Tag Archives: #materials

What Are The Effects Of Fiber Addition On The Properties Of High-Performance Concrete? (Civil Engineering)

Szymon Grzesiak and colleagues investigated the influence of fiber addition on the properties of high-performance concrete. They showed that addition of fibers reduced compressive strength and the modulus of elasticity of the concrete. Their study recently appeared in the Journal Materials.

High performance fiber reinforced concrete (HPFRC) is developing quickly to a modern structural material with a high potential. HPFRC is a ductile concrete with high metallic fiber content (1% or more by volume), with uniform or hybrid fibers. Experimental tests showed that fiber dosage improves the energy absorption capacity of concrete and enhances the robustness of concrete elements. However, the addition of fiber does not have always have a positive effect on the mechanical properties. Besides, due to increasing costs of the produced fiber reinforced concrete there is a demand to analyze the necessary fiber dosage in the concrete composition.

Now, Szymon Grzesiak and colleagues investigated the influence of fiber addition on the properties of high-performance concrete.

“It is expected that the surface and length of used fiber in combination with their dosage influence the structure of fresh and hardened concrete.”

— they said

In order to determine the influence of fiber addition, they carried out tests on a mixture with polypropylene (PP) and polyvinyl alcohol (PVA) fiber with dosages of 15, 25, and 35 kg/m³ as well as with control concrete without fiber.

Fig 1. (A) Slump experiment for MasterFiber 401 (PVA). (B) Fresh concrete with MasterFiber 401 (PVA). (C) Fresh concrete with MasterFiber 235 SPA (PP). © Authors

They found that, due to the addition of fibers to the concrete mix, a significant difference was observed in the compressive strength of the concrete. The fiber addition of 15 kg/m³ in the concrete composition reduced the compressive strength from 83.2 MPa to 79.6 MPa. The higher fiber dosage showed a similar trend. Furthermore, it reduced bulk density and the modulus of elasticity of the concrete.

“Due to the higher air content in the fiber-reinforced mixtures compared to normal concrete, the compressive strengths differed from each other.”

— they said.

They also showed that, PP and PVA fibers are effective in increasing the splitting tensile strength of concrete, which allows better utilization of material capacities and has an impact on the production costs of Fiber Reinforced Concrete (FRC) members. The comparison showed that the dosage of fibers increased from 4.0 MPa to 5.0 MPa (for 15 kg/m³), 6.7 MPa (25 kg/m³), and 6.9 MPa (35 kg/m³).

Additionally, the fiber dosage improved the flexural properties of concrete. The flexural strength increased the maximal 31% for a fiber dosage of 25 kg/m³ in comparison to the plain concrete. The bending tensile strength of concrete with added fibers also increased by up to 18% compared to materials without fibers.

© Authors
Figure 2. Bending-tensile strength of concrete with different fiber types (MasterFiber 235 SPA and MasterFiber 401) for a fiber dosage of 35 kg/m³ in accordance with EN12467 © authors

Moreover, it has been shown from stress–deflection curves that long MasterFiber 235 SPA (PP) is better than short MasterFiber 401 (PVA). This is because the stress–deflection curve of fiber type MasterFiber 401 (PVA) revealed a higher increase in deflection compared to fiber type MasterFiber 235 SPA (PP), which may indicate unfavorable adhesion forces between PVA fiber and the matrix. Shorter fibers pull-out of the matrix faster than longer fibers. This is attributed to the bonding forces between the fibers and the concrete matrix.

“The 30 mm long fibers provided a better friction range than the 12 mm long fibers and also provided a better stress transfer in the matrix.”

Finally, the highest PP fiber dosage examined in the concrete composition amounted to 35 kg/m³. However, the addition of more than 25 kg/m³ of fibers to the concrete mix had less influence on the bending tensile strength of the concrete. This concrete mix had an overcritical fiber dosage and was characterized by tensile strain-hardening behavior. A comparison of the stress–deflection curves with the addition of 25 kg/m³ and 35 kg/m³ of fibers also revealed that the cracking behavior of concrete for these two fiber contents did not differ significantly.

Fig 3. Top: Typical failure modes for specimens with MasterFiber 235 SPA (PP). (A) Images of the tensile fracture face of a fiber. (B) Images of the pull-out fracture face of a fiber. Middle: Typical failure modes for specimens with MasterFiber 401 (PVA). (A) Images of the pull-out fracture face of a fiber. Bottom: Typical failure modes for specimens without fiber. © Authors

Funding: Their research was funded by the Master Builders Solutions Deutschland GmbH.

