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Synthetic biology inspires smart materials

Information processing materials system. Credit: Wilfried Weber.
Information processing materials system. Credit: Wilfried Weber.

All living systems from single cells to entire organisms respond to external stimuli in a variety of different ways. Inspired by the way synthetic biology uses simple building blocks to create complex responsive systems, researchers from the University of Freiberg have designed ‘smart’ materials systems made from protein and polymer components that can perceive and process information [Wagner et al., Materials Today (2018), https://doi.org/10.1016/j.mattod.2018.04.006].

“We used principles and building blocks from synthetic biology to endow polymer materials with new functions,” explains first author of the study, Hanna J. Wagner.

The team led by Wilfried Weber assembled biohybrid materials able to process information and perform tasks such as detecting enzymes or small molecules. The construction of the system starts with specially designed protein building blocks with sensing, switching, transmitting, or output functions, which are engineered to couple with polymer materials. Then these material units are interconnected to create a signal detector and amplification – or positive feedback – system that responds to external stimuli.

“One material can, for example, sense an input and react by sending another signal to a second material,” explains Wagner. “The second material can again sense and react – depending on the design of the biomaterial. Based on this strategy, materials systems can be ‘programmed’ to process information.”

The team’s initial system is based on a tobacco etch virus protease construct immobilized in an agarose polymer network that can detect an external ‘input’ and transmit a signal to a second material, which further activates the first in a positive feedback loop. The second material releases a molecule – a red fluorescent protein, mCherry – that serves as the system’s output. The positive feedback loop boosts the output signal and makes the system sensitive to very low concentrations. From a user’s perspective, the system fluoresces red when it detects enzymes or small molecules such as antibiotics.

“A great thing about these synthetic biology-inspired materials systems is their versatility,” says Wagner. “In principle, we can use the whole collection of synthetic biological parts to incorporate new functions into materials, including therapeutics for biomedical purposes.”

The modular approach allows materials to be put together in different ways to sense various physical, chemical, or biological signals and respond with a useful function, such as amplifying a signal, storing information, or releasing a drug or active molecule.

“It is a versatile approach that offers the possibility of endowing polymer materials with a complete, new set of functions and engineering materials systems with different, customized computational functionalities,” Wagner told Materials Today.

The circuit function, biological components (receptors, transmitters, and output), and appropriate polymer can all be chosen depending on the goal of the system.


Dental decay gives up its secrets

Advanced synchrotron SAXS and WAXS analysis of the demineralization of human tooth enamel indicates a crystallographic-orientation-dependent anisotropic dissolution process.
Advanced synchrotron SAXS and WAXS analysis of the demineralization of human tooth enamel indicates a crystallographic-orientation-dependent anisotropic dissolution process.

Almost all adults suffer at one time or another from tooth decay or ‘dental caries’. The problem usually begins in the hard mineralized, enamel coating of a tooth and can undermine its strength and usability, as well as causing pain. But despite being one of the most common chronic diseases affecting teeth, relatively little is known about how dental caries cause demineralization and what structural changes take place in the enamel.

Now a team of researchers from the Universities of Oxford, Birmingham, and Surrey have used advanced synchrotron small-angle and wide-angle X-ray scattering (SAXS and WAXS) at the Diamond Light Source at Harwell in the UK to follow the evolution of dental caries formation and the resulting changes in structure at the nanoscale [Sui et al., Acta Biomaterialia (2018), https://doi.org/10.1016/j.actbio.2018.07.027].

The study, led by Alexander M. Korsunsky, is the first of its kind to examine enamel demineralization in vitro and in real time. The researchers devised a setup that mimics the natural demineralization process by allowing a controlled amount of lactic acid to be introduced onto a section of a human tooth. SAXS/WAXS analysis before and after the introduction of the acid enables the development of dental caries to be followed along with the corresponding changes in microstructure of the enamel.

Tooth enamel comprises a complex, hierarchical composite structure of interlocking rods and inter-rods in a keyhole-like arrangement. Each rod/inter-rod is made up of bundles of hydroxyapatite (HAp) crystallites, which range in length from a few tens of nanometers to the entire thickness of the enamel. When enamel is exposed to lactic acid, a very common agent involved in dental decay, demineralization can begin. The acid diffuses into the crystallites, dissolving the HAp and breaking down the structure of the enamel, which if left unchecked can lead to damage in the dentine below causing pain and loss of function.

The researchers found that along with a reduction in mineral volume, the rate and direction of dissolution of HAp crystals depends on the orientation of the crystal faces in the mineral. Moreover, they observed a dramatic initial decrease in the layer containing HAp crystallites with the smallest crystalline dimension. The SAXS/WAXS analysis indicates that the most severe demineralization occurs just beneath the surface of the enamel. When the pH level gradually recovers, remineralization also occurs.

One explanation of the researchers’ observations is that the dissolution rate depends on the contact surface area of the crystallites exposed to the acid. In other words, crystallites perpendicular to the dissolution direction dissolve faster than those in other orientations.

The researchers hope that better understanding of the changes in mineralization associated with dental caries will help lead to more effective treatments.


Dual-template approach produces three-layered nanostructures

These images show the completed triple layer nanowires. Image: KAUST.
These images show the completed triple layer nanowires. Image: KAUST.

