A new class of materials known as “glassy gels” could find use in areas ranging from batteries to adhesives, thanks to their unique set of physical properties.
Meixiang Wang, a post-doctoral fellow from Michael Dickey’s group at North Carolina State University, discovered these new materials while trying out different mixtures for making gels that she hoped would be useful ionic conductors.
Standard gels, such as those used to make contact lenses, are polymers with an added liquid solvent. The liquid weakens the interactions between the chains of molecules forming the polymer, allowing the gel to extend easily but leaving it soft and weak mechanically. In contrast, glassy polymers, like those suitable for airplane windows, contain no liquid and have strong interactions between their constituent polymer chains. This renders them stiff and strong but, in some cases, brittle.
Glassy gels, made by adding liquid solvent to glassy polymers, combine these properties: offering the high stiffness and high strength of glassy polymers alongside high extensibility – they can be stretched to over five times their original length without breaking.
“I thought it was eye-popping when Meixiang told me that these were the toughest gels ever reported by an order of magnitude, and had mechanical properties similar to plexiglass – even though plexiglass has no liquid, whereas these glassy gels are around 60% liquid,” Dickey tells Physics World.
Further tests by the research group, in collaboration with Wen Qian at the University of Nebraska–Lincoln, revealed that the glassy gels also show efficient electrical conduction (Wang’s original aim), good adhesive properties, shape memory characteristics and the ability to self-heal after being cut.
This unusual set of properties, detailed in Nature, is due to the solvent being an ionic liquid (salts in the liquid state). The ionic liquid solvent makes the glassy gels highly stretchable by pushing their polymer chains further apart. But simultaneously, its ions are strongly attracted to charged or polar molecules in the polymer, thereby keeping the polymer chains in place and making the material hard. The solvent ions also conduct electricity, resulting in better conduction than found in common plastics with similar stress–strain characteristics.
While the details of the ion–polymer bonding mechanism are not yet clear, early results indicate that it is electrostatic forces that act over a reasonably large distance. This, Dickey believes, is what makes the materials stiff despite containing so much liquid.
Another plus point for these new materials is their one-step manufacture. The mixture of ionic liquid solvent and liquid precursor of glassy polymers is simply poured into a mould before being cured for five minutes at room temperature with UV light to harden it ready for use.
“In contrast, almost all thermoplastics are made in chemical plants then shipped as resin to factories for melt processing,” says Dickey. He adds that glassy gels could also be 3D printed, and that products made from them would be easier to recycle than those manufactured from multiple plastics, which contain different constituents in order to get the required functionality.
In the future, Dickey plans to investigate why glassy gels are so sticky, alongside “tweaking the properties to optimize for particular applications” by changing the ratio of solvent to polymer and using differing types of both constituents. Optimized glassy gels could prove useful as mechanically robust, adhesive and conductive “separators” for keeping the two electrodes in a battery apart, for example, as adhesives, gaskets or seals, or even as heat-driven soft robotic grippers, since the material softens if sufficiently heated.
First, however, Dickey admits that a greater understanding of the gels’ characteristics – including UV stability and degradation over time – is required. But he is encouraged by enquiries from prospective users and optimistic about the potential for this chance discovery by Wang which, as he puts it, “was a bit of serendipity enabled by a researcher who was willing to follow her curiosity”.
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Information security is an important part of our digital world, and various techniques have been deployed to keep data safe during transmission. But while these traditional methods are efficient, the mere existence of an encrypted message can alert malicious third parties to the presence of information worth stealing. Researchers at the University of California, Los Angeles (UCLA), US, have now developed an alternative based on steganography, which aims to hide information by concealing it within ordinary-looking “dummy” patterns. The new method employs an all-optical diffractive camera housed within an electronic decoder network that the intended receiver can use to retrieve the original image.
