Categorie: Materiale noi cu proprietati fizicomecanice noi

Nu sunt necesare baterii: firele de nanotehnologie cu recoltare de energie generează energie electrică (No batteries required: Energy-harvesting nanotechnology yarns generate electricity )

recoltarea energiei din mișcarea undelor oceanice sau Fluctuațiile de temperatură. Când ați cusut într-o cămașă, aceste fire au servit ca un monitor de respirație auto-alimentat.Firele de nanotuburi cu colaci de carbon, create la Universitatea din Texas, la Dallas, și care sunt înregistrate aici cu un microscop electronic de scanare, generează energie electrică atunci când sunt întinse sau răsucite.

Posted: Aug 25, 2017

No batteries required: Energy-harvesting nanotechnology yarns generate electricity

(Nanowerk News) An international research team led by scientists at The University of Texas at Dallas and Hanyang University in South Korea has developed high-tech yarns that generate electricity when they are stretched or twisted.
In a study published in the Aug. 25 issue of the journal Science („Harvesting electrical energy from carbon nanotube yarn twist”), researchers describe „twistron” yarns and their possible applications, such as harvesting energy from the motion of ocean waves or from temperature fluctuations. When sewn into a shirt, these yarns served as a self-powered breathing monitor.
Coiled carbon nanotube yarn
Coiled carbon nanotube yarns, created at the University of Texas at Dallas and imaged here with a scanning electron microscope, generate electrical energy when stretched or twisted. (Image: University of Texas at Dallas)
„The easiest way to think of twistron harvesters is, you have a piece of yarn, you stretch it, and out comes electricity,” said Dr. Carter Haines, associate research professor in the Alan G. MacDiarmid NanoTech Institute at UT Dallas and co-lead author of the article. The article also includes researchers from South Korea, Virginia Tech, Wright-Patterson Air Force Base and China.

Yarns Based on Nanotechnology
The yarns are constructed from carbon nanotubes, which are hollow cylinders of carbon 10,000 times smaller in diameter than a human hair. The researchers first twist-spun the nanotubes into high-strength, lightweight yarns. To make the yarns highly elastic, they introduced so much twist that the yarns coiled like an over-twisted rubber band.
In order to generate electricity, the yarns must be either submerged in or coated with an ionically conducting material, or electrolyte, which can be as simple as a mixture of ordinary table salt and water.
„Fundamentally, these yarns are supercapacitors,” said Dr. Na Li, a research scientist at the NanoTech Institute and co-lead author of the study. „In a normal capacitor, you use energy – like from a battery – to add charges to the capacitor. But in our case, when you insert the carbon nanotube yarn into an electrolyte bath, the yarns are charged by the electrolyte itself. No external battery, or voltage, is needed.”
When a harvester yarn is twisted or stretched, the volume of the carbon nanotube yarn decreases, bringing the electric charges on the yarn closer together and increasing their energy, Haines said. This increases the voltage associated with the charge stored in the yarn, enabling the harvesting of electricity.
Stretching the coiled twistron yarns 30 times a second generated 250 watts per kilogram of peak electrical power when normalized to the harvester’s weight, said Dr. Ray Baughman, director of the NanoTech Institute and a corresponding author of the study.
„Although numerous alternative harvesters have been investigated for many decades, no other reported harvester provides such high electrical power or energy output per cycle as ours for stretching rates between a few cycles per second and 600 cycles per second.”

Lab Tests Show Potential Applications
In the lab, the researchers showed that a twistron yarn weighing less than a housefly could power a small LED, which lit up each time the yarn was stretched.
To show that twistrons can harvest waste thermal energy from the environment, Li connected a twistron yarn to a polymer artificial muscle that contracts and expands when heated and cooled. The twistron harvester converted the mechanical energy generated by the polymer muscle to electrical energy.
„There is a lot of interest in using waste energy to power the Internet of Things, such as arrays of distributed sensors,” Li said. „Twistron technology might be exploited for such applications where changing batteries is impractical.”
The researchers also sewed twistron harvesters into a shirt. Normal breathing stretched the yarn and generated an electrical signal, demonstrating its potential as a self-powered respiration sensor.
„Electronic textiles are of major commercial interest, but how are you going to power them?” Baughman said. „Harvesting electrical energy from human motion is one strategy for eliminating the need for batteries. Our yarns produced over a hundred times higher electrical power per weight when stretched compared to other weavable fibers reported in the literature.”

