In an advance toward stain-proof, spill-proof clothing, protective garments and other products that shrug off virtually every liquid — from blood and ketchup to concentrated acids — scientists are reporting development of new “superomniphobic” surfaces. Their report on surfaces that display extreme repellency to two families of liquids — Newtonian and non-Newtonian liquids — appears in the Journal of the American Chemical Society.
Anish Tuteja and colleagues point out that scientists have previously reported “omniphobic” surfaces, the term meaning that such surfaces can cause a range of different liquids to bead up and not spread on them. But typically very low surface tension liquids such as some oils and alcohols can adhere to those surfaces. Further, scientists have mostly focused on making surfaces that repel only one of the two families of liquids — Newtonian liquids, named for the great English scientist who described how they flow. Tuteja’s team set out to do the same for non-Newtonian liquids, which include blood, yogurt, gravy, various polymer solutions and a range of other liquids.
The new glass could be both for rigid and flexible displays
A new type of flexible ultra-thin glass has been unveiled by the firm that developed Gorilla Glass, currently used to make screens of many mobile devices.
Dubbed Willow Glass, the product can be “wrapped” around a device, said the New York-based developer Corning.
The glass was showcased at the Society for Information Display’s Display Week, an industry trade show in Boston.
Besides smartphones, it could also be used for displays that are not flat, the company said.
But until such “conformable” screens appear on the market, the glass could be used for mobile devices that are constantly becoming slimmer.
Researchers at Rice University and Penn State University have discovered that adding a dash of boron to carbon while creating nanotubes turns them into solid, spongy, reusable blocks that have an astounding ability to absorb oil spilled in water.
That’s one of a range of potential innovations for the material created in a single step. The team found for the first time that boron puts kinks and elbows into the nanotubes as they grow and promotes the formation of covalent bonds, which give the sponges their robust qualities.
The researchers, who collaborated with peers in labs around the nation and in Spain, Belgium and Japan, revealed their discovery in Nature’s online open-access journal Scientific Reports.
Lead author Daniel Hashim, a graduate student in the Rice lab of materials scientist Pulickel Ajayan, said the blocks are both superhydrophobic (they hate water, so they float really well) and oleophilic (they love oil). The nanosponges, which are more than 99 percent air, also conduct electricity and can easily be manipulated with magnets.
To demonstrate, Hashim dropped the sponge into a dish of water with used motor oil floating on top. The sponge soaked it up. He then put a match to the material, burned off the oil and returned the sponge to the water to absorb more. The robust sponge can be used repeatedly and stands up to abuse; he said a sample remained elastic after about 10,000 compressions in the lab. The sponge can also store the oil for later retrieval, he said.
“These samples can be made pretty large and can be easily scaled up,” said Hashim, holding a half-inch square block of billions of nanotubes. “They’re super-low density, so the available volume is large. That’s why the uptake of oil can be so high.” He said the sponges described in the paper can absorb more than a hundred times their weight in oil.
Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry, said multiwalled carbon nanotubes grown on a substrate via chemical vapor deposition usually stand up straight without any real connections to their neighbors. But the boron-introduced defects induced the nanotubes to bond at the atomic level, which tangled them into a complex network. Nanotube sponges with oil-absorbing potential have been made before, but this is the first time the covalent junctions between nanotubes in such solids have been convincingly demonstrated, he said.
All the way back in March of 2004, working in his laboratory at the University of Southern California in San Diego, Dr. Behrokh Khoshnevis, was working with a new process he had invented called Contour Crafting to construct the world’s first 3D printed wall.
His goal was to use the technology for rapid home construction as a way to rebuild after natural disasters, like the devastating earthquakes that had recently occurred in his home country of Iran.
While we have still not seen our first “printed home” just yet, they will be coming very soon. Perhaps within a year. Commercial buildings will soon follow.
For an industry firmly entrenched in working with nails and screws, the prospects of replacing saws and hammers with giant printing machines seems frightening. But getting beyond this hesitancy lies the biggest construction boom in all history.
