Materials Science

[Recusant]

While the previous item shows an intriguing possibility for materials science, this one is just cool, in my opinion.

"Radical Theory Suggests Earthquakes Spark Gold Nuggets Into Existence" | Science Alert

New findings by scientists in Australia could challenge what we thought we knew about the way gold nuggets bloom in vast reefs beneath our feet.

Under pressures of hundreds of megapascals (tens of thousands of pounds per square inch) and boiling hot temperatures, water squeezed up from the depths of Earth's crust carries dissolved gases, metals, and minerals to the surface with every quake and shudder of a seismic event.

As any good prospector knows, buried seams of crystalized silicon dioxide – better known as quartz – are fertile ground for gold mining, with both materials precipitating out of solution under strikingly similar conditions.

Though the basic mechanisms behind the precious ore's formation have been understood for some time, certain details have never quite added up, and new research from scientists at Australia's Monash University, the CSIRO, and the Australian Nuclear Science and Technology Organisation challenge the conventional views on how gold forms.

[. . .]

Silicon dioxide is an incredibly unique material. Where other crystals are relatively symmetrical, quartz forms with a bias that produces a voltage when stressed – a phenomenon known as the piezoelectric effect.

With every tremor of Earth's crust, seams of quartz will crackle with static currents as voltages emerge and electrons rebalance.

This charge jump is unlikely to move very far given quartz is an insulating material. Gold, on the other hand, is a great conductor of electricity, raising the possibility that electrochemical reactions within quartz seams might serve as a catalyst, drawing sufficient gold from solution in concentrated spots through repeated cycles of tiny shakes.

[. . .]

What was simulated in the lab using concentrated solutions and extensive periods of shaking would of course take far longer in the real world with dilute solutions and occasional tremors.

On geological timescales, however, the process could be relatively rapid. Without the added zap of stressed quartz, it's difficult to even explain how gold might accumulate in such rich deposits in the first place.

[Continues . . .]

The paper is behind a paywall.

Abstract:

Gold nuggets occur predominantly in quartz veins, and the current paradigm posits that gold precipitates from dilute (<1 mg kg⁻¹ gold), hot, water ± carbon dioxide-rich fluids owing to changes in temperature, pressure and/or fluid chemistry.

However, the widespread occurrence of large gold nuggets is at odds with the dilute nature of these fluids and the chemical inertness of quartz. Quartz is the only abundant piezoelectric mineral on Earth, and the cyclical nature of earthquake activity that drives orogenic gold deposit formation means that quartz crystals in veins will experience thousands of episodes of deviatoric stress.

Here we use quartz deformation experiments and piezoelectric modelling to investigate whether piezoelectric discharge from quartz can explain the ubiquitous gold–quartz association and the formation of gold nuggets. We find that stress on quartz crystals can generate enough voltage to electrochemically deposit aqueous gold from solution as well as accumulate gold nanoparticles.

Nucleation of gold via piezo-driven reactions is rate-limiting because quartz is an insulator; however, since gold is a conductor, our results show that existing gold grains are the focus of ongoing growth. We suggest this mechanism can help explain the creation of large nuggets and the commonly observed highly interconnected gold networks within quartz vein fractures.

[Recusant]

Direct observation of palladium acting as a catalyst to synthesize water.

"Watch The Smallest Water Droplet Ever Seen Grow, Molecule by Molecule" | Science Alert

We all know the ingredients for water. You take two atoms of hydrogen and one of oxygen, moosh them together just so, and voila – you have a molecule of the most important compound to life on Earth.

Now, for the first time, scientists have observed this process in action up close. In real-time, and on a molecular scale, materials scientist Vinayak Dravid of Northwestern University and his colleagues watched as the tiniest bubble of water ever seen bloomed seemingly out of thin air.

How did they do it? By harnessing the strange powers of palladium, a metal that is known to catalyze the two elements to synthesize water.

