Category: Chemistry

by Michael W. Crowder, The Conversation

Few beverages have as rich a heritage and as complicated a chemistry as bourbon whiskey, often called “America’s spirit.” Known for its deep amber hue and robust flavors, bourbon has captured the hearts of enthusiasts across the country.

But for a whiskey to be called a bourbon, it has to adhere to very specific rules. For one, it needs to be made in the U.S. or a U.S. territory—although almost all is made in Kentucky. The other rules have more to do with the steps to make it—how much corn is in the grain mixture, the aging process and the alcohol proof.

I’m a bourbon researcher and chemistry professor who teaches classes on fermentation, and I’m a bourbon connoisseur myself. The complex science behind this aromatic beverage reveals why there are so many distinct bourbons, despite the strict rules around its manufacture.

The mash bill

All whiskeys have what’s called a mash bill. The mash bill refers to the recipe of grains that makes up the spirit’s flavor foundation. To be classified as bourbon, a spirit’s mash bill must have at least 51% corn—the corn gives it that characteristic sweetness.

Almost all bourbons also have malted barley, which lends a nutty, smoky flavor and provides enzymes that turn starches into sugars later in the production process.

Many distillers also use rye and wheat to flavor their bourbons. Rye makes the bourbon spicy, while wheat produces a softer, sweeter flavor. Others might use grains like rice or quinoa—but each grain chosen, and the amount of each, affects the flavor down the line.

The chemistry of yeast

Once distillers grind the grains from the mash bill and mix them with heated water, they add yeast to the mash. This process is called “pitching the yeast.” The yeast consumes sugars and produces ethyl alcohol and carbon dioxide as byproducts during the process called fermentation—that’s how the bourbon becomes alcoholic.

The fermented mash is now called “beer.” While similar in structure and taste to the beer you might buy in a six-pack, this product still has a way to go before it reaches its final form.

Yeast fermentation yields other byproducts besides alcohol and carbon dioxide, including flavor compounds called congeners. Congeners can be esters, which produce a fruity or floral flavor, or complex alcohols, which can taste strong and aromatic.

The longer the fermentation period, the longer the yeast has to create more flavorful byproducts, which enhances the complexity of the spirit’s final taste. And different yeasts produce different amounts of congeners.

Separating the fermentation products

During distillation, distillers separate the alcohol and congeners from the fermented mash of grains, resulting in a liquid spirit. To do this, they use pot or column stills, which are large kettles or columns, respectively, often made at least partially of copper. These stills heat the beer and any congeners that have a boiling point of less than 350°F (176°C) to form a vapor.

The type of still will influence the beverages’ final flavor, because pot stills often do not separate the congeners as precisely as column stills do. Pot stills result in a spirit that often contains a more complex mixture of congeners.

The desired vapors that exit the still are condensed back to liquid form, and this product is called the distillate.

Different chemical compounds have different boiling points, so distillers can separate the different chemicals by collecting the distillate at different temperatures. So in the case of the pot still, as the kettle is heated, chemicals that have lower boiling points are collected first. As the kettle heats further, chemicals with higher boiling points vaporize and then are condensed and collected.

By the end of the distillation process with a pot still, the distillate has been divided into a few fractions. One of these fractions is called the “hearts,” containing mostly ethanol and water, but also small amounts of congeners, which play a big role in the final flavor of the product.

The alchemy of time and wood

After distillation, the “hearts” fraction (which is clear and resembles water) is placed in a charred oak barrel for the aging process. Here, the bourbon interacts with chemicals in the barrel’s wood, and about 70% of the bourbon’s final flavor is determined by this step. The bourbon gets all its amber color during the aging process.

Bourbon may rest in the barrel for several years. During the summer, when the temperature is hot, the distillate can pass through the inner charred layer of the barrel. The charred wood acts like a filter and strains out some of the chemicals before the distillate seeps into the wood. These chemicals bind to the charred layer and do not release, kind of like a water filter.

Under the charred layer of the barrel is a “red line,” a layer where the oak was toasted during the charring process of making the barrel. The toasting process breaks down starch and other polymers, called lignins and tannins, in the oak.

When the distillate seeps to the red-line layer, it dissolves the sugars in the barrel, as well as lignin byproducts and tannins.

During the cold winter months, the distillate retreats back into the barrel, but it takes with it these sugars, tannins and lignin byproducts from the wood, which enhance the flavors. If you disassemble a barrel after it has aged bourbon, you can see a “solvent line,” which shows how far into the wood the distillate penetrated. The type of oak barrel can have a profound effect on the final taste, along with the barrel’s size and how charred it is.

