In the July 12 issue of Nature, a Harvard-led team of engineers presented a strategy for building self-thermoregulating nanomaterials that can, in principle, be tailored to maintain a set pH, pressure, or just about any other desired parameter by meeting the environmental changes with a compensatory chemical feedback response.

Called SMARTS (Self-regulated Mechano-chemical Adaptively Reconfigurable Tunable System), this newly developed materials platform offers a customizable way to autonomously turn chemical reactions on and off and reproduce the type of dynamic self-powered feedback loops found in biological systems.

The advance represents a step toward more intelligent and efficient medical implants and even dynamic buildings that could respond to the weather for increased energy efficiency. The researchers also expect that their methodology could have considerable potential for translation into areas such as robotics, computing, and healthcare.

Structurally, SMARTS resembles a microscopic toothbrush, with bristles that can stand up or lie down, making and breaking contact with a layer containing chemical ‘nutrients’.

“Think about how goosebumps form on your skin,” explains lead author Joanna Aizenberg, Amy Smith Berylson Professor of Materials Science at the Harvard School of Engineering and Applied Sciences (SEAS) and a Core Faculty Member at the Wyss Institute for Biologically Inspired Engineering at Harvard. “When it is cold out, tiny muscles at the base of each hair on your arm cause the hairs to stand up in an insulating layer. As your skin warms up, the muscles contract and the hairs lie back down to keep you from overheating. SMARTS works in a similar way.”

Natural materials like skin are incredibly dynamic and can maintain control in a wide range of environments through self-regulation. By contrast, synthetic materials cannot easily replicate homeostasis. Even the “smartest” materials—like eyeglasses that darken in sunlight, or a piezoelectric sensor that converts the vibrations of an acoustic guitar into a digital audio signal—typically only react to one specific environmental stimulus and do not self-regulate.

“By building dynamic feedback loops into SMARTS from the bottom up, we were able to integrate the desired regulatory features into the material itself,” says co-lead author Ximin He, a postdoctoral fellow in the Aizenberg lab. “Whether it is the pH level, temperature, wetness, pressure, or something else, SMARTS can be designed to directly sense and modulate the desired stimulus using no external power or complex machinery, giving us a conceptually new robust platform that is customizable, reversible, and remarkably precise.”

To demonstrate SMARTS, He, Aizenberg, and the team chose temperature as the stimulus and embedded an array of tiny nanofibers, akin to little hairs, in a layer of hydrogel. The hydrogel, similar to a muscle, can either swell or contract in response to changes in the temperature. (See movie.)

When the temperature drops, the gel swells, and the hairs stand upright and make contact with the ‘nutrient’ layer; when it warms up, the gel contracts, and the hairs lie down. The key aspect is that molecular catalysts placed on the tips of the nanofibers can trigger heat-generating chemical reactions in the ‘nutrient’ layer.

“The bilayer system effectively creates a self-regulated on-and-off switch controlled by the motion of the hairs, turning the reaction on and generating heat when it is cold. Once the temperature has achieved a pre-determined level, the hydrogel contracts, causing the hairs to lie down, interrupting further generation of heat. When it cools again below the set-point the cycle restarts autonomously. It’s homeostasis, right down at the materials level,” says Aizenberg.

The researchers anticipate that with further refinement the technique could be integrated into materials for medical implants to help stabilize bodily functions, perhaps sensing and adjusting the level of glucose or carbon dioxide in the blood. Furthermore, the oscillating mechanical motion of the hairs could be put to work or used for propulsion, like cilia in a living organism.

“In principle, you can turn anything—heat, light, mechanical pressure—into a chemical signal within the gel. Likewise, the reactions triggered by the moving hairs can produce many different types of compensatory responses. By matching signals and responses, we can, in principle, create a wide variety of self-regulating feedback loops,” adds He.

Beside its technological applications, SMARTS is also an ideal “laboratory” to study the fundamental properties of biological and chemical systems, such as how living systems are able to so efficiently convert between chemical and mechanical processes.

“We found a new way to think about materials and created a fascinating system to look at some fundamental, deep questions about how living things maintain a stable state,” says Aizenberg.

Source: http://news.harvard.edu

Materials that can be both magnetically and electrically polarized and also have additional properties are called multiferroics and were previously discovered by Russian researchers in the 1960s. But the technology to examine the materials did not exist at that time. It is only now, in recent years, that researchers have once again focused on analyzing the properties of such materials. Now you have research facilities that can analyze the materials down to the atomic level.

