Research clarifies the physics of water repelling surfaces

Research clarifies the physics of water repelling surfaces
"Water droplet at DWR-coated surface1" by Brocken Inaglory. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

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 at a molecular level.

The work, published today in Physical 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 between the drop and the surface becomes, making the drop more round.

For extreme hydrophobicity the contact angle is 180°, 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°, 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 near hydrophobic surfaces, even for contact angles much less than 180°."


Explore further

Explained: Hydrophobic and hydrophilic

More information: Physical Review Letters, journals.aps.org/prl/abstract/ … ysRevLett.115.016103
Journal information: Physical Review Letters

Provided by University of Bath
Citation: Research clarifies the physics of water repelling surfaces (2015, July 3) retrieved 19 November 2019 from https://phys.org/news/2015-07-physics-repelling-surfaces.html
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