Featured image: (A) Polypropylene fiber MasterFiber 235 SPA (PP). (B) Polyvinyl alcohol fiber MasterFiber 401(PVA) used in the present study. © Authors

Reference: Grzesiak, S.; Pahn, M.; Schultz-Cornelius, M.; Harenberg, S.; Hahn, C. Influence of Fiber Addition on the Properties of High-Performance Concrete. Materials 2021, 14, 3736. https://doi.org/10.3390/ma14133736

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What Are The Effects Of Thermal Conductive Materials on The Freeze-thaw Resistance Of Concrete? (Material Science / Engineering)

Byeong-Hun Woo and colleagues studied the effects of thermal conductive materials on the freeze-thaw resistance of concrete. They performed two experiments: freeze-thaw and rapid cyclic thermal attack in order to evaluate the thermal durability of concrete with thermal conductive materials. They showed that the graphite had a negative effect on the freeze-thaw and rapid cyclic thermal attack. While, the use of silicon carbide (50%) and steel fiber significantly improved thermal durability of concrete. Their study recently appeared in the Journal Materials.

Cold regions have two kinds of threatening factors for vehicle users. One is black ice and the other is pot-holes caused by the freeze–thaw cycle. Black ice makes the surface of the road slippery and causes traffic accidents. To prevent the generation of black ice, people use chemical salts such as CaCl2. However, chemical salts cause deterioration of concrete and reduce the service life of the concrete. While, the water present in the concrete mix freezes and this freezing causes deterioration such as such as cracking, scaling etc. This is called freezing and thawing. This deterioration occurs due to lack of air on the surface layer of concrete mass. Study showed that the combination of both black ice and chemical salts accelerate deterioration of concrete.

However, to overcome this problem, many studies tried to enhance the thermal conductivity of the materials. Like, some suggested the use of carbon nanofibers and carbon nanotubes, while others suggested the use of graphene as they have good thermal conductivities. But, they have certain limitations such as properties and cost.

Thus, to overcome this limitation Byeong-Hun Woo and colleagues now applied a substitution method. The reason behind using substitution method is that, the aggregates occupies more than 65% of the volume fraction. They used silicon carbide (SiC) as the substituting material and substituted it for 50% and 100% of fine aggregate in order to improve the thermal conductivity.

“Silicon carbide was chosen as the substituting material of the fine aggregate; as silicon carbide has good thermal conductivity and hardness, it is considered sufficient as a fine aggregate substitution material.”

— they said

In addition, they used graphite at 5% of volume for enhancing the thermal conductivity, and the arched-type steel fiber for compensating the reduction in mechanical properties by the graphite. Furthermore, they used steel fiber (upto 1% vol. fraction) as the thermal conductive material because the steel fiber has a high level of thermal conductivity. However, there’s a risk if we apply all these various thermal conductive materials to the concrete, why? Because it would generate thermal damage by the difference in the thermal conductivity of each material in the cold environment, e.g., via freeze–thaw. Thus, it is necessary to verify or assess the thermal durability of concrete with thermal conductive materials, in conditions such as freeze-thaw.

For this reason, Byeong-Hun Woo and colleagues performed two experiments: freeze–thaw (FT) and rapid cyclic thermal attack (RCTA). Their concrete was made for application as road paving material, therefore, the FT resistance was important. In addition, cold regions usually change the air temperature very rapidly. Therefore, it was essential to performed RCTA test for assessing the thermal durability of concrete.

RCTA test concept © Woo et al.

They found that, Arched type steel fiber improves the mechanical properties of concrete due to the anchorage effect. On the contrary, it was demonstrated that using graphite brought about a negative effect on the mechanical properties. However, graphite is a good material for improving the thermal conductivity of concrete. Therefore, the decrease in mechanical properties caused by using graphite could be compensated by using arched type steel fiber.

They also found that, SiC is able to be used as fine aggregate and has sufficient thermal conductivity. In addition, it was demonstrated through the thermal conductivity results that the steel fiber could be used as a thermal conductive material. The combination of SiC and steel fiber maximized the improvement in the thermal conductivity of concrete. Adding graphite also brought about an increase in thermal conductivity.

“Using 100% silicon carbide was considered the acceptable range, but 50% of silicon carbide was the best. Graphite decreased all the properties except for the thermal conductivity.”

Finally, it has been demonstrated from the results of the FT test and RCTA test that use of graphite is not suitable for FT and RCTA resistance. However, the arched type steel fiber showed a remarkable improvement of the FT resistance and RCTA. In addition, SiC compensated for the negative effect of graphite on the FT and RCTA.

“We suggest the content of graphite and use of other conductive materials should be carefully consider in further studies”

— they concluded.

Featured image: Used thermal conductive materials. (a) Arched-type steel fiber; (b) SiC; (c) Graphite © Woo et al.

Reference: Woo, B.-H.; Yoo, D.-H.; Kim, S.-S.; Lee, J.-B.; Ryou, J.-S.; Kim, H.-G. Effects of Thermal Conductive Materials on the Freeze-Thaw Resistance of Concrete. Materials 2021, 14, 4063. https://doi.org/10.3390/ma14154063

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Thermal Waves Observed in Semiconductor Materials For The First Time (Physics)

A study published in Science Advances reports on the unexpected observation of thermal waves in germanium, a semiconductor material, for the first time. This phenomenon may allow a significant improvement in the performance of our electronic devices in a near future. The study is led by researchers from the Institute of Materials Science of Barcelona (ICMAB, CSIC) in collaboration with researchers from the Universitat Autònoma de Barcelona, and the University of Cagliari.