Surprising test results

“We have studied the rare, naturally occurring iron compound, TbFeO3, using powerful neutron radiation in a magnetic field. The temperature was cooled down to near absolute zero, minus 271 C. We were able to identify that the atoms in the material are arranged in a congruent lattice structure consisting of rows of the heavy metal terbium separated by iron and oxygen atoms. Such lattices are well known, but their magnetic domains are new. Normally, the magnetic domains lie a bit helter-skelter, but here we observed that they lay straight as an arrow with the same distance between them. We were completely stunned when we saw it,” explains Kim Lefmann, Associate Professor at the Nano-Science Center, University of Copenhagen.

They were very strange and very beautiful measurements and it is just such a discovery that can awaken the researchers’ intense interest. Why does it look like this?

Explaining physics

The experiments were conducted at the neutron research facility Helmholtz-Zentrum in Berlin in collaboration with researchers in Holland, Germany, at ESS in Lund and at Risø/DTU. They would like to get a general understanding of the material and with the help of calculations; and have now arrived at a more precise image of the relationship between the structure of the material and its physical properties.

“What the models are describing is that the terbium walls interact by exchanging waves of spin (magnetism), which is transferred through the magnetic iron lattice. The result is a Yukawa-like force, which is known from nuclear and particle physics. The material exhibits in a sense the same interacting forces that hold the particles together in atomic nuclei,” explains Heloisa Bordallo, Associate Professor at the Niels Bohr Institute.

It is precisely this interaction between the transition metal, iron, and the rare element, terbium, that plays an important role in this magneto-electrical material. The terbium’s waves of spin cause a significant increase in the electric polarization and the interaction between the ions of the elements creates one of the strongest magneto-electrical effects observed in materials.

“Through these results we found a new pathway to discover and develop new multiferroics”, emphasize the researchers in the group. Now it is up to further research to determine whether this new effect could lead to new applications of these materials with the amazing physical properties.

Source: http://www.nbi.ku.dk/english/

When you look at a gift-wrapped present, the basic properties of the wrapping paper — say, its colors and texture — are not generally changed by the nature of the gift inside.

But surprising new experiments conducted at MIT show that a one-atom-thick material called graphene, a form of pure carbon whose atoms are joined in a chicken-wire-like lattice, behaves quite differently depending on the nature of material it’s wrapped around. When sheets of graphene are placed on substrates made of different materials, fundamental properties — such as how the graphene conducts electricity and how it interacts chemically with other materials — can be drastically different, depending on the nature of the underlying material.

“We were quite surprised” to discover this altered behavior, says Michael Strano, the Charles and Hilda Roddey Professor of Chemical Engineering at MIT, who is the senior author of a paper published this week in the journalNature Chemistry. “We expected it to behave like graphite” — a well-known form of carbon, used to make the lead in pencils, whose structure is essentially multiple layers of graphene piled on top of each other.

But its behavior turned out to be quite different. “Graphene is very strange,” Strano says. Because of its extreme thinness, in practice graphene is almost always placed on top of some other material for support. When that material underneath is silicon dioxide, a standard material used in electronics, the graphene can readily become “functionalized” when exposed to certain chemicals. But when graphene sits on boron nitride, it hardly reacts at all to the same chemicals.

“It’s very counterintuitive,” Strano says. “You can turn off and turn on graphene’s ability to form chemical bonds, based on what’s underneath.”

The reason, it turns out, is that the material is so thin that the way it reacts is strongly affected by the electrical fields of atoms in the material beneath it. This means that it is possible to create devices with a micropatterned substrate — made up of some silicon dioxide regions and some coated with boron nitride — covered with a layer of graphene whose chemical behavior will then vary according to the hidden patterning. This could enable, for example, the production of microarrays of sensors to detect trace biological or chemical materials.

Qing Hua Wang, an MIT postdoc who is the lead author of the paper, says, “You could get different molecules of a delicate biological marker to interact [with these regions on the graphene surface] without disrupting the biomolecules themselves.” Most current fabrication techniques for such patterned surfaces involve heat and reactive solvents that can destroy these sensitive biological molecules.