For most distilleries, barrels are stored in large buildings called rickhouses. Ethyl alcohol and water in the distillate evaporate out of the barrel, and the humidity in that part of the rickhouse plays a big role.

Lower humidity often leads to higher-proof bourbon, as more water than ethanol leaves the barrel. In addition, air enters the barrel, and oxygen from the air reacts with some of the chemicals in the bourbon, creating new flavor chemicals. These reactions tend to soften the taste of the final product.

There are thousands of bourbons on the market, and they can be distinguished by their unique flavors and aromas. The variety of brands reflects the many choices that distillers make on the mash bill, fermentation and distillation conditions, and aging process. No two bourbons are quite the same.

Provided by The Conversation 

This article is republished from The Conversation under a Creative Commons license. Read the original article.

by Adam Hadhazy, Stanford University

New Stanford University research has revealed that the mineral silica, a common food additive and popular cosmetics ingredient, is not a chemically inert substance, as has long been supposed.

As described in a new study, researchers placed commercially available silica particles in a water solution with biomolecules containing compounds called thiols. These thiol-containing biomolecules are widespread in nature and in the human body, for instance, in the form of glutathione, a key antioxidant found in most cells.

When exposed to silica, the thiol biomolecules underwent redox chemical reactions. These reactions, in which electrons are lost, could degrade or alter the molecules’ function, potentially posing health risks. For instance, low levels of glutathione can lead to increased oxidative stress in the body that can damage all manner of cellular components, from membranes to DNA.

The findings highlight the need for further research into the reactivity of silica, especially given its extensive usage in everyday products.

“Silica particles are thought to be benign and inert, but our study’s results indicate that silica is actually reactive,” says Yangjie Li, a postdoctoral scholar in the Department of Chemistry in the Stanford School of Humanities and Sciences and lead author of the study, which published Aug. 17 in Proceedings of the National Academy of Sciences. “We encourage further investigation into whether silica particle exposure can deplete glutathione and other critical compounds in the body.”

“Our findings sound an alarm for the continued use of silica particles,” said senior author Richard Zare, the Marguerite Blake Wilbur Professor in Natural Science and a professor of chemistry in H&S. “While it’s too soon to say that silica is a health risk, at minimum silica poses the potential problem of introducing unwanted chemistry, particularly in food.”

Often consumed and applied

Silica—another name for compounds of silicon and oxygen—is a colorless, odorless, tasteless material. While silica occurs naturally in foods including leafy greens, manufacturers often add tiny, sand-like particles of silica as an anticaking agent to soups and coffee creamers, for instance. Currently, the Food and Drug Administration allows foods to contain as much as 2% by weight of silica particles.

For cosmetics, including skin care products, silica serves as a bulking or absorbing agent, or as an abrasive in scrubs. In health care, silica particles have also found significant use in the delivery of drugs and for medical imaging purposes. For those applications, silica particles are manufactured to have tiny holes, or pores, into which pharmaceuticals and other substances can be slotted.

Given this scope of applications, Li and Zare sought to examine the orthodoxy of silica as a chemically inert substance. Li has a background in probing presumed properties of everyday materials. For her doctoral dissertation work, Li investigated how glass—long relied on for stably storing medicines and other important materials—can, in certain circumstances, act as a catalyst and accelerate chemical reactions.

“We’ve seen before that so-called inert materials may not really be inert,” said Zare. “That story may be repeating itself with silica particles.”

Overlooked chemistry at work

For the study, the Stanford researchers purchased commercially available, pure silica particles, sold as a dry powder. Working with Kurt Kolasinski, a former graduate scholar of Zare and now a professor of physical chemistry at West Chester University, Li added silica to watery solutions containing one of three thiol-bearing biomolecules. The biomolecules studied were cysteine (a key amino acid), the aforementioned antioxidant glutathione, and penicillamine (a so-called heavy metal antagonist for treating Wilson’s disease, a condition that occurs when too much copper accumulates in the body).

Li incubated the solutions in the dark for a day at room temperature. She obtained small samples of the solutions at half-hour, 2-hour, 4-hour, and 24-hour marks to gauge the rates of any chemical reactions that might have occurred, using an instrument called a mass spectrometer.

Over time, the biomolecules were oxidized (a loss of electrons in a chemical reaction) by incubation with silica, to the surprising tune of as much as 95% of the molecules in solution ultimately reacting in this way, while the control experiments without silica incubation showed minimal oxidation.

