Water floating on oil can clean oil spills

Sydney, April 5 (IANS) Scientists have stumbled upon a discovery that challenges conventional wisdom -- water can sometimes float on oil, offering a potential solution to cleaning up of oil spills.

Chi M. Phan and colleagues from Curtin University department of chemical engineering point out that the ancient Greek philosopher Aristotle made an early attempt to explain flotation around 350 B.C.

Today, most people know that less dense liquids float on more dense liquids. So crude oil with a density of about 58 pounds per cubic foot floats on sea water, which has a density of 64 pounds per cubic foot - and not vice-versa. Correct?

Phan's team decided to test that notion with computer models and in the lab, the journal Langmuir reported.

They report that in certain cases, the conventional wisdom is wrong. By adding tiny amounts of water to a floating droplet of oil, they found that the ability of water drops to float on the surface of an oil bath depends on both the size of the droplet and the type of oil, according to a university statement.

Commercial vegetable oil has enough surface tension -- the force between liquid molecules that allows beads of water to form or insects to walk on water -- at its interfaces with air and water to support a droplet's weight, while pure mineral oils do not.

At the same time, they found that vegetable oil could not support drops bigger than about one-one hundredth of a cubic inch.

The authors suggest the new knowledge could help clean up oil spills, where water-borne, oil-eating microbes will mix more easily into the oil if suspended in the tiny droplets they describe.

"This result can lead to a new and advanced mechanism in processing oil/water mixtures, such as biodegrading process of unwanted oils, including vegetable oils, sand oil tailings and oil spillages," the authors said.