"Think of Matt Damon's character, Mark Watney, in the movie The Martian," Dravid says. "He burned rocket fuel to extract hydrogen and then added oxygen from his oxygenator. Our process is analogous, except we bypass the need for fire and other extreme conditions. We simply mixed palladium and gasses together."

We've known about palladium's strange ability to synthesize significant amounts of water in a relatively short amount of time. But how exactly it works has been tricky to pin down. This is because it's hard to observe the process on the scales at which it occurs.

"You really need to be able to combine the direct visualization of water generation and the structure analysis at the atomic scale in order to figure out what's happening," explains materials scientist Yukun Liu of Northwestern University.

To overcome this significant obstacle, the team developed a membrane that traps molecules inside tiny, hexagonal nanoreactor cells. This makes it easier to image molecular processes using transmission electron microscopy, down to the nanometer scale.

Even so, the researchers were not sure that their attempt to directly observe the palladium reaction would be successful. They added hydrogen and oxygen atoms to the surface of a 20 nanometer-wide piece of palladium, and used their membrane to capture the ensuing interaction.

A single water molecule is less than a third of a nanometer across, while the atoms they consist of are far, far smaller. To 'see' the bonding of these tiny compounds, the researchers used a form of electron microscopy that recorded energy lost by scattering electrons.

[Continues . . .]

The paper is behind a paywall.

Abstract:

Palladium (Pd) catalysts have been extensively studied for the direct synthesis of H₂O through the hydrogen oxidation reaction at ambient conditions. This heterogeneous catalytic reaction not only holds considerable practical significance but also serves as a classical model for investigating fundamental mechanisms, including adsorption and reactions between adsorbates.

Nonetheless, the governing mechanisms and kinetics of its intermediate reaction stages under varying gas conditions remain elusive. This is attributed to the intricate interplay between adsorption, atomic diffusion, and concurrent phase transformation of catalyst. Herein, the Pd-catalyzed, water-forming hydrogen oxidation is studied in situ, to investigate intermediate reaction stages via gas cell transmission electron microscopy.

The dynamic behaviors of water generation, associated with reversible palladium hydride formation, are captured in real time with a nanoscale spatial resolution. Our findings suggest that the hydrogen oxidation rate catalyzed by Pd is significantly affected by the sequence in which gases are introduced. Through direct evidence of electron diffraction and density functional theory calculation, we demonstrate that the hydrogen oxidation rate is limited by precursors' adsorption. These nanoscale insights help identify the optimal reaction conditions for Pd-catalyzed hydrogen oxidation, which has substantial implications for water production technologies. The developed understanding also advocates a broader exploration of analogous mechanisms in other metal-catalyzed reactions.

[Icarus]

Rec you do contribute some thoroughly fascinating posts. Thank you for periodically  elevating my mind for at least a few minutes of time.

 

[Tank]

Rec you do contribute some thoroughly fascinating posts. Thank you for periodically  elevating my mind for at least a few minutes of time.

 

Hear hear!

[Recusant]

Rec you do contribute some thoroughly fascinating posts. Thank you for periodically  elevating my mind for at least a few minutes of time.

 

It's my pleasure, Icarus and Tank! I know that though the science posts may not stimulate a lot of discussion, they can be interesting to members of this site. I appreciate your appreciation.   

You're no slouches when it comes to the thought-provoking department. I'm still reading that New Yorker article about various election interference efforts by non-US entities, for instance.

[Recusant]

A couple of good items for this thread today.

"Living Material Made From Blood Can Repair Bones, Study Shows" | Science Alert

When skin tissue is wounded, our blood starts clotting as part of the healing process. Scientists have now developed a blood-based implant that supercharges this mechanism for bigger repair projects: broken bones.

The international team of researchers behind the implant calls it a "biocooperative regenerative" material: it uses synthetic peptides to improve the structure and function of the barrier naturally formed by blood when it clots.

In tests on rats, the gel-like substance – which can be 3D-printed – was effective in repairing bone damage. If this can be adapted and scaled up for human use, it has huge potential as a way of boosting the body's natural healing processes.

