Mini-boats are 'strongest ever'

By Victoria Gill Science reporter, BBC News

The mesh keeps water out, even when the boat is below the surface

Researchers in China have made copper float, and used it to build some of the most buoyant boats ever made.

These postage stamp-sized vessels are made from copper mesh, which the scientists treated to make its surface extremely water-repellent.

Even when the upper edges of the boats are below the surface, the material is so efficient at repelling water that they are still able to float.

The work was published in the journal Applied Materials and Interfaces.

The team treated the copper in two stages. First, they deposited very tiny structures on its surface, essentially giving the metal a rough and uneven coating.

We believe these boats are some of the strongest ever built Qinmin Pan

The second stage was to dip it into a "hydrophobic", or water-repelling, chemical.

The result is a metal with a "superhydrophobic" surface, and a boat that floats despite being covered in holes.

"Water won't penetrate the pores in the bottom of the boats, even when they are carrying a load," said Dr Qinmin Pan, the chemist from Harbin Institute of Technology who led the research.

Robotic future

Superhydrophobic materials already have many hi-tech applications.

They are particularly useful in "microfluidic devices" where the flow of miniscule amounts of liquid have to be controlled. In these devices, water can be used to carry information on a chip.

But according to Dr Pan, this is the first time they have been used to make boats.

"We believe these boats are some of the strongest ever built - in terms of the mass they can carry," said Dr Pan.

Each tiny vessel is able to carry almost 15g - about the weight of an empty drinks can.

Although it will not be possible to scale up the use of these materials to full-sized ships, Dr Pan says the technology used to make his "novel boats" could, in future, be applied to aquatic robots.

Leaves and sharks

It is technology inspired by surfaces in nature.

The most famous example is that of the lotus leaf, which has waxy projections that reduce its contact with water.

The rough surface of a shark's skin reduces drag as it swims

When water hits the rough surface of the leaf, it forms beads which roll off and take any dirt with them - leaving it dry and pristine.

Professor Ralf Blossey's research, at the Interdisciplinary Research Institute in Lille, France, focuses on understanding exactly how superhydrophobic materials work.

"There are lots of ways that this [property] has evolved in nature," he said.

"Sharks, for example, have a rough surface; they have protrusions on their skin that reduce contact with water. This reduces drag and makes them faster and more efficient swimmers.

"Hydrophobic coatings are already being used to paint aeroplanes to exploit the same effect."

Professor Blossey says the miniature copper boats are "a very nice illustration" of the effect.