“Cryptography and steganography have long been used to protect sensitive data, but they have limitations, especially in terms of data embedding capacity and vulnerability to compression and noise,” explains Aydogan Ozcan, a UCLA electrical and computer engineer who led the research. “Our optical encoder-electronic decoder system overcomes these issues, providing a faster, more energy-efficient and scalable solution for information concealment.”
The image-hiding process starts with a diffractive optical process that takes place in a structure composed of multiple layers of 3D-printed features. Light passing through these layers is manipulated to transform the input image into a seemingly mundane and misleading pattern. “The optical transformation happens passively,” says Ozcan, “leveraging light-matter interactions. This means it requires no additional power once physically fabricated and assembled.”
The result is an encoded image that appears ordinary to human observers, but contains hidden information, he tells Physics World.
The encoded image is then processed by an electronic decoder, which uses a convolutional neural network (CNN) that has been trained to decode the concealed data and reconstruct the original image. This optical-to-digital co-design ensures that only someone with the appropriate digital decoder can retrieve the hidden information, making it a secure and efficient method of protecting visual data.
The researchers tested their technique using arbitrarily chosen hand-written digits as the input image. The diffractive processor successfully transformed these into a uniform-looking digit 8. The CNN was then able to reconstruct the original handwritten digits using information “hidden” in the 8.
All was not plain sailing, however, explains Ozcan. For one, the UCLA researchers had to ensure that the digital decoder could accurately reconstruct the original images despite the transformations applied by the diffractive optical processor. They also had to show that the device worked under different lighting conditions.
“Fabricating precise diffractive layers was no easy task either and meant developing the necessary 3D printing techniques to create highly precise structures that can perform the required optical transformations,” Ozcan says.
The technique, which is detailed in Science Advances, could have several applications. Being able to transmit sensitive information securely without drawing attention could be useful for espionage or defence, Ozcan suggests. The security of the technique and its suitability for image transmission might also improve patient privacy by making it easier to safely transmit medical images that only authorized personnel can access. A third application would be to use the technique to improve the robustness and security of data transmitted over optical networks, including free-space optical communications. A final application lies in consumer electronics. “Our device could potentially be integrated into smartphones and cameras to protect users’ visual data from unauthorized access,” Ozcan says.
The researchers demonstrated that their system works for terahertz frequencies of light. They now aim to expand its capabilities so that it can work with different wavelengths of light, including visible and infrared, which would broaden the scope of its applications. “Another area [for improvement] is in miniaturization to further reduce the size of the diffractive optical elements to make the technology more compact and scalable for commercial applications,” Ozcan says.
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Three years ago, researchers from institutions in the US and Israel discovered a new type of ferroelectricity in a material called boron nitride (BN). The team called this new mechanism “slidetronics” because the change in the material’s electrical properties occurs when adjacent atomically-thin layers of the material slide across each other.
Two independent teams have now made further contributions to the slidetronics field. In the first, members of the original US-Israel group fabricated ferroelectric devices from BN that can operate at room temperature and function at gigahertz frequencies. Crucially, they found that the material can endure many “on-off” switching cycles without losing its ferroelectric properties – an important property for a future non-volatile computer memory. Meanwhile, a second team based in China found that a different sliding ferroelectric material, bilayer molybdenum disulphide (MoS2), is also robust against this type of fatigue.
The term “ferroelectricity” refers to a material’s ability to change its electrical properties in response to an applied electric field. It was discovered over a 100 years ago in certain naturally-occurring crystals and is now exploited in a range of technologies, including digital information storage, sensing, optoelectronics and neuromorphic computing.
Being able to switch a material’s electrical polarization over small areas, or domains, is a key part of modern computational technologies that store and retrieve large volumes of information. Indeed, the dimensions of individually polarizable domains (that is, regions with a fixed polarization) within the silicon-based devices commonly used for information storage have fallen sharply in recent years, from roughly 100 nm to mere atoms across. The problem is that as the number of polarization switching cycles increases, an effect known as fatigue occurs in these conventional ferroelectric materials. This fatigue degrades the performance of devices and can even cause them to fail, limiting the technology’s applications.