From a chemistry perspective, the reactive pure silica particles converted thiol-containing molecules to disulfide molecules. Spelled out in terms of their elemental compositions, the former molecules, which contain sulfur-hydrogen (S-H) bonded groups, changed to have disulfide bridges, symbolized S-S.

The reverse reaction is familiarly encountered, Zare pointed out, when curly hair is straightened by applying heat with a flat iron. The process breaks disulfide bonds in the proteins in the hair, allowing the hair to be reshaped into straight hair strands. “When people use flat irons to straighten their hair, the chemistry of what’s going on there is breaking disulfides and turning them into thiols, the reverse reaction of our study,” said Zare.

For the observed reactions, the Stanford researchers think that upon contact with water, silica forms so-called surface-bound silyloxy radicals (a silicon atom bound to an oxygen atom in a configuration that has an unpaired electron). When encountering the radicals, thiol biomolecules in the solution transfer hydrogen atoms (H) to the radicals. Accordingly freed of bonded H, the sulfur atoms in two thiol molecules then recombine to form the S-S disulfides.

Looking ahead, the Zare lab researchers plan to further test how varying sizes of silica particles influence chemical reaction rates. Experiments with larger biomolecules are also ongoing.

Zare and Li hope that their initial findings prompt other researchers, and potentially regulators, to characterize the chemistry of silica more thoroughly.

“Silica is a material that shows up in a lot of places, in the things we eat, in the products we put on our skin, and in medical settings,” said Zare. “In light of this new study, we ought to know more about silica and its interactions with other materials.”

More information: Yangjie Li et al, Silica particles convert thiol-containing molecules to disulfides, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2304735120

Journal information: Proceedings of the National Academy of Sciences 

Provided by Stanford University 

by Hebrew University of Jerusalem

Research conducted at The Hebrew University of Jerusalem has shed light on the anti-inflammatory properties of black soldier fly larvae (BSFL) oil. Led by Prof. Betty Schwartz, from the Faculty of Agriculture, Food and Environment at the Hebrew University of Jerusalem, the study focuses on leveraging metabolomics to modulate toll-like receptor (TLR) signaling pathways. The findings hold significant promise for revolutionizing dietary approaches to inflammatory-related conditions, such as ulcerative colitis.

Ulcerative colitis, a persistent inflammatory bowel disease, often necessitates dietary adjustments. A pivotal factor is the profile of fatty acids within the diet. The research team’s investigation delves into the anti-inflammatory potential of BSFL oil, rich in medium chain fatty acids (MCFAs) like C12:0, and its potential role in mitigating inflammation linked to ulcerative colitis.

The study introduces an innovative methodology, comparing the anti-inflammatory effects of BSFL oil with those of C12:0 through the activation of cell lines (THP-1 and J774A.1) by TLR4 and TLR2. The research explores the protective effects of BSFL oil against acute colitis induced by dextran sulfate sodium (DSS). The study is published in the International Journal of Molecular Sciences.

The findings demonstrate that, while both BSFL oil and C12:0 suppress proinflammatory cytokines in lipopolysaccharide (LPS)-stimulated macrophages, only BSFL oil exhibits anti-inflammatory properties in Pam3CSK4-stimulated macrophages.

The study’s insights extend to the genetic level, revealing that BSFL oil could potentially influence cellular energy utilization and immune function through signaling pathways such as mTOR and PPAR, facilitating the utilization of fats for energy. In contrast, the impact of C12:0 mainly revolves around cholesterol synthesis.

Additionally, the study identifies beneficial compounds within BSFL oil, including eicosanoids, oxylipins, and isoprenoids, which appear to collaborate in quelling inflammation within the body.

The researchers ventured into an in vivo setting, where a diet enriched with BSFL oil (at 20%) yielded promising outcomes. This dietary intervention led to improvements in body weight restoration, decreased colon shortening, reduced splenomegaly, and an accelerated phase of secretory IgA response. These results underscore the innovative potential of BSFL oil as a modulator of inflammation.

The researchers assert that these findings present compelling evidence of BSFL oil’s potent anti-inflammatory characteristics and its capacity to counter inflammation associated with colitis.

The study’s distinct insights into TLR2 and TLR4 activation for macrophage innate immune function could pave the way for groundbreaking strategies in managing inflammatory diseases. Moreover, the identification of anti-inflammatory compounds in BSFL oil lays the groundwork for prospective investigations into precision anti-inflammatory approaches.