Heat, as we know it, originates from the vibration of atoms, and transfers by diffusion at ambient temperatures. Unfortunately, it is rather difficult to control, and leads to simple and inefficient strategies to manipulate it. This is why, for example, large amounts of residual heat can accumulate in our computers, mobile phones and, in general, most electronic devices.

However, if heat was transported through waves, such as light, it would offer new alternatives to control it, especially through the unique and intrinsic properties of waves.

Thermal waves have been observed to date only in few materials, such as solid helium or, more recently, in graphite. Now, the study published in Science Advances by researchers from the Institute of Materials Science of Barcelona (ICMAB, CSIC) in collaboration with researchers from the Universitat Autònoma de Barcelona, and the University of Cagliari, reports on the observation of thermal waves on solid germanium, a semiconductor material used typically in electronics, similar to silicon, and at room temperature. “It was not expected to encounter these wave-like effects, known as second sound, on this type of material, and in these conditions,” says Sebastián Reparaz, ICMAB Researcher at the Nanostructured Materials for Optoelectronics and Energy Harvesting (NANOPTO) Group and leader of this study.

The observation occurred when studying the thermal response of a germanium sample under the effect of lasers, producing a high-frequency oscillating heating wave on its surface. The experiments showed that, contrarily to what was believed until now, heat did not dissipate by diffusion, but it propagated into the material through thermal waves.

Apart from the observation itself, in the study, researchers unveil the approach to unlock the observation of thermal waves, possibly in any material system.

What is second sound and how can it be observed in any material

First observed in the 1960s on solid helium, thermal transport through waves, known as second sound, has been a recurrent subject for researchers who have repeatedly tried to demonstrate its existence in other materials. Recent successful demonstrations of this phenomenon on graphite have revitalized its experimental study.

“Second sound is the thermal regime where heat can propagate in the form of thermal waves, instead of the frequently observed diffusive regime. This type of wave-like thermal transport has many of the advantages offered by waves, including interference and diffraction”, says ICMAB researcher Sebastián Reparaz.

“Wave-like effects can be unlocked by driving the system in a rapidly varying temperature field. In other words, a rapidly varying temperature field forces the propagation of heat in the wave-like regime” explains Reparaz, and adds, “The interesting conclusion of our work is that these wave-like effects could be potentially observed by most materials at a sufficiently large modulation frequency of the temperature field. And, what is even more interesting, its observation is not restricted to some specific materials.”

Applications of second sound in a near future

“The possible applications of second sound are limitless”, says Sebastián Reparaz. Achieving these applications, however, will require a deep understanding on the ways to unlock this thermal propagation regime on any given material. Being able to control heat propagation through the properties of waves opens new ways to design the upcoming generations of thermal devices, in a similar way to the already established developments for light. “Specifically, the second sound thermal regime could be used to rethink how we deal with waste heat”, he adds.

From a theoretical point of view, “these findings allow unifying the current theoretical model, which until now considered that materials where this type of wave-like behavior was observed (such as graphite) were very different from the semiconductor materials currently used in the manufacture of electronic chips (such as silicon and germanium)” says F. Xavier Álvarez, researcher at the UAB. “Now all these materials can be described using the same equations. This observation establishes a new theoretical framework that may allow in the not too distant future a significant improvement in the performance of our electronic devices,” adds Álvarez.

Featured image: Amplified frequency-domain thermoreflectance setup used to study the existence of second sound in germanium. Two different lasers are focused onto the surface of the samples using a microscope objective. A rather large combination of optical elements allows to control and modify the spot size and shape, as well as the power and harmonic modulation of the lasers. Cold nitrogen gas is used for better visualization of the lasers optical path. © ICMAB, CSIC

Reference: Albert Beardo, Miquel López-Suárez, Luis Alberto Pérez, Lluc Sendra, Maria Isabel Alonso, Claudio Melis, Javier Bafaluy, Juan Camacho, Luciano Colombo, Riccardo Rurali, Francesc Xavier Alvarez, Juan Sebastián Reparaz, “Observation of second sound in a rapidly varying temperature field in Ge”, Science Advances  30 Jun 2021: Vol. 7, no. 27, eabg4677 DOI: 10.1126/sciadv.abg4677

Provided by UAB

Why Deep Freezing Iron-based Materials Makes Them Both Magnetic & Superconducting (Physics)

Physicists at Bath have uncovered a new mechanism for enabling magnetism and superconductivity to co-exist in the same material.

Physicists at the University of Bath, in collaboration with researchers from the USA, have uncovered a new mechanism for enabling magnetism and superconductivity to co-exist in the same material. Until now, scientists could only guess how this unusual coexistence might be possible. The discovery could lead to applications in green energy technologies and in the development of superconducting devices, such as next-generation computer hardware.

As a rule, superconductivity (the ability of a material to pass an electrical current with perfect efficiency) and magnetism (seen at work in fridge magnets) make poor bedfellows because the alignment of the tiny electronic magnetic particles in ferromagnets generally leads to the destruction of the electron pairs responsible for superconductivity. Despite this, the Bath researchers have found that the iron-based superconductor RbEuFe4As4, which is superconducting below -236°C, exhibits both superconductivity and magnetism below -258°C.