[. . .]

A key component of clotting blood is the solid regenerative hematoma (RH), and this was the main focus of the research. Custom molecules called peptide amphiphiles (PAs) were developed in the lab, which help guide and enhance what the RH does naturally.

When added to human blood, these molecules safely ramped up the clotting process. The researchers were able to get the nanofibers of the PAs to link with the scaffolding of the RH, for example, guiding the creation of stronger structures.

Using PAs added to the animal's own blood to create the material, the team was able to successfully repair small bone defects in the skulls of rats.

Different types of cells that are key to the repair process – including mesenchymal stromal cells, endothelial cells, and fibroblasts (which help form connective tissue) – were observed to be active in the new implant material.

[Continues . . .]

The paper is open access:

"Biocooperative Regenerative Materials by Harnessing Blood-Clotting and Peptide Self-Assembly" | Advanced Materials

Abstract:

The immune system has evolved to heal small ruptures and fractures with remarkable efficacy through regulation of the regenerative hematoma (RH); a rich and dynamic environment that coordinates numerous molecular and cellular processes to achieve complete repair. Here, a biocooperative approach that harnesses endogenous molecules and natural healing to engineer personalized regenerative materials is presented.

Peptide amphiphiles (PAs) are co-assembled with blood components during coagulation to engineer a living material that exhibits key compositional and structural properties of the RH. By exploiting non-selective and selective PA-blood interactions, the material can be immediately manipulated, mechanically-tuned, and 3D printed. The material preserves normal platelet behavior, generates and provides a continuous source of growth factors, and promotes in vitro growth of mesenchymal stromal cells, endothelial cells, and fibroblasts.

Furthermore, using a personalized autologous approach to convert whole blood into PA-blood gel implants, bone regeneration is shown in a critical-sized rat calvarial defect. This study provides proof-of-concept for a biocooperative approach that goes beyond biomimicry by using mechanisms that Nature has evolved to heal as tools to engineer accessible, personalized, and regenerative biomaterials that can be readily formed at point of use.

* * *

2nd item --

"Researchers develop new shape-changing polymer" | EurekAlert

A team of scientists has created a new shape-changing polymer that could transform how future soft materials are constructed.

Made using a material called a liquid crystalline elastomer (LCE), a soft rubber-like material that can be stimulated by external forces like light or heat, the polymer is so versatile that it can move in several directions.

Its behavior, which resembles the movements of animals in nature, includes being able to twist, tilt left and right, shrink and expand, said Xiaoguang Wang, co-author of the study and an assistant professor in chemical and biomolecular engineering at The Ohio State University.

"Liquid crystals are materials that have very unique characteristics and properties that other materials cannot normally achieve," said Wang. "They're fascinating to work with."

This new polymer's ability to change shapes could make it useful for creating soft robots or artificial muscles, among other high-tech devices in medicine and other fields.

[Continues . . .]

The paper is behind a paywall.

Abstract:

Ambidirectionality, which is the ability of structural elements to move beyond a reference state in two opposite directions, is common in nature. However, conventional soft materials are typically limited to a single, unidirectional deformation unless complex hybrid constructs are used.

We exploited the combination of mesogen self-assembly, polymer chain elasticity, and polymerization-induced stress to design liquid crystalline elastomers that exhibit two mesophases: chevron smectic C (cSmC) and smectic A (SmA).

Inducing the cSmC-SmA–isotropic phase transition led to an unusual inversion of the strain field in the microstructure, resulting in opposite deformation modes (e.g., consecutive shrinkage or expansion and right-handed or left-handed twisting and tilting in opposite directions) and high-frequency nonmonotonic oscillations. This ambidirectional movement is scalable and can be used to generate Gaussian transformations at the macroscale.

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As a bonus, though I think this is more engineering than materials science, it's a neat item.