More information: Hadas Richter et al, Anti-Inflammatory Activity of Black Soldier Fly Oil Associated with Modulation of TLR Signaling: A Metabolomic Approach, International Journal of Molecular Sciences (2023). DOI: 10.3390/ijms241310634

Provided by Hebrew University of Jerusalem 

by Anna Ettlin, Swiss Federal Laboratories for Materials Science and Technology

Empa researchers have developed an epoxy resin that can be repaired and recycled, in addition to being flame-retardant and mechanically strong. Potential applications range from coating for wooden flooring to composites in aerospace and railways.

Epoxy resins are tough and versatile polymers. In combination with glass or carbon fibers, they are used, for example, to manufacture components for aircraft, cars, trains, ships and wind turbines. Such epoxy-based fiber-reinforced polymers have excellent mechanical and thermal properties and are much lighter than metal. Their weakness: They are not recyclable—at least not yet.

Now Empa researchers led by Sabyasachi Gaan at Empa’s Advanced Fibers laboratory have developed an epoxy resin-based plastic that is fully recyclable, repairable and also flame retardant—all while retaining the favorable thermomechanical properties of epoxy resins. They have published their findings in the Chemical Engineering Journal.

Recycling epoxy resins is anything but trivial, because these plastics are so-called thermosets. In this type of polymer, the polymer chains are closely crosslinked. These chemical crosslinks make melting impossible. Once the plastic has hardened, it can no longer be reshaped.

This is not the case for thermoplasts, such as PET or polyolefins. Their polymer chains lie close together but are not chemically linked to each other. When heated, these polymers can be melted and formed into new shapes. However, because of the lack of crosslinks, their mechanical properties at elevated temperatures are generally not as good as those of thermosets.

A new kind of polymer

The unique epoxy resin that the Empa researchers have developed in collaboration with national and international partners is technically a thermoset—but unlike other thermosets, it can be reshaped like a thermoplast. The key is the addition of a very special functional molecule from the class of phosphonate esters into the new resin matrix.

“We originally synthesized this molecule as a flame retardant,” says co-inventor of this technology and Empa scientist Wenyu Wu Klingler. However, the bond the molecule forms with the polymer chains of the epoxy resin is dynamic and can be broken under certain conditions. This loosens the crosslinking of the polymer chains so that they can be melted and reshaped.

Such materials, also known as vitrimers, have only been known for about ten years and are considered particularly promising. “Today, fiber-reinforced composites are not recyclable at all, except under very harsh conditions, which damage the recovered fibers,” explains Wu Klingler. “Once they have reached the end of their service life, they are incinerated or disposed of in landfills. With our plastic, it would be possible for the first time to bring them back into circulation again.”

“Our vision for the future,” adds group leader Sabyasachi Gaan, “is a composite material, in which both the fibers and the plastic matrix can be completely separated and reused.” The researcher sees an opportunity in carbon-fiber-reinforced plastics in particular, as they’re commonly used in the construction of airplanes, trains, boats, cars, bicycles and more.

“The production of carbon fibers requires a lot of energy and releases an enormous amount of CO₂,” he explains. “If we could recycle them, their environmental footprint would be a lot better—and the price a lot lower.” Moreover, the recovery of valuable elements like phosphorus connected to the matrix polymer would be possible.

A material made to measure

Fiber-reinforced composites are not the only application for the new polymer. For example, it could be used to coat wooden floors, as a transparent, resistant layer that has good flame-retardant properties—and where scratches and dents can be “healed” with a little pressure and heat.

“We didn’t develop a single material for a specific purpose, but rather a toolbox,” Gaan explains. “Flame retardancy, recyclability and repairability are a given. We can optimize all other properties depending on the intended use.” For example, he says, flow characteristics are particularly important for the production of fiber-reinforced plastics, while exterior wood coatings should also be weather-resistant.

To pursue these and other applications of the material, the researchers are now looking for industrial partners. The chances of commercial success are good: In addition to all its other advantageous properties, the modified epoxy polymer is also inexpensive and easy to manufacture.

More information: Wenyu Wu Klingler et al, Recyclable flame retardant phosphonated epoxy based thermosets enabled via a reactive approach, Chemical Engineering Journal (2023). DOI: 10.1016/j.cej.2023.143051

Provided by Swiss Federal Laboratories for Materials Science and Technology 

by Li Yuan, Chinese Academy of Sciences

Lithium metal batteries (LMBs) have attracted much attention for their potential in electronics and electric vehicle applications. However, issues such as the growth of Li dendrites and undesirable side reactions with electrolytes during electrochemical cycling hinder their widespread commercialization.

A research team led by Prof. Xue Dongfeng and Dr. Peng Chao from the Shenzhen Institute of Advanced Technology (SIAT) of the Chinese Academy of Sciences (CAS) has recently introduced a novel inorganic-organic hybrid interphase layer strategy based on self-assembled monolayers method.