Physics postgraduate research student David Collomb, who led the research, explained: “There’s a state in some materials where, if you get them really cold – significantly colder than the Antarctic – they become superconducting. But for this superconductivity to be taken to next-level applications, the material needs to show co-existence with magnetic properties. This would allow us to develop devices operating on a magnetic principle, such as magnetic memory and computation using magnetic materials, to also enjoy the benefits of superconductivity.

“The problem is that superconductivity is usually lost when magnetism is turned on. For many decades, scientists have tried to explore a host of materials that have both properties in a single material, and material scientists have recently had some success fabricating a handful of such materials. However, so long as we don’t understand why the coexistence is possible, the hunt for these materials can’t be done with as fine a comb.

“This new research gives us a material that has a wide temperature range where these phenomena co-exist, and this will allow us to study the interaction between magnetism and superconductivity more closely and in great detail. Hopefully, this will result in us being able to identify the mechanism through which this co-existence can occur.”

In a study published in Physical Review Letters, the team investigated the unusual behaviour of RbEuFe4As4 by creating magnetic field maps of a superconducting material as the temperature was dropped. To their surprise, they found the vortices (the points in the superconducting material where the magnetic field penetrates) showed a pronounced broadening near the temperature of -258°C, indicating a strong suppression of superconductivity as the magnetism turned on.

crystals coasted in gold
On the left: a crystal coated in gold – the gold coating allows the magnetic imaging tool to get within nanometers of the material’s surface. On the right: a magnetic picture of a segment of the crystal showing the vortices (dark holes) that were studied. © University of Bath

These observations agree with a theoretical model recently proposed by Dr Alexei Koshelev at Argonne National Laboratory in the USA. This theory describes the suppression of superconductivity by magnetic fluctuations due to the Europium (Eu) atoms in the crystals. Here, the magnetic direction of each Eu atom begins to fluctuate and align with the others, as the material drops below a certain temperature. This causes the material to become magnetic. The Bath researchers conclude that while superconductivity is considerably weakened by the magnetic effect, it is not fully destroyed.

“This suggests that in our material, the magnetism and superconductivity are held apart from each other in their own sub-lattices, which only minimally interact,” said Mr Collomb.

“This work significantly advances our understanding of these rare coexisting phenomena and could lead to possible applications in the superconducting devices of the future. It will spawn a deeper hunt into materials that display both superconductivity and magnetism. We hope it will also encourage researchers in more applied fields to take some of these materials and make the next-generation computing devices out of them.

“Hopefully, the scientific community will gradually enter an era where we move from blue-sky research to making devices from these materials. In a decade or so, we could be seeing prototype devices using this technology that do a real job.”

The American collaborators for this project were the Argonne National Laboratory, Hofstra University and Northwestern University.

Featured image: Magnetism can be generated simply by passing a current through a wire, but how it interacts with other physical phenomena (such as superconductivity) is shrouded in mystery. © University of Bath

Reference: D. Collomb, S. J. Bending, A. E. Koshelev, M. P. Smylie, L. Farrar, J.-K. Bao, D. Y. Chung, M. G. Kanatzidis, W.-K. Kwok, and U. Welp, “Observing the Suppression of Superconductivity in RbEuFe4As4 by Correlated Magnetic Fluctuations”, Phys. Rev. Lett. 126, 157001 – Published 14 April 2021. DOI: https://doi.org/10.1103/PhysRevLett.126.157001

Provided by University of Bath

Scientists Report New Wideband Two-Dimensional Nonlinear Optical Materials and Devices (Chemistry)

Recently, Chinese scientists reported a new class of two-dimensional (2D) third-order nonlinear optical (NLO) materials, called metallated graphynes. The new material, exhibits broadband (at both 532 and 1064 nm) saturable absorption NLO property and high laser damage threshold.

Researchers prepared two free-standing mercurated graphyne nanosheets by applying an interface-assisted bottom-up method. The large-area nanosheets derived from the chemical growth have shown their layered molecular structural arrangement, controllable thickness and enhanced π-conjugation. The mercurated graphyne nanosheets are therefore having stable and outstanding broadband nonlinear saturable absorption properties.  

With the help of the absorption ability, the metallated graphynes are acting as saturable absorbers. And it has better pulse properties and Q-switched performances, especially comparing with traditional 2D materials (like graphene, black phosphorus).

The work reveals that the metallated graphyne materials can go beyond graphyne. The new material could not only be a new family of stable 2D carbon-rich materials under ambient conditions, but also possess unique properties and application prospects. It could be helpful in the future design of various structures for optoelectronic materials and devices.   

Besides, the nanosheets with controllable thickness and high transparency can be transferred on the optical glass and other substrates. It could be directly applied as free-standing films in optoelectronic devices.   

