Breathing underwater

What can be simpler than a block of white foam? When the foam has a hydrophobic surface it becomes superhydrophobic and when it is immersed in water it retains a silvery looking layer of air around its surface. This provides a water-air interface across which oxygen can diffuse from the water into the internal cavity of the foam. In nature, this idea is used by some aquatic insects and water spiders to breathe underwater without the need for a gill. This is called plastron respiration.

Experimental apparatus showing superhydrophobic foam, a fuel cell (to burn oxygen) and an oxygen sensor
SEM image of plastron foam

The image above left shows a superhydrophobic foam with mounted oxygen sensor used to create and investigate a model plastron. By using a zinc-oxide cell inside the foam block to burn up the oxygen, it is possible to show that oxygen is extracted from the water. On the right is a scanning electron microscope image of the pore structure of a methyltriethoxysilane foam; the inset shows a magnified view (x 3).

In the Press

This story caught the attention of the Nottingham Evening Post.

Cartoon from Nottingham Evening Post
Article from Nottingham Evening Post

BBC Radio 4’s Material World also ran a segment: