Cercetătorii de la Columbia Engineering au inventat o acoperire polimerică de înaltă performanță PDRC cu goluri de aer nano-microscale care acționează ca un răcitor spontan de aer și pot fi fabricate, vopsite și aplicate ca vopseaua pe acoperișuri, clădiri, rezervoare de apă, chiar și nave spațiale – orice poate fi vopsit. Ei au folosit o tehnică bazată pe soluție bazată pe fază, care conferă polimerului o structură poroasă asemănătoare spumei. Vasele de aer din polimerul poros se împrăștie și reflectă lumina soarelui, datorită diferenței în indicele de refracție dintre golurile de aer și polimerul înconjurător. Polimerul devine alb și astfel evită încălzirea solară, în timp ce emitentul său intrinsecă îl face să piardă eficient căldura spre cer. Studiul este publicat astăzi online în știință („Acoperiri polimerice poroase ierarhice pentru o răcire radiativă pasivă în timpul zilei” ).
Posted: Sep 27, 2018
Polymer coating cools down buildings
(Nanowerk News) With temperatures rising and heat-waves disrupting lives around the world, cooling solutions are becoming ever more essential. This is a critical issue especially in developing countries, where summer heat can be extreme and is projected to intensify. But common cooling methods such as air conditioners are expensive, consume significant amounts of energy, require ready access to electricity, and often require coolants that deplete ozone or have a strong greenhouse effect.
An alternative to these energy-intensive cooling methods is passive daytime radiative cooling (PDRC), a phenomenon where a surface spontaneously cools by reflecting sunlight and radiating heat to the colder atmosphere. PDRC is most effective if a surface has a high solar reflectance (R) that minimizes solar heat gain, and a high, thermal emittance (ε) that maximizes radiative heat loss to the sky. If R and ε are sufficiently high, a net heat loss can occur, even under sunlight.
Developing practical PDRC designs has been challenging: many recent design proposals are complex or costly, and cannot be widely implemented or applied on rooftops and buildings, which have different shapes and textures. Up to now, white paints, which are inexpensive and easy to apply, have been the benchmark for PDRC. White paints, however, usually have pigments that absorb UV light, and do not reflect longer solar wavelengths very well, so their performance is only modest at best.
Researchers at Columbia Engineering have invented a high-performance exterior PDRC polymer coating with nano-to-microscale air voids that acts as a spontaneous air cooler and can be fabricated, dyed, and applied like paint on rooftops, buildings, water tanks, vehicles, even spacecraft—anything that can be painted. They used a solution-based phase-inversion technique that gives the polymer a porous foam-like structure. The air voids in the porous polymer scatter and reflect sunlight, due to the difference in the refractive index between the air voids and the surrounding polymer. The polymer turns white and thus avoids solar heating, while its intrinsic emittance causes it to efficiently lose heat to the sky. The study is published online today in Science („Hierarchically porous polymer coatings for highly efficient passive daytime radiative cooling”).
Passive daytime radiative cooling (PDRC) involves simultaneously reflecting sunlight and radiating heat into the cold sky to achieve a net heat loss. The process, which is spontaneous, can cool down structures to sub-ambient temperatures.
The team – Yuan Yang, assistant professor of materials science and engineering; Nanfang Yu, associate professor of applied physics; and Jyotirmoy Mandal, lead author of the study and a doctoral student in Yang’s group (all department of applied physics and applied mathematics) – built upon earlier work that demonstrated that simple plastics and polymers, including acrylic, silicone, and PET, are excellent heat radiators and could be used for PDRC. The challenges were how to get these normally transparent polymers to reflect sunlight without using silver mirrors as reflectors and how to make them easily deployable.
They decided to use phase-inversion because it is a simple, solution-based method for making light-scattering air-voids in polymers. Polymers and solvents are already used in paints, and the Columbia Engineering method essentially replaces the pigments in white paint with air voids that reflect all wavelengths of sunlight, from UV to infrared.