The strategy endows the Li metal anode interface with good mechanical stability and excellent ionic conductivity and induces Li uniform deposition and suppression of Li dendrite growth. The results were published in the journal Matter.

The researchers applied the high-throughput data-driven workflow to enable intelligent design of self-assembled molecules. The workflow contains screening criterions of self-assembled molecule characteristics, electrochemical stability of molecules, chemical stability and ionic conductivity of interphase protection layer, and it can automatically capture targeted self-assembled molecules from the PubChem database.

This new research paradigm accelerates the screening process for selecting the most promising candidate molecules, and allows intelligent design of artificial interphase layer of Li metal anode by leveraging machine learning techniques.

Furthermore, the researchers revealed the structure-performance relationship between the molecule structural characteristics (head group, tail group and middle group) as well as the electronic properties and the performance of the protection layer, where the quantum mechanical dipole and electrostatic potential of molecules were identified as significant descriptors to predict the energy barrier of Li diffusion through the hybrid protection layer.

They established a database consisting of 128 self-assembled organic molecule candidates selected from the PubChem database and suggested eight best molecules to favor constructing the inorganic-organic hybrid interphase layer at Li metal anode.

These molecules with a terminated fluoride head group (-F) allow the formation of an LiF inner inorganic interphase that improves the stability and ionic conductivity of the interphase layer on the Li metal anode, while the outer linear organic layer provides enriched 3D porous channels that facilitate Li diffusion and guide Li uniform deposition and suppress Li dendrite growth.

“Our study opens up new possibilities for the development of more efficient and safer lithium metal batteries,” said Dr. Peng, corresponding author of the study.

More information: Qi Zhang et al, Data-driven discovery and intelligent design of artificial hybrid interphase layer for stabilizing lithium-metal anode, Matter (2023). DOI: 10.1016/j.matt.2023.06.010

Journal information: Matter 

Provided by Chinese Academy of Sciences 

by Ute Schönfelder, Friedrich-Schiller-Universität Jena

Researchers from the University of Jena, the Westphalian University of Applied Sciences and the University of Chemistry and Technology Prague have developed a platform that uses artificial neural networks to translate chemical structural formulae into machine-readable form.

With this platform, they have created a tool with which information from scientific publications can be automatically fed into databases. Until now, this had to be done literally by hand and was time-consuming. In the current issue of Nature Communications, the team led by Prof. Christoph Steinbeck and Prof. Achim Zielesny presents the latest version of their tool, DECIMER.ai, which researchers can use worldwide.

Structural formulae show how chemical compounds are constructed, i.e., which atoms they consist of, how these are arranged spatially and how they are connected. Chemists can deduce from a structural formula, among other things, which molecules can react with each other and which cannot, how complex compounds can be synthesized or which natural substances could have a therapeutic effect because they fit together with target molecules in cells.

Developed in the 19th century, the representation of molecules as structural formulae has stood the test of time and is still used in every chemistry textbook. But what makes the chemical world intuitively comprehensible for humans is just a collection of black and white pixels for software. “To make the information from structural formulae usable in databases that can be searched automatically, they have to be translated into a machine-readable code,” explains Steinbeck, professor for analytical chemistry, cheminformatics and chemometrics at the University of Jena.

And that is precisely what can be done using the artificial intelligence tool DECIMER, developed by the team led by Steinbeck and his colleague Zielesny from the Westphalian University of Applied Sciences. DECIMER stands for “deep learning for chemical image recognition.” It is an open-source platform that is freely available to everyone on the Internet and can be used in a standard web browser. Scientific articles containing chemical structural formulae can be uploaded there simply by dragging and dropping, and the AI tool will immediately get to work.

“First, the entire document is searched for images,” explains Steinbeck. The algorithm then identifies the image information contained and classifies it according to whether it is a chemical structural formula or some other image. Finally, the structural formulae recognized are translated into the chemical structure code or displayed in a structure editor, so that they can be further processed. “This step is the core of the project and the real achievement,” adds Steinbeck.

In this way, the chemical structural formula for the caffeine molecule becomes the machine-readable structure code CN1C=NC2=C1C(=O)N(C(=O)N2C)C. This can then be uploaded directly into a database and linked to further information on the molecule.

To develop DECIMER, the researchers used modern AI methods that have only recently become established and are also used, for example, in the Large Language Models (such as ChatGPT) that are currently the subject of much discussion. To train its AI tool, the team generated structural formulas from the existing machine-readable databases and used them as training data—some 450 million structural formulas to date. In addition to researchers, companies are also already using the AI tool, for example to transfer structural formulae from patent specifications into databases.