The new proposed nanosheet has advantages in optical property, mechanical processability and control of molecular dimensions. And this could be benefited the design of optoelectronic materials and fabrication of their devices in applications such as nonlinear optics, optical limiting, optical communications and so on. 

This work, published in Angewandte Chemie International Edition, was directed by the joint group of Prof. Wai-Yueng Wong from The Hong Kong Polytechnic University, Prof. XIE Zheng from the Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences, and Prof. WANG Zhengping from Shandong University. 

Featured image: Chemical Structures, Interface-assisted Preparation, and Nonlinear Optical Passively Q-switched Performances of Metallated Graphynes (Image by Wong et al.)

Reference: Dr. Linli Xu, Dr. Jibin Sun et al., “Metallated Graphynes as a New Class of Photofunctional 2D Organometallic Nanosheets”, Angewandte Chemie, Volume 133, Issue 20 p. 11427-11435. https://doi.org/10.1002/ange.202014835

Provided by Chinese Academy of Sciences

Research Team Develops New Class of Soft Materials (Material Science)

Innovation Opens New Possibilities for 3D-Printing Human Tissue

“I think you’re on mute.” This was the most-used phrase of 2020, according to Human Resources Online. Emblazoned on T-shirts and embossed on coffee-mugs, we used the meme to make fun of ourselves while learning video-conferencing tools like Zoom and Microsoft’s Teams.

But for the more than 7 million Americans who suffer from vocal disorders, not being heard is a serious matter. Many people who have normal speaking skills have great difficulty communicating when their voice box, the larynx, fails. This can occur if the vocal cords, the two bands of smooth muscle tissue in the larynx, suffer damage from an accident, surgical procedure, viral infection or cancer.

There is no replacement for the vocal cords when the damage is severe or permanent. Now, a team of materials scientists at the University of Virginia School of Engineering has developed a soft material with promise of new treatments in the future. Their novel soft material, called an elastomer, is very stretchable and 10,000 times softer than a conventional rubber, matching the mechanical properties of vocal cords. The elastomer can be 3D printed for use in health care.

LIHENG CAI, assistant professor of materials science and engineering and chemical engineering, oversees this research. Cai also holds a courtesy appointment in biomedical engineering and leads the SOFT BIOMATTER LAB at UVA. Cai’s lab works to understand and control the interactions between active soft materials, such as responsive polymers or biological gels, and living systems, such as bacteria or cells and tissues in the human body.

Cai’s post-doctoral researcher Shifeng Nian and Ph.D. student Jinchang Zhu co-first authored the team’s paper, “THREE-DIMENSIONAL PRINTABLE, EXTREMELY SOFT, STRETCHABLE, AND REVERSIBLE ELASTOMERS FROM MOLECULAR ARCHITECTURE-DIRECTED ASSEMBLY,” published and featured as a COVER ARTICLE in Chemistry of Materials. Collaborators include Baoxing Xu, associate professor of mechanical and aerospace engineering at UVA, who conducted simulations to understand the deformation of 3D-printed, extremely soft structures.

The team developed a novel strategy to make such 3D-printable soft elastomers. They used a new type of polymer with a special architecture reminiscent of the bottlebrush for cleaning small glassware, but on the molecular scale. The bottlebrush-like polymer, when linked to form a network, enables extremely soft materials mimicking biological tissues.

Cai began to prove the potential of bottlebrush polymers as a postdoctoral fellow at Harvard University’s John H. Paulson School of Engineering and Applied Sciences. Cai’s collaborative engineering of soft yet ‘dry’ rubber was published in ADVANCED MATERIALS.

Now, Cai and his team have developed a new way to use strong – yet reversible depending upon the temperature – associations to crosslink bottlebrush-like polymers to form a rubber. The idea is to use chemical synthesis to append one glassy polymer to each end of a bottlebrush-like polymer. Such glassy polymers spontaneously self-organize to form nanoscale spheres that are the same as that of plastic water bottles. They are rigid at room temperature but melt at high temperature; this can be exploited to 3D print soft structures. 

Their material’s elasticity can be fine-tuned from approximately 100 to 10,000 pascals on the scale of pressure the material can withstand. The lower limit, approximately 100 pascals, is a million times softer than plastics and 10,000 times softer than conventional 3D-printable elastomers. Moreover, they can be stretched up to 600%.

“Their extreme softness, stretchiness and thermostability bode well for future applications,” Cai said.

Cai credits Nian for developing the chemistry for synthesizing bottlebrush polymers with precisely controlled architecture to prescribe the softness and stretchability of elastomers. The elastomer can be used as an ink in a 3D printer to create a geometric shape with the qualities of rubber.

The 3D printer itself is about the size of a dorm room refrigerator. Zhu custom-designed the nozzle for the extruder system that shoots the materials in a prescribed amount in a 3D space, guided by a computer program specific to the object desired.

Nian earned his Ph.D. in chemistry from UVA in 2018, and joined Cai’s Soft Biomatter lab as a post-doc. “Dr. Cai’s group gives me an opportunity to expand my research from classical chemistry to materials development; we’re inventing a lot of cool materials with special mechanical, electrical and optical properties,” Nian said.

