When oil met water

When oil and water are poured together they meet each other head-on to form a strong and rigid boundary between each other.

The discovery by researchers at Imperial College contradicts previous research that suggested that when oil and water meet, a tiny layer of water vapour, invisible to the human eye, forms between them, keeping them apart and creating a weak and fluctuating boundary between the two substances.

Oils are hydrophobic substances, which means they repel water and cannot mix with it. This is illustrated by the way any kind of oil and water remain separate if they are poured into the same vessel.

Scientists are interested in understanding exactly how this separation works because these oil-water boundaries play a key role in many chemical and biological processes, from the design of detergents to the function of oily biological membranes, such as the walls of human cells that enclose their content.

The Imperial team used computer simulations of water and oil to show that there is no thin layer of water vapour between the oil and the water as had been predicted - instead, the two liquids were shown to be in direct contact with each other along the length of a boundary, which was strong and robust and not weakly fluctuating as expected.