Electricity from Ocean Waves
„In the lab we showed that our energy harvesters worked using a solution of table salt as the electrolyte,” said Baughman, who holds the Robert A. Welch Distinguished Chair in Chemistry in the School of Natural Sciences and Mathematics. „But we wanted to show that they would also work in ocean water, which is chemically more complex.”
In a proof-of-concept demonstration, co-lead author Dr. Shi Hyeong Kim, a postdoctoral researcher at the NanoTech Institute, waded into the frigid surf off the east coast of South Korea to deploy a coiled twistron in the sea. He attached a 10 centimeter-long yarn, weighing only 1 milligram (about the weight of a mosquito), between a balloon and a sinker that rested on the seabed.
Every time an ocean wave arrived, the balloon would rise, stretching the yarn up to 25 percent, thereby generating measured electricity.
Even though the investigators used very small amounts of twistron yarn in the current study, they have shown that harvester performance is scalable, both by increasing twistron diameter and by operating many yarns in parallel.
„If our twistron harvesters could be made less expensively, they might ultimately be able to harvest the enormous amount of energy available from ocean waves,” Baughman said. „However, at present these harvesters are most suitable for powering sensors and sensor communications. Based on demonstrated average power output, just 31 milligrams of carbon nanotube yarn harvester could provide the electrical energy needed to transmit a 2-kilobyte packet of data over a 100-meter radius every 10 seconds for the Internet of Things.”
Source: University of Texas at Dallas

Read more: No batteries required: Energy-harvesting nanotechnology yarns generate electricity

2D van der Waals heterostructuri cu cuplaj optic-electronice-magnetic (2D van der Waals heterostructures with tunable optical-electronic-magnetic coupling )

Deoarece vdWH-urile noastre au răspuns multifuncțional extern dependent de stimulente (cum ar fi piezoresistance, electroresistiv și magnetoconductanță), ele pot fi aplicate pentru senzori multifuncționali”, spune Ren. „De exemplu, vdWHs prezintă o sensibilitate excelentă pe presiune, cu un coeficient de piezoresistance ridicat de -4,4 × 10 -6 Pa -1 „.
„Heterostructurile organice vdW formate prin combinarea a două perechi de complexe CT organice cu cuplaj interfacial de reglabil arată avantaje copleșitoare față de o singură componentă”, adaugă el. „Ele prezintă proprietăți fizico-chimice unice care acoperă o mare parte a subiectelor opto-electrice-magnetice-mecanice.”

Posted: Aug 23, 2017

2D van der Waals heterostructures with tunable optical-electronic-magnetic coupling