What’s cool about the team’s soft material is its ability to self-organize and assemble as each drop is deposited. When the silicone-based material is first loaded into the ink cartridge, it has the consistency of honey, half solid and half liquid. As printing progresses, the solvent binds the layers and then evaporates to seamlessly build the object. Moreover, you can re-do it if you make any mistakes, as the material is 100% reprocessable and recyclable.

“Conventional 3D-printable elastomers are intrinsically stiff; the process of printing often requires external mechanical support or post-treatment,” Cai said. “Here, we demonstrate our elastomer’s applicability as inks for direct-write printing 3D structures.”

Ph.D. student Jinchang Zhu calibrates the 3D printer.

To study the way the material’s molecules interconnect, Cai’s team collaborated with Guillaume Freychet and Mikhail Zhernenkov, beamline scientists at the U.S. Department of Energy’s Brookhaven National Laboratory. They conducted experiments using the NATIONAL SYNCHROTRON LIGHT SOURCE II’s  sophisticated X-ray tool, specifically the soft matter interfaces beamline, to reveal the inner makeup of the printed materials without damaging the samples.

“The SMI beamline is ideally suited for this type of research due to its high x-ray beam intensity, excellent energy and momentum transfer tunability, and very low background. Working with Cai’s team, we were able to see how the bottlebrush-like polymer assemble into a cross-linked network,” Zhernenkov said.

Cai estimates that the team is two or three years away from seeing their elastomers in practical use, an accelerated pace enabled by the team’s 3D-printing method. Sometimes called additive manufacturing, 3D printing is a research strength of UVA’s Department of Materials Science and Engineering; researchers in this arena seek to understand the physics underlying additive manufacturing processes as they create new material systems.

Improving health is just one motivator for their research.

“We believe our findings will stimulate the development of new soft materials as inks for 3D printing, which can be the basis for a broad range of adaptive devices and structures such as sensors, stretchable electronics and soft robotics,” Cai said.

A National Science Foundation CAREER award and ACS Petroleum Research Fund Doctoral New Investigator award support Cai’s research on the SUPER RUBBER he envisions for biomedical implants and tissue engineering, among other applications. His research team is continuing to work on printability to produce objects that are closer to their desired shape.

Featured image: Post-doctoral researcher Shifeng Nian seeks to understand and manipulate the properties of soft materials. © University of Virginia

Provided by University of Virginia

Materials Scientists Discover Faster, More Efficient Way to Manufacture Multifunctional Vascular Materials (Material Science)

Beckman researchers use frontal polymerization to manufacture environmentally-adaptive multifunctional materials in a matter of minutes instead of days.

Developing self-healing materials is nothing new for Nancy Sottos, Swanlund Endowed Chair, head of the Department of Materials Science and Engineering, and lead of the Autonomous Materials Systems Group.

Drawing inspiration from biological circulatory systems — such as blood vessels or the leaves on a tree — University of Illinois researchers have worked on developing vascularized structural composites for more than a decade, creating materials that are lightweight and able to self-heal and self-cool.

But now, a team of Beckman researchers led by Sottos and Mayank Garg, postdoctoral research associate and lead author of the newly published Nature Communications paper, “Rapid Synchronized Fabrication of Vascularized Thermosets and Composites,” have shortened a two-day manufacturing process to approximately two minutes by harnessing frontal polymerization of readily available resins.

“For the past several years we’ve been looking for ways to make vascular networks in high-performance materials,” Sottos said. “This is a real breakthrough for making vascular networks in structural materials in a way that saves a lot of time and saves a lot of energy.”

Synchronized manufacturing of a bioinspired structure with a hierarchical vascular network. © Beckman Institute

Garg said the simplest way to understand their work is to picture the composition of a leaf with its internal channels and structural networks. Now, imagine that the leaf is made from a tough structural material; inside, fluid flows through different spouts and channels of its interconnected vasculature. In the case of the researchers’ composites, the liquid is capable of a variety of functions, such as cooling or heating in response to extreme environments.

“We want to create these life-like structures, but we also want them to maintain their performance over substantially longer times compared to existing infrastructure by adopting an approach biology uses ubiquitously,” Garg said. “Trees have networks for transporting nutrients and water from the ground against gravity and transporting synthesized food from the leaf to the rest of the tree. The fluids flow in both directions to regulate temperature, grow new material, and repair existing material over the entire lifecycle of the tree. We try to replicate these dynamic functions in a non-biological system.”

However, creating these complex materials has historically been a long, daunting process for the Autonomous Materials Systems Group. In previous research on self-healing materials, researchers needed a hot oven, vacuum, and at least a day to create the composites. The lengthy manufacturing cycle involved curing the host material and subsequently burning or vaporizing a sacrificial template to leave behind hollow, vascular networks. Sottos said the latter process can take 24 hours. The more complicated the vascular network, the more difficult and time-consuming it is to remove.