By combining multiple nanomaterials into a single structure, researchers at the King Abdullah University of Science & Technology (KAUST) in Saudi Arabia have been able to create hybrid materials that incorporate the best properties of each component and outperform any single substance.

The researchers have developed a controlled method for making triple-layered hollow nanostructures consisting of a conductive organic core sandwiched between layers of electrocatalytically active metals. The potential uses for these nanostructures, which are reported in a paper in Nature Communications, range from better battery electrodes to renewable fuel production.

Although several methods exist to create two-layer nanomaterials, making three-layered nanostructures has proven much more difficult, says Peng Wang from KAUST’s Water Desalination and Reuse Center. Wang co-led the current research with Yu Han, a member of the Advanced Membranes and Porous Materials Center at KAUST. This difficulty inspired the researchers to develop a new, dual-template approach, explains Sifei Zhuo, a postdoctoral member of Wang's team.

The researchers grew their hybrid nanomaterial directly on carbon paper – a mat of electrically conductive carbon fibers. They first produced a bristling forest of nickel cobalt hydroxyl carbonate (NiCoHC) nanowires on the surface of each carbon fiber. Each tiny inorganic bristle was coated with an organic layer called hydrogen-substituted graphdiyne (HsGDY).

Next came the key dual-template step. When the team added a chemical mixture that reacts with the inner NiCoHC, the HsGDY acted as a partial barrier. Some nickel and cobalt ions from the inner layer diffused outward, where they reacted with thiomolybdate from the surrounding solution to form an outer nickel- and cobalt-co-doped molybdenum disulfide (Ni,Co-MoS2) layer. Meanwhile, some sulfur ions from the added chemicals diffused inwards to react with the remaining nickel and cobalt. The resulting substance had the structure Co9S8, Ni3S2@HsGDY@Ni,Co-MoS2, in which the conductive organic HsGDY layer is sandwiched between two inorganic layers.

This triple layer material showed good ability at electrocatalytically splitting water molecules to generate hydrogen, a potential renewable fuel. The researchers also created other triple-layer materials using the same dual-template approach.

"These triple-layered nanostructures hold great potential in energy conversion and storage," says Zhuo. "We believe it could be extended to serve as a promising electrode in many electrochemical applications, such as in supercapacitors and sodium-/lithium-ion batteries, and for use in water desalination."

This story is adapted from material from KAUST, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


Composite machine manufacturing on the rise

Recent studies suggest that machine manufacturing is set to be a big growth factor in the composites industry.
Recent studies suggest that machine manufacturing is set to be a big growth factor in the composites industry.

Recent studies suggest that machine manufacturing is set to be a big growth factor in the composites industry.

This is according to the organizers of Composites Europe, who have cited surveys conducted by Composites Germany and VDMA-Forum Composite Technology.

According to Reed Expo, automotive, construction, aviation and wind power are the major customer industries for fiber composites, a sector where more and more mass-production applications can be found. By contrast, machine manufacturing as an application area for composite structures is still doomed to a shadowy existence. Quantities are still too small, challenges too complex. However, their lightweight construction properties due to their low density and mass, high strength and stiffness, abrasion, corrosion, temperature and chemical resistance, adjustable thermal expansion coefficient, electrical conductivity as well as their potential for incorporating smart components, make these materials increasingly attractive for machine manufacturers.

A report entitled Taking Stock of Lightweight Construction in Germany published in 2015 the VDI Centre for Resource Efficiency sees machinery and plant construction as a large and growing market for lightweight construction solutions, said the composite event organizers.

Composites Europe, taking place from 6–8 November 2018, will showcase the manufacturing processes used to make fiber-reinforced plastics, from raw materials to processing methods to lightweight construction innovations in automotive engineering, aerospace, boatbuilding, wind energy and construction.

This story is reprinted from material from Composites Europe, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.


Magnus Eriksson new Höganäs CFO

Magnus Eriksson has been appointed as the new CFO of Höganäs.
Magnus Eriksson has been appointed as the new CFO of Höganäs.

Magnus Eriksson has been appointed as the new CFO of Höganäs. He joins the company from Sandvik Hyperion, where he was vice president finance and IT.

‘Magnus has an extensive and solid experience of working in international groups of companies and heavy industry,’ said Fredrik Emilson, CEO. ‘With his passion for leadership issues and business development, Magnus will be a valuable addition to the Höganäs management team.’

This story is reprinted from material from Höganäs, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.


Recipients of the 2017 Acta Student Awards

Top left- right: Nima Haghdadi, Locke Davenport, Tamás Csanádi. Bottom left- right: Konstantin Molodov, Jiao-Jiao Li, Philipp Kürnsteiner. Right, Françoise S.L. Bobbert.
Top left- right: Nima Haghdadi, Locke Davenport, Tamás Csanádi. Bottom left- right: Konstantin Molodov, Jiao-Jiao Li, Philipp Kürnsteiner. Right, Françoise S.L. Bobbert.