Here’s why I think this will happen.
Contour Crafting is a form of 3D printing that uses robotic arms and nozzles to squeeze out layers of concrete or other materials, moving back and forth over a set path in order to fabricate a large component. It is a construction technology that has great potential for low-cost, customized buildings that are quicker to make and can therefore reduce energy and emissions.
Using a quick-setting, concrete-like material, contour crafting forms the house’s walls layer by layer until topped off by floors and ceilings that are set into place by the crane. In its current state of thinking, buildings will still require the insertion of structural components, plumbing, wiring, utilities, and even consumer devices like entertainment and audiovisual systems, as the layers are being built.
After using the technology to form simple things like walls and benches, discussions began to focus on other far-reaching opportunities like constructing rapid shelters after natural disasters, building operational structures on the moon out of moon dust, and building cheap houses for people in impoverished countries.
But those early visions were too much for an industry steeped in regulation and tradition, and the laudable ideas of helping the less fortunate will likely give way to a more mainstream approach of working with pieces before building the whole enchilada.
Breaking Through the Barriers
Starting with a mortgage industry that’s becoming increasingly wary of lending on virtually any houses, let alone something that looks radically different, coupled with city planning and zoning departments that have no way of deciding what the code should be on a “non-traditional structure,” and thousands of aging industry experts who can’t imagine building houses in any way other than we do today, we find ourselves up against a slow-moving, massively resistant building culture that will take years to overcome.
That said, this industry will have plenty of opportunity to move forward.
Early on, a number of industries will form around printed components and construction material. Printed blocks, cabinets, wall panels, toilets, and even doors will catch on quickly.
Printed artwork will begin to show up everywhere, including three dimensional “wall printings.”
A natural extension of printing new buildings will be devices that recycle the old ones. Ideally, the old material will be ground up and reformulated into new composites that can be re-printed into whatever is needed.
As an example, an old patio deck could be automatically “eaten” by some sort of PacMan device, ground up and mixed with other materials, and used to “print” a new patio deck - all within a couple hours.
By replacing our traditional techniques for pouring concrete, 3d printers could be used to print driveways, sidewalks, benches, fences, foundations, and much more.
When it comes to roofing, small bots will be used to create seamless coatings on the tops of houses. The small army of people needed to reroof a house today will be replaced with a single person who’s job is to place the bot at its initial starting point and make sure there is a consistent supply of material to coat the entire roof.
Only after gaining traction in a myriad of these component industries will we see the public warming up to entire houses being printed from the ground up.
Here are a few examples of this type of 3D printed construction projects already taking place:
Engineering researchers at Rensselaer Polytechnic Institute have developed a new method for creating advanced nanomaterials that could lead to highly efficient refrigerators and cooling systems requiring no refrigerants and no moving parts. The key ingredients for this innovation are a dash of nanoscale sulfur and a normal, everyday microwave oven.
At the heart of these solid-state cooling systems are thermoelectric materials, which can convert electricity into a range of different temperatures—from hot to cold. Thermoelectric refrigerators employing these principles have been available for more than 20 years, but they are still small and highly inefficient. This is largely because the materials used in current thermoelectric cooling devices are expensive and difficult to make in large quantities, and do not have the necessary combination of thermal and electrical properties. A new study, published today in the journal Nature Materials, overcomes these challenges and opens the door to a new generation of high-performance, cost-effective solid state refrigeration and air conditioning.
Rensselaer Professor Ganpati Ramanath led the study, in collaboration with colleagues Theodorian Borca-Tasciuc and Richard W. Siegel.
Driving this research breakthrough is the idea of intentionally contaminating, or doping, nanostructured thermoelectric materials with barely-there amounts of sulfur. The doped materials are obtained by cooking the material and the dopant together for few minutes in a store-bought $40 microwave oven. The resulting powder is formed into pea-sized pellets by applying heat and pressure in a way that preserves the properties endowed by the nanostructuring and the doping. These pellets exhibit properties better than the hard-to-make thermoelectric materials currently available in the marketplace. Additionally, this new method for creating the doped pellets is much faster, easier, and cheaper than conventional methods of making thermoelectric materials.