(Nanowerk Spotlight) Ever since the first demonstration of graphene in 2004, the scientific community has pursued the possibility of building man-made materials by artificial stacking of different ultrathin materials one on top of the other. These materials are called van der Waals heterostructures.Due to their unique interlayer coupling and optoelectronic properties, these materials are of considerable interest for the next generation nanoelectronics.Conventional 2D heterostructures usually are composed of two layers of opposite charge carrier type using inorganic materials. One of the challenges when creating 2D heterostructures is the painstaking stacking of the individual components on top of each other.Researchers have now found, for the first time, that there can also be charge transfer (CT) induced interfacial coupling between two different pairs of organic CT layers.Moreover, external stimuli can be harnessed to tune the interfacial coupling to control the physical properties of organic van der Waals heterostructures (vdWHs).”The interface of heterostructures can provide many possibilities to generate new phenomena,” Shenqiang Ren, an Associate Professor in the Mechanical Engineering at Temple University, tells Nanowerk. „Our group has years of investigation on organic CT complexes. As the interface between two layers of organic CT complex is different from single phase, such as intra-layer and inter-layer CT interactions, it is exciting to investigate the interfacial coupling within organic van der Waals heterostructures.”The most significant finding in this work, just published in Nature Communications („Tunable two-dimensional interfacial coupling in molecular heterostructures”), is that the researchers found strong and anisotropic interfacial charge transfer coupling in two-dimensional organic van der Waals heterostructures.Organic van der Waals heterostructures exhibit multi-stimuli controlled physical propertiesOrganic van der Waals heterostructures exhibit multi-stimuli controlled physical properties. (Image: Dr. B Xu)As the team (a collaboration between Ren’s group and Prof. Michael L Klein’s High-Performance Computing group at Temple University) points out, such interfacial CT coupling enables external stimuli controlled physical properties in organic vdWHs.To prepare 2D vdWH, researchers widely use a conventional chemical vapor deposition approach. However, the weak interlayer interaction between the monolayer 2D film and the substrate leads to island growth rather than continuous monolayers.The approach demonstrated by the Temple University team allows for large-scale (mm2 range) assembly of free-standing 2D CT heterostructures with controlled orientation and unique physicochemical properties. As they note, the interfacial coupling can be tuned in over a large range by external fields (ferroelectric and magnetic) with strong enhancement of current and capacitance, due to the coupling across two CT pairs along the vertical and horizontal orientations.”As our vdWHs show multifunctional external stimuli dependent response (such as piezoresistance, electroresistive and magnetoconductance), they can be applied for multifunctional sensors,” says Ren. „For example, the vdWHs exhibit excellent pressure dependent sensitivity with a high piezoresistance coefficient of -4.4×10-6 Pa-1.””The organic vdW heterostructures formed by the combination of two pairs of organic CT complex with tunable interfacial coupling show overwhelming advantages over single component,” he adds. „They exhibit unique physicochemical properties covering vast majority of opto-electrical-magnetic-mechanical topics.”The researchers’ next steps will be focused on the synthesis of wafer-scale two-dimensional vdWHs towards artificial intelligence applications.Since the organic vdWHs demonstrate a fast response to external stimuli with the change of conductivity, this opens up the practical applications for multi-stimuli sensors.By Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology and Nanotechnology: The Future is Tiny. Copyright © Nanowerk

Read more: 2D van der Waals heterostructures with tunable optical-electronic-magnetic coupling

Celulele de biocombustibili extensibile extrag energia de la transpirație la dispozitive portabile de putere (Stretchable biofuel cells extract energy from sweat to power wearable devices)

Celulele de biocombustibili sunt echipate cu o enzimă care oxidează acidul lactic prezent în transpirația umană pentru a genera curent. Acest lucru transformă transpirația într-o sursă de energie.

Read more: Stretchable biofuel cells extract energy from sweat to power wearable devices

Posted: Aug 22, 2017

Stretchable biofuel cells extract energy from sweat to power wearable devices

(Nanowerk News) A team of engineers has developed stretchable fuel cells that extract energy from sweat and are capable of powering electronics, such as LEDs and Bluetooth radios. The biofuel cells generate 10 times more power per surface area than any existing wearable biofuel cells. The devices could be used to power a range of wearable devices.
The epidermal biofuel cells are a major breakthrough in the field, which has been struggling with making the devices that are stretchable enough and powerful enough. Engineers from the University of California San Diego were able to achieve this breakthrough thanks to a combination of clever chemistry, advanced materials and electronic interfaces. This allowed them to build a stretchable electronic foundation by using lithography and by using screen-printing to make 3D carbon nanotube-based cathode and anode arrays.
The biofuel cells are equipped with an enzyme that oxidizes the lactic acid present in human sweat to generate current. This turns the sweat into a source of power.
Flexible, Stretchable Biofuel Cell
The biofuel cell can stretch and flex, conforming to the human body. (Image: University of California San Diego)
Engineers report their results in the June issue of Energy & Environmental Science („Soft, stretchable, high power density electronic skin-based biofuel cells for scavenging energy from human sweat „). In the paper, they describe how they connected the biofuel cells to a custom-made circuit board and demonstrated the device was able to power an LED while a person wearing it exercised on a stationary bike. Professor Joseph Wang, who directs the Center for Wearable Sensors at UC San Diego, led the research, in collaboration with electrical engineering professor and center co-director Patrick Mercier and nanoegnineering professor Sheng Xu, both also at the Jacobs School of Engineering UC San Diego.

Islands and bridges
To be compatible with wearable devices, the biofuel cell needs to be flexible and stretchable. So engineers decided to use what they call a „bridge and island” structure developed in Xu’s research group. Essentially, the cell is made up of rows of dots that are each connected by spring-shaped structures. Half of the dots make up the cell’s anode; the other half are the cathode. The spring-like structures can stretch and bend, making the cell flexible without deforming the anode and cathode.
The basis for the islands and bridges structure was manufactured via lithography and is made of gold. As a second step, researchers used screen printing to deposit layers of biofuel materials on top of the anode and cathode dots.

