TWENTE, Netherlands, July 14 (UPI) -- To get a better idea of the fluid behaviors underlying the so-called ouzo effect, researchers decided to study the phenomenon on a hydrophobic surface under a microscope.
The ouzo effect is the milky or cloudy appearance that results when water is added to ouzo or other anise-flavored liquors.
Ouzo is a combination of water, alcohol and anise oil. The addition of water causes the solubility of the anise oil to diminish. The oil nucleates, forming nano-size droplets, which coalesce into larger droplets and scatter light, yielding the milky appearance.
The same effect can be watched in detail by putting a single drop of ouzo on a hydrophobic surface, a surface that repels water. That's what scientists at the University of Twente did recently.
As the alcohol evaporates, it leaves behind a higher water-to-anise oil ratio and triggers the ouzo effect. Differences in surface tension causes the oil to spread out and move toward the rim of the hydrophobic petri dish. When all the alcohol evaporates the ouzo effect ceases. The ring of oil droplets begins to move back toward the center as the water evaporates. Eventually, all that is left is a single drop of oil. At room temperature, the process happens in just 15 minutes.
A better understanding of the fluid dynamics of the ouzo effect may help scientists improve fluid-based techniques and technologies, with applications for medical diagnostics and ink-jet printing.
Researchers detailed their study of the ouzo effect in the journal PNAS.