The freezing point of water may seem like a simple fact, but the story of how water freezes is a little more complicated. In water at the freezing temperature, ice crystals usually form around a dust particle in the water. Without dust particles, the temperature can get even lower before the water turns to ice. In the laboratory, for example, researchers have shown that it’s possible to cool water down to -40º C — without producing a single ice cube. This “supercooled” water has many uses, such as playing an important part in helping frogs and fish survive low temperatures.

In a more recent study, scientists showed how the temperature at which water freezes can be changed using electric charges. In this experiment, water exposed to a positive charge froze at higher temperatures than water exposed to a negative charge.

“We are very, very surprised by this result,” Igor Lubomirsky told Science News. Lubomirsky, who worked on the experiment, works at the Weizmann Institute of Science in Rehovot, Israel.

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Charge depends on tiny particles called electrons and protons. These particles, together with particles called neutrons, make up atoms, which are the building blocks of all matter. An electron is a negative charge and a proton is a positive charge. In atoms with the same number of protons as electrons, the positive and negative charges cancel each other out and make the atom act like it has no charge.

Water already has its own kind of charge. A water molecule is made of one oxygen atom and two hydrogen atoms, and when these atoms get together they make a shape like Mickey Mouse’s head, with the two hydrogen atoms being the ears. The atoms bond together by sharing their electrons. But the oxygen atom tends to hog the electrons, pulling them more toward itself. As a result, the side with the oxygen atom has a bit more negative charge. On the side with two hydrogen atoms, the protons aren’t balanced out as well by electrons, so that side has a bit of positive charge.

Because of this imbalance, scientists have long suspected that forces due to electric charges could change the freezing point of water. But this idea has been hard to test and harder to verify. Earlier experiments looked at water freezing on metal, which is a good material to use because it holds electric charges, but water can freeze on metal with or without a charge. Lubomirsky and his colleagues got around this problem by separating the water and the charged metal with a special type of crystal that could generate electric fields when heated or cooled.

In the experiment, the scientists placed four crystal discs inside four copper cylinders, then lowered the temperature of the room. As the temperature dropped, water droplets formed on the crystals. One disc was designed to give the water a positive charge; one a negative charge; and two gave no charge at all to the water.

The water droplets on the crystal with no electric charge froze at -12.5º C on average. Those on a crystal with a positive charge froze at a higher temperature of -7º C. And on the crystal with a negative charge, the water froze at -18º C — the coldest of all.

Lubomirsky told Science News he was “delighted” with his experiment, but the hard work is only beginning. They’ve taken the first step — observation — but now they have to explore the deep science of what is causing what they observed. These scientists have managed to show that electric charges affect the freezing temperature of water. But they don’t yet know why.

POWER WORDS

electron A stable, negatively charged subatomic particle.

proton A stable, positively charged subatomic particle

electric charge The property of matter responsible for all electric phenomena, in particular for the force of the electromagnetic interaction, occurring in two forms arbitrarily designated negative and positive.

electric field A region of space characterized by the existence of a force generated by electric charge.

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To help support themselves, the Huichol create beautiful artwork, including paintings made from yarn and sculptures made from beads. They sell their art in cities hundreds of miles away from their villages. Often, they travel long distances by foot. And without electricity—at home or on the road, they can only work during daylight hours.

Portable lights are bringing much-needed light to the Huichol people, who live in the beautiful and rugged Sierra Madre of Mexico.Huichol art is full of symbols and meaning. This traditional yarn painting (above) was made by Huichol artist Rojelio Beuites

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When it gets dark, they must stop whatever they’re doing, explains Huichol community leader Miquel Carillo. The sales of their artwork are essential to this economy, where farming is difficult and crops often fail.

“We can only work during the day,” Carillo tells a group of researchers as night approached. “Because now, as you see, we can’t see anything, and it’s still so early. Nobody can do anything. We just wait for the sun to come up again.”

Now, a team of scientists, designers, and architects is using new technologies to provide the Huichol with light after the sun sets—no plugs necessary. The scientists’ technique involves weaving tiny electronic crystals into fabrics that can be made into clothes, bags, or other items.

A Huichol woman weaves new, light-producing technology into a traditional cloth bag.

Kennedy & Violich Architecture, Ltd.

By collecting the sun’s energy during the day, these lightweight textiles provide bright white light at night. Their inventors have named the textiles “Portable Lights.”

Portable Lights have the potential to transform the lives of people without electricity around the world, says project leader Sheila Kennedy, head of Kennedy & Violich Architecture, Ltd., in Boston, Mass.

“Our invention,” Kennedy says, “came from seeing how we could transform technology we saw everyday in the United States and move it into new markets for people who didn’t have a lot of money.”