Increasing energy density
The researchers’ biggest challenge was increasing the biofuel cell’s energy density, meaning the amount of energy it can generate per surface area. Increasing energy density is key to increasing performance for the biofuel cells. The more energy the cells can generate, the more powerful they can be.
„We needed to figure out the best combination of materials to use and in what ratio to use them,” said Amay Bandodkar, one of the paper’s first authors, who was then a Ph.D. student in Wang’s research group. He is now a postdoctoral researcher at Northwestern University.
To increase power density, engineers screen printed a 3D carbon nanotube structure on top the anodes and cathodes. The structure allows engineers to load each anodic dot with more of the enzyme that reacts to lactic acid and silver oxide at the cathode dots. In addition, the tubes allow easier electron transfer, which improves biofuel cell performance.

Testing applications
The biofuel cell was connected to a custom-made circuit board manufactured in Mercier’s research group. The board is a DC/DC converter that evens out the power generated by the fuel cells, which fluctuates with the amount of sweat produced by a user, and turns it into constant power with a constant voltage.
Researchers equipped four subjects with the biofuel cell-board combination and had them exercise on a stationary bike. The subjects were able to power a blue LED for about four minutes.

Next steps
Future work is needed in two areas. First, the silver oxide used at the cathode is light sensitive and degrades over time. In the long run, researchers will need to find a more stable material.
Also, the concentration of lactic acid in a person’s sweat gets diluted over time. That is why subjects were able to light up an LED for only four minutes while biking. The team is exploring a way to store the energy produced while the concentration of lactate is high enough and then release it gradually.
Source: University of California – San Diego

Read more: Stretchable biofuel cells extract energy from sweat to power wearable devices

Un polițist de trafic pentru molecule(A traffic cop for molecule)

Oamenii de stiinta au creat un material rigid cu pori ultra-mici, cu diametrul mai mic de 7Å, (mai putin de un milion pe diametrul parului uman) care sunt ultra selectivi pe baza dimensiunilor. Porii permit oamenilor de stiinta sa proiecteze filme care pot diferentia molecule de dimensiuni asemanatoare bazate pe diferente mici in forma unei molecule.

Posted: Aug 22, 2017

A traffic cop for molecules

(Nanowerk News) Whether making a plastic coating or fuel, saving energy reduces costs. A vital target for cost savings is separating chemicals that are slightly different from each other. Nearly every processing industry must separate chemicals.
Scientists created a rigid material with ultra-small pores with diameter less than 7Å, (less than one-millionth the diameter of a human hair) that are ultra selective based on size. The pores enable scientists to design films that can differentiate between similarly sized molecules based on small differences in a molecule’s shape.
Membranes are separation agents. Scalable, efficient membranes reduce the cost and the environmental impact of producing vital commodities. How? The best membranes use a fraction of the energy of traditional approaches.
This study (Nature Materials, „Materials for next-generation molecularly selective synthetic membranes”) shows how a material with ultra small pores can be scaled to separate large quantities of molecules effectively by allowing an efficient sorting process based on size.
Carbon molecular sieves (CMS) with rigid ultra small pores
Carbon molecular sieves (CMS) with rigid ultra small pores (pores with diameter less than 7Å) and tailorable size and shape selectivity can enable the membrane-based separation of gas and liquid organic molecules.
Materials with rigid ultra small micropores provide selectivity that controls the motion of individual molecules to improve separation between similarly sized molecules by making it difficult for the “chubby ones” to get through.
Next-generation membranes based on these advanced materials overcome the deficiencies of conventional polymers to separate alkanes and alkenes, natural gases, and isomers. Additionally, these next-generation membranes will achieve solute-solute discrimination in organic solvents, which was also a problem for conventional methods.
Mass-producing molecular-scale separators must be economical. The key is to use hollow fibers with selective thin layers using an advanced version of the process to make textile fibers like those used to make inexpensive clothes.
The advanced version of this technology relies upon hundreds of “spinnerets” to produce the fibers in parallel and then collect them into a holder. When the fibers are extruded and contact air, a skin forms—like it does when glue is in contact with air. Because these advanced materials are scalable, scientists can create molecularly selective membranes that could provide large payoffs in reducing carbon dioxide emissions and energy consumption for a more sustainable future.
Source: U.S. Department of Energy, Office of Science
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Read more: A traffic cop for molecules

