New Material Emits Near-Infrared Light For Weeks

Researchers have created a material that can absorb one minute of sunlight and release that energy through near-infrared light for 360 hours, or over two weeks. It can also be charged by indoor lighting. The light it releases is invisible to the human eye, but can be seen with the right equipment. More from PhysOrg:

The material can be fabricated into nanoparticles that bind to cancer cells, for example, and doctors could visualize the location of small metastases that otherwise might go undetected. For military and law enforcement use, the material can be fashioned into ceramic discs that serve as a source of illumination that only those wearing night vision goggles can see. Similarly, the material can be turned into a powder and mixed into a paint whose luminescence is only visible to a select few…

In a process that Pan likens to perfecting a recipe, he and postdoctoral researcher Feng Liu and doctoral student Yi-Ying Lu spent three years developing the material. Initial versions emitted light for minutes, but through modifications to the chemical ingredients and the preparation—just the right amounts of sintering temperature and time—they were able to increase the afterglow from minutes to days and, ultimately, weeks.

“Even now, we don’t think we’ve found the best compound,” Pan said. “We will continuously tune the parameters so that we may find a much better one.”

The researchers spent an additional year testing the material—indoors and out, as well as on sunny days, cloudy days and rainy days—to prove its versatility. They placed it in freshwater, saltwater and even a corrosive bleach solution for three months and found no decrease in performance.

In addition to exploring biomedical applications, Pan’s team aims to use it to collect, store and convert solar energy. “This material has an extraordinary ability to capture and store energy,” Pan said, “so this means that it is a good candidate for making solar cells significantly more efficient.”

Very cool. It sounds like the kind of thing very clever people will find very clever things to do with. 

This material is phosphorescent, which basically means that it emits light like this: photons of light (ex. from the sun) hit electrons in the material. The electrons absorb that energy (generally one electron can absorb one photon) and as a result orbit farther from their atom’s nucleus, better resisting the positive pull of the protons. Eventually the electrons drop back to a less-energetic state that’s closer to the nucleus, and in the process emit their energy back as a photon. This photon is less energetic than the one they first absorbed, so where the sun’s photon was in the visible light range, the emitted photon is, at least in this case, in the near-infrared range.

If all of this happens in one rapid step then it’s called fluorescence, but if the energized electrons take a detour and take a while to emit a photon, it’s called phosphorescence. This is also what happens in fluorescent lightbulbs: electricity causes mercury in the bulbs to emit ultraviolet light, which is more energetic than visible light. This light is absorbed by fluorescent material in the bulbs, then emitted as visible light. In contrast, incandescent lightbulbs emit light because the filament wire inside is heated to a high temperature, causing it to glow. 

Yes, there are awesome things happening in your lightbulbs. Thanks science! Keep in mind though that mercury is toxic, so remember to take your CFLs to the appropriate recycling center instead of trashing them.

The World’s Lightest Material

Via PhysOrg: Researchers have created a material that’s about 100 times as light as styrofoam. 99.99% of it is composed of air, and the other 0.01% is composed very, very carefully.

“The trick is to fabricate a lattice of interconnected hollow tubes with a wall thickness 1,000 times thinner than a human hair,” said lead author Dr. Tobias Schaedler of HRL.

The material’s architecture allows unprecedented mechanical behavior for a metal, including complete recovery from compression exceeding 50 percent strain and extraordinarily high energy absorption.

“Materials actually get stronger as the dimensions are reduced to the nanoscale,” explained UCI mechanical and aerospace engineer Lorenzo Valdevit, UCI’s principal investigator on the project. “Combine this with the possibility of tailoring the architecture of the micro-lattice and you have a unique cellular material.”

Developed for the Defense Advanced Research Projects Agency, the novel material could be used for battery electrodes and acoustic, vibration or shock energy absorption.

This is very interesting. I’m curious about the ratio of lightness to energy absorption (which they pin at “extraordinarily high”) – simplistically, how proportionally strong is it? If you could make armour that weighed as much as a shirt but absorbed a bullet impact, well, that’d be just dandy. However, it seems like future experiments and applications would be limited by the difficulty of creating this material – mass-producing objects with specific features on the nanometre scale is not yet an easy task. The cost, of course, goes without saying. 