Steinbeck and Zielesny came up with the idea of developing an AI tool for decoding chemical images a few years ago. The two chemists were interested the development of AI methods in connection with the millennia-old Asian board game Go. In 2016, together with millions of people around the world, they watched the spectacular tournament between the best Go player at the time, the South Korean Lee Sedol, and the computer software AlphaGo, which the machine won 4:1.

“It was a bolt from the blue that showed us how powerful AI can be,” Steinbeck recalls. Until then, it had been considered practically unthinkable that an algorithm could rival human creativity and intuition in this game.

“When, a little later, an AI tool developed quasi-superhuman playing strength by not being trained laboriously through countless sessions of human games—as was still the case with AlphaGo—but simply through the process of the system playing against itself again and again, and optimizing its playing style as it did so, we realized that these new methods could also solve other very complex problems with enough training data. We wanted to use that for our research area.”

Making scientific information sustainably usable

With DECIMER, Steinbeck and his team hope at some point to be able to machine-read all chemical literature of interest to them, going back to the 1950s, and translate it into open databases.

After all, a key concern for Steinbeck, also the coordinator of the National Research Data Infrastructure for Chemistry in Germany, is to sustainably secure existing knowledge and make it available to the global scientific community.

The DECIMER AI tool is available online: https://decimer.ai

More information: Kohulan Rajan et al, DECIMER.ai: an open platform for automated optical chemical structure identification, segmentation and recognition in scientific publications, Nature Communications (2023). DOI: 10.1038/s41467-023-40782-0

Journal information: Nature Communications 

Provided by Friedrich-Schiller-Universität Jena

by Thamarasee Jeewandara , Phys.org

Materials scientists aim to develop autonomous materials that function beyond stimulus responsive actuation. In a new report in Science Advances, Yang Yang and a research team in the Center for Bioinspired Energy Science at the Northwestern University, U.S., developed photo- and electro-activated hydrogels to capture and deliver cargo and avoid obstacles on return.

To accomplish this, they used two spiropyran monomers (photoswitchable materials) in the hydrogel for photoregulated charge reversal and autonomous behaviors under a constant electric field. The photo/electro-active materials could autonomously perform tasks based on constant external stimuli to develop intelligent materials at the molecular scale.

Bioengineering a charged hydrogel

Soft materials with life-like functionality have promising applications as intelligent, robotic materials in complex dynamic environments with significance in human-machine interfaces and biomedical devices. Yang and colleagues designed a photo- and electro-activated hydrogel to capture and deliver cargo, avoid obstacles, and return to its point of departure, based on constant stimuli of visible light and applied electricity. These constant conditions provided energy to guide the hydrogel.

The research team covalently integrated spiropyran moieties with varying substituents into the constructs to regulate the net charge of the soft materials. They used finite element simulations to guide the design and movement of the charged hydrogels and engineer 3D surface profiles to maximize the dielectrophoretic effect. Yang and the team further studied the scope of electroactive locomotion and photoactuation in the spiropyran hydrogels.

Charge reversal of spiropyran-functionalized polymers

Yang and colleagues used two different spiropyran molecules with different net charges. They synthesized each of the molecules with a polymerizable methacrylate group based on existing reports.

They incorporated different ratios of the spiropyran molecules into N-isopropylacrylamide polymer chains (PNIPAM) to form hydrogels. In this instance, they tuned the charge reversal functionalities using copolymers of the spiropyran structural units to show photoswitchable potential and charge reversible behaviors with tunable charge. The scientists tuned the charge reversal time by changing the ratio of the two spiropyran moieties, without changing the switching and recovery rates.

Photo-activated electroactive motion of the spiropyran-PNIPAM hydrogels

Based on charge reversal behavior of the polymers, Yang’s team photoregulated the electroactive hydrogels by using a crosslinker to prepare them.

At first, the team could positively charge the hydrogel to move towards the cathode under a direct current electric field, where the positive charge transferred from the spiropyran moieties into the hydrogel network. Thereafter, the permanently bound sulfonate groups on the polymer chain made the net charge of the construct negative, allowing the negatively charged hydrogel to navigate back to the anode.

The team studied the photoregulated electroactive locomotion speeds of the hydrogel disks across multiple light-dark cycles to examine their locomotion speed, and determined the relationship between the charge and speed of the hydrogel disks. They based this on the balance between the electrostatic force and hydrodynamic drag force, where the higher applied voltage and larger diameter of the hydrogel disks delivered higher locomotion speed. Such polymeric devices are well-suited to capture and deliver cargo through autonomous hunting.

Capturing and delivering cargo

Yang and colleagues explored the cargo delivery potential of the constructs by engineering simple disk-shaped spiropyran-PNIPAM hydrogels and sphere-shaped constructs embedded with nanoparticles as cargos. The strong dielectrophoretic force allowed the materials to undergo autonomous hunting and picking up functions.

Based on simulations, Yang and colleagues formed a 3-arm spiropyran PNIPAM hydrogel object using photoinitiated free radical polymerization with superior capture capability of the cantilever arms. When uncharged, the electric field gradient around the hydrogel vanished, enabling autonomous cargo release during charge reversal. The cargo release also occurred by turning off the electric field

Automatically avoiding obstacles

The research team showed how materials with a high dielectric constant induced an attractive electrophoretic force, and materials with a lower dielectric constant exerted a repulsive electrophoretic force on the adjacent charged hydrogel object.

Using finite element calculations, they showed the possibility of low dielectric constants to guide the charged hydrogel through obstacles. Under constant stimuli of the electric field and light irradiation, the hydrogel automatically bypassed barriers and traveled back after charge reversal, without human intervention.

Outlook

In this way, Yang and colleagues designed a photo- and electroactive hydrogel that can cargo capture and deliver, as well as avoid obstacles under constant external stimuli. The scientists used two different ratios of spiropyran moieties in the hydrogel and facilitated the net charge in the chemically random network to be tunable under irradiation with blue light. This enabled photoregulated, electroactive motion with autonomous behavior under the direction of light and electricity.

The autonomous soft matter products elegantly captured and delivered cargo while avoiding obstacles with applications suited for scenarios to ensure the safety of monitoring a situation from afar—for instance, where human intervention is impractical. These new biomaterials with autonomous functionality can be resourcefully engineered using environmentally sensitive electrostatic interactions and photoactuation in soft materials.

More information: Yang Yang et al, Autonomous hydrogel locomotion regulated by light and electric fields, Science Advances (2023). DOI: 10.1126/sciadv.adi4566

Anne Helene Gelebart et al, Making waves in a photoactive polymer film, Nature (2017). DOI: 10.1038/nature22987

Journal information: Science Advances  , Nature 

© 2023 Science X Network

by Li Yuan, Chinese Academy of Sciences

The stress-induced reorientation of low-symmetry defects due to substitution atom pairs can give rise to an internal friction peak called Zener relaxation. It is one of the most representative point defect relaxations in metal.

Recently, researchers from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences have revealed that Zener relaxation in the body-centered cubic (BCC) Fe-Ga single crystals originates primarily from the stress-induced reorientation of the second-nearest-neighbor Ga-Ga atom pairs, not the previously thought first-nearest-neighbor substitutional atom pairs. The study was published in Acta Materialia.

Fe-Ga alloys have great potential in the field of actuators, sensors, and micro-vibration suppression. However, their magnetostriction and damping capacity are closely related to the occupation of Ga atoms. The internal friction technique is sensitive to internal defect relaxation, so it is expected to solve the problem of evaluating Ga atom occupation and provide guidance for improving Fe-Ga alloy properties.

In this study, the team prepared large FeGa single crystals and FeGa binary single-crystal alloys with different orientation factors. A comparative study of the internal friction behavior of FeGa polycrystals and single crystals confirmed that the relaxation peak near 450°C originated from Zener relaxation behavior within the grains. It was observed that the net peak height of Zener relaxation increased with the orientation factor of single crystals.

Further analysis revealed that the relaxation strengths of BCC cells with different atom-pair configurations varied. Trigonal and orthorhombic configurations exhibited decreased relaxation strengths with increased orientation factors, while tetragonal configuration showed the opposite trend. The relaxation activation energy for Fe-17at.% Ga single crystals was found to be around 1.8 eV, lower than that measured in polycrystalline materials.

Additionally, the researchers revealed a positive correlation between Zener relaxation strength and the magnetostriction coefficient through electronic structure and strain analysis.

More information: Meng Sun et al, Tetragonal dipole dominated Zener relaxation in BCC-structured Fe-17at.%Ga single crystals, Acta Materialia (2023). DOI: 10.1016/j.actamat.2023.119245

Journal information: Acta Materialia 

Provided by Chinese Academy of Sciences 

by Newcastle University in Singapore

A team of researchers from Thailand, Malaysia and Singapore has successfully harnessed pineapple waste materials from agriculture to create biodegradable rigid composite foams. The foam’s base was formulated using starch extracted from pineapple stems, known for their high amylose content, while the filling material was derived from non-fibrous cellulosic components found in pineapple leaves.