Eticheta inteligentă vă poate informa când să aruncați alimente și produse cosmetice (Smart label could let you know when to toss food and cosmetics )

Detectarea degradării produselor alimentare și cosmetice și a contaminării.Oamenii de știință au dezvoltat un senzor cu cost redus, portabil, pe suport de hârtie, care poate realiza toate aceste funcții cu rezultate ușor de citit.dezvoltând dispozitive pe bază de hârtie care își schimbă culoarea, în timp ce produsele cosmetice și produsele alimentare sunt proaste. Acești senzori se leagă de speciile reactive de oxigen pe care produsele se acumulează în timp ce îmbătrânesc și, eventual, strică.

Posted: Aug 22, 2017

Smart label could let you know when to toss food and cosmetics

(Nanowerk News) Detecting food and cosmetic spoilage and contamination. Identifying new medicinal plants in a remote jungle. Authenticating tea and wine. Scientists have developed a low-cost, portable, paper-based sensor that can potentially carry out all of these functions with easy-to-read results.
The researchers are presenting their results at the 254th National Meeting & Exposition of the American Chemical Society (ACS).
“I’ve always been interested in developing technologies that are accessible to both industry and the general population,” Silvana Andreescu, Ph.D., says. “My lab has built a versatile sensing platform that incorporates all the needed reagents for detection in a piece of paper. At the same time, it is adaptable to different targets, including food contaminants, antioxidants and free radicals that indicate spoilage.”
What sets Andreescu’s sensors apart from others, she says, are the nanostructures they use to catch and bind to compounds they’re looking for.
“Most people working on similar sensors use solutions that migrate on channels,” Andreescu says. “We use stable, inorganic particles that are redox active. When they interact with the substances we want to detect, they change color, and the intensity of the change tells us how concentrated the analyte is.”
Additionally, because all of the reagents needed to operate the device are incorporated in the paper, users don’t need to add anything other than the sample being tested.
The potential applications are wide-ranging. For example, much of her sensor work thus far has focused on detecting antioxidants in tea and wine. Andreescu, who’s at Clarkson University, and her colleagues have found that these products have unique antioxidant “fingerprints” that could be used for authentication purposes. The portable sensor could also be used by researchers exploring remote locations, such as the Amazon rainforest, in search of natural sources of antioxidants, she notes.
More recently, Andreescu extended her work to root out food contamination and environmental pollutants. One sensor prototype can spot ochratoxin A, a fungal toxin commonly found in a range of products, including cereals and coffee. She says this direction could be expanded further to look for salmonella and E. coli.
Now, her team is taking the work in yet another direction, developing paper-based devices that change color as cosmetics and food go bad. These sensors bind to the reactive oxygen species that products accumulate as they age and eventually spoil. Although testing for this application is still ongoing, Andreescu says this technology could one day be incorporated into smart labels that would tell consumers when to throw a product out.
Source: American Chemical Society

Read more: Smart label could let you know when to toss food and cosmetics

Materiale din ceramică ușoară un model pentru armura mai ușoara( Light-weight ceramic materials a model for lighter armor )

Modelul îmbunătățit sa dovedit a prezice mai bine rezistența unei game largi de ținte ceramice atunci când a fost împușcată de un proiectil cu tijă lungă la viteze de până la 3 km / s. Parametrii importanți ai performanței de penetrare a unei ținte ceramice au fost identificați prin acest efort de colaborare, care va ghida modul în care procesele de defecțiuni din ceramică pot fi controlate printr-o proiectare îmbunătățită a materialelor sau printr-o abordare a sistemelor multimateriale