Ultimately, graphene could even become a protective coating for many materials, Strano says. For example, the one-atom-thick material, when bonded to copper, completely eliminates that metal’s tendency to oxidize (which produces the characteristic blue-green surface of copper roofs). “It can completely turn off the corrosion,” he says, “almost like magic … with just the whisper of a coating.”

To explain why graphene behaves the way it does, “we came up with a new electron-transfer theory” that accounts for the way it is affected by the underlying material, Strano says. “A lot of chemists had missed this,” and as a result had been confused by seemingly unpredictable changes in how graphene reacts in different situations. This new understanding can also be used to predict the material’s behavior on other substrates, he says.

James Tour, a professor of chemistry and of computer science at Rice University who was not involved in this research, says, “This is the first systematic study of the substrate’s effect on graphene’s chemical reactivity. This is a very carefully conducted study with convincing results. I predict that it will become a frequently cited publication.”

Wang adds that “it’s a pretty general result” that can be used to predict the chemical behavior of many different configurations. “We think other groups can take this idea and really develop different things with it,” she says. Tour agrees, saying, “The graphene-sensing community will be inspired by this work to explore many more substrates in an effort to optimize graphene reactivity.”

As for the MIT team, she says, “the next step is, we’re digging into the details of how bilayer graphene reacts. It seems to behave differently” than the single-layer material.

The work was primarily supported by the U.S. Office of Naval Research.

The work was reported April 16 in the online edition of Proceedings of the National Academy of Sciences.

The research focused on an inexpensive phase-change memory alloy composed of germanium, antimony and tellurium, called GST for short. The material is already used in rewritable optical media, including CD-RW and DVD-RW discs. But by using diamond-tipped tools to apply pressure to the materials, the Johns Hopkins-led team uncovered new electrical resistance characteristics that could make GST even more useful to the computer and electronics industries.

“This phase-change memory is more stable than the material used in the current flash drives. It works 100 times faster and is rewritable about 100,000 times,” said the study’s lead author, Ming Xu, a doctoral student in the Department of Materials Science and Engineering in Johns Hopkins’ Whiting School of Engineering. “Within about five years, it could also be used to replace hard drives in computers and give them more memory.”

GST is called a phase-change material because, when exposed to heat, areas of GST can change from an amorphous state, in which the atoms lack an ordered arrangement, to a crystalline state, in which the atoms are neatly lined up in a long-range order. In its amorphous state, GST is more resistant to electric current. In its crystalline state, it is less resistant. The two phases also reflect light differently, allowing the surface of a DVD to be read by A tiny laser. The two states correspond to one and zero, the language of computers.

Although this phase-change material has been used for at least two decades, the precise mechanics of this switch from one state to another have remained something of a mystery because it happens so quickly — in nanoseconds — when the material is heated.

To solve this mystery, Xu and his team used another method to trigger the change more gradually. The researchers used two diamond tips to compress the material. They employed a process called X-ray diffraction and a computer simulation to document what was happening to the material at the atomic level. The researchers found that they could “tune” the electrical resistivity of the material during the time between its change from amorphous to crystalline form.

“Instead of going from black to white, it’s like finding shades or a shade of gray in between,” said Xu’s doctoral adviser, En Ma, a professor of materials science and engineering, and a co-author of the PNAS paper. “By having a wide range of resistance, you can have a lot more control. If you have multiple states, you can store a lot more data.”

Source: http://www.jhu.edu/

The researchers demonstrated that a single layer of atoms can disrupt or enhance heat flow across an interface. Their results are published this week in Nature Materials.

Improved control of heat exchange is a key element to enhancing the performance of current technologies such as integrated circuits and combustion engines as well as emerging technologies such as thermoelectric devices, which harvest renewable energy from waste heat. However, achieving control is hampered by an incomplete understanding of how heat is conducted through and between materials.

“Heat travels through electrically insulating material via ‘phonons,’ which are collective vibrations of atoms that travel like waves through a material,” said David Cahill, a Willett Professor and the head of materials science and engineering at Illinois and co-author of the paper. “Compared to our knowledge of how electricity and light travel through materials, scientists’ knowledge of heat flow is rather rudimentary.”

One reason such knowledge remains elusive is the difficulty of accurately measuring temperatures, especially at small-length scales and over short time periods – the parameters that many micro and nano devices operate under.