"Magnetically Controlled Kirigami Surfaces Move Objects: No Grasping Needed" | NCSU News

Researchers have developed a novel device that couples magnetic fields and kirigami design principles to remotely control the movement of a flexible dimpled surface, allowing it to manipulate objects without actually grasping them – making it useful for lifting and moving items such as fragile objects, gels or liquids. The technology has potential for use in confined spaces, where robotic arms or similar tools aren't an option.

"We were trying to address two challenges here," says Jie Yin, co-corresponding author of a paper on the work and an associate professor of mechanical and aerospace engineering at North Carolina State University. "The first challenge was how to move objects that you can't pick up with grippers – such as fragile objects or things in confined spaces. The second challenge was how to use a magnetic field to remotely lift and move objects that are not magnetic."

To address those challenges, the researchers created a "metasheet" that consists of an elastic polymer that is embedded with magnetic microparticles. A pattern was then cut into the sheet. The outer edges of the metasheet are attached to a rigid frame.

By moving a magnetic field under the metasheet, you can force sections of the metasheet to bulge upward or sink downward.

"You can actually cause the surface of the metasheet to move like a wave by controlling the direction of the magnetic field," Yin says. "And adjusting the strength of the magnetic field determines how much the wave rise or fall."

[Continues . . .]

The paper is open access:

"Magnetic kirigami dome metasheet with high deformability and stiffness for adaptive dynamic shape-shifting and multimodal manipulation" | Science Advances

Soft shape-shifting materials offer enhanced adaptability in shape-governed properties and functionalities. However, once morphed, they struggle to reprogram their shapes and simultaneously bear loads for fulfilling multifunctionalities.

Here, we report a dynamic spatiotemporal shape-shifting kirigami dome metasheet with high deformability and stiffness that responds rapidly to dynamically changing magnetic fields. The magnetic kirigami dome exhibits over twice higher doming height and 1.5 times larger bending curvature, as well as sevenfold enhanced structural stiffness compared to its continuous counterpart without cuts. The metasheet achieves omnidirectional doming and multimodal translational and rotational wave-like shape-shifting, quickly responding to changing magnetic fields within 2 milliseconds.

Using the dynamic shape-shifting and adaptive interactions with objects, we demonstrate its applications in voxelated dynamic displays and remote magnetic multimodal directional and rotary manipulation of nonmagnetic objects without grasping. It shows high-load transportation ability of over 40 times its own weight, as well as versatility in handling objects of different materials (liquid and solid), sizes, shapes, and weights.

[Icarus]

^ ^ Will wonders never cease? One would hope not.

[Recusant]

^ ^ Will wonders never cease? One would hope not.

Fully agree Icarus!  In the course of assembling that post I learned three new words. "Voxelated" I think I should have already known--a voxel is basically a three dimensional pixel. "Mesogen" (general descriptor of liquid crystal) and "smectic" (of, relating to, or being the phase of a liquid crystal characterized by arrangement of molecules in layers with the long molecular axes in a given layer being parallel to one another and those of other layers and perpendicular or slightly inclined to the plane of the layer) on the other hand, being more or less specific to the field of liquid crystal, are a bit more arcane.

[Recusant]

Creating small-scale structures that interlock in interesting ways is apparently a branch of materials science. Previously I'd have considered it more an exercise in engineering of a sort, but then I'm not a materials scientist. As the article explains, creating this stuff at a molecular level was too much of a challenge so they scaled up. It remains to be seen whether that particular challenge can be overcome but they seem optimistic. In any case, they've produced some interesting stuff.

"Reimagining chain mail" | Science Daily

Experiments from the Caltech lab of Chiara Daraio, G. Bradford Jones Professor of Mechanical Engineering and Applied Physics and Heritage Medical Research Institute Investigator, have yielded a fascinating new type of matter, neither granular nor crystalline, that responds to some stresses as a fluid would and to others like a solid. The new material, known as PAM (for polycatenated architected materials) could have uses in areas ranging from helmets and other protective gear to biomedical devices and robotics.