Posted: Aug 18, 2017

Light-weight ceramic materials a model for lighter armor

(Nanowerk News) „While various ceramic materials possess high hardness, they fail easily when pulled apart. That is, when subjected to tensile forces. The amount of tension that these materials can withstand before failure, is a small fraction of the compression they can withstand. As a result, high velocity impact of bullets and fragments causes extensive cracking and fragmentation of the material, reducing its ability to fully utilize its superior hardness to resist complex stress states generated by the impact event,” explained Dr. Sikhanda Satapathy, of ARL’s Soldier Protection Sciences Branch.
side image of a laboratory projectile impacting a ceramic disk backed by polycarbonate
This is a side image of a laboratory projectile impacting a ceramic disk backed by polycarbonate captured using high speed cameras. (Image: US Army Research Laboratory)
Traditionally, the relationship between the granular material’s ability to withstand compression and its ability to resist shearing deformation, which causes material to change shape has been described by the Mohr-Coulomb model. This model approximates the material’s resistance to shearing deformation (shear strength) as a linear function of applied pressure. In reality, the shear strength does not increase linearly with pressure and will saturate at high pressures.
The University of Florida (UF) researchers developed a new model that describes the granular material response more accurately by studying the stress state at which a variety of ceramics fail as reported in the literature by various research teams (International Journal of Solids and Structures, „An improved dynamic expanding cavity model for high-pressure and high-strain rate response of ceramics”).
simulation of a laboratory projectile impacting ceramic backed by polycarbonate showing damage in the ceramic
This is a simulation of a laboratory projectile impacting ceramic backed by polycarbonate showing damage in the ceramic. (Image: US Army Research Laboratory)
The ARL and the UF team collaborated to employ this improved granular response model in conjunction with a dynamic cavity expansion modeling framework to capture the response of ceramics to the complex impact-induced stress state that includes compression, tension and shear. The dynamic cavity expansion modeling framework uses the pressure required to expand a cavity in an intact material to characterize its ability to resist deep penetration. This pressure, of course, is dependent on how the material responds to compression, tension and shear forces.
Due to the applicability of this new model to a broad class of ceramics, the need for expensive experiments to characterize penetration response is significantly reduced. The new penetration model improves the understanding of how brittle ceramic responds to high impact stress by fracturing and comminuting to granular like material, and increases modeling ability of penetration events.
Ceramic Disk
This is the rear surface of the ceramic disk viewed through the polycarbonate backer showing the failure of a ceramic disk as a result of impact by a laboratory projectile. (Image: US Army Research Laboratory)
The improved model has been shown to better predict the resistance of a wide range of ceramic targets when shot at by a long-rod projectiles at velocities up to 3km/s. The important material parameters for penetration performance of a ceramic target have been identified through this collaborative effort, which will guide how the failure processes in ceramic can be controlled through improved material design or through a multi-materials systems approach.
„Understanding the mechanics of material response to projectile impact generated stress conditions is crucial in this research,” Satapathy said.
Source: U.S. Army Research Laboratory

Read more: Light-weight ceramic materials a model for lighter armor

Fabricarea spumei de nitrura bor de hexagon pentru absorbtia de CO2( Fabricating hexagonal boron nitride foam for CO2 absorption)

Cu structura sa stratificată naturală, nitrura de bor hexagonală (h-BN) a apărut ca un material important 2D, având proprietăți excelente, cum ar fi stabilitatea la temperaturi ridicate, conductivitatea termică ridicată, precum și rezistența mecanică.Spuma are, de asemenea, o absorbție excelentă de CO 2 de 340% și depozitare la valori de presiune variabile, în principal datorită grupărilor funcționale cu azot și o suprafață crescută.
Mai mult, când este acoperit cu polidimetilsiloxan (PDMS), spuma prezintă proprietăți superioare de ecranare prin laser, rezistând unei cantități variate de energie laser, cu o degradare structurală minimă.

