clhs sciblog

Leaves from the lotus plant have an ability to repel nearly all the rain and dew that hits them. Scientists who want to make new waterproof materials are beginning to look at them. Chuan-Hua Chen and his team from Duke University have created a material that repels water like the lotus plant. They took high speed videos that show the small droplets of water bouncing off of their surfaces. Scientists already knew that the microscopic spikes and fibers covering the leaves work together to repel the water. Larger drops of water tend to roll off, but smaller drops bounce off without using any outside force. Chen found that large droplets roll off the side of the lotus leaf when it shakes. He tested this by strapping a leaf to the middle of a 100 watt speaker and filming the drops as they rolled off. When the speaker was off, the drops stuck to the spikes and the hairs on the leaf. Chen thinks that lotuses may have evolved their long thin stems to pick up and amplify vibrations to repel the water and keep their leaves dry. So, Chen coated a bumpy silicon base with carbon nanotubes and water-proof compound hexadecanethiol. He left it to collect water condensation, but he discovered just a few big droplets on the surface. He used a high speed camera to find out that when two small drops merge, a “liquid bridge” forms between them and then expands out to make one big drop. The force of the liquid bridge hitting the surface makes the drops bounce off.

Chen and his team have looked into several potential applications for this kind of material. They have mainly looked at the clothing industry. They also thought it would make cleaning easier.