So what does that mean? What does it always mean? We wait and see! In 10 years I’ll want my Macbook 99.99% Air. 

Material Marvels with Ainissa Ramirez

Yale University has a new video series on its YouTube channel by Dr. Ainissa Ramirez explaining some of the materials used in modern engineering. Her first video, below, is on ceramics used in space shuttles and how they allow space shuttles to survive the incredible heat of atmospheric reentry. The videos are very short and accessible, although I’d like if they had a bit more details.

Her videos don’t have their own channel, unfortunately, but you can easily find them by searching for Material Marvels; there are four so far. I found these videos via the USA Science & Engineering Festival blog at Science Blogs.

An Explosive Material Based on Nanoparticles and DNA

Researchers have created an explosive composite material using nanoparticles and DNA. Aluminum and copper oxide put together are known to produce energy, but now by using nanoparticles of them their surface area can be increased, and by using DNA to link them together they can be made to self-assemble. DNA exists in organisms in two complementary strands tightly stuck together; these researchers took advantage of this by grafting individual DNA strands onto nanoparticles, mixing them up and letting the complementary DNA strands stick together.

From PhysOrg:

As a result, the complementary strands on each type of nanoparticle bind, turning the original aluminium and copper oxide powder into a compact, solid material which spontaneously ignites when heated to 410 °C (one of the lowest spontaneous ignition temperatures hitherto described in the literature).

If I’m not mistaken, spontaneous ignition here just means that it begins burning (combustion) without being “lit” by a flame or a spark. 

In addition to its low ignition temperature, this composite also offers the advantage of having a high energy density, similar to nitroglycerine: for the same quantity of material, it produces considerably more heat than aluminium and copper oxide taken separately, where a significant part of the energy is not released. In contrast, by using nanoparticles, with their large active surfaces, the researchers were able to approach the maximum theoretical energy for this exothermic chemical reaction.

The high energy density of this composite makes it an ideal fuel for nanosatellites, which weigh a handful of kilograms and are increasingly used. Such satellites are too light to be equipped with a conventional propulsion system once in orbit. However, a few hundred grams of this composite would give them sufficient energy to adjust their trajectory and orientation.

The composite could also have a host of terrestrial applications: ignitors for gas in internal combustion engines or for fuel in aircraft and rocket nozzles, miniature detonators, on-site welding tools, etc. Once its heat is turned into electrical energy, the composite could also be used as a back-up source for microsystems (such as pollution detectors scattered through the environment).

This article really caught my attention due, of course, to their use of DNA as a sort of glue. While the article explains why DNA works, and it seems like using DNA to bind nanoparticles is not a new idea, unfortunately it doesn’t explain why DNA is the best choice in this particular case. Double-stranded DNA normally comes apart at temperatures way below 410°C, which seems like it would be relevant here. 

In trying to find another article to explain the DNA thing, I found the one I just linked above (and here) about using DNA to form crystal lattices out of nanoparticles; you should check it out. Maybe this line of research will open up nanoparticles for wider use and greater self-assembly, which would probably be pretty revolutionary for all of us. 

Skin-Like Pressure Sensor

Researchers at Stanford University have developed a thin, elastic pressure-sensing device that could have applications for restoring touch-sensitive skin to burn victims or amputees, or for giving a subtle sense of touch to machines. They have a pretty decent video explaining and demonstrating it:

From PhysOrg:

That enviable elasticity is one of several new features built into a new transparent skin-like pressure sensor that is the latest sensor developed by Stanford’s Zhenan Bao, associate professor of chemical engineering, in her quest to create an artificial “super skin.” The sensor uses a transparent film of single-walled carbon nanotubes that act as tiny springs, enabling the sensor to accurately measure the force on it, whether it’s being pulled like taffy or squeezed like a sponge.

“This sensor can register pressure ranging from a firm pinch between your thumb and forefinger to twice the pressure exerted by an elephant standing on one foot,” said Darren Lipomi, a postdoctoral researcher in Bao’s lab, who is part of the research team.