Posted: Aug 13, 2017

Fabricating hexagonal boron nitride foam for CO2 absorption

(Nanowerk News) In ACS Nano („Lightweight Hexagonal Boron Nitride Foam for CO2 Absorption”), scientists report a technique to fabricate lightweight 3D macroscopic porous structures formed from hexagonal boron nitride (h-BN) nanosheets.
With its naturally occurring layered structure, hexagonal boron nitride (h-BN) has emerged as an important 2D material, possessing excellent properties such as high temperature stability, high thermal conductivity, as well as mechanical strength.
The fabrication of three-dimensional porous nanostructures from interconnected two-dimensional (2D) materials such as graphene, clays, metal dichalcogenides, etc. has proven to be a promising technique to exploit their properties for several applications including catalysis, energy storage, biological and environmental applications, mechanical damping, and gas sequestration.
Characterization and morphology of h-BN/PVA foams
Characterization and morphology of h-BN/PVA foams. (a) Schematic representation depicting the h-BN nanosheets connected by poly(vinyl alcohol) (PVA) molecules. Typical chains contain 30 monomers (∼6.2 nm chain length). The PVA molecules act like a glue to link the nanosheets through van der Waals interactions between the hydroxyl groups in the PVA and boron/nitrogen atoms in the nanosheets. (b) Structural stability of the h-BN/PVA foam. (c) Mechanical stability of the lightweight foam carrying a vial without any visible degradation. (d) Stable structure of the foam when subjected to liquids. (e) Pristine foam disintegrates in the presence of water, whereas h-BN/PVA maintains its stable interconnected morphology (Rice University owns the copyright for the logo displayed and is used with permission). (f,g) Lowmagnification and high-magnification image of the foam. (© ACS) (click on image to enlarge)
In this new work, the researchers first liquid-phase-exfoliated h-BN in water to separate the layers, and then poly(vinyl alcohol) (PVA) was added (1-1.5 wt %), followed by in situ freeze-drying.
The hybrid structure exhibits enhanced mechanical properties, large surface area, and increased porosity.
According to the team, their fabrication method allows for the creation of intermolecular bonding between h-BN layers, where PVA acts like a bridge to link the individual layers, thus forming a network structure at the nanoscale.
Unlike pristine h-BN foams, which normally disintegrate immediately once removed from a freeze-drier, h-BN/PVA foams show a robust freestanding structure with favorable mechanical stability.
A detailed molecular dynamics study further verified and provided insights on the origins of such interconnections in improving the mechanical integrity.
The foam also exhibits excellent CO2 absorption of 340% and storage under varying pressure values, mainly due to nitrogen functional groups and an increased surface area.
Furthermore, when coated with polydimethylsiloxane (PDMS), the foam shows superior laser shielding properties by withstanding a varied amount of laser energy with minimal structural degradation.
By Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology and Nanotechnology: The Future is Tiny.

Read more: Fabricating hexagonal boron nitride foam for CO2 absorption

Pietrele de călcat din fier pentru o tehnologie mai bună purtată fără semiconductori(The iron stepping stones to better wearable tech without semiconductors )

Nanotuburile sunt structura principală a acestui material nou. BNNT-urile sunt mari izolatori și teribili la conducerea electricității. În timp ce la început pare o alegere ciudată pentru electronică, efectul izolator al BNNT-urilor este esențial pentru a preveni scurgerile și supraîncălzirea curentă. În plus, fluxul de electroni va apărea numai pe punctele metalice de pe BNNT-uri.

Posted: Feb 05, 2016

The iron stepping stones to better wearable tech without semiconductors

(Nanowerk News) The road to more versatile wearable technology is dotted with iron. Specifically, quantum dots of iron arranged on boron nitride nanotubes (BNNTs). The new material is the subject of a study published in Scientific Reports in February („New Flexible Channels for Room Temperature Tunneling Field Effect Transistors”), led by Yoke Khin Yap, a professor of physics at Michigan Technological University.
Yap says the iron-studded BNNTs are pushing the boundaries of electronics hardware. The transistors modulating electron flow need an upgrade.
Iron-dotted boron nitride nanotubes
Iron-dotted boron nitride nanotubes, made in Yoke Khin Yaps’ lab at Michigan Tech, could make for better wearable tech because of their flexibility and electronic behaviors. (Image: Michigan Tech, Sue Hill)
“Look beyond semiconductors,” he says, explaining that materials like silicon semiconductors tend to overheat, can only get so small and leak electric current.
The key to revamping the fundamental base of transistors is creating a series of stepping-stones that use quantum tunneling.
quantum tunneling on bendable nanotubes
Using a transmission electron microscope, Yoke Khin Yap and his research team observed quantum tunneling on bendable nanotubes. The material could make wearable tech better. (Image: Michigan Tech, Yoke Khin Yap)
The nanotubes are the mainframe of this new material. BNNTs are great insulators and terrible at conducting electricity. While at first that seems like an odd choice for electronics, the insulating effect of BNNTs is crucial to prevent current leakage and overheating. Additionally, electron flow will only occur across the metal dots on the BNNTs.
In past research, Yap and his team used gold for quantum dots, placed along a BNNT in a tidy line. With enough energy potential, the electrons are repelled by the insulating BNNT and hopscotch from gold dot to gold dot. This electron movement is called quantum tunneling.
“Imagine this as a river, and there’s no bridge; it’s too big to hop over,” Yap says. “Now, picture having stepping stones across the river—you can cross over, but only when you have enough energy to do so.”
Yoke Khin Yap explains how electrons jump between quantum dots and why flexible nanotubes will improve wearable tech.
Unlike with semiconductors, there is no classical resistance with quantum tunneling. No resistance means no heat. Plus, these materials are very small; the nanomaterials enable the transistors to shrink as well. An added bonus is that BNNTs are also quite flexible, a boon for wearable electronics.
Source: Michigan Technological University

