Defying conventional wisdom, water can float on oil

April 4, 2012

Defying thousands of years of conventional wisdom, scientists are reporting that it is possible for water to float on oil, a discovery they say has important potential applications in cleaning up oil spills that threaten seashores and fisheries. Their report appears in ACS' journal Langmuir.

Chi M. Phan and colleagues 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 float on more dense liquids. So with a density of about 58 pounds per cubic foot floats on , 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.

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

This video is not supported by your browser at this time.
A video of the experiment. Video: ACS

Explore further: Hurricane-caused oil spills threaten gulf

More information: Can Water Float on Oil? Langmuir, 2012, 28 (10), pp 4609–4613

The floatability of water on oil surface was studied. A numerical model was developed from the Young–Laplace equation on three interfaces (water/oil, water/air, and oil/air) to predict the theoretical equilibration conditions. The model was verified successfully with an oil/water system. The stability of the floating droplet depends on the combination of three interface tensions, oil density, and water droplet volume. For practical purposes, however, the equilibrium contact angle has to be greater than 5° so the water droplet can effectively float. This result has significant applications for biodegrading oil wastes.

Related Stories

'Frozen smoke:' The ultimate sponge for cleaning up oil spills

February 16, 2009

Scientists in Arizona and New Jersey are reporting that aerogels, a super-lightweight solid sometimes called "frozen smoke," may serve as the ultimate sponge for capturing oil from wastewater and effectively soaking up environmental ...

Sugar battles oil spills

August 12, 2010

The environment has often suffered from the catastrophic effects of an oil spill, the most recent example being the oil spill in the Gulf of Mexico. The search for ways to remove oil from polluted water is therefore urgent. ...

Recommended for you

Yarn from slaughterhouse waste

July 29, 2015

ETH researchers have developed a yarn from ordinary gelatine that has good qualities similar to those of merino wool fibers. Now they are working on making the yarn even more water resistant.

Findings illuminate animal evolution in protein function

July 27, 2015

Virginia Commonwealth University and University of Richmond researchers recently teamed up to explore the inner workings of cells and shed light on the 400–600 million years of evolution between humans and early animals ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.