To overcome this problem, researchers have been studying the possibility of replacing silicon with two-dimensional materials such as hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMDs). These materials are made up of stacked layers held together by weak van der Waals interactions, and they can be as little as one atom thick, yet they remain crystalline, with a well-defined lattice and symmetry.
In one of the new works, researchers led by Kenji Yasuda of the School of Applied and Engineering Physics at Cornell University made a ferroelectric field-effect transistor (FeFET) based on sliding ferroelectricity in BN. They did this by sandwiching a monolayer of graphene between top and bottom layers of bulk BN, which behaves like a dielectric rather than a ferroelectric. They then inserted a parallel layer of stacked bilayer BN – the sliding ferroelectric – into this structure.
Yasuda and colleagues measured the endurance of ferroelectric switching in their device by repeatedly applying 100-nanosecond-long 3V pulses for up to 104 switching cycles. They then applied another square-shaped pulse with the same duration and a frequency of up to 107 Hz and measured the graphene’s resistance to show that the device’s ferroelectricity performance did not degrade. They found that the devices remained robust after more than 1011 switching cycles.
Meanwhile, a team led by Fucai Liu of the University of Electronic Science and Technology of China, in collaboration with colleagues at Ningbo Institute of Materials Technology and Engineering (NIMTE) of the Chinese Academy of Sciences, Fudan University and Xi Chang University, demonstrated a second fatigue-free ferroelectric system. Their device was based on sliding ferroelectricity in bilayer 3R-MoS2 and was made by sandwiching this material between two BN layers using a process known as chemical vapour transport. When the researchers applied pulsed voltages of durations between 1 ms and 100 ms to the device, they measured a switching speed of 53 ns. They also found that it retains its ferroelectric properties even after 106 switching cycles of different pulse durations.
Based on theoretical calculations, Liu and colleagues showed that the material’s fatigue-free properties stem from immobile charged defects known as sulphur vacancies. In conventional ferroelectrics, these defects can migrate along the direction of the applied electrical field.
Reporting their work in Science, they argue that “it is reasonable to assume that fatigue-free is an intrinsic property of sliding ferroelectricity” and that the effect is an “innovative” solution to the problem of performance degradation in conventional ferroelectrics.
For their part, Yasuda and colleagues, whose work also appears in Science, are now exploring ways of synthesizing their material on a larger, wafer scale for practical applications. “Although we have shown that our device is promising for applications, we have only demonstrated the performance of a single device until now,” Yasuda tells Physics World. “In our current method, it takes many days of work to make just a single device. It is thus of critical importance to develop a scalable synthesis method.”
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The ITER fusion reactor currently being built in France will not achieve first operation until 2034 – almost a decade later than previously planned and some 50 years after the project was first conceived in 1985. The decision by ITER management to take another 10 years constructing the machine means that the first experiments using “burning” fusion fuel – a mixture of deuterium and tritium (D–T) – will now have to wait until 2039. The new “baseline” was agreed as a “working reference” by ITER’s governing council and will be further examined before a meeting in November.
ITER is an experimental fusion reactor that is currently being built in Cadarache, France, about 70 km north-west of Marseille. Expected to cost tens of billions of euros, it is a collaboration between China, Europe, India, Japan, Korea, Russia and the US. Its main aim is to generate about 500 MW of fusion power over 400 seconds using a plasma heating of 50 MW, a power gain of 10. The reactor would also test a “steady state” operation under a power gain of five.
Yet since its conception in the 1980s (see timeline below), ITER has been beset with cost hikes and delays. In 2016, a baseline was presented in which the first deuterium plasma would be delayed until 2025.
