Tag Archives: nanotechnology

Technica

Waterproof Clothes

Another technology barrier falls by the wayside as textile and materials science researchers perfect an ultra-hydrophobic spray. No more getting your clothes wet in a downpour.

From the Guardian:

I hate being rained on. I especially hate it when it’s cold. You’d have thought that with all our 21st-century Google-Glass exploring-Mars engineering marvellousness, we would have made more progress on the problem of rain. But no. The umbrella is a few thousand years old and is nowhere near an optimal solution, especially in blustery windy weather. Wet-weather clothing works if you wear it, but most people don’t because it looks so awful.

From a materials-science perspective, the best solution for the British weather would be an invisible waterproof coating that you can spray on the clothes you actually do want to wear. Excitingly such materials have now been invented; they borrow tricks from nature, and they may yet get us singing in the rain.

Traditional waterproofing involves materials that are hydrophobic – in other words molecules that repel water. Waxes and other oily materials fall into this category because of the way they share their electrons at an atomic scale. Water molecules are polar, which means they have plus and minus charged ends. Waxes and oils prefer their electrons more equally distributed and so find it hard to conform to the polarity of water, and in the stand-off they repel each other. Hence oil and water don’t mix. This hydrophobic behaviour is bad for vinaigrettes but good for waterproofing.

Nature uses this trick too but is much better at it. Go into a garden during a rain shower and have a look at how many leaves repel water so effectively that water droplets sit like jewels glistening on their surface. Lotus leaves have long been known to have this superhydrophobic property, but no one knew why until electron microscopes revealed something very odd about the surface of the lotus leaf. There is a waxy material there, yes, but it is arranged on the surface in the form of billions of tiny microscopic bumps. When a drop of water sits on a hydrophobic surface it tries to minimise its area of contact, because it wants to minimise its interaction with the non-polar waxy material.

The bumps on the lotus leaf drastically increase this area of waxiness, forcing the droplet to sit up precariously on the tips of the bumps. In this, the Cassie-Baxter state, the droplet becomes very mobile and quickly slides off the leaf. So by manipulating just the bumpiness of its surface, lotus leaves are far better at repelling water.

The mobility of the droplets has another effect. By zooming around the surface of the leaf rather than sticking, the droplets of water collect small particles of dust, hoovering them up. This cleaning mechanism of these superhydrophobic surfaces is called the lotus effect.

Superhydrophobic surfaces have been synthesised and studied in labs for decades, but it is only recently that commercial versions have been produced. Now there are quite a few coming on to the market (eg neverwet.com), and they are impressive – when water is poured on to these surfaces it behaves like mercury and bounces off.

The trick, as with the lotus leaf, is to create a microscale patterned non-polar surface. The fact that these sophisticated surfaces can be sprayed out of a can is a triumph of nanotechnology. As with the lotus leaf these coatings not only keep things dry, they also keep them clean, since a lot of what constitutes dirt arrives on your clothes as splashes of liquid that subsequently dry leaving a residue. If the droplets of bolognese sauce, curry or mud don’t stick but bounce off, then they won’t leave a stain.

There are many other applications for these coatings, such as reducing the window cleaning bills on skyscrapers; keeping paint clean on cars; making sofas immune to red wine; and in its key role as waterproofer extraordinaire, keeping your mobile phone safe when it is dropped down the loo.

Read the entire article here.

Technica

Steam Without Boiling Water

Despite what seems to be an overwhelmingly digital shift in our lives, we still live in a world of steam. Steam plays a vital role in generating most of the world’s electricity, steam heats our buildings (especially if you live in New York City), steam sterilizes our medical supplies.

So, in a research discovery with far-reaching implication, scientists have succeeded in making steam at room temperature without actually boiling water. All courtesy of some ingenious nanoparticles.

[div class=attrib]From Technology Review:[end-div]

Steam is a key ingredient in a wide range of industrial and commercial processes—including electricity generation, water purification, alcohol distillation, and medical equipment sterilization.

