For much of the last half century, botanists have known that the lotus leaf exhibits very high water repellence, or superhydrophobicity. This is useful to the plant because as water is slicked off the surface of the lotus leaves, dirt, bacteria, and algae are also washed off by this water. This allows the lotus to prevent blockage of photosynthesis by dirt, and protects it against other parasitic organisms (the bacteria and algae).
|Water sticks to most surfaces, but not the lotus leaf - From Ralf Pfeifer via Wikipedia|
The reason for this strong water repellence was elucidated by examining the surface of the lotus leaf at the microscopic level. When looked at with an electron microscope by the botanist Wilhelm Barthlott, the lotus leaf was seen to have tiny pyramids or papillae. These points minimize the contact the water has with the surface, preventing strong bonds from forming between the leaf and water droplet. This is illustrated below.
|Graphic by William Thielicke showing pyramidal structure of the surface of the Lotus leaf. This surface guarantees that water won't stick to the surface of the lotus leaf, or the Groasis Waterboxx lid that has similar microscopic pyramids on its surface.|
As the water won't stick to the surface of the leaf, it slides off, taking substances and organisms harmful to the lotus with it.
A device which mimics this property was developed a few years ago for the planting of trees in very dry places. Its designer knew that for as much rain and dew to be collected as possible, the lid or collecting dish would need to hold onto very little water, instead channeling it to the roots of a plant. This device was called the Groasis Waterboxx.
When Pieter Hoff was designing the Groasis Waterboxx, he wanted to ensure that all possible condensation and rainwater that fell on the lid of his Waterboxx was channeled into the Waterboxx basin for later use by the plant. He of course used a sloped, corrugated lid, made of polypropylene (a plastic known to be water repellent). However, he also added pyramids to the surface of the lid at the microscopic level, mimicking the ingenious lotus effect. All of these features meant that even a very thin layer of dew deposited each night could be saved and used by the growing plant. The ability of the Groasis Waterboxx to propel water downward in shown in this video.
People assume the smoothest surfaces are the slickest, but this is not true when it comes to water. Water cannot form strong bonds on the surface of the lotus leaf, and for the same reason it can't stick to the surface of the Waterboxx.
|Here you see morning dew on the tomato leaves as well as the edge of the lid (which lacks the lotus leaf inspired pyramids) but none on the corrugated lotus leaf inspired lid - water that settled here and already been stored.|
|The thorny devil's spikes aren't just for protection - they are also to collect dew and funnel it to his mouth. Photo by Baras, public domain|
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