This research was recently published in Science Advances.

In some human-interactive electronics, such as temperature gauges or health sensors, polymers are used that are capable of changing color depending on stimuli. This phenomenon is referred to as stimuli-interactive structural colors because the material reacts and changes color due to environmental changes, such as a solvent or solution.

A material that has a one-dimensional periodic structure comprised of two (A and B) layers acts like a photonic crystal and can reflect light of a given wavelength (color) depending on the thickness of each layer. Stimuli-interactive structural color works by altering photonic crystals using external stimuli or forces. The thickness of each polymer layer affects the color of the light reflected: if all the layers in a material are of the same thickness, a single color will be reflected. If different parts of the material are composed of stacks of layers, each having a different thickness, each layer will reflect a different color and the material will appear like a normal metal material, reflecting all colors.

In some cases, a preferential solvent is used to swell one of the particular polymer layers, purposefully causing color changes. The researchers noticed that the expected layers were swelling in these materials. However, it was unclear how the solvent was seeping/crossing through layers that did not swell to those that were supposed to swell.

“Let’s say we put a solvent over multiple polymer A and B layers,” said Thomas. “The first A layer swells, the B layer doesn’t swell, but the next layer A will. How does the second layer of solvent A get through the B layer? We realized there must be something in the overall polymer structure that allows the passage of solvent to the other layers.”

To understand what was occurring within the polymers, the researchers used an electron beam to develop a tomogram — a reconstruction technique that takes very thin, two-dimensional images of sections of 3D objects to uncover what is inside.

“Suppose you had a loaf of bread, and you wanted to know if there was a hole somewhere within the loaf,” said Thomas. “If you sliced it thin, you’d eventually hit the hole. You keep slicing, and then the hole would disappear. If you looked at all the slices, you could understand exactly where the holes are. This process is similar to the idea of a tomograph.”

Using this method, the researchers found that within the polymer photonic crystal material, helicoidal screw dislocations (defects) were present, allowing the solvent to easily and rapidly cross through to different layers, causing the swelling and producing the stimuli-interactive structural color changes.

Typically, defects are associated with high energy and are singular (abruptly disrupting the periodicity occurring in one location). In contrast, the helicoidal defects are nonsingular and spontaneously formed — an advantage for the materials.

“This is a good kind of defect that helps properties and allows swift and efficient penetration into the material with solvent and rapid swelling. If these things didn’t exist, the only way the layers could sweat would be from the edges,” said Thomas.

Because stimuli-interactive structural color presents an excellent potential for devices such as health sensors and human-interactive electronics, controlling the lateral spacing or amount of helicoidal defects could be a critical factor in future applications.

“These defects currently produce a favorable effect, but it depends on the application,” he said. “Our next challenge is deciphering how to control the spacing and amount of these defects and, in turn, having more control over the time it takes for the fluid to move through the layers. Understanding these defects is key for increasing the number of applications this technology can be used in.”

The Hagler Institute Fellowship supported the research completed on this project at Texas A&M.

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Materials provided by Texas A&M University. Original written by Michelle Revels. Note: Content may be edited for style and length.

Under anaerobic conditions, a carbon-carbon double bond is crucial for the shattering the ultra-strong carbon-fluorine bond by microbial communities. While breaking the carbon-carbon bond does not completely degrade the molecule, the resulting products could be relayed to other microorganisms for defluorination under in aerobic conditions.

The achievement builds upon prior work by the same researchers, who were the first to report successful microbial defluorination of a fully fluorinated PFAS structure by replacing carbon-fluorine bonds with carbon-hydrogen bonds.

Per- and polyfluoroalkyl substances, or PFAS, are a group of over 9,000 chemicals used in countless industrial processes and commercial products since the 1940s. As a result, PFAS have found their way into the water cycle and are now found in virtually every water source. These chemicals contain a bond between fluorine and carbon atoms that is the strongest single bond known, rendering PFAS non-biodegradable and resistant to conventional water treatment methods. They wind up in the tissues of organisms, including humans, where they have been associated with some types of cancer, thyroid and liver problems, and likely other, still poorly understood, health problems.

In an earlier paper, Yujie Men, an assistant professor of chemical and environmental engineering, and her colleagues reported using anaerobic microbial communities often used for dechlorination to degrade two specific PFAS, including one fully fluorinated, or perfluorinated, structure.

The new paper takes this research a step further by showing that the point of entry for the anaerobic microbes was a double bond between carbon atoms located next to the carboxyl group of the FCA molecules. Trifluoromethyl branches on the double bond could further enhance the biodegradability.

Microbes capable of doing this type of defluorination are not rare. Using activated sludge — microbial communities commonly used in wastewater treatment facilities to break down and remove organic matter — and an anaerobic condition, the researchers successfully repeated their earlier experiment with more structurally similar PFAS.

“Currently biocatalysts that can do defluorination of perfluorinated compounds like PFOA are very rare. We still know very little about which microbes or enzymes can do the defluorination of PFAS in general and how,” said Men. “Our work is at the leading edge of finding this information.”

Even when scientists figure out ways to break the initial carbon-fluorine bond in perfluorinated compounds, their work isn’t done because the molecules are likely broken down into other molecules that could also be harmful. Successful remediation of PFAS-contaminated environments requires initial breakdown of the PFAS parent molecule followed by complete degradation of the secondary molecules.

One recent study by the Men group demonstrated that activated sludge communities were able to completely degrade the secondary molecule from chemical degradation of one type of perfluorinated chemical via a process known as cometabolism. Their new study further implies that simply through the cooperation among different microbial groups, such as anaerobic and aerobic bacteria, deeper defluorination could also be achieved for certain perfluorinated chemicals.