“This is not a one-off discovery. Rather, we have developed and demonstrated a new way to create a whole new class of doped thermoelectric materials with superior properties,” said Ramanath, a faculty member in the Department of Materials Science and Engineering at Rensselaer. “Our findings truly hold the potential to transform the technology landscape of refrigeration and make a real impact on our lives.”
Results of the study are detailed in the Nature Materials paper “A new class of doped nanobulk high figure of merit thermoelectrics by scalable bottom-up assembly.” See the paper online at: dx.doi.org
It looks like bone. It feels like bone. For the most part, it acts like bone.
And it came off an inkjet printer.
Washington State University researchers have used a 3D printer to create a bone-like material and structure that can be used in orthopedic procedures, dental work and to deliver medicine for treating osteoporosis. Paired with actual bone, it acts as a scaffold for new bone to grow on and ultimately dissolves with no apparent ill effects.
The authors report on successful in vitro tests in the journal Dental Materials and say they’re already seeing promising results with in vivo tests on rats and rabbits. It’s possible that doctors will be able to custom order replacement bone tissue in a few years, said Susmita Bose, co-author and professor in WSU’s School of Mechanical and Materials Engineering.
“If a doctor has a CT scan of a defect, we can convert it to a CAD file and make the scaffold according to the defect,” Bose said.
The material grows out of a four-year interdisciplinary effort involving chemistry, materials science, biology and manufacturing. A main finding of the paper is that the addition of silicon and zinc more than doubled the strength of the main material, calcium phosphate.
The researchers - who include mechanical and materials engineering Professor Amit Bandyopadhyay, doctoral student Gary Fielding and research assistant Solaiman Tarafder - also spent a year optimizing a commercially available ProMetal 3D printer designed to make metal objects.
The printer works by having an inkjet spray a plastic binder over a bed of powder in layers of 20 microns, about half the width of a human hair. Following a computer’s directions, it creates a channeled cylinder the size of a pencil eraser.
After just a week in a medium with immature human bone cells, the scaffold was supporting a network of new bone cells.
The team of Professor Keon Jae Lee (Department of Materials Science and Engineering, KAIST) has developed fully functional flexible non-volatile resistive random access memory (RRAM) where a memory cell can be randomly accessed, written, and erased on a plastic substrate.
Memory is an essential part in electronic systems, as it is used for data processing, information storage and communication with external devices. Therefore, the development of flexible memory has been a challenge to the realization of flexible electronics.
Although several flexible memory materials have been reported, these devices could not overcome cell-to-cell interference due to their structural and material limitations. In order to solve this problem, switching elements such as transistors must be integrated with the memory elements. Unfortunately, most transistors built on plastic substrates (e.g., organic/oxide transistors) are not capable of achieving the sufficient performance level with which to drive conventional memory. For this reason, random access memory operation on a flexible substrate has not been realized thus far.
Recently, Prof. Lee’s research team developed a fully functional flexible memory that is not affected by cell-to-cell interference. They solved the cell-to-cell interference issue by integrating a memristor (a recently spotlighted memory material as next-generation memory elements) with a high-performance single-crystal silicon transistor on flexible substrates. Utilizing these two advanced technologies, they successfully demonstrated that all memory functions in a matrix memory array (writing/reading/erasing) worked perfectly.
Prof. Lee said, “This result represents an exciting technology with the strong potential to realize all flexible electronic systems for the development of a freely bendable and attachable computer in the near future.”
This result was published in the October online issue of the Nano Letters ACS journal.
Solar or photovoltaic cells represent one of the best possible technologies for providing an absolutely clean and virtually inexhaustible source of energy to power our civilization. However, for this dream to be realized, solar cells need to be made from inexpensive elements using low-cost, less energy-intensive processing chemistry, and they need to efficiently and cost-competitively convert sunlight into electricity. A team of researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) has now demonstrated two out of three of these requirements with a promising start on the third.