PAMs are not found in nature, though their basic form is known to us through the millennia-old manufacture of chain mail: small metal rings linked together to form a mesh, most often used as a flexible form of armor. PAMs, however, are like chain mail on steroids. Following the basic principle of interlocking shapes, like those found in a chain, PAMs are made up of a variety of shapes linked together to form three-dimensional patterns whose configurations are almost unimaginably variable. The resulting materials, which Daraio and her colleagues have rendered using 3D printers, exhibit behaviors not found in other types of materials.

Wenjie Zhou, postdoctoral scholar research associate in mechanical and civil engineering, has been working on these types of materials for two years in Daraio's lab. "I was a chemist, and I wanted to make these structures at a molecular scale, but that proved too challenging. In order to get answers to the questions I had about how these structures behave, I decided to join Chiara's group and study PAMs at a larger scale."

The PAMs that Daraio's group created and studied were first modeled on a computer and were designed to replicate lattice structures found in crystalline substances but with the crystal's fixed particles replaced by entangled rings or cages with multiple sides.

These lattices were then printed out three-dimensionally using a variety of materials, including acrylic polymers, nylon, and metals. Once the PAMs could be held in the palm of one's hand—most of the prototypes are 5-centimeter (2-inch) cubes or spheres with a 5-centimeter diameter—they were exposed to various types of physical stress. "We started with compression," Zhou explains, "compressing the objects a bit harder each time. Then we tried a simple shear, a lateral force, like what you would apply if you were trying to tear the material apart. Finally, we did rheology tests, seeing how the materials responded to twisting, first slowly and then more quickly and strongly."

In some scenarios, these PAMs behaved like liquids. "Imagine applying a shear stress to water," Zhou says. "There would be zero resistance. Because PAMs have all these coordinated degrees of freedom, with the rings and cages they are composed of sliding against one another as the links of a chain would, many have very little shear resistance." But when these structures are compressed, they may become fully rigid, behaving like solids.

This dynamism makes PAMs unique. "PAMs are really a new type of matter," Daraio says. "We all have a clear distinction in mind when we think of solid materials and granular matter. Solid materials are often described as crystalline lattices. This is what you see in the classic ball-and-stick models of atomic, chemical, or larger crystalline structures. It is these materials that have formed our conventional understanding of solid matter. The other class of materials is granular, as we see in substances like rice, flour, or ground coffee. These materials are made up of discrete particles, free to move and slide relative to one another."

PAMs defy this binary classification. "With PAMs, the individual particles are linked as they are in crystalline structures, and yet, because these particles are free to move relative to one another, they flow, they slide on top of each other, and they change their relative positions, more like grains of sand," Daraio explains. "PAMs can be very different from one another. You can print them in squishy materials or hard ones. You can change the shape of each particle, and you can change the lattice that you use to connect these particles. Each of these parameters affects the behavior of the resulting material. But all of them show a characteristic transition between fluid and solid-like behavior. This transition may happen under different circumstances, but it always happens."

[Continues . . .]

The paper is behind a paywall.

Abstract:

Architected materials derive their properties from the geometric arrangement of their internal structural elements. Their designs rely on continuous networks of members to control the global mechanical behavior of the bulk. In this study, we introduce a class of materials that consist of discrete concatenated rings or cage particles interlocked in three-dimensional networks, forming polycatenated architected materials (PAMs).

We propose a general design framework that translates arbitrary crystalline networks into particle concatenations and geometries. In response to small external loads, PAMs behave like non-Newtonian fluids, showing both shear-thinning and shear-thickening responses, which can be controlled by their catenation topologies.

At larger strains, PAMs behave like lattices and foams, with a nonlinear stress-strain relation. At microscale, we demonstrate that PAMs can change their shapes in response to applied electrostatic charges. The distinctive properties of PAMs pave the path for developing stimuli-responsive materials, energy-absorbing systems, and morphing architectures.