This first plasma, however, would have been a brief machine test before further assembly, such as adding a divertor heat-exhaust system and further shielding. “The first plasma [in 2025] was rather symbolic,” claims ITER director-general Pietro Barabaschi, who took up the position in October 2022 following the death of former ITER director general Bernard Bigot.
ITER would only have reached full plasma current in 2032 with the first D–T reaction waiting until 2035 after the installation of additional components.
Barabaschi notes that since 2020 it was “clear” that the 2025 “first plasma” date was no longer achievable. This was due to several reasons, one of which was the COVID-19 pandemic, which led to supply-chain and quality-control delays.
Manufacturing issues also emerged such as the discovery of cracks in the water pipes that cool the thermal shields. In early 2022 the French Nuclear Safety Authority briefly halted assembly due to concerns over radiological shielding.
Officials then began working on a more realistic timeline for construction to allow for more testing of certain components such as the huge D-shaped toroidal-field coils that will be used to confine the plasma.
The plan now is to start operation in 2034 with a deuterium-only plasma but with more systems in place as compared to the previous “first plasma” baseline of 2025. Research on the tokamak would then be carried out for just over two years before the machine reaches full plasma current operation in 2036. The reactor would then shut down for further assembly to prepare for D-T operation, which is now expected to begin in 2039.
Speaking today at a press conference, Barabaschi notes that the delay will cost an extra €5bn. “We are still addressing the issue of cost with the ITER council,” adds Barabaschi, who did not want to be drawn on how much ITER will now cost overall due to the “complexity” of the way it is funded via “in-kind” contributions.
Sibylle Günter, scientific director of the Max Planck Institute for Plasma Physics in Garching, Germany, says that depite the news being of “no cause for celebration”, ITER is still relevant and necessary. “We are not aware of any project that will analyse the challenges as comprehensively as ITER in the foreseeable future,” she adds. “ITER has also already achieved ground-breaking engineering work up to this point, which will be important for all the fusion projects now underway and those still to come.”
In the meantime, some changes have been to ITER’s design. The material used for the “first wall” that directly faces the plasma will change from beryllium to tungsten. Barabaschi points out that tungsten is more relevant for a potential fusion demonstration plant, known as DEMO.
Officials were also celebrating the news this week that the 19 toroidal-field coils have been completed and delivered to the ITER site. Each coil – made of niobium-tin and niobium-titanium – is 17 m tall and 9 m across, and weighs about 360 tonnes. They will generate a magnetic field of 12 T and store 41 GJ of energy.
1985 US president Ronald Reagan and Soviet Union leader Mikhail Gorbachev, at their first summit meeting in Geneva, resolve to develop fusion energy “for the benefit of all mankind”.
1987 Work on the conceptual design begins, with the EU and Japan joining the US and Russia on the project. Conceptual design completed two years later.
1992 Work on the engineering design begins with teams at San Diego, Garching and Naka. Completed in 1997.
1998 US withdraws due to €10bn price tag.
2001 Revised design completed, resulting in the cost of the project being halved to €5bn.
2003 US re-joins ITER with China and South Korea also signing up. Partners meet but fail to agree on a site leading to an 18-month stalemate.
2005 The EU and Japan agree on ITER’s home being Cadarache in southern France.
2006 India joins ITER. The ITER Organization is formally established by treaty and civil engineering begins.
2010 Detailed design finalized. Cost estimate rises to around €15bn, with building construction starting.
2011 Construction delays push back the date of first plasma from 2016 to 2019, revised to 2020 a year later.
2014 An independent report warns that the project is in “a malaise” and recommends a management overhaul. Manufactured components of the reactor begin to arrive for assembly.
2016 ITER Council agrees new “baseline” plan with first plasma set for 2025 and deuterium–tritium fuel only being used from 2035 onwards.