When exposed to the sky, the porous polymer PDRC coating reflects sunlight and emits heat to attain significantly cooler temperatures than typical building materials or even the ambient air.
“This simple but fundamental modification yields exceptional reflectance and emittance that equal or surpass those of state-of-the-art PDRC designs, but with a convenience that is almost paint-like,” says Mandal.
The researchers found their polymer coating’s high solar reflectance (R > 96%) and high thermal emittance (ε ∼ 97%) kept it significantly cooler than its environment under widely different skies, e.g. by 6°C in the warm, arid desert in Arizona and 3°C in the foggy, tropical environment of Bangladesh.
“The fact that cooling is achieved in both desert and tropical climates, without any thermal protection or shielding, demonstrates the utility of our design wherever cooling is required,” Yang notes.
When exposed to the sky, the porous polymer PDRC coating reflects sunlight and emits heat to attain significantly cooler temperatures than typical building materials or even the ambient air.
When exposed to the sky, the porous polymer PDRC coating reflects sunlight and emits heat to attain significantly cooler temperatures than typical building materials or even the ambient air.
The team also created colored polymer coatings with cooling capabilities by adding dyes. “Achieving a superior balance between color and cooling performance over current paints is one of the most important aspects of our work,” Yu notes. “For exterior coatings, the choice of color is often subjective, and paint manufacturers have been trying to make colored coatings, like those for roofs, for decades.”
The group took environmental and operational issues, such as recyclability, bio-compatibility, and high-temperature operability, into consideration, and showed that their technique can be generalized to a range of polymers to achieve these functionalities. “Polymers are an amazingly diverse class of materials, and because this technique is generic, additional desirable properties can be conveniently integrated into our PDRC coatings, if suitable polymers are available,” Mandal adds.
“Nature offers many ways for heating and cooling, some of which are extremely well known and widely studied and others that are poorly known. Radiative cooling—by using the sky as a heat sink—belongs to the latter group, and its potential has been strangely overlooked by materials scientists until a few years ago,” says Uppsala University Physics Professor Claes-Göran Granqvist, a pioneer in the field of radiative cooling, who was not involved with the study. “The publication by Mandal et al. highlights the importance of radiative cooling and represents an important breakthrough by demonstrating that hierarchically porous polymer coatings, which can be prepared cheaply and conveniently, give excellent cooling even in full sunlight.”
Illustration showing how passive daytime radiative cooling (PDRC) involves simultaneously reflecting sunlight and radiating heat into the cold sky to achieve a net heat loss. The process, which is spontaneous, can cool down structures to sub-ambient temperatures.
Yang, Yu, and Mandal are refining their design in terms of applicability, while exploring possibilities such as the use of completely biocompatible polymers and solvents. They are in talks with industry about next steps.
“Now is a critical time to develop promising solutions for sustainable humanity,” Yang notes. “This year, we witnessed heat waves and record-breaking temperatures in North America, Europe, Asia, and Australia. It is essential that we find solutions to this climate challenge, and we are very excited to be working on this new technology that addresses it.”
Yu adds that he used to think that white was the most unattainable color: “When I studied watercolor painting years ago, white paints were the most expensive. Cremnitz white or lead white was the choice of great masters, including Rembrandt and Lucian Freud. We have now demonstrated that white is in fact the most achievable color. It can be made using nothing more than properly sized air voids embedded in a transparent medium. Air voids are what make snow white and Saharan silver ants silvery.”
As if “stealth camouflage” adaptive camouflage/visual cloaking tech isn’t enough, Russian military defense contractor Rostec just demonstrated “operative passive exoskeletons” for Russian Ratnik-3-type future soldiers/warfighters. Oh, and they’re not done. Rostec is also reportedly developing an active exoskeleton, and they’ve already designed a prototype that’ll be shown at an exhibition, soon. So, it would appear that US military infantry warfighters are going to have their hands full, if World War III (WWIII) ever breaks out, and the Russians are on the opposition.
