Scientists in China said on Thursday they had designed a “smart” window that can both save and generateenergy, and may ultimately reduce heating and cooling costs for buildings.
Scientists in China have designed a window that can save and generate energy. Photo: Reuters
While allowing us to feel close to the outside world, windows cause heat to escape from buildings in winter and let the sun’s unwanted rays enter in summer.
This has sparked a quest for “smart” windows that can adapt to weather conditions outside.
Today’s smart windows are limited to regulating light and heat from the sun, allowing a lot of potential energy to escape, study co-author Yanfeng Gao of the Chinese Academy of Sciences said.
“The main innovation of this work is that it developed a concept smart window device for simultaneous generation and saving of energy.”
Engineers have long battled to incorporate energy-generating solar cells into window panes without affecting their transparency.
Gao’s team discovered that a material called vanadium oxide (VO2) can be used as a transparent coating to regulate infrared radiation from the sun.
VO2 changes its properties based on temperature. Below a certain level it is insulating and lets through infrared light, while at another temperature it becomes reflective.
A window in which VO2 was used could regulate the amount of sun energy entering a building, but also scatter light to solar cells the team had placed around their glass panels, where it was used to generate energy with which to light a lamp, for example.
“This smart window combines energy-saving and generation in one device, and offers potential to intelligently regulate and utilise solar radiation in an efficient manner,” the study authors wrote in the journal Nature Scientific Reports.
(Nanowerk Spotlight) For a long time, scientists have been fascinated by the dramatic changes in color used by marine creatures like squids and octopuses, but they never quite understood the mechanism responsible for this.
Only recently they found out that a neurotransmitter, acetylcholine, sets in motion a cascade of events that culminate in the addition of phosphate groups to a family of unique proteins called reflectins. This process allows the proteins to condense, driving the animal’s color-changing process. The latest findings revealed that there is a nanoscale mechanism behind cephalopods’ ability to change color. Watch this amazing video of a camouflaging octopus:
Having begun to unravel the natural mechanisms behind these amazing abilities, researchers are trying to use this knowledge to make artificial camouflage coatings. New work from the lab of Alon A. Gorodetsky, Assistant Professor at the Henry Samueli School of Engineering at the University of California, Irvine, addresses the challenge of making something appear and disappear when visualized with standard infrared detection equipment.
In a paper in the July 30, 2013, online edition of Advanced Materials (“Reconfigurable Infrared Camouflage Coatings from a Cephalopod Protein”), the team demonstrates graphene-templated, biomimetic camouflage coatings that possess several important advantages. “We used reflectin, a protein that is important for cephalopod structural coloration, as a functional optical material,” Gorodetsky explains to Nanowerk. “We fabricated thin films from this protein, whose reflectance – and coloration – could be dynamically tuned over a range of over 600 nm and even into the infrared (in the presence of an appropriate stimulus).
Our approach is environmentally friendly and compatible with a wide range of surfaces, potentially allowing many simple objects to acquire camouflage capabilities.” The novelty of these findings lies in the functionality of the team’s thin-films within the infrared region of the electromagnetic spectrum, roughly 700nm to 1200nm, which matches the standard imaging range of infrared visualization equipment. This region is not commonly accessible to biologically derived materials. Gorodetsky notes that reflectin’s tunable optical properties compare favorably to those of artificial polymeric materials.
“Given these advantages, our dynamically tunable, infrared-reflective films represent a crucial first step towards the development of reconfigurable and disposable biomimetic camouflage technologies for stealth applications,” says Gorodetsky. ” I can also imagine applications in energy efficient reflective coatings and biologically inspired optics.” The team began their studies by developing a protocol for the production of the histidine-tagged reflectin A1 (RfA1). Experimenting with a variety of substrates and surface treatments for the reliable formation of RfA1 thin films, they achieved best results by spincasting 5 to 10 nm films of graphene oxide on glass substrates. They then spread RfA1 onto the graphene oxide-coated substrates, yielding smooth films over centimeter areas.
Illustration depicting the appearance of the RfA1 film in the absence and presence of an external stimulus (acetic acid), when visualized with an infrared camera. (Reprinted with permission from Wiley-VCH Verlag)
These films showed a distinct coloration, depending on their thickness. For instance, a 125 nm-thick film was blue and a 207 nm-thick film was orange. “Inspired by the dynamic optical properties of reflectin nanostructures, we sought to shift the reflectance of our RfA1 films into the infrared region of the electromagnetic spectrum,” says Gorodetsky.
“Given that some squid can dynamically modulate their skin reflectance across the entire visible spectrum and even out to near infrared wavelengths of ∼800 nm, we postulated that it should also be possible to tune the reflectance of our RfA1 thin films across a similar, or even larger, wavelength range. Thus, we sought conditions that would significantly increase the thickness of our RfA1 films and, consequently, shift their reflectance spectra toward the infrared.”
To that end, the researchers explored the response of their RfA1 coatings to a variety of chemical stimuli. They discovered that exposing the films to vapor from a concentrated acetic acid solution induced a large, reversible shift in the reflectance spectra, caused by the acid-induced swelling of the closely packed RfA1 nanoparticles in the film. “With the goal of fabricating dynamically tunable camouflage materials, which will self-reconfigure in response to an external signal, we are currently developing alternative, milder strategies for triggering coloration changes in our material,” Gorodetsky describes the team’s future work plans.