Diverging from conventional techniques which involve preparing a batter, this study introduced a unique methodology. It began by creating a starch gel mixed with glycerol, achieved through the use of a common household microwave oven. The resulting mixture was then blended with the filling material using a two-roll mill. Subsequently, the amalgam was transformed into foam through compression molding at a temperature of 160°C.

The produced foams exhibited densities ranging from 0.43 to 0.51 g/cm³ and displayed a notably amorphous structure. Impressively, the foams showcased equilibrium moisture levels of approximately 8%–10%, demonstrating their capacity to absorb 150%–200% of their weight without deteriorating. The foams’ flexural strengths varied between 1.5 and 4.5 MPa, with fluctuations based on the filler and glycerol contents.

Furthermore, biodegradability assessments utilizing a soil burial method demonstrated that the foam disintegrated completely into particles measuring 1 mm or smaller within a mere 15 days. Additionally, the researchers fabricated an environmentally friendly, single-use foam tray to illustrate potential practical applications.

This innovative approach, encompassing gel formation followed by filler integration, distinguishes itself from prior methodologies. The study’s outcomes underscore the substantial potential of pineapple waste materials in crafting sustainable biodegradable foams with desirable attributes. Ultimately, these findings contribute significantly to the advancement of sustainable materials.

The paper is published in the journal Polymers.

More information: Atitiya Namphonsane et al, Development of Biodegradable Rigid Foams from Pineapple Field Waste, Polymers (2023). DOI: 10.3390/polym15132895

Provided by Newcastle University in Singapore 

by JooHyeon Heo, Ulsan National Institute of Science and Technology

A research team, led by Professor Jong-Beom Baek and his team in the School of Energy and Chemical Engineering at UNIST have achieved a significant breakthrough in battery technology. They have developed an innovative method that enables the safe synthesis of fluorinated carbon materials (FCMs) using polytetrafluoroethylene (PTFE) and graphite.

Fluorinated carbon materials have garnered considerable attention due to their exceptional stability, attributed to the strong C-F bonding—the strongest among carbon single bonds. However, traditional methods of fluorination involve highly toxic reagents such as hydrofluoric acid (HF), making them unsuitable for practical applications.

In this study, the research team introduced a straightforward and relatively safe approach for scalable synthesis of FCMs through mechanochemical depolymerization of PTFE—a commonly used compound found in everyday items—and fragmentation of graphite. By utilizing ball-milling techniques that induce both mechanical and chemical reactions, they successfully produced FCMs with significantly improved performance compared to graphite.

The use of hazardous compounds like fluorine gas or HF in conventional carbon fluoride production raises safety concerns, increasing manufacturing costs associated with stringent safety measures. To address these challenges, Professor Baek’s team devised a solid-phase fluorination method using PTFE—an inert polymer known for its stability under atmospheric conditions and harmlessness when consumed orally.

Through experiments, it was observed that subjecting PTFE to higher energy than it can withstand leads to molecular chain breakage and radical formation—initiating a reaction resulting in the production of carbon fluoride complexes. These complexes then adhere to the surface and edges of graphite particles during subsequent processes.

The resulting FCMs demonstrated superior storage capacity and electrochemical stability compared to traditional graphite anodes. At a low charging rate of 50 mA/g, the FCMs exhibited storage capacities 2.5 times higher (951.6 mAh/g) than graphite, while at a high charging rate of 10,000 mA/g, their storage capacity was tenfold higher (329 mAh/g). Remarkably, even after more than 1,000 charge/discharge cycles at a rate of 2,000 mA/g, the FCMs retained 76.6% of their initial capacity compared to only 43.8% for graphite.

“This study highlights not just safe fluorination methods but also the broader potential of solid-phase reactions,” stated Boo-Jae Jang, a researcher in the School of Energy and Chemical Engineering at UNIST.

“This research prompts us to reconsider materials that are commonly found in our surroundings,” added Professor Baek. He further emphasized the significance of understanding solid-phase reactions as it opens doors to developing novel materials that were previously unexplored.

The study findings have been published in Advanced Functional Materials.

More information: Boo‐Jae Jang et al, Direct Synthesis of Fluorinated Carbon Materials via a Solid‐State Mechanochemical Reaction Between Graphite and PTFE, Advanced Functional Materials (2023). DOI: 10.1002/adfm.202306426

Journal information: Advanced Functional Materials 

Provided by Ulsan National Institute of Science and Technology