This is the part that intrigues DefenseReview (DR), though:
“The passive exoskeletons are completely autonomous and require no power sources, servomotors, electronics and sensors.”
We’re interested to see how that actually works, and how its capabilities differ from the active exoskeleton tech, which we assume is even more capable in terms of strengh, speed and load-bearing enhancement.
Defense Review will try to glean as much information as possible on Rostec’s active exoskeleton technology, and do a follow-up piece on it. If it weren’t already being used for yogurt, a good name for the technology would be “Activia”–has a nice Russian ring to it.
Efectuarea de piele electronică pentru a imita proprietățile tactile de detectare a pielii umane este o zonă activă de cercetare pentru diverse aplicații, cum ar fi electronica portabilă, robotică și proteză. Una dintre provocările majore în cercetarea electronică a pielii este diferențierea diverselor stimuli externi, în special între tulpină și presiune. O altă problemă este depozitarea uniformă a pielii electrice pe obiecte tridimensionale în formă neregulată.
Posted: Sep 24, 2018
Robotic electronic skin made from spray-coated tactile sensor
(Nanowerk News) Robots will be able to conduct a wide variety of tasks as well as humans if they can be given tactile sensing capabilities.
The solution-based process is easily scalable to accommodate for large areas and can be coated as a thin-film on 3-dimensional irregularly shaped objects via spray coating.
These conditions make their processing technique unique and highly suitable for robotic electronic skin or wearable electronic applications.
Spray Coated Tactile Sensor on a 3-D Surface for Robotic Skin. (Video: KAIST)
The making of electronic skin to mimic the tactile sensing properties of human skin is an active area of research for various applications such as wearable electronics, robotics, and prosthetics. One of the major challenges in electronic skin research is differentiating various external stimuli, particularly between strain and pressure. Another issue is uniformly depositing electrical skin on 3-dimensional irregularly shaped objects.
To overcome these issues, the research team led by Professor Steve Park from the Department of Materials Science and Engineering and Professor Jung Kim from the Department of Mechanical Engineering developed electronic skin that can be uniformly coated on 3-dimensional surfaces and distinguish mechanical stimuli.
The new electronic skin can also distinguish mechanical stimuli analogous to human skin. The structure of the electronic skin was designed to respond differently under applied pressure and strain. Under applied strain, conducting pathways undergo significant conformational changes, considerably changing the resistance.
On the other hand, under applied pressure, negligible conformational change in the conducting pathway occurs; e-skin is therefore non-responsive to pressure. The research team is currently working on strain insensitive pressure sensors to use with the developed strain sensors.
Detecting mechanical stimuli using electrical impedance tomography. (Image: KAIST)
The research team also spatially mapped the local strain without the use of patterned electrode arrays utilizing electrical impedance tomography (EIT). By using EIT, it is possible to minimize the number of electrodes, increase durability, and enable facile fabrication onto 3-dimensional surfaces.
Professor Park said, “Our electronic skin can be mass produced at a low cost and can easily be coated onto complex 3-dimensional surfaces. It is a key technology that can bring us closer to the commercialization of electronic skin for various applications in the near future.”
Prin înființarea mai multor senzori, cercetătorii au învățat să „vadă” ce nu se află în evidență;au dezvoltat o metodă de a vedea în jurul colțurilor prin calcularea modului în care undele luminoase emise de o sursă reflectă obiecte ca oamenii și apoi reflectă zidurile
au reusit sa creeze materiale asemanatoare cu grafenul dintr-o sinteza moleculara. Acestea sunt materiale MUV-1, robuste, cu o mare versatilitate chimică, care sunt capabile să aibă proprietăți fizice diferite, cum ar fi magnetismul.Această prelucrabilitate, adăugată faptului că MUV-1 are stabilitate mecanică și chimică, a permis oamenilor de știință să construiască membrane bazate pe aceste materiale și să izoleze primele monostraturi magnetice pe baza chimiei de coordonare.