Read more: The iron stepping stones to better wearable tech without semiconductors

Cel mai eficient lasere nanowire din lume(World’s most efficient nanowire lasers)

Cunoscuți pentru costul redus, prelucrarea simplă și eficiența ridicată, perovskiții sunt materiale populare în cercetarea panoului solar. Acum, cercetatorii au demonstrat ca nanofirele fabricate din perovskitul cu halogenuri de plumb sunt cele mai eficiente lasere nanowire cunoscute ( Materialele Naturale , „Lasere cu perovskite cu nanoparticule de plumb cu praguri de lasere joase si factori de inalta calitate” ).Aceste nanofire pot avansa în aplicații nanofotonice și dispozitive optoelectronice. În special, laserele care funcționează în regiunea apropiată cu infraroșu ar putea beneficia de comunicații cu fibră optică și de avansarea caracterizării poluării din spațiu.

Posted: Jun 17, 2016

World’s most efficient nanowire lasers

(Nanowerk News) Known for their low cost, simple processing and high efficiency, perovskites are popular materials in solar panel research. Now, researchers demonstrated that nanowires made from lead halide perovskite are the most efficient nanowire lasers known (Nature Materials, „Lead halide perovskite nanowire lasers with low lasing thresholds and high quality factors”).
Perovskite-based nanowire lasers
Perovskite-based nanowire lasers are the most efficient known. A topological image of a nanowire is shown (left insert). Room temperature emission images above the lasing threshold for two nanowires composed of different halides, iodide (red in center) and bromide (green on the right), are shown in top inserts. (Image: Xiaoyang Zhu, Columbia University)
Efficient nanowire lasers could benefit fiber optic communications, pollution characterization, and other applications. The challenge is getting the right material. These ultra-compact wires have a superior ability to emit light, can be tuned to emit different colors, and are relatively easy to synthesize. The development of these perovskite wires parallels the rapid development of the same materials for efficient solar cells.
Semiconductor nanowire lasers, due to their ultra-compact physical sizes, highly localized coherent output, and efficiency, are promising components for use in fully integrated nanoscale photonic and optoelectronic devices. Lasing requires a minimum (threshold) excitation density, below which little light is emitted. A high “lasing threshold” not only makes critical technical advances difficult, but also imposes fundamental limits on laser performance due to the onset of other losses.
In searching for an ideal material for nanowire lasing, researchers at Columbia University and the University of Wisconsin-Madison investigated a new class of hybrid organic-inorganic semiconductors, methyl ammonium lead halide perovskites (CH3NH3PbX3), which is emerging as a leading material for high-efficiency photovoltaic solar cells due to low cost, simple processing and high efficiencies.
The exceptional solar cell performance in these materials can be attributed to the long lifetimes of the carriers that move energy through the systems (electrons and holes) and carrier diffusion lengths. These properties, along with other attributes such as high fluorescence yield and wavelength tunability, also make them ideal for lasing applications. Room temperature lasing in these nanowires was demonstrated with:
  • The lowest lasing thresholds and the highest quality factors reported to date
  • Near 100% quantum yield (ratio of the number of photons emitted to those absorbed)
  • Broad tunability of emissions covering the near infrared to visible wavelength region.
Specifically, the laser emission shifts from near infrared to blue with decreasing atomic number of the halides (X=I, Br, Cl) in the nanowires. These nanowires could advance applications in nanophotonics and optoelectronic devices. In particular, lasers that operate in the near infrared region could benefit fiber optic communications and advance pollution characterization from space.
Source: Department of Energy, Office of Science