Over the past decade, Cahill’s group has refined a measurement technique using very short laser pulses, lasting only one trillionth of a second, to probe heat flow accurately with nanometer-depth resolution. Cahill teamed up with Paul Braun, the Racheff Professor of Materials Science and Engineering at the U. of I. and a leader in nanoscale materials synthesis, to apply the technique to understanding how atomic-scale features affect heat transport.

“These experiments used a ‘molecular sandwich’ that allowed us to manipulate and study the effect that chemistry at the interface has on heat flow, at an atomic scale,” Braun said.

The researchers assembled their molecular sandwich by first depositing a single layer of molecules on a quartz surface. Next, through a technique known as transfer-printing, they placed a very thin gold film on top of these molecules. Then they applied a heat pulse to the gold layer and measured how it traveled through the sandwich to the quartz at the bottom.

By adjusting just the composition of the molecules in contact with the gold layer, the group observed a change in heat transfer depending on how strongly the molecule bonded to the gold. They demonstrated that stronger bonding produced a twofold increase in heat flow.

“This variation in heat flow could be much greater in other systems,” said Mark Losego, who led this research effort as a postdoctoral scholar at Illinois and is now a research professor at North Carolina State University. “If the vibrational modes for the two solids were more similar, we could expect changes of up to a factor of 10 or more.”

The researchers also used their ability to systematically adjust the interfacial chemistry to dial-in a heat flow value between the two extremes, verifying the ability to use this knowledge to design materials systems with desired thermal transport properties.

“We’ve basically shown that changing even a single layer of atoms at the interface between two materials significantly impacts heat flow across that interface,” said Losego.

Scientifically, this work opens up new avenues of research. The Illinois group is already working toward a deeper fundamental understanding of heat transfer by refining measurement methods for quantifying interfacial bonding stiffness, as well as investigating temperature dependence, which will reveal a better fundamental picture of how the changes in interface chemistry are disrupting or enhancing the flow of heat across the interface.

“For many years, the physical models for heat flow between two materials have ignored the atomic-level features of an interface,” Cahill said. “Now these theories need to be refined. The experimental methods developed here will help quantify the extent to which interfacial structural features contribute to heat flow and will be used to validate these new theories.”

Braun and Cahill are affiliated with the Frederick Seitz Materials Research Laboratory at the U. of I. Braun is also affiliated with the department of chemistry and the Beckman Institute for Advanced Science and Technology. The Air Force Office of Scientific Research supported this work.

Source: http://www.news.illinois.edu

GraphExeter could also be used for the creation of ‘smart’ mirrors or windows, with computerised interactive features. Since this material is also transparent over a wide light spectrum, it could enhance by more than 30% the efficiency of solar panels.

Adapted from graphene, GraphExeter is much more flexible than indium tin oxide (ITO), the main conductive material currently used in electronics. ITO is becoming increasingly expensive and is a finite resource, expected to run out in 2017.

These research findings are published in the journal Advanced Materials, a leading journal in materials science.

At just one-atom-thick, graphene is the thinnest substance capable of conducting electricity. It is very flexible and is one of the strongest known materials. The race has been on for scientists and engineers to adapt graphene for flexible electronics. This has been a challenge because of its sheet resistance, which limits its conductivity. Until now, no-one has been able to produce a viable alternative to ITO.

To create GraphExeter, the Exeter team sandwiched molecules of ferric chloride between two layers of graphene. Ferric chloride enhances the electrical conductivity of graphene, without affecting the material’s transparency.

The material was produced by a team from the University of Exeter’s Centre for Graphene Science. The research team is now developing a spray-on version of GraphExeter, which could be applied straight onto fabrics, mirrors and windows.

Lead researcher, University of Exeter engineer Dr Monica Craciun said: “GraphExeter could revolutionise the electronics industry. It outperforms any other carbon-based transparent conductor used in electronics and could be used for a range of applications, from solar panels to ‘smart’ teeshirts. We are very excited about the potential of this material and look forward to seeing where it can take the electronics industry in the future.”

Source: http://www.exeter.ac.uk

Piezoelectric materials are key materials for the fabrication of various transducers, pressure sensors and actuators, piezoelectric oscillator and actuators, transformer, surface acoustic wave (SAW) and bulk acoustic wave (BAW) devices, which are widely used in the fields of information, energy, machinery, electronics, national defense, among others. Because of their excellent piezoelectric property, lead (Pb)-based piezoelectric materials is one of the most widely exploited and extensively used piezoelectric materials. However, Pb is highly toxic and its toxicity can be further enhanced due to its easy volatilization during processing. Thus, processing and use of Pb-based piezoelectric materials can contaminate environments and damage human health, thereby limiting their applications. With the rise in environmental awareness, lead-free piezoelectric materials have received greater attention, the prevailing trend being that environment-friendly lead-free piezoelectric materials will replace Pb-based piezoelectric materials.