Posted: Sep 20, 2018
Scientists develop 2D materials capable of having magnetism
(Nanowerk News) An international team of physicists and chemists, headed by Eugenio Coronado and Guillermo Mínguez Espallargas, researchers of Valencia University’s Molecular Science Institute (ICMol) have been able to create materials similar to graphene from a molecular synthesis. These are MUV-1, robust materials with great chemical versatility that are capable of having different physical properties such as magnetism.
Different bidimensional metallic-organic materials have been designed in this project – the MUV-1, or Materials of the University of Valencia – from a molecular synthesis. Unlike with graphene and other bidimensional materials, this new synthesis makes it possible to modify the surface’s properties at will, changing it for example from hydrophobic to hydrophilic, or adding physical properties such as magnetism, which are complicated to insert.
The study opens the possibility to integrate and apply these materials in different technological areas such as nanoelectronics and spintronics, or to the development of ultrasensitive molecular sensors, which can recognise and selectively detect certain molecules.
Since the discovery of graphene – the first bidimensional material comprised of a layer of carbon atoms -, numerous inorganic bidimensional materials have been created. One of the problems of said materials is that it is not possible to modify their properties by anchoring the molecules of its surface, which blocks the addition of new properties or the improvement of its processability.
Furthermore, the study of magnetism in bidimensional materials of an inorganic nature known to date represents a scientific challenge, as they are all chemically unstable in environmental conditions.
The new molecular synthesis of bidimensional materials that the ICMol proposes to the international scientific community offers solutions to both problems. On one hand, the possibility to functionalise these 2D materials at will makes it possible to easily alter their properties, making them hydrophobic or hydrophilic, for example.
Said processability, added to the fact that the MUV-1 have mechanical and chemical stability, has allowed scientists to build membranes based on these materials and isolate the first magnetic monolayers based on coordination chemistry.
The international group that has developed this research is comprised of scientists from seven European institutions – ICMol of Valencia, Institute of Chemical Technology of Valencia’s Polytechnic University, Spanish National Research Council, University of Manchester (United Kingdom), Laue Langevin Institute of Grenoble (France), University of Lisbon (Portugal) and Technologic University of Delft (Netherlands).
The Valencia University team, which heads the work, is comprised of Javier López Cabrelles, Samuel Mañas Valero, Guillermo Mínguez Espallargas and Eugenio Coronado.
Un nou costum anti-război rezistent la înțepături a fost lansat în ordine pentru a ajuta în mod eficient la protecția profesioniștilor care au de-a face cu revolte de închisoare, dezordine publică, căutări în masă sau alte perturbări serioase
Oamenii de știință de la Laboratorul Național Lawrence Berkeley (Berkeley Lab) și Universitatea din California (UC) Berkeley au elaborat o manta ultra-subțire de invizibilitate „pielii”, care poate fi conformă cu forma unui obiect și ascunde-l din detecție cu lumină vizibilă. Deși această mantie este doar de dimensiuni microscopice, principiile care stau la baza tehnologiei ar trebui să îi permită să fie redimensionate pentru a ascunde și elementele macroscopice.Invizibilitatea mantalelor de piele la scară microscopică s-ar putea dovedi valoroasă pentru ascunderea aspectului detaliat al componentelor microelectronice sau pentru scopurile de criptare a securității. La macroscala, printre alte aplicații, mantalele de invizibilitate s-ar putea dovedi utile pentru afișajele 3D.
Posted: Sep 18, 2015
Nano-thin invisibility cloak makes 3D objects disappear (w/video)
(Nanowerk News) Invisibility cloaks are a staple of science fiction and fantasy, from Star Trek to Harry Potter, but don’t exist in real life, or do they? Scientists at the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have devised an ultra-thin invisibility „skin” cloak that can conform to the shape of an object and conceal it from detection with visible light. Although this cloak is only microscopic in size, the principles behind the technology should enable it to be scaled-up to conceal macroscopic items as well.