A team of judges consisting of Acta Materialia, Scripta Materialia, and Acta Biomaterialia editors has completed the evaluation of nominees for the above awards. Each year we receive many excellent nominations and selecting the winners is a challenging task.  Several factors are considered in the evaluation of each nominee: the quality of paper, or papers, for which he or she was nominated, recommendation letters, and leadership potential.  The awardees selected from papers published in 2017 in the Acta Journals are:

Ms. Françoise S.L. Bobbert, Delft University of Technology, THE NETHERLANDS, Advisor: Prof. Amir A. Zadpoor. "Additively manufactured metallic porous biomaterials based on minimal surfaces: A unique combination of topological, mechanical, and mass transport properties," Acta Biomaterialia 53 (2017) 572-584

Dr. Silvia Budday, Friedrich-Alexander Universität Erlangen-Nürnberg, GERMANY.

Advisor: Prof. Paul Steinmann. "Mechanical characterization of human brain tissue," Acta Biomaterialia 48 (2017) 319-340

Dr. Tamás Csanádi, Institute of Materials Research - Slovak Academy of Sciences (IMR-SAS), Košice, SLOVAKIA.  Advisor: Prof. Ján Dusza.  "Slip activation controlled nanohardness anisotropy of ZrB2 ceramic grains," Acta Materialia 140 (2017) 452-464

Mr. Locke Davenport-Huyer, University of Toronto, CANADA. Advisor: Prof. Milica Radisic. "Moldable elastomeric polyester-carbon nanotube scaffolds for cardiac tissue engineering," Acta Biomaterialia 52 (2017) 81-91

Ms. Yun Deng, Norwegian University of Science and Technology (NTNU), NORWAY.  Advisor:  Prof. Afrooz Barnoush. "In-situ micro-cantilever bending test in environmental scanning electron microscope: Real time observation of hydrogen enhanced cracking," Scripta Materialia 127 (2017) 19-23

Dr. Nima Haghdadi, Deakin University, AUSTRALIA.  Advisors:  Prof. Peter Hodgson, Dr. Hossein Beladi, Dr. Pavel Cizek.  "A novel high-strain-rate ferrite dynamic softening mechanism facilitated by the interphase in the austenite/ferrite microstructure," Acta Materialia 126 (2017) 44-57

Mr. Philipp Kürnsteiner, Max-Planck Institut für Eisenforschung GmbH, GERMANY. Advisor:  Prof. Dierk Raabe. "Massive nanoprecipitation in an Fe-19Ni-xAl maraging steel triggered by the intrinsic heat treatment during laser metal deposition," Acta Materialia 129 (2017) 52-60

Ms. Jiao-Jiao Li, University of Shanghai for Science and Technology, CHINA. Advisor: Prof. Deng-Guang Yu. "Nanosized sustained-release drug depots fabricated using modified tri-axial electrospinning," Acta Biomaterialia 53 (2017) 233-241

Dr. Konstantin Molodov, RWTH Aachen University, GERMANY.  Advisor:  Prof. Günter Gottstein.  Profuse slip transmission across twin boundaries in magnesium," Acta Materialia 124 (2017) 397-409

The editors would like to congratulate the awardees and thank all the nominees for their participation.  We look forward to continuing to work with and support these excellent young researchers as their careers unfold.

Christopher A. Schuh

Coordinating Editor, Acta Journals


Stacking 2D material switches on novel property

When two monolayers of WTe2 are stacked into a bilayer, a spontaneous electrical polarization occurs, one layer becoming positively charged and the other negatively charged. This polarization can be flipped by applying an electric field. Image: Joshua Kahn.
When two monolayers of WTe2 are stacked into a bilayer, a spontaneous electrical polarization occurs, one layer becoming positively charged and the other negatively charged. This polarization can be flipped by applying an electric field. Image: Joshua Kahn.

The 21st century may be seen by many as an era of revolutionary technological platforms, such as smartphones or social media. But for many scientists, this century is the era of another type of platform: two-dimensional (2D) materials and their unexpected secrets.

These 2D materials can be prepared in crystalline sheets as thin as a single monolayer, only one or a few atoms thick. Within a monolayer, electrons are restricted in how they can move: like pieces on a board game, they can move front to back, side to side or diagonally – but not up or down. This constraint makes monolayers functionally two-dimensional.

The 2D realm exposes properties predicted by quantum mechanics – the probability-wave-based rules that underlie the behavior of all matter. Since graphene – the first monolayer – debuted in 2004, scientists have isolated many other 2D materials and shown that they harbor unique physical and chemical properties that could revolutionize computing and telecommunications, among other fields.

For a team led by scientists at the University of Washington (UW), the 2D form of one metallic compound – tungsten ditelluride (WTe2) – is a bevy of quantum revelations. In a paper published in Nature, the scientists report their latest discovery about WTe2: its 2D form can undergo ‘ferroelectric switching’. When two monolayers are combined, the resulting ‘bilayer’ develops a spontaneous electrical polarization, which can be flipped between two opposite states by an applied electric field.

"Finding ferroelectric switching in this 2D material was a complete surprise," said senior author David Cobden, a UW professor of physics. "We weren't looking for it, but we saw odd behavior and after making a hypothesis about its nature we designed some experiments that confirmed it nicely."

Materials with ferroelectric properties can have applications in memory storage, capacitors, RFID card technologies and even medical sensors. "Think of ferroelectrics as nature's switch," explained Cobden. "The polarized state of the ferroelectric material means that you have an uneven distribution of charges within the material – and when the ferroelectric switching occurs, the charges move collectively, rather as they would in an artificial electronic switch based on transistors."

The UW team created the WTe2 monolayers from its 3D crystalline form, which was grown by co-authors Jiaqiang Yan at Oak Ridge National Laboratory and Zhiying Zhao at the University of Tennessee, Knoxville. Then the UW team, working in an oxygen-free isolation box to prevent WTe2 from degrading, used Scotch Tape to exfoliate thin sheets of WTe2 from the crystal – a technique widely used to isolate graphene and other 2D materials. With the sheets isolated, they could measure their physical and chemical properties, which led to the discovery of the ferroelectric characteristics.

WTe2 is the first exfoliated 2D material known to undergo ferroelectric switching. Before this discovery, scientists had only seen ferroelectric switching in electrical insulators. But WTe2 isn't an electrical insulator, it is actually a metal, albeit not a very good one. WTe2 also maintains the ferroelectric switching at room temperature, and this switching is reliable and doesn't degrade over time, unlike many conventional 3D ferroelectric materials, according to Cobden. These characteristics may make WTe2 a more promising material for smaller, more robust technological applications than other ferroelectric compounds.

"The unique combination of physical characteristics we saw in WTe2 is a reminder that all sorts of new phenomena can be observed in 2D materials," said Cobden.

Ferroelectric switching is the second major discovery Cobden and his team have made about monolayer WTe2. In a 2017 paper in Nature Physics, the team reported that this material is also a ‘topological insulator’, the first 2D material with this exotic property.

In a topological insulator, the electrons' wave functions – mathematical summaries of their quantum mechanical states – have a kind of built-in twist. Thanks to the difficulty of removing this twist, topological insulators could have applications in quantum computing – a field that seeks to exploit the quantum-mechanical properties of electrons, atoms or crystals to generate computing power that is exponentially faster than today's technology. The UW team's discovery also stemmed from theories developed by David Thouless, a UW professor emeritus of physics who shared the 2016 Nobel Prize in Physics in part for his work on topology in the 2D realm.

Cobden and his colleagues plan to keep exploring monolayer WTe2 to see what else they can learn. "Everything we have measured so far about WTe2 has some surprise in it," said Cobden. "It's exciting to think what we might find next."

This story is adapted from material from the University of Washington, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


New designs get a grip on auxetic materials

This illustration shows the ratcheting building block that could be embedded in new materials. After vertical compression, the ratcheting block can keep the materials collapsed, releasing its energy in response to a sideways pull. Image: Stoyan Smoukov.
This illustration shows the ratcheting building block that could be embedded in new materials. After vertical compression, the ratcheting block can keep the materials collapsed, releasing its energy in response to a sideways pull. Image: Stoyan Smoukov.

What do a flea and an eagle have in common? They can both store energy in their feet so that they don’t have to continuously contract their muscles to jump high or hold on to prey. Now scientists at Queen Mary University of London and the University of Cambridge, both in the UK, have created materials that can store energy this way, allowing them to be squeezed repeatedly without damage and even change shape if necessary.

These kinds of materials are called auxetics and behave quite differently from regular materials. Instead of bulging out when squeezed, they collapse in all directions, storing the energy inside.

Current auxetic material designs have sharp corners that allow them to fold onto themselves, achieving a higher density. This is a property that has been incorporated recently in lightweight armor designs, where the material can collapse in front of a bullet upon impact. This is important because the mass in front of a bullet is the biggest factor in armor effectiveness.

The sharp corners also concentrate forces and cause the material to fracture if squeezed multiple times, but this is not a problem for armor as it is only designed to be used once. In this study, reported in a paper in Frontiers in Materials, the scientists redesigned auxetic materials with smooth curves for distributing the forces, making repeated deformations possible for applications where energy storage and shape-changing material properties are required. The work establishes the basis for designs of lightweight three-dimensional (3D) supports, which can also fold in specific ways and store energy that could be released on demand.

"The exciting future of new materials designs is that they can start replacing devices and robots," said principal investigator Stoyan Smoukov from Queen Mary University of London. "All the smart functionality is embedded in the material, for example the repeated ability to latch onto objects the way eagles latch onto prey and keep a vice-like grip without spending any more force or effort."

The team expects its nature-inspired designs could be used in energy-efficient gripping tools required by industry, re-configurable shape-on-demand materials and even lattices with unique thermal expansion behavior.

"A major problem for materials exposed to harsh conditions, such as high temperature, is their expansion," added Eesha Khare, a visiting undergraduate student from Harvard University who was instrumental in defining the project. "A material could now be designed so its expansion properties continuously vary to match a gradient of temperature farther and closer to a heat source. This way, it will be able to adjust itself naturally to repeated and severe changes."

The flexible auxetic material designs, which were not possible before, were adapted specifically to be easily 3D-printed, a feature the authors consider essential. "By growing things layer-by-layer from the bottom up, the possible material structures are mostly limited by imagination, and we can easily take advantage of inspirations we get from nature," said Smoukov.

This story is adapted from material from Queen Mary University of London, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


Universal method shakes up quantum dot production

Schematic of the process to prepare MoS2 two-dimensional QDs, illustrating the benefits of the reflux pre-treatment-mediated sonication process. Nanostructure and concentration of MoS2 samples prepared with combination of reflux and sonication: AFM image of MoS2, thickness distribution of MoS2 and size distribution of MoS2.
Schematic of the process to prepare MoS2 two-dimensional QDs, illustrating the benefits of the reflux pre-treatment-mediated sonication process. Nanostructure and concentration of MoS2 samples prepared with combination of reflux and sonication: AFM image of MoS2, thickness distribution of MoS2 and size distribution of MoS2.