Peidong Yang, a chemist with Berkeley Lab’s Materials Sciences Division, led the development of a solution-based technique for fabricating core/shell nanowire solar cells using the semiconductors cadmium sulfide for the core and copper sulfide for the shell. These inexpensive and easy-to-make nanowire solar cells boasted open-circuit voltage and fill factor values superior to conventional planar solar cells. Together, the open-circuit voltage and fill factor determine the maximum energy that a solar cell can produce. In addition, the new nanowires also demonstrated an energy conversion efficiency of 5.4-percent, which is comparable to planar solar cells.
“This is the first time a solution based cation-exchange chemistry technique has been used for the production of high quality single-crystalline cadmium sulfide/copper sulfide core/shell nanowires,” Yang says. “Our achievement, together with the increased light absorption we have previously demonstrated in nanowire arrays through light trapping, indicates that core/shell nanowires are truly promising for future solar cell technology.”
Typical solar cells today are made from ultra-pure single crystal silicon wafers that require about 100 micrometers in thickness of this very expensive material to absorb enough solar light. Furthermore, the high-level of crystal purification required makes the fabrication of even the simplest silicon-based planar solar cell a complex, energy-intensive and costly process.
A highly promising alternative would be semiconductor nanowires – one-dimensional strips of materials whose width measures only one-thousandth that of a human hair but whose length may stretch up to the millimeter scale. Solar cells made from nanowires offer a number of advantages over conventional planar solar cells, including better charge separation and collection capabilities, plus they can be made from Earth abundant materials rather than highly processed silicon. To date, however, the lower efficiencies of nanowire-based solar cells have outweighed their benefits.
“Nanowire solar cells in the past have demonstrated fill factors and open-circuit voltages far inferior to those of their planar counterparts,” Yang says. “Possible reasons for this poor performance include surface recombination and poor control over the quality of the p–n junctions when high-temperature doping processes are used.”
At the heart of all solar cells are two separate layers of material, one with an abundance of electrons that function as a negative pole, and one with an abundance of electron holes (positively-charged energy spaces) that function as a positive pole. When photons from the sun are absorbed, their energy is used to create electron-hole pairs, which are then separated at the p-n junction – the interface between the two layers – and collected as electricity.
‘The solution-based cation exchange reaction provides us with an easy, low-cost method to prepare high-quality hetero-epitaxial nanomaterials,’ Yang says. ‘Furthermore, it circumvents the difficulties of high-temperature doping and deposition for typical vapor phase production methods, which suggests much lower fabrication costs and better reproducibility. All we really need are beakers and flasks for this solution-based process. There’s none of the high fabrication costs associated with gas-phase epitaxial chemical vapor deposition and molecular beam epitaxy, the techniques most used today to fabricate semiconductor nanowires.’
Yang and his colleagues believe they can improve the energy conversion efficiency of their solar cell nanowires by increasing the amount of copper sulfide shell material. For their technology to be commercially viable, they need to reach an energy conversion efficiency of at least ten-percent.
Scientists from the University of Kentucky and the University of Louisville have determined that an inexpensive semiconductor material can be “tweaked” to generate hydrogen from water using sunlight.
The research, funded by the U.S. Department of Energy, was led by Professors Madhu Menon and R. Michael Sheetz at the UK Center for Computational Sciences, and Professor Mahendra Sunkara and graduate student Chandrashekhar Pendyala at the UofL Conn Center for Renewable Energy Research. Their findings were published Aug. 1 in the Physical Review Journal (Phys Rev B 84, 075304).
The researchers say their findings are a triumph for computational sciences, one that could potentially have profound implications for the future of solar energy.
Using state-of-the-art theoretical computations, the UK-UofL team demonstrated that an alloy formed by a 2 percent substitution of antimony (Sb) in gallium nitride (GaN) has the right electrical properties to enable solar light energy to split water molecules into hydrogen and oxygen, a process known as photoelectrochemical (PEC) water splitting. When the alloy is immersed in water and exposed to sunlight, the chemical bond between the hydrogen and oxygen molecules in water is broken. The hydrogen can then be collected.
