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Researchers have gained valuable insights into the behaviour of water on strongly hydrophobic (water-repelling) surfaces. Understanding this behaviour should help scientists develop new types of surfaces with applications ranging from textiles to surgical tools.

In a GW4 collaboration, Professor Nigel Wilding and Professor Robert Evans of the University of Bristol used Bath's High Performance Computer to simulate the properties of water at hydrophobic surfaces at a molecular level.

The work, published today in 萌妹社区ical Review Letters, reveals that the physics of hydrophobic surfaces is controlled by a phenomenon known as critical drying.

When water is placed on a substance that is hydrophobic, it reduces its contact with the substance by rolling up into a drop, like rain on a freshly waxed car. The more hydrophobic a surface is, the larger the contact angle between the drop and the surface becomes, making the drop more round.

For extreme hydrophobicity the contact angle is 180掳, the drop is spherical in shape, and we say that the substance is "dry".

Professor Wilding explained: "Previously the nature of the dry state has been poorly understood.

"Our simulations have established that it is an example of a surface critical phenomenon. This is because as the contact angle approaches 180掳, the compressibility of water close to the surface diverges to infinity.

"At a microscopic level this means that the density of water molecules near the surface undergo huge fluctuations: some regions have a liquid-like density, while others will have a much lower vapour-like density.

"We have shown that critical drying causes these density fluctuations near hydrophobic surfaces, even for contact angles much less than 180掳."