The next time you buy flowers for that special someone, keep in mind that scientists are constructing tiny bouquets smaller than the width of a human hair. As this ScienCentral News video explains, these "nanoflowers" could be used as the ultimate waterproof coating.
Teeny, Tiny Flowers
When people plant gardens, they have to wait for weeks or months to see the beauty of their efforts. But in the lab at the University of Cambridge's Nanoscience Centre, these nanoflowers — tiny blossoms of silicon carbide one thousand times thinner than the diameter of a human hair — "grow" almost instantly. The "gardeners" are nanotechnologists Mark Welland and Ghim Wei Ho, and they're using microscopic metal particles as the "seeds".
"The basic principle for growing all of these types of structures is you take a tiny seed particle, and then you expose that particle to a mixture of 'nutrients,' just like a seed in a real plant," explains Welland. "And in this case the nutrients are different mixtures of gases."
But they don't just grow the nanoflowers for their beauty, they repel water so well that they could be used to waterproof car windshields, eliminating the need for wipers.
Tiny wires of silicon and carbon. image: Mark Welland and Ghim Wei Ho
The researchers begin by heating a tiny droplet of the metal gallium — only a few thousand atoms wide — in a computer-controlled oven. Then they flow methane gas over the droplet, which is attracted to it's molten surface and induces tiny, rigid rods, or wires, of silicon (what sand is made of) and carbon to grow there. By controlling the temperature and flow of the gas, Ho and Welland can weave the wires into flower-like shapes. As well as gardening, Welland also likens the process to baking a cake.
"If you think of an ordinary oven, and you put a piece of pastry in it and heated it up to 300 degrees Fahrenheit, you might get a banana shape; if you heated it to 400 degrees Fahrenheit you might get a bun; and if you heated it to 500 degrees Fahrenheit you might get a flower," he says. "That allows us to control very precisely what kind of structure we get. We can literally sit on the computer that controls this oven, and say, 'we'd like flowers today, please,' press the buttons, and we have a surface coated in flowers."
However, the researchers weren't expecting such beautiful structures when they began the experiment. According to Welland, it was his student Ho who had the original idea to try out the process with the particular mixture of gas and heat they now use. Forming the rigid nanowires, he says, is already a relatively well-known process, "but when we saw these extraordinary flowerlike structures forming, that was really very exciting for us."
Ho entered the images — made using a scanning electron microscope with added color — in a photography contest sponsored by Cambridge's engineering department. Not surprisingly, her strangely beautiful nanoflowers won first prize. But as reported in Discover Magazine, the nanoflowers offer more than just beauty. They also repel moisture so well that a droplet of water bounces off their surface like a beach ball. Nanoflowers could be used to waterproof things like car windshields, and even buildings, making wear and tear from weather a thing of the past. (Because making the nanoflowers requires such high temperatures, however, they could only be applied to materials like glass, concrete, and steel.)
They weave the wires of silicon and carbon into flower-like shapes image: Mark Welland and Ghim Wei Ho
"Because the material itself is made from these tiny wires, and they're all wound up to make the flowers, they're like tiny springs," Welland explains. " It's an example of a property that is unique to nanotechnology, to make a coating of extremely small particles that can completely change the properties of the substance it's applied to."
Even when not woven into visually stunning blossoms, the nanowires themselves exhibit some amazing properties of their own apart from being water-resistant. Welland says they just happen to be ideal for constructing super-efficient solar panels. When spread out over a flat surface facing upwards "like a field of grass" and coated with a special kind of plastic, the nanowires form a "tiny forest" that lets solar energy in, but not back out.
"When you walk into a forest it gets dark because the light is trapped," he says. "The geometry of the wires lets the electricity pop onto them and get immediately carried away, so it can be used."
If mass-produced, such super-efficient solar panels could have potentially world-changing effects, especially in the developing world, where the sun's energy is all too plentiful, but usable electricity is a scarce and expensive commodity. Welland gives an example of transporting temperature-sensitive medicines to a needy community through the unforgiving heat of an African desert. "If you had a cheap and efficient solar panel powering a refrigerator, you could keep those medicines cool and safe."
While the technology is extremely promising, Welland still cautions about putting too much stock in nanoflowers too soon. "As far as publishing a landmark paper that says, 'We've solved the world's energy problems,' that's a long way off," he says. "It's an incremental process." Still, he agrees that nanoscience is advancing at a furious rate. He estimates that his nanoflower technology could be blooming as soon as the end of the decade — no green thumb necessary.