To create the host materials, scientists opt for frontal polymerization, a reaction-thermal diffusion system that uses the generation and diffusion of heat to promote two different chemical reactions concurrently. The heat is created internally during solidification of the host and surplus heat deconstructs an embedded template in tandem to manufacture the vascular material. This means the researchers are able to shorten the process by combining two steps into one, creating the vascular networks as well as the polymerized host material without an oven. Additionally, the new process enables researchers to have more control in the creation of the networks, meaning the materials could have increased complexity and function in the future.

“With this research, we’ve figured out how to put in vascular networks by using frontal polymerization to drive the vascularization,” Sottos said. “It gets done in minutes now instead of days — and we don’t have to put it in an oven.”

Self-healing materials can be beneficial wherever strong materials are essential to maintain function under sustained damage — such as the construction of a skyscraper. But in the case of the researchers, the most likely applications are for planes, spaceships, and even the International Space Station. Sottos explained materials produced in this manner could be commercially manufactured in five to 10 years, though the researchers note that all required materials and processing equipment are currently commercially available.

Beckman Institute Director Jeff Moore, a Stanley O. Ikenberry Endowed Chair of chemistry, as well as Bliss Professor of aerospace engineering and Executive Associate Dean of The Grainger College of Engineering Philippe Geubelle were also involved in the project.

From a computational standpoint, Geubelle explained that he was able to capture the frontal polymerization and endothermic phase change taking place in the sacrificial templates.

“We performed adaptive, transient, nonlinear finite element analyses to study this competition and determine the conditions under which this simultaneous frontal polymerization and vascularization of the gel can be achieved,” he said. “This technology will lead to a more energy efficient and substantially faster way to create composites with complex microvascular networks.”

Mayank Garg © Beckman Institute

Thanks to the team’s interdisciplinary discovery, dynamic multifunctional materials are now easier to manufacture than ever before.

“This research is a combination of experimental work as well as computational work,” Garg said. “It requires synchronized communication among team members from various disciplines — chemistry, engineering, and materials science — to overhaul traditional non-sustainable manufacturing strategies.”

“There’s nothing better than to see ideas bubble up from students and postdocs in the AMS group resulting from interactions and joint group meetings,” Moore added. “The Moore Group has studied chain unzipping depolymerization reactions for years. I was delighted when I learned that the AMS team recognized how the thermal energy produced in a heat-evolving polymerization reaction could be synced to chain unzipping depolymerization in another material for the purpose of fabricating channels. The first time I saw Mayank’s results, I thought to myself, ‘I wish I’d have thought of that idea.’

Featured image: Nancy Sottos © Beckman Institute

Editor’s note: The paper “Rapid Synchronized Fabrication of Vascularized Thermosets and Composites,” can be found at https://doi.org/10.1038/s41467-021-23054-7.

Provided by Beckman Institute

New Frontier For 3D Printing: Developed Soft Materials That Repair Themselves (Material Science)

The scientific community is concentrating many studies on the multiple applications of hydrogels , polymeric materials containing large quantities of water, potentially capable of reproducing the characteristics of biological tissues. This aspect is of particular importance in the field of regenerative medicine , which has long recognized and is using the potential of these materials. In order to be effectively used to replace organic tissues, hydrogels must meet two fundamental requirements: they must have a high geometric complexity and be able to self-repair themselves following damage, just like living tissues.

The development of these materials can now be easier and cheaper thanks to the use of 3D printing: the researchers of the MP4MNT (Materials and Processing for Micro and Nanotechnologies) team of the Department of Applied Science and Technology of the Politecnico , coordinated by Professor Fabrizio Pirri , have demonstrated for the first time the possibility of manufacturing hydrogels with complex architectures that can self-repair following a tear thanks to light-activated 3D printing . The research was published by the prestigious journal Nature Communication in an article entitled “3D-printed self-healing hydrogels via Digital Light Processing” ( DOI 10.1038 / s41467-021-22802-z)

Self-healing of complex geometries© Politecnico di Torino

In reality, hydrogels with self-healing or modelable properties in complex architectures through 3D printing had already been created in the laboratory, but in this case it is a solution that encompasses both characteristics, namely the complexity of the architecture and the ability to regenerate afterwards. of damage.

Furthermore, the hydrogel was made using materials available on the market, processed by a commercial printer , thus making the proposed approach extremely flexible and potentially applicable everywhere, with new development possibilities both in the biomedical field and in that of soft-robotics.

The research was developed as part of the HYDROPRINT3D doctoral project, funded by the Compagnia di San Paolo from the “Joint Projects with Top University” initiative and conducted by the doctoral student Matteo Caprioli , under the supervision of DISAT researcher Ignazio Roppolo , in collaboration with the research group of Professor Magdassi of the Hebrew University of Jerusalem (Israel).

“For several years – says Ignazio Roppolo – within the MP4MNT group a research unit has been created, coordinated by me and Dr. Annalisa Ch Japan, which is specifically concerned with developing new materials that can be processed through light-activated 3D printing. 3D printing is able to offer a synergistic effect between the design of the object and the intrinsic properties of the materials, allowing to obtain artifacts with unique characteristics. In our perspective, it is necessary to take advantage of this synergy to best develop the potential of 3D printing so that it can truly become an element present in our everyday life. And this study falls exactly in the wake of this philosophy ”.