As a piezoelectric material, ZnO has various advantages. Firstly, it has the strongest piezoelectric response among the tetrahedrally-bonded semiconductors. Secondly, it is structurally simple and easy to fabricate. Moreover, ZnO films are compatible with semiconductor processes, and therefore has been widely used as sensors and actuators in micro-electromechanical systems and as SAW and BAW devices in the field of communications. However, performance improvements in piezoelectric devices demand significant piezoelectric behavior and stronger piezoresponse; in that regard d33 is the important parameter for evaluating piezoelectric property in ZnO. For bulk ZnO, and for an oriented ZnO film, the piezoresponses are ~9.9 pC/N and ~12.4 pC/N, respectively, which are approximately one or two orders of magnitude lower compared with Pb-based piezoelectric materials. Many researchers have focused on pure ZnO films and attempted to improve its properties by optimizing the preparation conditions; the results though were ineffective.

Doping is a good method to improve the piezoelectric properties of Pb-based piezoelectric materials, and there are many successful examples of improvements in the properties of ZnO films by doping. Doping with Al and Ga can improve the quality and conductivity of ZnO films. Co-doping can induce room-temperature ferromagnetism in Co-doped ZnO films. For this reason, transition-metal doping of ZnO films has been investigated and piezoresponses quantified. It is found that Zn0.975V0.025O and Zn0.94Cr0.06O films possess maximum d33 values of ~170 and ~120 pC/N, respectively, which are about one order of magnitude larger than for pure ZnO films, but quite comparable with those of perovskite piezoelectrics. As shown in Figure 1, the displacement-applied voltage (D-V) curve of Zn0.975V0.025O is typically a butterfly-like loop. The corresponding piezoresponse hysteresis loop is switchable. From a macroscopic point of view, the giant piezoresponse in ZnO films is considered to be the emergence of switchable spontaneous polarization as well as to a relatively high permittivity. In contrast, 2 at.% Cu-doped ZnO films have a d33 of ~13.6 pC/N, and Fe- and Co-doped ZnO films with the same doping concentration have d33 values of ~6pC/N and ~11 pC/N, both smaller than for pure ZnO films (~12) pC/N. Through analyzing and calculating the X-ray absorption spectroscopy spectrum of the dopant, it was found that V5+ (radii of 0.59 Å), Cr3+ (radii of 0.63 Å), Cu2+ (radii of 0.72 Å), Fe2+ (radii of 0.76 Å), and Co2+ (radii of 0.79 Å) substitute for Zn2+ (radii of 0.74 Å) in Zn0.975V0.025O, Zn0.94Cr0.06O films Zn0.98Cu0.02O, Zn0.98Fe0.02O, and Zn0.98Co0.02O respectively. From a microscopic point of view, the piezoresponse in ZnO is mainly governed by the ease of noncollinear bonds along the polar c axis toward the direction of the applied field. Small-ion substitution, i.e. V5+ (0.59Å), Cr3+ (0.63 Å), and Cu2+ (0.72 Å), for Zn2+(0.74 Å) make the V-O1, Cr-O1, and Cu-O1 bonds rotate easier in the direction of the applied field and enhance the corresponding electromechanical responses. For 2 at. % Fe- and Co-doped ZnO films, the bigger ionic size in the Zn2+ site makes the rotation of the Fe-O1 and Co-O1 bonds difficult, thus decreasing the piezoresponse.

In ZnO:Mn films where Mn2+ (0.80Å) with a big radius gets substituted at the Zn2+ sites, the piezoresponse is only 8.2 pC/N, which is smaller for pure ZnO films. Substitution of Mn3+/Mn4+ (0.66Å/0.60Å), with small radius and greater positive charge, at Zn2+ site, yields an enhanced piezoresponse of up to 86 pC/N. Through investigating the relationship between Mn ionic size and the piezoresponse values, the ionic size and the chemical state of the dopant have been confirmed as the key factors in the piezoresponse of doped-ZnO films.