Generating that steam, however, typically requires vast amounts of energy to heat and eventually boil water or another fluid. Now researchers at Rice University have found a shortcut. Using light-absorbing nanoparticles suspended in water, the group was able to turn the water molecules surrounding the nanoparticles into steam while scarcely raising the temperature of the remaining water. The trick could dramatically reduce the cost of many steam-reliant processes.

The Rice team used a Fresnel lens to focus sunlight on a small tube of water containing high concentrations of nanoparticles suspended in the fluid. The water, which had been cooled to near freezing, began generating steam within five to 20 seconds, depending on the type of nanoparticles used. Changes in temperature, pressure, and mass revealed that 82 percent of the sunlight absorbed by the nanoparticles went directly to generating steam while only 18 percent went to heating water.

“It’s a new way to make steam without boiling water,” says Naomi Halas, director of the Laboratory for Nanophotonics at Rice University. Halas says that the work “opens up a lot of interesting doors in terms of what you can use steam for.”

The new technique could, for instance, lead to inexpensive steam-generation devices for small-scale water purification, sterilization of medical instruments, and sewage treatment in developing countries with limited resources and infrastructure.

The use of nanoparticles to increase heat transfer in water and other fluids has been well studied, but few researchers have looked at using the particles to absorb light and generate steam.

In the current study, Halas and colleagues used nanoparticles optimized to absorb the widest possible spectrum of sunlight. When light hits the particles, their temperature quickly rises to well above 100 °C, the boiling point of water, causing surrounding water molecules to vaporize.

Precisely how the particles and water molecules interact remains somewhat of a mystery. Conventional heat-transfer models suggest that the absorbed sunlight should dissipate into the surrounding fluid before causing any water to boil. “There seems to be some nanoscale thermal barrier, because it’s clearly making steam like crazy,” Halas says.

The system devised by Halas and colleagues exhibited an efficiency of 24 percent in converting sunlight to steam.

Todd Otanicar, a mechanical engineer at the University of Tulsa who was not involved in the current study, says the findings could have significant implications for large-scale solar thermal energy generation. Solar thermal power stations typically use concentrated sunlight to heat a fluid such as oil, which is then used to heat water to generate steam. Otanicar estimates that by generating steam directly with nanoparticles in water, such a system could see an increased efficiency of 3 to 5 percent and a cost savings of 10 percent because a less complex design could be used.

[div class=attrib]Read the entire article after the jump.[end-div]

[div class=attrib]Image: Stott Park Bobbin Mill Steam Engine. Courtesy of Wikipedia.[end-div]

Technica

Nanotech: Bane and Boon

An insightful opinion on the benefits and perils of nanotechnology from essayist and naturalist, Diane Ackerman.

[div class=attrib]From the New York Times:[end-div]

“I SING the body electric,” Walt Whitman wrote in 1855, inspired by the novelty of useful electricity, which he would live to see power streetlights and telephones, locomotives and dynamos. In “Leaves of Grass,” his ecstatic epic poem of American life, he depicted himself as a live wire, a relay station for all the voices of the earth, natural or invented, human or mineral. “I have instant conductors all over me,” he wrote. “They seize every object and lead it harmlessly through me… My flesh and blood playing out lightning to strike what is hardly different from myself.”

Electricity equipped Whitman and other poets with a scintillation of metaphors. Like inspiration, it was a lightning flash. Like prophetic insight, it illuminated the darkness. Like sex, it tingled the flesh. Like life, it energized raw matter. Whitman didn’t know that our cells really do generate electricity, that the heart’s pacemaker relies on such signals and that billions of axons in the brain create their own electrical charge (equivalent to about a 60-watt bulb). A force of nature himself, he admired the range and raw power of electricity.