This research represents a first step towards the development of highly complex devices that can exploit complex geometries and intrinsic self-repair properties in various fields. In particular, once the biocompatibility studies in progress at the Polytechnic Interdepartmental Polito BIO Med Lab have been refined , it will be possible to use these structures both for basic studies on cellular mechanisms and for applications in the field of regenerative medicine.

Reference: Caprioli, M., Roppolo, I., Chiappone, A. et al. 3D-printed self-healing hydrogels via Digital Light Processing. Nat Commun 12, 2462 (2021). https://doi.org/10.1038/s41467-021-22802-z

Provided by Politecnico Di Torino

Better Metric For Thermoelectric Materials Means Better Design Strategies (Material Science)

New quantity helps experimentally classify dimensionality of thermoelectric materials

Researchers from Tokyo Metropolitan University have shown that a quantity known as “thermoelectric conductivity” is an effective measure for the dimensionality of newly developed thermoelectric nanomaterials. Studying films of semiconducting single-walled carbon nanotubes and atomically thin sheets of molybdenum sulfide and graphene, they found clear distinctions in how this number varies with conductivity, in agreement with theoretical predictions in 1D and 2D materials. Such a metric promises better design strategies for thermoelectric materials.

Thermoelectric devices take differences in temperature between different materials and generate electrical energy. The simplest example is two strips of different metals welded together at both ends to form a loop; heating one of the junctions while keeping the other cool creates an electrical current. This is called the Seebeck effect. Its potential applications promise effective usage of the tremendous amount of power that is wasted as dissipated heat in everyday life, whether it be in power transmission, industrial exhaust, or even body heat. In 1993, it was theorized that atomically thin, one-dimensional materials would have the ideal mix of properties required to create efficient thermoelectric devices. The resulting search led to nanomaterials such as semiconducting single-walled carbon nanotubes (SWCNTs) being applied.

However, there was an ongoing issue that prevented new designs and systems from being accurately characterized. The key properties of thermoelectric devices are thermal conductivity, electrical conductivity, and the Seebeck coefficient, a measure of how much voltage is created at the interface between different materials for a given temperature difference. As material science advanced into the age of nanotechnology, these numbers weren’t enough to express a key property of the new nanomaterials that were being created: the “dimensionality” of the material, or how 1D, 2D or 3D-like the material behaves. Without a reliable, unambiguous metric, it becomes difficult to discuss, let alone optimize new materials, particularly how the dimensionality of their structure leads to enhanced thermoelectric performance.

To tackle this dilemma, a team led by Professor Kazuhiro Yanagi of Tokyo Metropolitan University set out to explore a new parameter recently flagged by theoretical studies, the “thermoelectric conductivity.” Unlike the Seebeck coefficient, the team’s theoretical calculations confirmed that this value varied differently with increased conductivity for 1D, 2D and 3D systems. They also confirmed this experimentally, preparing thin films of single-walled carbon nanotubes as well as atomically thin sheets of molybdenum sulfide and graphene, archetypal materials in 1D and 2D respectively. Measurements conclusively showed that the thermoelectric conductivity of the 1D material decreased at higher values of conductivity, while the curve for 2D materials plateaued. They also note that this demonstrates how the dimensionality of the material is retained even when the material is prepared in macroscopic films, a great boost for efforts to leverage the specific dimensionality of certain structures to improve thermoelectric performance.

Combined with theoretical calculations, the team conclude that high thermoelectric conductivity, high conventional electrical conductivity, and low thermal conductivity are key goals for the engineering of new devices. They hope these measurable, tangible targets will bring much needed clarity and unity to the development of state-of-the-art thermoelectric devices.

This work was supported by JSPS KAKENHI Grants-in-Aid for Scientific Research (17H06124, 17H01069, 18H01816, 19J21142, 20H02573, 20K15117, 26102012, 25000003, 19K22127, 19K15383, 20H05189) and the JST CREST Program (MJCR17I5).

Featured image: Theoretical calculations of Seebeck coefficient and thermoelectric conductivity for 1D, 2D and 3D materials: (a)-(c) show how the Seebeck coefficient varies for 1D, 2D and 3D materials, while (d)-(f) show the thermoelectric conductivity for the same systems. No major changes in the shape of the curves are seen for (a)-(c); drastic changes are seen for (d)-(e) beyond a threshold range marked in yellow, making thermoelectric conductivity a much more sensitive, unambiguous measure for dimensionality. © Tokyo Metropolitan University

Reference: Yota Ichinose, Manaho Matsubara, Yohei Yomogida, Akari Yoshida, Kan Ueji, Kaito Kanahashi, Jiang Pu, Taishi Takenobu, Takahiro Yamamoto, and Kazuhiro Yanagi, “One-dimensionality of thermoelectric properties of semiconducting nanomaterials”, Phys. Rev. Materials 5, 025404 – Published 26 February 2021. https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.5.025404

Provided by Tokyo Metropolitan University