2020 Assembly of ITER begins while the COVID-19 pandemic hits the project’s supply chain and quality control.
2024 New “baseline” announced for start of operation in 2034.
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There’s a lot of physics in a cup of tea. Compounds in the tea leaves start to diffuse as soon as you pour over hot water and – if you look closely enough – you’ll see turbulence as your milk mixes in. This humble beverage also displays conservation of momentum in the parabolic vortex that forms when tea is stirred.
Tea is just one of the many topics covered in Physics in the Kitchen by George Vekinis, director of research at the National Research Centre “Demokritos” (NCSRD) in Greece. In writing this book, Vekinis – who is a materials physicist by training – joins a long tradition of scientists writing about cooking.
The book is full of insights into the physics and chemistry underlying creative processes in a kitchen, from making sauces and cooking vegetables to the use of acid and the science behind common equipment. One of the book’s strengths is that, while it has a logical structure, it is possible to dip in and out without reading everything.
Talking of dips, I particularly enjoyed the section on sauces. My experience in this area is confined to rouxs that are thickened with flour, and I was surprised to discover that Vekinis considers this to be a “bit of a cheat”. Sauces prepared in the “Greek way”, he points out, often don’t involve starch at all.
Instead, a smooth sauce can be made just by heating an acid such as wine or lemon with egg and broth. This ancient method, which the author describes in a long section on “Creamy emulsion or curdled mess?”, involves the extraction of small molecules and requires extra care to prevent curdling or splitting.
However, as a food physicist myself, I did have some issues with the science in this and later sections.
For example, Vekinis uses the word “gel” far too loosely. Sometimes he’s talking about the gels created when dissolved proteins form a solid-like network despite it mostly being liquid – such as the brown gel that appears below a roast ham or chicken that has cooled. However, he also uses the same word to describe what you get when starch granules swell and thicken when making a roux sauce, which is a very different process.
Moreover, Vekinis describes both kinds of gel as forming through “polymerization”, which is inaccurate. Polymerization is what happens when small molecular building blocks bond chemically together to form spindly, long-chain molecules. If these molecules link up, they can then form a branched gel, such as silicone, which has some structural similarities to a protein gel. However, the bonding process is very different, and I found this comparison with polymer science unhelpful.
Meanwhile, in the section “Wine, vinegar, and lemon”, we are told that to prepare a smooth sauce you have to boil “an acidic agent as a catalyst for a polymerization reaction” and that “dry wine does the job too”. Though the word is sometimes used colloquially, what is described here is not, in the scientific sense, a catalytic reaction.
Towards the end of the book, Vekinis moves beyond food and looks at the physics behind microwaves, fridges and other kitchen appliances. He describes, for example, how the oscillation of polar molecules such as water in microwaves produces heating that is completely distinct to a conventional oven.
It’s well known that a microwave oven doesn’t heat food uniformly and the book describes how standing waves in the oven produce hot and cold spots. However, I feel more could have been said about the effect of the shape and size of food on how it heats. There has been interesting work, for example, investigating the different heating patterns in square- and round-edged foods.
Overall, I found the book an enjoyable read even if Vekinis sometimes over-simplifies complicated subjects in his attempts to make tricky topics accessible. I shared the book with some teacher friends of mine, who all liked it too, saying they’d use it in their food-science lessons. They appreciated the way the book progresses from the simple (such as heat and energy) to the complex (such as advanced thermodynamic concepts).
Physics in the Kitchen is not meant to be a cookbook, but I do wonder if Vekinis – who describes himself as a keen cook as well as a scientist – could have made himself clearer by including a few recipes to illustrate the processes he describes. Knowing how to put them into practice will not only help us to make wonderful meals – but also enhance our enjoyment of them too.
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The Kyrenia Ship is an ancient merchant vessel that sank off the coast of Cyprus in the 3rd century BCE. Through fresh analysis, a team led by Sturt Manning at Cornell University has placed tighter constraints on the age of the shipwreck. The researchers achieved this through a combination of techniques that improve the accuracy of radiocarbon dating, and reversing wood treatments that make dating impossible.
