To create hydrophilic/superhydrophobic surfaces, nanoscientists meet the beetles

Filed in archive Materials on June 28, 2006

Researchers at MIT have copied the structure of a beetle's wings to make surfaces with hydrophilic/superhydrophobic patterning, says a report at nanotechweb.org:

The Stenocara beetle, which lives in Africa's Namib desert, uses its wings to capture moisture from the morning fogs that are the most reliable source of water in the region. The fog is so light that normal condensation can't take place.

The insect angles its wings forwards and upwards into the wind. Water droplets in the fog coalesce onto hydrophilic bumps about 100 µm in diameter on the wing surfaces. Eventually the droplets become so heavy that they pull away and roll down the surrounding hydrophobic surface areas of the wing to the beetle's mouth.

To create their artificial structures, Robert Cohen, Michael Rubner and colleagues first made superhydrophic coatings by decorating microporous microstructures with nanoparticles. They coated the resulting rough surface with a hydrophobic network of molecules.
Next the researchers created hydrophilic regions by adding droplets of polyelectrolytes in a water/2-propanol solution.

When such a structure incorporating 750 µm diameter hydrophilic spots was sprayed with a fine mist of water, it caused the droplets to aggregate together at the hydrophilic regions. According to the scientists, the hydrophilic patterns could be created using techniques such as inkjet printing, micropipetting and microcontact printing.

The artificial surfaces could have applications in water harvesting, controlled drug release, open-air microchannel devices and labs-on-a-chip. (photo Gateway-Africa)