As part of the Portable Light Project, Kennedy and colleagues have already donated light-producing textiles to two Huichol communities. They are working now with a group of wandering, or semi-nomadic, people in Australia. Eventually, they hope to deliver Portable Lights to similar groups around the world.

See the light

At the core of Portable Light technology are devices called high-brightness light-emitting diodes, or HB LEDs. These tiny lights appear in digital clocks, televisions, streetlights, and the blinking red lights on some sneakers.

LEDs are completely different from the light bulbs that you screw into lamps at home. Most of those glass bulbs belong to a type called incandescent lights. Inside, electricity heats a metal coil to about 4,000 degrees Fahrenheit, or 2,200 degrees Celsius. At that scorching temperature, bulbs give off light we can see.

In an incandescent light bulb, like the one above, electricity heats a metal coil until it becomes extremely hot and gives off light.

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Ninety percent of energy produced by incandescent lights, however, is heat–and invisible. With all that wasted energy, bulbs burn out quickly. They are also bulky, can get hot, and are easily broken.

LEDs, on the other hand, are like tiny pieces of rock made up of molecules that are arranged in a crystal structure. When an electric current passes through an LED, the crystal structure vibrates and produces light.

Unlike incandescent bulbs, they can produce light of various colors. Within an LED, the type of molecules and their particular arrangement determines what color is produced.

For example, green LEDs make up the blinking, hand-shaped signals that tell pedestrians when it’s safe to cross a street. LEDs in a remote control, on the other hand, give off invisible infrared light that tells a television to change channels.

Light-emitting diodes come in a variety of sizes and colors. What they all share in common is their tiny size compared to incandescent bulbs. The purple-colored LED in the lineup above emits infrared light.

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LEDs are tiny and extremely lightweight. There are no breakable glass parts. While the technology is still somewhat expensive, researchers are increasingly looking to LEDs for a wide variety of applications, including Portable Lights.

“A lot of people see LEDs as being the future of lighting,” says Casey Smith, a technologist in Bozeman, Mont., and a member of the Portable Light team. He developed much of the technology that make Portable Lights work.

The spark

The Portable Light team found a way to weave two LEDs into a plastic-coated textile. When turned on, these LEDs can make the entire piece of fabric glow.

Their next challenge was to figure out how to power the LEDs without electricity. The researchers knew that they wanted to tap the sun’s energy, but they couldn’t use standard solar panels such as those found on rooftops. These bulky glass panels would be too big and heavy for the Huichol to carry as they traveled through the mountains.

Instead, the researchers used a new type of solar panel, which is flat and flexible, like a placemat. Just 10 inches long and 5 inches wide, these panels can be easily sewn onto a piece of fabric.

A Mexican boy who lives in the Sierra Madre carries a woven bag, complete with LED’s and a solar panel.

Kennedy & Violich Architecture, Ltd.

Circuits connect the solar panel to a lithium ion battery—the type of battery found in laptops and cellular phones. And the battery, in turn, is connected to the two LEDs in the fabric. A tough layer of plastic protects the circuitry.

With just 3 hours of exposure to sunlight, the battery accumulates enough charge to power a portable light for 10 hours, Kennedy says. A membrane switch, like the soft buttons on a microwave oven, allows a user to turn the lights on or off.

Portable light technology provides enough light for this Huichol girl to do her homework at night, even though there is no electricity in her village.

Kennedy & Violich Architecture, Ltd.

A Portable Light weighs less than a pound and can withstand abuse because textiles are strong for their weight. Kennedy has dropped Portable Light units from as high as 30 feet off the ground without damaging them.

“With no heavy parts to break, they just float down,” she says.

Lighting the way

The Huichol have quickly accepted Portable Light technology by incorporating it into their cultural traditions.

Huichol women have long woven colorful bags on a handmade device called a backstrap loom. They use these bags to tote their belongings because their traditional clothing does not have pockets.

Each bag contains intricate patterns and symbols that reflect cultural stories and family identities. Bags and patterns are passed from generation to generation.

“It is more than just a bag,” Kennedy says. “It is vital to their life.”

Portable lights are bringing much-needed light to the Huichol people, who live in the beautiful and rugged Sierra Madre of Mexico.

Tim&Annette/Wikipedia

The Huichol are now weaving Portable Lights into new patterns in their bags, Kennedy says. And the researchers on the Portable Light team can’t keep up with demand. More than 40 women have put their names on a waiting list.

On the other side of the world, in the Central Australian desert, Kennedy and colleagues are working to bring Portable Lights to the Arrernte people, who travel across large stretches of desert without electricity.

One goal is to use the technology to power cell phones that teachers in local schools can use to download lesson plans. That way, Kennedy says, kids won’t have to travel to cities to get an education.

It may be hard to imagine life without access to lights at night. As the Portable Light project expands, researchers hope that fewer and fewer people will have that problem.

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