In the late 1960s, a diving expedition off the coast of Kyrenia, Northern Cyprus, uncovered the wreck of an ancient Greek merchant ship. With over half of its hull timbers still in good condition, the wreck was remarkably well preserved, and carried an archaeological treasure trove of valuable coins and artefacts.
“Ancient shipwrecks like these are amazing time capsules, since their burial in deeper water creates a near oxygen-free environment,” Manning explains. “This means that we get a remarkable preservation of materials like organics and metals, which usually do not preserve well in archaeological contexts.”
Following the discovery, the Kyrenia ship was carefully excavated and brought to the surface, where its timbers were treated to prevent further decay. In accordance with preservation techniques at the time, this involved impregnating the wood with polyethylene glycol (PEG) – but as archaeologists attempted to determine the age of the wreck through radiocarbon dating, this approach soon created problems.
To perform radiocarbon dating, researchers need to measure the amount of carbon-14 (14C) that a sample contains. This isotope is created naturally in the atmosphere and absorbed into wood through photosynthesis, but after the tree is cut down, it gradually decays into more stable isotopes (mainly 12C and 13C). This means that researchers can accurately estimate the age of a sample by measuring the proportion of 14C it contains, compared with 12C and 13C.
However, when samples from the Kyrenia ship were treated with PEG, the wood became contaminated with far older, petroleum-derived carbon. “Initially, it was not possible to get useful radiocarbon dates on the PEG-conserved wood,” Manning explains.
Recent archaeological studies indicate that the Kyrenia ship had likely sunk between 294 and 290 BCE. But radiocarbon dating using the most up-to-date version of the radiocarbon “calibration curve” for this period – which accounts for how concentrations of 14C in the atmosphere vary over time – still didn’t align with the archaeological constraints.
“With the current internationally approved methods, radiocarbon dates on some of the non-PEG-treated materials, such as almonds in the cargo, gave results inconsistent with any of the archaeological assessments,” says Manning.
To address this disparity, the researchers employed a combination of approaches to improve on previous estimates of the Kyrenia ship’s true age. Part of their research involved analysing the most up-to-date calibration curve for the period when the ship sank, and comparing it with wood samples that had been dated using a different technique: analysing their distinctive patterns of tree rings.
Tree-ring patterns vary from year to year due to short-term variations in rainfall, but are broadly shared by all trees growing in the same region at a given time. Taking advantage of this, Manning’s team carried out radiocarbon dating on a number of samples that had already been dated from their tree ring patterns.
“We used known-age tree-rings from the western US and the Netherlands to redefine the atmospheric radiocarbon record in the northern hemisphere over the period between 400 and 250 BCE,” Manning explains. Variations between atmospheric concentrations of 14C differ between Earth’s hemispheres, since the northern hemisphere contains far more vegetation overall.
In addition to revising the radiocarbon calibration curve, the team also investigated new techniques for cleaning PEG from contaminated samples. They tested the techniques on samples dating from around 60 CE, which had undergone radiocarbon dating before being treated with PEG. They showed that with the appropriate sample pretreatment, they could closely reproduce these known dates.
By combining these techniques, the researchers had all the tools that they needed to constrain the age of the Kyrenia ship. “With a technique called Bayesian chronological modelling, we combined all the tree-ring information from the ship timbers, the radiocarbon dates, and the ship’s archaeological time sequence – noting how the ship’s construction must predate its last cargo and sinking,” Manning describes.
“The date for the ship is most likely between 293 and 271 BCE: confirming other recent arguments that the original late 4th century BCE date for the ship needs a little revision,” he says.
By constraining this date, Manning’s team hopes that the work could enable researchers to better understand where the Kyrenia ship and its numerous artefacts fit within the wider chronology of ancient Greece. In turn, their discoveries could ultimately help archaeologists and historians to deepen their understanding of a fascinating era in history.
The researchers report their findings in PLOS ONE.
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