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Materials provided by University of California – Riverside. Original written by Holly Ober. Note: Content may be edited for style and length.

The team developed a low-cost gel film made of abundant materials that can pull water from the air in even the driest climates. The materials that facilitate this reaction cost a mere $2 per kilogram, and a single kilogram can produce more than 6 liters of water per day in areas with less than 15% relative humidity and 13 liters in areas with up to 30% relative humidity.

The research builds on previous breakthroughs from the team, including the ability to pull water out of the atmosphere and the application of that technology to create self-watering soil. However, these technologies were designed for relatively high-humidity environments.

“This new work is about practical solutions that people can use to get water in the hottest, driest places on Earth,” said Guihua Yu, professor of materials science and mechanical engineering in the Cockrell School of Engineering’s Walker Department of Mechanical Engineering. “This could allow millions of people without consistent access to drinking water to have simple, water generating devices at home that they can easily operate.”

The new paper appears in Nature Communications.

The researchers used renewable cellulose and a common kitchen ingredient, konjac gum, as a main hydrophilic (attracted to water) skeleton. The open-pore structure of gum speeds the moisture-capturing process. Another designed component, thermo-responsive cellulose with hydrophobic (resistant to water) interaction when heated, helps release the collected water immediately so that overall energy input to produce water is minimized.

Other attempts at pulling water from desert air are typically energy-intensive and do not produce much. And although 6 liters does not sound like much, the researchers say that creating thicker films or absorbent beds or arrays with optimization could drastically increase the amount of water they yield.

The reaction itself is a simple one, the researchers said, which reduces the challenges of scaling it up and achieving mass usage.

“This is not something you need an advanced degree to use,” said Youhong “Nancy” Guo, the lead author on the paper and a former doctoral student in Yu’s lab, now a postdoctoral researcher at the Massachusetts Institute of Technology. “It’s straightforward enough that anyone can make it at home if they have the materials.”

The film is flexible and can be molded into a variety of shapes and sizes, depending on the need of the user. Making the film requires only the gel precursor, which includes all the relevant ingredients poured into a mold.

“The gel takes 2 minutes to set simply. Then, it just needs to be freeze-dried, and it can be peeled off the mold and used immediately after that,” said Weixin Guan, a doctoral student on Yu’s team and a lead researcher of the work.

The research was funded by the U.S. Department of Defense’s Defense Advanced Research Projects Agency (DARPA), and drinking water for soldiers in arid climates is a big part of the project. However, the researchers also envision this as something that people could someday buy at a hardware store and use in their homes because of the simplicity.

Yu directed the project. Guo and Guan co-led experimental efforts on synthesis, characterization of the samples and device demonstration. Other team members are Chuxin Lei, Hengyi Lu and Wen Shi.

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Oulasvirta and colleagues tested an alternative, computer-assisted method that uses an algorithm to search through a design space, the set of possible solutions given multi-dimensional inputs and constraints for a particular design issue. They hypothesized that a guided approach could yield better designs by scanning a broader swath of solutions and balancing out human inexperience and design fixation.

Along with collaborators from the University of Cambridge, the researchers set out to compare the traditional and assisted approaches to design, using virtual reality as their laboratory. They employed Bayesian optimization, a machine learning technique that both explores the design space and steers towards promising solutions. ‘We put a Bayesian optimizer in the loop with a human, who would try a combination of parameters. The optimizer then suggests some other values, and they proceed in a feedback loop. This is great for designing virtual reality interaction techniques,’ explains Oulasvirta. ‘What we didn’t know until now is how the user experiences this kind of optimization-driven design approach.’

To find out, Oulasvirta’s team asked 40 novice designers to take part in their virtual reality experiment. The subjects had to find the best settings for mapping the location of their real hand holding a vibrating controller to the virtual hand seen in the headset. Half of these designers were free to follow their own instincts in the process, and the other half were given optimizer-selected designs to evaluate. Both groups had to choose three final designs that would best capture accuracy and speed in the 3D virtual reality interaction task. Finally, subjects reported how confident and satisfied they were with the experience and how in control they felt over the process and the final designs.

The results were clear-cut: ‘Objectively, the optimizer helped designers find better solutions, but designers did not like being hand-held and commanded. It destroyed their creativity and sense of agency,’ reports Oulasvirta. The optimizer-led process allowed designers to explore more of the design space compared with the manual approach, leading to more diverse design solutions. The designers who worked with the optimizer also reported less mental demand and effort in the experiment. By contrast, this group also scored lower on expressiveness, agency and ownership, compared with the designers who did the experiment without a computer assistant.

‘There is definitely a trade-off,’ says Oulasvirta. ‘With the optimizer, designers came up with better designs and covered a more extensive set of solutions with less effort. On the other hand, their creativity and sense of ownership of the outcomes was reduced.’ These results are instructive for the development of AI that assists humans in decision-making. Oulasvirta suggests that people need to be engaged in tasks such as assisted design so they retain a sense of control, don’t get bored, and receive more insight into how a Bayesian optimizer or other AI is actually working. ‘We’ve seen that inexperienced designers especially can benefit from an AI boost when engaging in our design experiment,’ says Oulasvirta. ‘Our goal is that optimization becomes truly interactive without compromising human agency.’

This paper was selected for an honourable mention at the ACM CHI Conference on Human Factors in Computing Systems in May 2022.

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