Message #39 From:
TheMachine Date: May 6, 2008 05:13:22 PM
Nano-coating makes for an awesome splash
18:00 25 February 2007
NewScientist.com news service
Gaia Vince
When a spherical object such as a ball is dropped onto water, it
sometimes pierces the surface with a gentle “plop”, and sometimes slams
through creating a big splash.
Lydéric
Bocquet at the Claude-Bernard University in Lyon, France, and
colleagues found these varied impacts a puzzling phenomenon. Why would
two spheres of the same size, shape and material create such different
effects?
Now
Bocquet believes his team has found the answer: the molecular treatment
of the surface of the spheres – whether it attracts or repels water –
is paramount, he says.
The
team tried balls of various materials, including aluminium, steel and
glass, before choosing the sphere with the most hydrophilic (water
attracting) surface. This turned out to be a glass ball, cleaned
thoroughly with hydrogen peroxide, sulphuric acid and alcohol. Watch the ball plop gently though the water (requires Quicktime, 1.5 MB).
The
reason for the difference is that during impact, the hydrophobic
molecules create an air cavity where the water molecules retreat, which
leads to the splash, Bocquet explains. In contrast, liquid reaches up
the sides of the hydrophilic glass surface, so no air can enter, and no
splash occurs.
The
finding could prove useful in reducing splashing that occurs during
high-speed water impacts, for example during air-to-water torpedo
entries, he says. Here, a nano-layer could prevent air bubbles forming
at the tip of the torpedo.
