BREAKTHROUGHS Tiny particles repel water, dirt

Now, the ever-clean suit may be closer than you think.
Imagine washing your clothes by walking in the rain. No laundry. No dry-cleaning bills. A little water from the skies -- or a spray bottle in dry climates -- and you could wipe the dirt off your coat, dress, or trousers.
This vision is a step closer to reality thanks to a new coating developed by researchers at Clemson University in South Carolina. Highly water-repellent, it helps keep dirt from accumulating.
"The concept is based on the lotus plant, whose leaves are well-known for their ability to 'self-clean' by repelling water and dirt," explains Phil Brown, a member of the research team.
One reason lotus leaves are so water-repellent and self-cleaning is that their surfaces contain countless miniature protrusions coated with a water-repellent substance. Water cannot spread out on the leaves and instead rolls around as droplets, removing grime and soil as it moves.
To mimic that effect, the Clemson team uses silver nanoparticles -- 1/1000th the thickness of a human hair -- in its new coating. The particles create miniature protrusions on fabric while the polymer coating binds them to the fabric.
When the treated fabric is exposed to water, "the dirt will be carried away more easily," Dr. Brown says. "You will still need some water to rinse away dirt and stains, but cleaning will be quicker and less frequent."
Unbreakable bond
Unlike today's water-repellent coatings, which wear off over time, the new coating permanently bonds to fibers. It's a polymer film called polyglycidyl methacrylate. Since it only alters the surface of fibers, it can be applied to any commercial textiles, including polyester, cotton, and silk, says Brown.
That versatility could make the treatment popular. The new coating could be applied to children's clothes, hospital garments, sportswear, military uniforms, and raincoats, Brown says. Other possible applications include awning material for buildings and outdoor campers and fabrics for lawn furniture and automobile convertible tops.
Other researchers are also working on self-cleaning clothes using different processes, such as sunlight. Walid Daoud of Hong Kong Polytechnic University is impregnating fabrics with titanium dioxide nanoparticles, which react with natural light to break down dirt. He says his self-cleaning clothes would be ideal for military personnel and travelers who don't have the time or facilities to wash their garments.
Still others are developing odor-fighting fabrics. Two researchers at Hanyang University in South Korea, for example, have tested silver nanoparticles in socks, rugs, napkins, and surgical masks. Brown's team is also trying to engineer antimicrobial particles into the coating to repel body odor and cigarette smoke.
A number of companies have expressed interest in self-cleaning fabrics, according to Andrew Garland of the Institute of Nanotechnology in Scotland. Using Chinese and Korean technology, JR Nanotech in London has developed "SoleFresh" socks that contain silver nanoparticles to reduce foot odor.

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