In ZnO:Fe films, Fe2+ (0.76 Å), with a big radius, also gets substituted at Zn2+ sites, the piezoresponse is only 7 pC/N. After annealing in O2, Fe2+ is oxidized to Fe3+ (0.64 Å) and the piezoresponse improved to 120 pC/N. The modified ZnO films with high piezoresponses can be used as promising environment-friendly piezoelectric materials. The substitution rule has provided a new way in seeking lead-free piezoelectric materials. Pure ZnO and V-doped ZnO films were used to fabricate SAW devices. Compared with devices based on pure ZnO films, the devices based on ZnO:V films with giant piezoresponses have smaller insertion losses and higher electromechanical coupling coefficients.

By enhancing the piezoresponse of ZnO and made comparable to that of Pb-based piezoelectric materials, the performances of available ZnO-based SAW devices were improved significantly. Additionally, the enhanced piezoelectricity can widely extend the applications range of ZnO. Because ZnO not only possesses high piezoelectric response, but also is an abundant raw material that is environment-friendly, it competes and stands to replace Pb-based piezoelectric materials as the promising piezoelectric materials.

Source: http://www.eurekalert.org

Today, to separate hydrocarbon gas mixtures into the pure chemicals needed to make plastics, refineries “crack” crude oil at high temperatures – 500 to 600 degrees Celsius – to break complex hydrocarbons into lighter, short-chain molecules. They then chill the gaseous mixture to 100 degrees below zero Celsius to liquefy and divide the gases into those destined for plastics and those used as fuel for home heating and cooking.

“Cryogenic distillation at low temperatures and high pressures is among the most energy-intensive separations carried out at large scale in the chemical industry, and an environmental problem because of its contributions to global climate change,” said Jeffrey Long, a professor of chemistry at the UC Berkeley and a faculty researcher at Lawrence Berkeley National Laboratory.

Long and his UC Berkeley colleagues now have created an iron-based material – a metal-organic framework, or MOF – that can be used at high temperatures to efficiently separate these gases while eliminating the chilling.

“You need a very pure feedstock of propylene and ethylene for making some of the most important polymers, such as polypropylene, for consumer products, but refineries dump a lot of energy into bringing the high temperature gases down to cryogenic temperatures,” Long said. “If you can do the separation at higher temperatures, you can save that energy. This material is really good at doing these particular separations.”

“The research conducted by the Long group exemplifies the potential of MOF-based materials relative to olefin/paraffin separations,” said chemist Peter Nickias, a Dow Fellow at Dow Chemical Company in Michigan who was not involved in the research. “More specifically, the ability of the reported iron-based MOF to separate a variety of unsaturated hydrocarbons from saturated species not only shows the versatility of the iron-MOF system, but also clearly reveals the potential of MOFs as alternative adsorbents.”

In the chemical industry, ethylene and propylene are called olefins, while methane, ethane and propane are called paraffins.

Long and his colleagues at UC Berkeley and the National Institute of Standards and Technology (NIST) in Gaithersburg, Md., report their findings in the March 30 issue of Science.

MOFs for natural gas purification

The iron-MOF is also good at purifying natural gas, which is a mixture of methane and various types of hydrocarbon impurities that have to be removed before the gas can be used by consumers. These impurities can then be sold for other uses, Long said.

“MOF compounds have a very high surface area, which provides lots of area a gas mixture can interact with, and that surface contains iron atoms that can bind the unsaturated hydrocarbons,” Long said. “Acetylene, ethylene and propylene will stick to those iron sites much more strongly than will ethane, propane or methane. That is the basis for the separation.”

Nickias noted that increased supplies of natural gas from shale have provided more opportunity to extract and use ethylene and propylene from natural gas, and a variety of materials and approaches are being examined to cut energy use during the refining and purification of olefins.

“Significant energy savings could be achieved if a non-distillation separation could be implemented, or more realistically, the load on a cryogenic distillation unit can be reduced via upstream modifications to the process,” Nickias said.

Petroleum refined for the chemical industry is typically a mix of hydrocarbons, primarily two-carbon molecules – ethane, ethylene and acetylene – and three-carbon chains – propane and propylene. Cryogenic distillation separates these compounds – all of them gases at room temperature – by liquefying them at low temperatures and high pressure, which causes them to separate by density. Ethylene and propylene go into plastic polymers, while ethane and propane are typically used for fuel.