This image shows a 3-D illustration of a metasurface skin cloak made from an ultrathin layer of nanoantennas (gold blocks) covering an arbitrarily shaped object. Light reflects off the cloak (red arrows) as if it were reflecting off a flat mirror. (Image courtesy of Xiang Zhang group, Berkeley Lab/UC Berkeley)
Working with brick-like blocks of gold nanoantennas, the Berkeley researchers fashioned a „skin cloak” barely 80 nanometers in thickness, that was wrapped around a three-dimensional object about the size of a few biological cells and arbitrarily shaped with multiple bumps and dents. The surface of the skin cloak was meta-engineered to reroute reflected light waves so that the object was rendered invisible to optical detection when the cloak is activated.
„This is the first time a 3D object of arbitrary shape has been cloaked from visible light,” said Xiang Zhang, director of Berkeley Lab’s Materials Sciences Division and a world authority on metamaterials – artificial nanostructures engineered with electromagnetic properties not found in nature. „Our ultra-thin cloak now looks like a coat. It is easy to design and implement, and is potentially scalable for hiding macroscopic objects.”
Zhang, who holds the Ernest S. Kuh Endowed Chair at UC Berkeley and is a member of the Kavli Energy NanoSciences Institute at Berkeley (Kavli ENSI), is the corresponding author of a paper describing this research in Science („An ultrathin invisibility skin cloak for visible light”).
It is the scattering of light – be it visible, infrared, X-ray, etc., – from its interaction with matter that enables us to detect and observe objects. The rules that govern these interactions in natural materials can be circumvented in metamaterials whose optical properties arise from their physical structure rather than their chemical composition. For the past ten years, Zhang and his research group have been pushing the boundaries of how light interacts with metamaterials, managing to curve the path of light or bend it backwards, phenomena not seen in natural materials, and to render objects optically undetectable. In the past, their metamaterial-based optical carpet cloaks were bulky and hard to scale-up, and entailed a phase difference between the cloaked region and the surrounding background that made the cloak itself detectable – though what it concealed was not.
This short video clip shows how the activation of a metasurface cloak made from an ultrathin layer of nanoantennas can render a 3D object invisible. When the cloak is turned “on,” the bump-shaped object being illuminated in the center white spot disappears from view. The object reappears when the cloak is turned “off.” (Video courtesy of Xiang Zhang and his research group, Berkeley Lab/UC Berkeley)
„Creating a carpet cloak that works in air was so difficult we had to embed it in a dielectric prism that introduced an additional phase in the reflected light, which made the cloak visible by phase-sensitive detection,” says co-lead author Xingjie Ni, a recent member of Zhang’s research group who is now an assistant professor at Penn State University. „Recent developments in metasurfaces, however, allow us to manipulate the phase of a propagating wave directly through the use of subwavelength-sized elements that locally tailor the electromagnetic response at the nanoscale, a response that is accompanied by dramatic light confinement.”
In the Berkeley study, when red light struck an arbitrarily shaped 3D sample object measuring approximately 1,300 square microns in area that was conformally wrapped in the gold nanoantenna skin cloak, the light reflected off the surface of the skin cloak was identical to light reflected off a flat mirror, making the object underneath it invisible even by phase-sensitive detection. The cloak can be turned „on” or „off” simply by switching the polarization of the nanoantennas.
„A phase shift provided by each individual nanoantenna fully restores both the wavefront and the phase of the scattered light so that the object remains perfectly hidden,” says co-lead author Zi Jing Wong, also a member of Zhang’s research group.
The ability to manipulate the interactions between light and metamaterials offers tantalizing future prospects for technologies such as high resolution optical microscopes and superfast optical computers. Invisibility skin cloaks on the microscopic scale might prove valuable for hiding the detailed layout of microelectronic components or for security encryption purposes. At the macroscale, among other applications, invisibility cloaks could prove useful for 3D displays.
