According to the American Fun Science website, Austrian researchers wrote in the recent issue of Science magazine that they have created the purest water droplets in the world. This pure water will help explain why some self-cleaning surfaces (such as those coated with titanium dioxide) are covered with a mysterious molecular film when in contact with air and water.
When the surface of titanium dioxide is exposed to ultraviolet light, a reaction occurs, "devouring" any organic compounds on it, which endows this surface with some useful properties, such as mirrors coated with titanium dioxide being able to disperse water vapor even when installed in a bathroom filled with water vapor. But if it is left in a dark room for a long time, a mysterious substance will form on its surface. One of the authors of the research report, chemist Rick Dybold from the Technical University of Vienna, said: 'There are four laboratories worldwide studying this issue, and currently there are four different explanations.'“
Most of the explanations proposed by scientists involve a chemical reaction between titanium dioxide and surrounding water vapor, but after applying ultrapure water to this surface, Debold and colleagues found that the presence of water did not cause the formation of this film.
Creating such ultra pure water droplets is a major challenge, as water is easily contaminated by fine impurities and absolutely pure water does not exist. For this purpose, the Debold team designed a specialized device to increase the purity of water to its limit.
One chamber of the device is vacuum, and a finger hanging from its top is cooled to minus 140 ° C. Researchers release purified water vapor samples from a nearby chamber into this vacuum chamber, and the water forms an ice column at the tip of the finger. Then heat and melt this ice column, and it will drip onto a piece of titanium dioxide below, which will quickly evaporate in this ultra-low pressure chamber. During this period, there was no formation of molecular films on the surface of titanium dioxide that some researchers suspected were related to water.
Subsequent scanning of titanium dioxide using a microscope and spectroscope revealed that the film is completely composed of no water or water related compounds. On the contrary (vinegar has a sour taste) and formic acid appear on the surface. Both are by-products of plant growth and only exist in trace amounts in the air. But obviously, these materials are enough to float around and dirty the self-cleaning surface.