“Previous research on PEC has focused on complex materials,” Menon said. “We decided to go against the conventional wisdom and start with some easy-to-produce materials, even if they lacked the right arrangement of electrons to meet PEC criteria. Our goal was to see if a minimal ‘tweaking’ of the electronic arrangement in these materials would accomplish the desired results.”
Gallium nitride is a semiconductor that has been in widespread use to make bright-light LEDs since the 1990s. Antimony is a metalloid element that has been in increased demand in recent years for applications in microelectronics. The GaN-Sb alloy is the first simple, easy-to-produce material to be considered a candidate for PEC water splitting. The alloy functions as a catalyst in the PEC reaction, meaning that it is not consumed and may be reused indefinitely. UofL and UK researchers are currently working toward producing the alloy and testing its ability to convert solar energy to hydrogen.
Hydrogen has long been touted as a likely key component in the transition to cleaner energy sources. It can be used in fuel cells to generate electricity, burned to produce heat, and utilized in internal-combustion engines to power vehicles. When combusted, hydrogen combines with oxygen to form water vapor as its only waste product. Hydrogen also has wide-ranging applications in science and industry.
Because pure hydrogen gas is not found in free abundance on Earth, it must be manufactured by unlocking it from other compounds. Thus, hydrogen is not considered an energy source, but rather an “energy carrier.” Currently, it takes a large amount of electricity to generate hydrogen by water splitting. As a consequence, most of the hydrogen manufactured today is derived from non-renewable sources such as coal and natural gas.
Sunkara says the GaN-Sb alloy has the potential to convert solar energy into an economical, carbon-free source for hydrogen.
“Hydrogen production now involves a large amount of CO2 emissions,” Sunkara said. “Once this alloy material is widely available, it could conceivably be used to make zero-emissions fuel for powering homes and cars and to heat homes.”
Menon says the research should attract the interest of other scientists across a variety of disciplines.
“Photocatalysis is currently one of the hottest topics in science,” Menon said. “We expect the present work to have a wide appeal in the community spanning chemistry, physics and engineering.”
Duke electrical engineers have developed a man-made material that they say literally allows them to manipulate light at will.
They say that the results of their latest proof-of-concept experiments could lead to the replacement of electrical components with those based on optical technologies, which should allow for faster and more efficient transmission of information, much in the same way that replacing wires with optical fibers revolutionized the telecommunications industry.
The breakthrough revolves around a novel man-made structure known as a metamaterial. These exotic composite materials are not so much a single substance, but an entire structure that can be engineered to exhibit properties not readily found in nature. The structure used in these experiments resembles a miniature set of tan Venetian blinds.
When light passes through a material, even though it may be reflected, refracted or weakened as it passes through, it is still the same light coming out. This is known as linearity.
“For highly intense light, however, certain ‘nonlinear’ materials violate this rule of thumb, converting the incoming energy into a brand new beam of light at twice the original frequency, called the second-harmonic,” said Alec Rose, graduate student in the laboratory of David R. Smith, William Bevan Professor of electrical and computer engineering at Duke’s Pratt School of Engineering.
As an example, he used the crystal in some laser pointers, which transforms the normal laser light into a beam – the output can’t be any stronger than the input beam — in another color, such as green, which would be the second-harmonic. Though they contain nonlinear properties, designing such devices requires a great deal of time and effort to be able to control the direction of the second harmonic, and natural nonlinear materials are quite weak, Rose said.
“Normally, this frequency-doubling process occurs over a distance of many wavelengths, and the direction in which the second-harmonic travels is strictly determined by whatever nonlinear material is used,” Rose said. “Using the novel metamaterials at microwave frequencies, we were able to fabricate a nonlinear device capable of ‘steering’ this second-harmonic. The device simultaneously doubled and reflected incoming waves in the direction we wanted.”