Textiles That Don’t Get Wet
August 29, 2013
By mimicking the properties of some natural surfaces, researchers at the Łódź University of Technology in central Poland have developed special textiles that do not get wet because they have a special hydrophobic layer.
These textiles not only stay dry in the rain, but the water rolls off them, picking up any dirt with it and thus making the textile cleaner than it was before.
This self-cleaning, so-called lotus effect, is every homemaker’s dream. The lotus effect refers to the high water repellence exhibited by the leaves of the lotus flower. Dirt particles are picked up by water droplets due to the complex micro- and nanoscopic architecture of the surface, which minimizes adhesion.
In some Asian religions, the lotus plant is revered as a symbol of purity. The roots of the lotus plant take hold in the muddy bottoms of ponds and riverbeds. From there, thick stems rise above the water’s surface and issue giant, pristine leaves and flowers. The leaves remain clean despite the water and mud on which they rest. Water refuses to stick to the leaves of the lotus plant. Instead, it rolls off at the slightest disturbance.
Using the lotus effect, nanotechnologists worldwide started making paints, roof tiles and fabrics with similar characteristics. These are obtained by different methods, including chemical and plasma-based methods. The hydrophobic effect depends on the degree of surface wetness. Also crucial is the angle at which water droplets come into contact with the surface and at which they roll off. So far, researchers worldwide have only been able to achieve a contact angle of 145 degrees and a roll-off angle of several dozen degrees.
The Polish researchers from Łódź have achieved much better results by covering textiles with a superhydrophobic layer with a nano-structure resembling that of a lotus leaf. For this purpose they used the so-called cold plasma, or low-pressure ionized gas, produced in strictly defined conditions.
“We made a lot of attempts to get this effect. So far, no one has been more successful and achieved a longer lasting effect when covering material with a layer protecting its surface from water,” says Prof. Jacek Tyczkowski from the Department of Molecular Engineering at the Łódź University of Technology, head of the research team.
A textile modified in this way is characterized by a contact angle of 164 degrees and a roll-off angle of about 4 degrees, Tyczkowski says.
As a result, water spilled on such a superhydrophobic surface does not wet the surface, but simply rolls off. Additionally, as water moves across the superhydrophobic surface, it picks up and carries away any foreign material, such as dust or dirt. A drop of water does not soak into the fabric and retains its perfectly spherical shape. So, for example, when it rains, the textile stays dry and actually cleans itself.
According to Przemysław Makowski, a Ph.D. student and a member of the research team, materials with such properties are good news for producers and users of specialist clothing. But this technology is also an excellent choice for manufacturers of everyday goods such as upholstery, tablecloths, textile shoes and many other items.
The coating method developed by the Łódź scientists has been applied to polyester and polyamide fabrics, which are usually used to make specialist clothing. But such coatings can also be used in natural fabrics, such as linen or cotton, the researchers say. Importantly, all these materials retain their semipermeability properties in terms of water vapor and air, and have practically unchanged mechanical strength and flexibility, according to the researchers. The nano-coating is chemically bound with the textile material, as a result of which the lotus effect is essentially permanent, they say.
Mountaineering equipment producer Pracownia Sprzętu Alpinistycznego Małachowski, based at Dębowiec near the southern city of Bielsko-Biała, has partnered up with the Łódź University of Technology to put its invention to commercial use. The company is building a large facility in which it be possible to coat large batches of textiles. Interest in the project from industry runs high, according to the researchers, which is hardly surprising, they say: after all everyone wants to stay dry and clean with as little effort as possible.
The invention is the result of a project called “Innovative textiles with hydrophobic and self-cleaning properties for specialist clothing” and financed by the National Center for Research and Development (NCBiR) as part of its IniTech program.
The project was carried out by a consortium made up of the Faculty of Process and Environmental Engineering at the Łódź University of Technology and mountaineering equipment producer Pracownia Sprzętu Alpinistycznego Małachowski. The project lasted two years and was completed in December last year. The project’s budget was zl.1,109,000, including zl.109,000 contributed by Małachowski.
The invention won a gold medal at the 41st International Exhibition of Inventions in Geneva, Switzerland, in April.
Danuta K. Gruszczyńska