Using ultrasonic waves and a salt bath, a research team has altered the surface of glass. The brand-new method may lead to glass made without the use of harsh chemicals for self-cleaning windshields, germ-busting surfaces, or maybe even better beer.
When creating specialized glass, such as glass that is water-resistant (hydrophobic), engineers usually have two routes they can take. One is a process that utilizes silanization reactions, in which molecular compounds bind with the surface of the glass. The other involves coating the glass with polymers. Both of these methods rely on the use of toxic chemicals and, in the case of the coatings, the unique properties conveyed to the glass can wear off over time.
Thanks to the new sound-based technique, however, the glass undergoes a permanent structural change without the addition of any other chemicals. The result is glass that can completely shed water or be imbued with a positive electrical charge.
Salt-water bathing
To create the material, a team of scientists at Australia's Curtin University (CU) submerged ordinary glass in a nontoxic bath of organic compounds known as diazonium salts. They then beamed it with a relatively mild set of ultrasound waves tuned to the 24kHz frequency. This created fireworks of sorts, which permanently altered the glass.
"The sound waves create microscopic bubbles in a diazonium salt solution, which then collapse rapidly creating tiny bursts of heat and pressure," said lead researcher Nadim Darwish, from CU's School of Molecular and Life Sciences. "This triggers a reaction that forms a stable, organic layer to the glass, making it either permanently water-repellent or positively charged, depending on the type of diazonium salt used. Unlike conventional coatings that wear off over time, our method creates a chemical bond at the molecular level, making it far more durable and environmentally friendly."
Getting germy
While the water-repellency of the glass created via the new method could lead to self-cleaning skyscrapers or clearer car windshields, it could also play a more serious role in combating germs, enhancing biofuel production, or creating better water filtration systems. That's because there's a range of bacterial and fungal species that are attracted to hydrophobic surfaces. In fact, the water-shedding version of the glass proved to be effective at capturing E. coli. Glass fibers produced with the new method, therefore, could be used in filters to pull such germs out of the water supply.
The researchers also found that the hydrophobic glass was effective in adhering to a species of yeast known as S. cerevisiae, commonly known as baker's or brewer's yeast. This means that the material could have a role in creating more efficient and precise control over fermentation processes, which just might deliver better-tasting beers.
Alternatively, there are species of microalgae that are attracted to positively charged surfaces. As part of the study, the researchers found that a species of microalgae known as C. vulgaris adhered well to the charged version of the glass. This means it could be a good material to use in biofuel production, where the accumulation of this organism is an important step.
The researchers point out that their new method can be applied to any type of glass, and that it can be carried out in any lab that has a basic ultrasonic bath setup.
Their findings have been published in the journal, Advanced Functional Materials.
Source: Curtin University