Deeply as he believed the vow “I sing the body electric” — a line sure to become a winning trademark — I suspect one of nanotechnology’s recent breakthroughs would have stunned him. A team at the University of Exeter in England has invented the lightest, supplest, most diaphanous material ever made for conducting electricity, a dream textile named GraphExeter, which could revolutionize electronics by making it fashionable to wear your computer, cellphone and MP3 player. Only one atom thick, it’s an ideal fabric for street clothes and couture lines alike. You could start your laptop by plugging it into your jeans, recharge your cellphone by plugging it into your T-shirt. Then, not only would your cells sizzle with electricity, but even your clothing would chime in.

I don’t know if a fully electric suit would upset flight electronics, pacemakers, airport security monitors or the brain’s cellular dispatches. If you wore an electric coat in a lightning storm, would the hairs on the back of your neck stand up? Would you be more likely to fall prey to a lightning strike? How long will it be before a jokester plays the sound of one-hand-clapping from a mitten? How long before late-night hosts riff about electric undies? Will people tethered to recharging poles haunt the airport waiting rooms? Will it become hip to wear flashing neon ads, quotes and designs — maybe a name in a luminous tattoo?

Another recent marvel of nanotechnology promises to alter daily life, too, but this one, despite its silver lining, strikes me as wickedly dangerous, though probably inevitable. As a result, it’s bound to inspire labyrinthine laws and a welter of patents and to ignite bioethical debates.

Nano-engineers have developed a way to coat both hard surfaces (like hospital bed rails, doorknobs and furniture) and also soft surfaces (sheets, gowns and curtains) with microscopic nanoparticles of silver, an element known to kill microbes. You’d think the new nano-coating would offer a silver bullet, be a godsend to patients stricken with hospital-acquired sepsis and pneumonia, and to doctors fighting what has become a nightmare of antibiotic-resistant micro-organisms that can kill tens of thousands of people a year.

It does, and it is. That’s the problem. It’s too effective. Most micro-organisms are harmless, many are beneficial, but some are absolutely essential for the environment and human life. Bacteria were the first life forms on the planet, and we owe them everything. Our biochemistry is interwoven with theirs. Swarms of bacteria blanket us on the outside, other swarms colonize our insides. Kill all the gut bacteria, essential for breaking down large molecules, and digestion slows.

Friendly bacteria aid the immune system. They release biotin, folic acid and vitamin K; help eliminate heavy metals from the body; calm inflammation; and prevent cancers. During childbirth, a baby picks up beneficial bacteria in the birth canal. Nitrogen-fixing bacteria ensure healthy plants and ecosystems. We use bacteria to decontaminate sewage and also to create protein-rich foods like kefir and yogurt.

How tempting for nanotechnology companies, capitalizing on our fears and fetishes, to engineer superbly effective nanosilver microbe-killers, deodorants and sanitizers of all sorts for home and industry.

[div class=attrib]Read the entire article after the jump.[end-div]

[div class=attrib]Image courtesy of Technorati.[end-div]

Technica

Viral Nanoelectronics

[div class=attrib]From Scientific American:[end-div]

M.I.T. breeds viruses that coat themselves in selected substances, then self-assemble into such devices as liquid crystals, nanowires and electrodes.

For many years, materials scientists wanted to know how the abalone, a marine snail, constructed its magnificently strong shell from unpromising minerals, so that they could make similar materials themselves. Angela M. Belcher asked a different question: Why not get the abalone to make things for us?

She put a thin glass slip between the abalone and its shell, then removed it. “We got a flat pearl,” she says, “which we could use to study shell formation on an hour-by-hour basis, without having to sacrifice the animal.” It turns out the abalone manufactures proteins that induce calcium carbonate molecules to adopt two distinct yet seamlessly melded crystalline forms–one strong, the other fast-growing. The work earned her a Ph.D. from the University of California, Santa Barbara, in 1997 and paved her way to consultancies with the pearl industry, a professorship at the Massachusetts Institute of Technology, and a founding role in a start-up company called Cambrios in Mountain View, Calif.
[div class=attrib]More from theSource here.[end-div]