Despite the enormous promise of two-dimensional materials, there is no simple and low-cost way of producing such materials in quantum dot form in large quantities. Until now, that is, according to a team from Rice University, Sichuan University, Fujian University of Technology, University of Cincinnati, Sanatana Dharma College, University of Central Florida, Hefei University of Technology, and Saudi Basic Industries Corporation [Liu et al., Materials Today (2018), https://doi.org/10.1016/j.mattod.2018.06.007].

The researchers have developed a simple and universal reflux pre-treatment and sonication method that produces measurable amounts of two-dimensional quantum dots (QDs) from bulk raw materials including graphene, hexagonal boron nitride (h-BN), semiconducting SnS2, and transition metal dichalcogenides (TiS2, MoS2, WSe2, NbS2).

The simple process begins by refluxing the starting bulk material in a chemical solvent for 24 hours. The resulting dispersion is then sonicated for 4 hours before being centrifuged for 30 minutes. Filtering off the liquid that separates from the solid residue, known as the supernatant, yields two-dimensional quantum dots (QDs) typically 2-7 nm wide and a monolayer (0.8-1 nm) thick.

The crucial part of the process is the reflux pre-treatment because this allows the solvent to permeate into cracks and channels between the layers of the bulk material, which are held together by weak van der Waals’ forces. The confined solvent helps force apart – or delaminate – the layers and break them up into QDs during the sonication part of the process. The solvent has to be carefully chosen to match the bulk material.

“A solvent with a surface tension components ratio best matched to the bulk material has to be found before sonication,” explains first author of the study, Yang Liu of Fujian University of Technology. “The surface tension components ratio is the ratio between the polar and dispersive parts of a material or solvent; when the value of the solvent is close to that of a two-dimensional material, it will show good immersion and insertion.”

Although the reported yield of 1.5wt% may not sound very high, this far exceeds any previous reported yields for top-down fabrication of QDs, which have been too low to measure.

“This method is universal and could be applied to various two-dimensional materials, including other transition metal dichalcogenides,” says Liu. “Moreover, the process doesn’t involve any surfactants and should be easy to industrialize.”

The researchers are now working on improving the efficiency of the process by increasing the amount of solvent confined in the channels in between the layers of the bulk materials after refluxing. The resulting two-dimensional QDs could be useful in catalysis, energy storage, bioimaging, biosensing, photovoltaics, and optical applications.


Gurit reports 2018 net sales

Gurit says that it received net sales of CHF195.3 million for the first six months of 2018, a growth of 11.5%.

The company’s composite materials business unit achieved net sales of CHF102.8 million in the first half-year 2018, compared to CHF104.2 million, a decrease of 1.3%. Sales to the wind energy industry declined by 10.2% to CHF62.1 million in the first six months of 2018 compared to CHF69.1 million, due to ongoing weak wind material demand in the wind energy markets in India and China which could not be fully compensated by the demand in Europe and good growth in North America, Gurit said.

In the aerospace business unit, sales decreased by 2.2% to CHF 25.0 million in the first six months of 2018 compared to net sales of CHF 25.5 million in the first half-year 2017, while Gurit’s  composite components business unit reported net sales of CHF 7.3 million for the first half-year 2018, a decrease of 25.4% over net sales of CHF 9.8 million generated in the first half-year 2017.

In Gurit’s tooling business unit, however, net sales of wind turbine blade molds and related equipment increased by 68.9% to CHF 60.2 million compared to CHF 35.6 million in the first half-year 2017.

This story is reprinted from material from Gurit, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.


Defects offer way to give MOFs enhanced abilities

This illustration shows how defects in the structure of a MOF can help improve its ability at capturing carbon dioxide. Image: Swansea University.
This illustration shows how defects in the structure of a MOF can help improve its ability at capturing carbon dioxide. Image: Swansea University.

The word ‘defect’ usually suggests some negative, undesirable feature, but researchers at the Energy Safety Research Institute (ESRI) at Swansea University in the UK have a different opinion. They’ve found that, in the realm of nanoporous materials, defects can be put to a good use, if one knows how to tame them.

A team led by Marco Taddei at Swansea University is investigating how the properties of metal-organic frameworks, a class of materials resembling microscopic sponges, can be adjusted by taking advantage of their defects to make them better at capturing carbon dioxide (CO2).

"Metal-organic frameworks, or MOFs, are extremely interesting materials because they are full of empty space that can be used to trap and contain gases," explained Taddei. "In addition, their structure can be manipulated at the atomic level to make them selective to certain gases, in our case CO2.

"MOFs containing the element zirconium are special, in the sense that they can withstand the loss of many linkages without collapsing. We see these defects as an attractive opportunity to play with the properties of the material."

The researchers investigated how defects take part in a process known as ‘post-synthetic exchange’, a two-step procedure whereby a MOF is initially synthesized and then modified through the exchange of some of the components of its structure. They studied the phenomenon in real time using nuclear magnetic resonance, which allowed them to understand the role of defects during the process. They report their findings in a paper in Angewandte Chemie.