The researchers found that when pumping a gas mixture through the iron-based MOF (Fe-MOF-74), the propylene and ethylene bind to the iron embedded in the matrix, letting pure propane and ethane through. In their trials, the ethane coming out was 99.0 to 99.5 percent pure. The propane output was close to 100 percent pure, since no propylene could be detected.

After the ethane and propane emerge, the MOF can be heated or depressurized to release ethylene and propylene pure enough for making polymers.

“Once you saturate the material with ethylene, for example – you shut off the valve, stop the feed gas, warm up the absorber unit and the ethylene would come out in pure form as a gas,” Long said.

MOFs like packed soda straws

Through a microscope, Fe-MOF-74 looks like a collection of narrow tubes packed together like drinking straws in a box. Each tube is made of organic materials and six long strips of iron, which run lengthwise along the tube. Analysis by Long’s colleagues at the NIST Center for Neutron Research showed that different light hydrocarbons have varied levels of attraction to the tubes’ iron. By passing a mixed-hydrocarbon gas through a series of filters made of the tubes, the hydrocarbon with the strongest affinity can be removed in the first filter layer, the next strongest in the second layer, and so forth.

“It works well at 45 degrees Celsius, which is closer to the temperature of hydrocarbons at some points in the distillation process,” said Wendy Queen, a postdoctoral fellow at NIST who worked for six months in Long’s UC Berkeley lab. “The upshot is that if we can bring the MOF to market as a filtration device, the energy-intensive cooling step potentially can be eliminated. We are now trying out metals other than iron in the MOF in case we can find one that works even better.”

Long and his laboratory colleagues are developing iron-based MOFs to capture carbon from smokestack emissions and sequester it to prevent its release into the atmosphere as a greenhouse gas. Similar MOFs, which can be made with different pore sizes and metals, turn out to be ideal for separating different types of hydrocarbons and for storing hydrogen and methane for use as fuel.

Source: http://newscenter.berkeley.edu

Using cutting edge equipment and specially designed MEM’s sensors on loan from Mettler-Toledo, scientists from the University of Southampton’s Optoelectronic Research Centre and the University of Cambridge’s Department of Materials Science were able to probe the behaviour of phase change memory materials, the semiconductors that store information in the next generation of electronics, as they were heated at rates up to 10,000 degree C per second.

Insight and a detailed understanding of measurement results was provided by Professor Lindsay Greer, from the University of Cambridge’s Department of Materials Science, whose analysis showed that crystal growth rates differed considerably from other materials such as glass and silicon and the behaviour of these materials on such rapid heating was not as expected.

The results, which are published this week in Nature Materials, show that crystal growth rates are much faster than we previously believed in these materials and that the growth behaviour is independent of the surroundings. While it is not surprising that properties of materials change significantly when they are shrunk to nanoscale dimensions, we now have a method of directly screening materials for improved memory performance; this means faster, smaller and less power hungry smart phones, ipods and computers are one step closer.

Professor Dan Hewak from the University of Southampton, whose team, led by Behrad Gholipour, provided the phase change materials and deposited them as very thin films, comments:

“We have been studying novel glasses and phase change materials for two decades here at the Optoelectronics Research Centre. However, our understanding of what happens when these materials are heated, that is, their crystallization and melting behaviours, has been limited to heating rates of about 10 degrees C per minute using conventional thermal analysis. In reality, in the memory devices we fabricate, heating rates are millions of times faster and it is reasonable to expect that in order to improve these devices, an understanding of their properties at the same heating rates they will be used is needed.”

Writing in the same issue of Nature Materials, Professors Matthias Wuttig and Martin Salinga at RWTH Aachen University in Germany explain why this breakthrough is so important: “Jiri Orava (Cambridge University) and colleagues now provide a completely new insight in our understanding of the fast transformations that occur in the materials that make up today’s memory devices. Reading and writing of data in optical memory such as rewriteable compact discs (CD-RWs and DVDs) and emerging new electronic memory can take place at speeds of tens of nanoseconds but our understanding of what happens when these materials are heated is based on experiments where heating rates are much slower.”

“Unravelling the mysteries of chocolate making, comprehending the formation of amethyst geodes, or producing advanced steels requires an understanding of the relevant crystallization phenomena.”

Source: http://www.southampton.ac.uk