“None of it causes any permanent deformation,” he said…

The sensors could be used in making touch-sensitive prosthetic limbs or robots, for various medical applications such as pressure-sensitive bandages or in touch screens on computers.

The key element of the new sensor is the transparent film of carbon “nano-springs,” which is created by spraying nanotubes in a liquid suspension onto a thin layer of silicone, which is then stretched.

When the nanotubes are airbrushed onto the silicone, they tend to land in randomly oriented little clumps. When the silicone is stretched, some of the “nano-bundles” get pulled into alignment in the direction of the stretching.

When the silicone is released, it rebounds back to its original dimensions, but the nanotubes buckle and form little nanostructures that look like springs.

“After we have done this kind of pre-stretching to the nanotubes, they behave like springs and can be stretched again and again, without any permanent change in shape,” Bao said.

Basically, pressure is detected because the silicone in the middle layer of the sensor stores varying amounts of electric charge depending on how far the two carbon nanotube-covered outer silicone layers are from each other, i.e. how compressed the sensor is. 

Earlier, I discussed prosthetic limbs that have a rudimentary sense of touch; I hope more advanced sensors like this one can eventually be applied to prosthetic limbs to more legitimately restore feeling for amputees. That being said, I should note that sensing pressure is only one part of our idea of “touch”; there are separate mechanisms in our nervous system for sensing pain, temperature, and body positioning

Invisibility Using Carbon Nanotubes: Creating a Mirage

This is very cool: researchers have achieved pretty convincing invisibility in a completely different way from the antimagnet I discussed earlier, by creating a mirage using carbon nanotubes. 

Here’s a video of those nanotubes in action, posted by the Institute of Physics and found via Wired:

 

If you’re curious as to how this works – and don’t even pretend like you’re not – I’ll explain the phenomenon, but I have to take a few steps back (or you can skip the next two paragraphs if you’re comfortable with refraction and mirages):

Every medium, like a gas or liquid, has an index of refraction, meaning the speed of light traveling through that medium. It’s called an index of refraction (or refractive index) because when light changes speed – when it hits the border of two media with different refractive indices – it refracts, changing direction slightly. This is why, for example, images underwater, when seen from above water, can look distorted – the light refracts when it hits the air-water surface, so it doesn’t come straight from the visible object to your eye like it would if it were just going through air or water.

(Edit: Here’s a One-Minute-Physics video from New Scientist explaining why light changes speed in different media.)

A refractive index depends on the medium but also the temperature of the medium. Hot air has a lower refractive index than cold air, and this is the cause of mirages, in the common oasis-in-the-desert sense. When light from the sky nears the ground, it refracts, bending away from the highest heat (the ground), meaning it bends up towards your eyes. This means that you see blue light coming from the direction of the ground, and since we’re usually safe to assume that light travels in a straight line (otherwise we really couldn’t trust anything we see), our brain interprets it as something blue on the ground – water. 

So how did these University of Dallas researchers use this to create invisibility? Well, carbon nanotubes – one-molecule-thick sheets of carbon rolled into tubes – are apparently very good at transferring heat to the surrounding air. They can be electrically heated, causing the air around them to rapidly heat up – like sunlight heating up sand, which heats up the air above it – and (some) light that approaches them will be refracted away.

Because the nanotubes shed heat so quickly, they can also be turned on and off very quickly – pretty awesome. I don’t know that I’d want to wear a suit of extremely hot carbon, but I’m sure they’ll put it to amazing use somehow; apparently (via New Scientist) they can use this effect for acoustical cloaking, possibly for submarines. 

“Diamonds are for everything”

I was a bit skeptical at first about this article from Chemistry World, broadly about the uses of diamonds. Why do I care about diamonds? It’s actually pretty cool though; it explains in just the right amount of detail a wide variety of modern and emerging applications of diamonds, from making better solar panels, to single-photon lasers, to stable windows for missions to Venus.

I don’t want to summarize all these summaries of applications, since I think they’re already written pretty succinctly and well, so go check out the article if you want some insight into emerging technology in quite a variety of fields.

With diamonds getting easier to create in a lab, I wonder what the diamond market and culture will look like in 50 years? Many a young fiancé may be in better luck than our generation.

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