"We found that defects are very reactive sites within the structure of the MOF, and that their modification affects the property of the material in a unique way." said Taddei. "The fact that we did this by making extensive use of a technique that is easily accessible to any chemist around the globe is in my opinion one of the highlights of this work."

"In ESRI, our research efforts are focused on making an impact on the way we produce energy, making it clean, safe and affordable," said co-author Andrew Barron, ESRI director. "However, we are well aware that progress in applied research is only possible through a deep understanding of fundamentals. This work goes exactly in that direction."

The study is a proof of concept, but these findings lay the foundation for future work. The researchers want to learn how to chemically manipulate defective structures to develop new materials with enhanced performance for CO2 capture from steelworks waste gases, in collaboration with Tata Steel and University College Cork in Ireland.

"Reducing the CO2 emissions derived from energy production and industrial processes is imperative to prevent serious consequences on climate," said co-author Enrico Andreoli, a senior lecturer at Swansea University and leader of the CO2 capture and utilization group within ESRI. "Efforts in our group target the development of both new materials to efficiently capture CO2 and convenient processes to convert this CO2 into valuable products."

This story is adapted from material from Swansea University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


Seed coat suggests design principles for novel smart materials

Characteristic features of the seedcoat of Portulaca oleracea, an annual succulent commonly known as verdolaga or purslane. A) Photograph of the P. oleracea flower. B) Photograph of the tiny black seeds from P. oleracea. C) Scanning electron microscope image of the P. oleracea seedcoat. D) Magnified area of the seedcoat of P. oleracea. Image: UNH.
Characteristic features of the seedcoat of Portulaca oleracea, an annual succulent commonly known as verdolaga or purslane. A) Photograph of the P. oleracea flower. B) Photograph of the tiny black seeds from P. oleracea. C) Scanning electron microscope image of the P. oleracea seedcoat. D) Magnified area of the seedcoat of P. oleracea. Image: UNH.

According to researchers at the University of New Hampshire, the puzzle-like wavy structure of the delicate seed coat, found in plants like succulents and some grasses, could hold the secret to creating new smart materials strong enough to be used in body armor, screens and airplane panels.

"The seed coat's major function is to protect the seed, but it also needs to become soft to allow the seed to germinate, so the mechanical property changes," said Yaning Li, associate professor of mechanical engineering at the University of New Hampshire. "By learning from nature, it may be possible to tailor the geometry and create the architecture for a smart material that can be programmed to amplify the strength and toughness but also be flexible and have many different applications."

The building blocks of the seed coat are star-shaped epidermal cells that move via zigzag intercellular joints to form a compact, tiled exterior that protects the seed inside from mechanical damage and other environmental stresses, such as drought, freezing and bacterial infection. To better understand the relationship between the structural attributes and functions of the seed coat's unique microstructure, the researchers designed and fabricated prototypes using multi-material 3D printing. They then performed mechanical experiments and finite element simulations on these prototypes.

"Imagine a window, or the exterior of an airplane, that is really strong but not brittle," said Li. "That same concept could create a smart material that could be adapted to behave differently in different situations, whether it's a more flexible body armor that is still protective or other such materials."

The results, published in a paper in Advanced Materials, show that the waviness of the mosaic-like tiled structures of the seed coat, known as sutural tessellations, plays a key role in determining the mechanical response. Generally, the wavier the seed coat, the more that applied loads can effectively transit from the soft wavy interface to the hard phase, allowing both overall strength and toughness to increase simultaneously.

The researchers say that these design principles offer a promising way to increase the mechanical performance of tiled composites made from man-made materials. The overall mechanical properties of the prototypes could be tuned over a very large range by simply varying the waviness of the mosaic-like structures. This approach could thus provide a roadmap for the development of new functionally graded composites that could be used in protection, as well as energy absorption and dissipation.

This story is adapted from material from the University of New Hampshire, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.


US base for German 3D printing specialist

America Makes says that it has congratulated the University of Texas at El Paso (UTEP) regarding its agreement with German 3D printing company Aconity3D to function as its North American base of operations.

UTEP’s campus includes the Keck Center, which offers a number of additive manufacturing (AM) technologies.

‘We can apply this economic development model to build other businesses around their technologies, recruit other 3D printing businesses to our region and create new businesses from our own 3D printing technologies coming out of UTEP,’ said Dr Ryan Wicker, a professor at the center.

This story is reprinted from material from America Makes, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.


Core composites benefit Australian fishing vessel

The Barcoo Drift will be used on the Barcoo River in Queensland, Australia and was designed by Roger Hill Yacht Design, based in New Zealand.
The Barcoo Drift will be used on the Barcoo River in Queensland, Australia and was designed by Roger Hill Yacht Design, based in New Zealand.

A new 14 m long fishing vessel designed in Australia reportedly features sandwich core composite materials from ATL Composites in co-operation with core specialist Diab.

The Barcoo Drift will be used on the Barcoo River in Queensland, Australia and was designed by Roger Hill Yacht Design, based in New Zealand.

The power catamaran was constructed using a combination of DuFLEX composite panels with Diab’s Divinycell H80 and HM100 structural foam cores. Some panels were laminated with unidirectional laminates so they could be strip-planked to conform to the more compound sections of the outer topsides and wing-deck areas.

