Oil and water do mix, a group of scientists have discovered. The two substances normally repel one another, but under extreme conditions oil molecules can dissolve in water.
A group of physicists from the University of Edinburgh in the UK filled tiny capsules with water and methane gas and subjected them to intense pressures. It is believed that similar conditions exist below the surface of Neptune and Uranus and on Earth’s ocean bed.
Methane is the simplest hydrocarbon and is often used to investigate how hydrophobic substances, like oil, interact with moisture. The results have been published in Science Advances.
To get the molecules to mingle, they were wedged in between two diamond pieces and squeezed tightly together. The diamond anvil cell applied pressures of up to 20,000 bars (290,075 psi) – about 20 times greater than the pressure at the bottom of the Mariana Trench, the deepest area of the Earth’s ocean.
Water is a polar molecule – the oxygen and hydrogen atoms carry slight positive and negative charges. It’s a good solvent as the charges attract other charged atoms, breaking apart the covalent bonds in other polar molecules like sugars so they can be dissolved.
Substances like oil and methane aren’t polar and are not affected by the charges in water, so they don’t mix. But when the researchers observed the methane in water under such powerful pressures, the methane droplets had disappeared.
They believe that the pressures shrank the methane molecules, but the water molecules stayed roughly the same size as before. The miniature methane molecules can then fit in between the bigger water molecules, allowing them to mix.
The experiment gives researchers a new way to indirectly study conditions at the bottom of the ocean or in planets on the edge of the Solar System.
John Loveday, lead author of the paper and researcher at the University of Edinburgh's Centre for Science at Extreme Conditions in the School of Physics and Astronomy, said: "This is the first time that methane has been shown to mix with water. These exciting findings shed light on how water-repelling substances behave under high pressures, such as those found at the ocean floor or inside planets.
“This could have a huge range of applications, from replacing expensive and environmentally hazardous industrial solvents to modelling planetary bodies like Saturn's largest moon, Titan." ®