Yang’s lab developed an earlier form of the solar cell with a near-infrared light-sensitive polymer. The cell produces energy by absorbing mainly infrared light, not visible light. The cell developed in that first round was 70 percent transparent, and achieved a power-generating efficiency of 4 percent.
The new version of the solar cell from Yang’s lab is a tandem device with two thin light-activated polymer solar cells that absorb more light than the single-cell version. The new device also combines transparent and semi-transparent polymer cells, and a layer between the two cells to reduce energy loss.
Tests conducted by Yang’s team show the tandem device achieves a conversion rate — percentage of energy from the sun converted to electric power — of 7.3 percent, compared to 4 percent in the earlier version. The new device captures up to 80 percent of infrared light, with a small amount of light from the visible spectrum, compared to about 40 percent of infrared light absorbed in the earlier single-cell version.
The process to generate the solar cells, say the researchers, uses low temperatures, which makes production of the cells more feasible. The cells can also be produced to appear in various shades of light gray, green, or brown to blend in with building exteriors, windows, or electronic surfaces.
“We anticipate this device,” says Yang, “will offer new directions for solar cells, including the creation of solar windows on homes and office buildings.”
Abstract: Recently, significant research efforts have been made to develop complex nanostructures to provide more sophisticated control over the optical and electronic properties of nanomaterials. However, there are only a handful of semiconductors which allow control over their geometry via simple chemical processes. Here, we present a molecularly seeded synthesis of a complex nanostructure, SiC tetrapods, and report on their structural and optical properties. The SiC tetrapods exhibit narrow linewidth photoluminescence at wavelengths spanning the visible to near infrared spectral range. Synthesized from low-toxicity, earth abundant elements, these tetrapods are a compelling replacement for technologically important quantum optical materials that frequently require toxic metals such as Cd and Se. This new, previously unknown geometry of SiC nanostructures is a compelling platform for biolabeling, sensing, spintronics and optoelectronics.
Stanford scientists have developed a new technique for watching blood flow in living animals. It involves carbon nanotubes and lasers, and will allow researchers to better study arterial diseases and therapies.
By Bjorn Carey
These images of a mouse’s blood vessels show the difference in resolution between traditional near-infrared fluorescence imaging (top) and Stanford’s new NIR-II technique (bottom).
Stanford scientists have developed a fluorescence imaging technique that allows them to view the pulsing blood vessels of living animals with unprecedented clarity. Compared with conventional imaging techniques, the increase in sharpness is akin to wiping fog off your glasses.
The technique, called near infrared-II imaging, or NIR-II, involves first injecting water-soluble carbon nanotubes into the living subject’s bloodstream.
The researchers then shine a laser (its light is in the near-infrared range, a wavelength of about 0.8 micron) over the subject; in this case, a mouse.
The light causes the specially designed nanotubes to fluoresce at a longer wavelength of 1-1.4 microns, which is then detected to determine the blood vessels’ structure.
That the nanotubes fluoresce at substantially longer wavelengths than conventional imaging techniques is critical in achieving the stunningly clear images of the tiny blood vessels: longer wavelength light scatters less, and thus creates sharper images of the vessels. Another benefit of detecting such long wavelength light is that the detector registers less background noise since the body does not does not produce autofluorescence in this wavelength range.
In addition to providing fine details, the technique – developed by Stanford scientists Hongjie Dai, professor of chemistry; John Cooke, professor of cardiovascular medicine; and Ngan Huang, acting assistant professor of cardiothoracic surgery – has a fast image acquisition rate, allowing researchers to measure blood flow in near real time.
The ability to obtain both blood flow information and blood vessel clarity was not previously possible, and will be particularly useful in studying animal models of arterial disease, such as how blood flow is affected by the arterial blockages and constrictions that cause, among other things, strokes and heart attacks.
L.A. CiceroGraduate student Guosong Hong, left, and chemistry Professor Hongjie Dai look at the vascular structures in a mouse model of peripheral arterial disease with blood vessels shown in great detail using their new imaging technique called near-infrared II fluorescence imaging.
“For medical research, it’s a very nice tool for looking at features in small animals,” Dai said. “It will help us better understand some vasculature diseases and how they respond to therapy, and how we might devise better treatments.”
Because NIR-II can only penetrate a centimeter, at most, into the body, it won’t replace other imaging techniques for humans, but it will be a powerful method for studying animal models by replacing or complementing X-ray, CT, MRI and laser Doppler techniques.
The next step for the research, and one that will make the technology more easily accepted for use in humans, is to explore alternative fluorescent molecules, Dai said. “We’d like to find something smaller than the carbon nanotubes but that emit light at the same long wavelength, so that they can be easily excreted from the body and we can eliminate any toxicity concerns.”
The lead authors of the study are graduate student Guosong Hong of the Department of Chemistry and research assistant Jerry Lee of the School of Medicine. Other co-authors include graduate student Joshua Robinson and postdoctoral scholars Uwe Raaz and Liming Xie. The work was supported by the National Cancer Institute, the National Heart, Lung and Blood Institute and a Stanford Graduate Fellowship. The work was published online in Nature Medicine.
Scientists in China said on Thursday they had designed a “smart” window that can both save and generate energy, and may ultimately reduce heating and cooling costs for buildings.