To provide extra strength while keeping the vessel light, Divinycell HM100 was engineered into the hull bottoms and lower topsides. All other structural sections including bulkheads, hull soles, cabin sides and side decks were supplied as CNC-routed DuFLEX component packs cored with Divinycell H80 in a variety of thicknesses and e-glass fiber reinforcements.

The interior fit-out was supplied as a CNC-routed component pack in Featherlight FF1015X6 Marine Grade panels from ATL Composites. The panels were cored with 15mm Divinycell H60, a low density IPN foam.

ATL Composites makes composite materials, epoxy laminating and adhesive systems for the boatbuilding market in New Zealand and Australia and provides other industries with sandwich core composite materials. The company has a long-standing relationship with the Diab Group as distributor for its product range. 

This story is reprinted from material from Diab, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.


Caged nanoparticles boost catalytic power

(a) Schematic of the encapsulation process that creates Pd nanoclusters inside an RCC3 matrix. (b) Reduction of CC3R to RCC3 cage using NaBH4. Desolvated RCC3 looses porosity as the flexible cage cavities collapse but can be restored to its original crystalline state by adding a few drops of CH2Cl2.
(a) Schematic of the encapsulation process that creates Pd nanoclusters inside an RCC3 matrix. (b) Reduction of CC3R to RCC3 cage using NaBH4. Desolvated RCC3 looses porosity as the flexible cage cavities collapse but can be restored to its original crystalline state by adding a few drops of CH2Cl2.

Catalysts provide a surface for chemical reactions to take place, the greater the surface the better the catalyst. Nanostructured metals make ideal catalysts and there has been much interest in nanoclusters in particular because of their remarkable catalytic properties. But, in practice, metal nanocluster catalysts can suffer from various drawbacks such as aggregation, leaching, and irregular distribution on or weak attachment to support materials.

To get around these problems, researchers from the National Institute of Advanced Industrial Science and Technology in Osaka and Kobe University in Japan, and Yangzhou University in China have come up with a clever solution. Qiang Xu and his colleagues developed a fabrication method that produces individual palladium (Pd) catalytic nanoclusters inside porous organic cages [Yang et al., Nature Catalysis (2018), doi: https://doi.org/10.1038/s41929-018- 0030-8].

By creating catalytically active Pd nanoclusters inside organic molecular cages, aggregation and other problems are avoided, while making the entire surface available for catalytic reactions. The open channels of the porous organic cages make access easy for reactants.

“Not only do the Pd nanoclusters retain extremely high catalytic activity, they also show excellent solubility, dispersibility and stability,” says Xu.

The process used is a reverse double-solvents approach (RDSA), whereby a metal precursor in a water solution is combined with a hydrophobic organic liquid. The addition of a small amount of a hydrophobic solvent, containing the metal precursor, to a large amount of hydrophilic solvent drives the metal precursor into the hydrophobic cavities of, in this case, the reduced amine cage RCC3. The addition of NaBH4 reduces the metal precursor rapidly to create tiny Pd nanoclusters inside the cages (Fig. 1). The organic molecular cage is stable in air, water, and certain solvents, very flexible, and easy to fabricate.

“In particular, desolvated RCC3 are very ‘thirsty’ when it comes to hydrophobic molecules, which could benefit the diffusion of hydrophobic molecules into the cage cavities,” points out Xu.

The researchers believe that the majority of the Pd nanoclusters produced during the process (70%) are encapsulated inside the cages. They tested their caged catalysts with some classic reactions: hydrogen generation from ammonia borane, hydrogenation of nitroarenes, and the reduction of organic dyes, which is particularly important in environmental terms as organic dyes can be highly toxic pollutants. In each case, the caged Pd catalysts show very promising or significantly improved catalytic activity.

“Compared with traditional heterogeneous catalysts, our ultrafine Pd nanoclusters have excellent stability owing to the unique confinement of porous organic cages, while the open skeletons of the cage shells provide excellent accessibility to the Pd cores for reactants,” explains Xu.

The researchers believe that encapsulating metal nanoclusters within soluble, porous organic cages is a promising strategy for the development of advanced catalysts.

“This is exciting work,” comments Andy Cooper, professor of chemistry and director of the Materials Innovation Factory at the University of Liverpool in the UK. “The materials have high catalytic activities and clusters seem stable over several reaction cycles.”

However, he adds the caveat that it will be interesting to confirm where the Pd actually resides, whether it is indeed inside the cages, which could mean that the material is more like a Pd organic complex, or elsewhere.

Suresh Kalidindi of Poornaprajna Institute of Scientific Research in India agrees that confirmation is needed that the nanoclusters are residing within the cages.

“The role played by the organic cage is limited to restricting the size of Pd nanoparticles to <1 nm, but one clear novelty is the stabilization of sub-nanometer Pd nanoparticles, which is always a challenge in this size regime,” he points out. He also cautions that scaling up the approach looks difficult at this stage, which could limit its practical use.

This article was first published in Nano Today 20 (2018) 1-6.


