celsius (153 degrees Fahrenheit) is also transparent to (and hence not absorptive of) thermal-infrared light. But once vanadium dioxide reaches 67 degrees Celsius, it switches to a metal state, becoming absorptive of thermal-infrared light. This ability to switch from one phase to another – in this case, from an insulator to a metal – is characteristic of what’s known as a phase-change material.

To see how vanadium dioxide would perform in a roof system, Wu and his team engineered a 2-centimeter-by-2-centimeter TARC thin-film device.

TARC “looks like Scotch tape, and can be affixed to a solid surface like a rooftop,” Wu said.

In a key experiment, co-lead author Kechao Tang set up a rooftop experiment at Wu’s East Bay home last summer to demonstrate the technology’s viability in a real-world environment.

A wireless measurement device set up on Wu’s balcony continuously recorded responses to changes in direct sunlight and outdoor temperature from a TARC sample, a commercial dark roof sample, and a commercial white roof sample over multiple days.

How TARC outperforms in energy savings

The researchers then used data from the experiment to simulate how TARC would perform year-round in cities representing 15 different climate zones across the continental U.S.

Wu enlisted Ronnen Levinson, a co-author on the study who is a staff scientist and leader of the Heat Island Group in Berkeley Lab’s Energy Technologies Area, to help them refine their model of roof surface temperature. Levinson developed a method to estimate TARC energy savings from a set of more than 100,000 building energy simulations that the Heat Island Group previously performed to evaluate the benefits of cool roofs and cool walls across the United States.

Finnegan Reichertz, a 12th grade student at the East Bay Innovation Academy in Oakland who worked remotely as a summer intern for Wu last year, helped to simulate how TARC and the other roof materials would perform at specific times and on specific days throughout the year for each of the 15 cities or climate zones the researchers studied for the paper.

The researchers found that TARC outperforms existing roof coatings for energy saving in 12 of the 15 climate zones, particularly in regions with wide temperature variations between day and night, such as the San Francisco Bay Area, or between winter and summer, such as New York City.

“With TARC installed, the average household in the U.S. could save up to 10% electricity,” said Tang, who was a postdoctoral researcher in the Wu lab at the time of the study. He is now an assistant professor at Peking University in Beijing, China.

Standard cool roofs have high solar reflectance and high thermal emittance (the ability to release heat by emitting thermal-infrared radiation) even in cool weather.

According to the researchers’ measurements, TARC reflects around 75% of sunlight year-round, but its thermal emittance is high (about 90%) when the ambient temperature is warm (above 25 degrees Celsius or 77 degrees Fahrenheit), promoting heat loss to the sky. In cooler weather, TARC’s thermal emittance automatically switches to low, helping to retain heat from solar absorption and indoor heating, Levinson said.

Findings from infrared spectroscopy experiments using advanced tools at Berkeley Lab’s Molecular Foundry validated the simulations.

“Simple physics predicted TARC would work, but we were surprised it would work so well,” said Wu. “We originally thought the switch from warming to cooling wouldn’t be so dramatic. Our simulations, outdoor experiments, and lab experiments proved otherwise – it’s really exciting.”

The researchers plan to develop TARC prototypes on a larger scale to further test its performance as a practical roof coating. Wu said that TARC may also have potential as a thermally protective coating to prolong battery life in smartphones and laptops, and shield satellites and cars from extremely high or low temperatures. It could also be used to make temperature-regulating fabric for tents, greenhouse coverings, and even hats and jackets.

Co-lead authors on the study were Kaichen Dong and Jiachen Li.

The Molecular Foundry is a nanoscience user facility at Berkeley Lab.

This work was primarily supported by the DOE Office of Science and a Bakar Fellowship.

The technology is available for licensing and collaboration. If interested, please contact Berkeley Lab’s Intellectual Property Office, ipo@lbl.gov.

Here’s a link to and a citation for the paper,

Temperature-adaptive radiative coating for all-season household thermal regulation by Kechao Tang, Kaichen Dong, Jiachen Li, Madeleine P. Gordon, Finnegan G. Reichertz, Hyungjin Kim, Yoonsoo Rho, Qingjun Wang, Chang-Yu Lin, Costas P. Grigoropoulos, Ali Javey, Jeffrey J. Urban, Jie Yao, Ronnen Levinson, Junqiao Wu. Science • 16 Dec 2021 • Vol 374, Issue 6574 • pp. 1504-1509 • DOI: 10.1126/science.abf7136

This paper is behind a paywall.

An interesting news release from the AAAS

While it’s a little confusing as it cites only the ‘window’ research from NTU, the body of this news release offers some additional information about the usefulness of thermochromic materials and seemingly refers to both papers, from a December 16, 2021 AAAS news release,

Temperature-adaptive passive radiative cooling for roofs and windows

When it’s cold out, window glass and roof coatings that use passive radiative cooling to keep buildings cool can be designed to passively turn off radiative cooling to avoid heat loss, two new studies show.  Their proof-of-concept analyses demonstrate that passive radiative cooling can be expanded to warm and cold climate applications and regions, potentially providing all-season energy savings worldwide. Buildings consume roughly 40% of global energy, a large proportion of which is used to keep them cool in warmer climates. However, most temperature regulation systems commonly employed are not very energy efficient and require external power or resources. In contrast, passive radiative cooling technologies, which use outer space as a near-limitless natural heat sink, have been extensively examined as a means of energy-efficient cooling for buildings. This technology uses materials designed to selectively emit narrow-band radiation through the infrared atmospheric window to disperse heat energy into the coldness of space. However, while this approach has proven effective in cooling buildings to below ambient temperatures, it is only helpful during the warmer months or in regions that are perpetually hot. Furthermore, the inability to “turn off” passive cooling in cooler climes or in regions with large seasonal temperature variations means that continuous cooling during colder periods would exacerbate the energy costs of heating. In two different studies, by Shancheng Wang and colleagues and Kechao Tang and colleagues, researchers approach passive radiative cooling from an all-season perspective and present a new, scalable temperature-adaptive radiative technology that passively turns off radiative cooling at lower temperatures. Wang et al. and Tang et al. achieve this using a tungsten-doped vanadium dioxide and show how it can be applied to create both window glass and a flexible roof coating, respectively. Model simulations of the self-adapting materials suggest they could provide year-round energy savings across most climate zones, especially those with substantial seasonal temperature variations. 

I wish them all good luck with getting these materials to market.