Iron Napkin
by the University of Rochester press release
In nature, trees pump tons of water from the roots to the very tops, sometimes tens of meters in height. And this happens thanks to capillary forces. But scientists have learned to evoke the same abilities in a flat piece of metal, and so effectively that trees can only envy.
The new technology was developed by Chunlei Guo and Anatoly Vorobyov, who use a powerful femtosecond laser to work real miracles with metals. Another miracle can open a new page in the creation of diagnostic equipment and chemical analyzers, coolers for processors, or simply turn almost any metal surface into an effective protection against bacteria.
"We can change the structure of the surface layers of almost any piece of metal," rejoices Chunlei Guo, "in such a way as to control its interaction with the liquid. We can make the liquid flow through it and choose the direction of this flow ourselves."
Exposure to very short-term pulses of powerful laser radiation leads to a radical restructuring of the structure of the surface layers of the metal. A femtosecond laser acts literally a few quadrillionths of a second. At the same time, a variety of formations, nanoscale depressions, or bulges, or grooves can be obtained on the metal.
The process in which water rises against the forces of gravity on a piece of metal is very similar to what happens when we collect tea spilled on the table with a napkin. This is a manifestation of the capillary effect associated with wetting, the interaction of liquid and solid molecules.
It is the nanoscale structures that are formed during laser processing that change the strength of this interaction, and they do it at the request of scientists. Under certain conditions, the force of attraction of the liquid molecules to the metal surface becomes higher than to each other, and forces the liquid to be distributed over it as thinly as possible – even if this "contradicts" the forces of gravity. And the larger the surface area, the faster the evaporation process goes, so that the metal treated by Go and Vorobyov becomes a kind of "napkin".
But if, during laser treatment, tiny tubules are also created on the metal surface, then you can also control the direction in which the liquid will be distributed. "Imagine a system of water channels, but reduced to the size of a miniature metal chip," says Guo, "and we will be able to conduct chemical or biological analysis of the liquid, having the smallest amounts of it on our hands." For a blood test, you will not need to squeeze half a test tube out of your finger: a barely noticeable drop will be enough.
By the same method, scientists have learned to achieve the opposite effect: a sharp decrease in the efficiency of the interaction between water and metal molecules – that is, the creation of a hydrophobic ("water-repellent") effect. This allows us to say that after a certain laser treatment, the metal surface receives effective antibacterial properties, because the vast majority of bacteria require water for life.
So far, such processing of a metal fragment with an area of a coin requires more than 30 minutes of processing. However, scientists are confident that they will be able to improve the technology.
Portal "Eternal youth" http://vechnayamolodost.ru/11.06.2009