Gallium spreads itself thin

Theoretically predicted two distinct atomic arrangements of monolayer of Ga oriented along two crystallographic (010) and (100) directions, respectively. Electron localization function (ELF) of 2% strained structure of b010 along x direction and 6% strained structures of a100, monolayers. The ELF is shown by the color bar, with red (blue) showing maxima (minima). The ELF shows uniform covalent bonding behavior in a100 gallenene and a mixture of covalent and metallic in b010 gallenene. A simple exfoliation technique of surface solid layers from the molten phase of Ga to synthesize these 2D metallic sheets is also shown. The shown transmission electron microscopy images and the theoretically predicted structures are in excellent agreement.
Theoretically predicted two distinct atomic arrangements of monolayer of Ga oriented along two crystallographic (010) and (100) directions, respectively. Electron localization function (ELF) of 2% strained structure of b010 along x direction and 6% strained structures of a100, monolayers. The ELF is shown by the color bar, with red (blue) showing maxima (minima). The ELF shows uniform covalent bonding behavior in a100 gallenene and a mixture of covalent and metallic in b010 gallenene. A simple exfoliation technique of surface solid layers from the molten phase of Ga to synthesize these 2D metallic sheets is also shown. The shown transmission electron microscopy images and the theoretically predicted structures are in excellent agreement.

Researchers from Rice University, Bruker Nano Surfaces, the Indian Institute of Science and the Indian Institute of Technology have created atomically thin layers of the metal gallium on silicon substrates [Kochat et al., Sci. Adv. 4 (2018) e1701373, https://doi. org/10.1126/sciadv.1701373].

Two-dimensional materials just a few atoms thick have attracted much attention since the discovery of graphene and its unique combination of properties. Numerous other two-dimensional materials have since joined the family, such as hexagonal boron nitride and semiconducting transition metal dichalcogenides. However, two-dimensional metallic materials have proved more elusive.

Inspired by the simple exfoliation of graphene from graphite, Abhishek K. Singh, Chandra S. Tiwary, Pulickel M. Ajayan and colleagues devised a simple means of producing very thin layers of gallium, which they nickname ‘gallenene’.

“Weak interlayer forces in graphite can be utilized to separate atomically thin layers with the help of scotch tape,” explains Tiwary. “In case of solid metals, such phenomena cannot be utilized. But the solid-liquid interface is weak in metals, and we have utilized this to separate the solidified solid from the top surface.”

Atomically thin layers of gallium are exfoliated by simply dipping a Si/SiO2 substrate mounted on a diamond indenter into the molten metal. As the molten metal cools on the solid substrate, the forces between the top few atomic layers of the solidified metal and the liquid melt below are much less than within the completely solid material.

“We can utilize the surface adhesion properties of a solid with a substrate to separate a few atomically thin layers of gallium from its molten liquid,” says Tiwary.

Gallenene appears to take up two distinctive atomic arrangements, depending on the orientation during exfoliation, either retaining its usual lattice structure (gallenene b010) or taking up a honeycomb-like structure (gallenene a100) (Fig. 1). Of the two crystalline arrangements, gallenene b010 appears more stable than the other form, but both show good stability under normal, room temperature conditions.

“The novelty of our work is its simplicity and easy scalability,” says Tiwary. “We can exfoliate large-scale areas of atomically thin sheets of gallenene without the need for large amounts of energy or complicated processing parameters.”

It is early days to talk about applications of gallenene as yet, say the researchers, as no one has explored the properties of the atomically thin metal. But they envisage that metallic two-dimensional materials such as gallenene could be very useful in the construction of contacts for two-dimensional circuits and electronic devices.

“We want to understand the basic properties of the material first before we can start to explore different applications,” explains Tiwary.

This article was first published in Nano Today 20 (2018) 1-6.


Focus on 3D printing open market

Materialise plans to develop applications with BASF using its 3D printing facilities.
Materialise plans to develop applications with BASF using its 3D printing facilities.

3D printing software company Materialise and chemicals specialist BASF have formed a strategic alliance to promote a more open market model in the additive manufacturing (AM) market.

Materialise plans to identify applications that can benefit from 3D printing and develop them with   BASF using the latter’s 3D printing facilities, in order to launch or certify new materials in markets such as aerospace, automotive and wearables.

BASF has agreed to invest US$25 million in Materialise through a private placement of new shares and Materialise has also made a public offering of up to $50 million in new shares.

This story is reprinted from material from Materialise, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.


Boost for H.C. Starck

Metals and ceramics manufacturer H.C. Starck, said that it had a significant increase in sales for 2017. Sales for the past fiscal year rose to €767.3 million, an increase of 11% over the previous year. According to the company, this was driven by the recovery of important core markets and by the implementation of a series of initiatives aimed at boosting sales and profitability.

Development of the company’s STC Division will continue under the leadership of Swedish metal powder manufacturer Höganäs AB, and Starck has also decided to work with JX Nippon Mining & Metals in its tantalum niobium division.

The tungsten division of H.C. Starck also posted significantly increased sales and results in 2017 compared with the previous year, and H.C. Starck Tantalum and Niobium GmbH benefited from strong demand for tantalum for sputter targets and capacitor applications.

This story is reprinted from material from H.C. Starck, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.


Euro PM2018 gets set for Bilbao

The European Powder Metallurgy Associations (EPMA) says that its Euro PM Congress & Exhibition, taking place in Bilbao, Spain, has attracted a record number of abstracts.

The event has reportedly recorded over 300 abstracts provided by the powder metallurgy community, an increase of over 30% compared to previous Euro PM Events.

The exhibition also covers over 5,000m2 of dedicated space, containing over 100 PM related supply chain companies.

This story is reprinted from material from the EPMA, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.