A strange leaf has inspired a new type of material that can affect the flow of liquids. The scaly texture of the leaf forces fluids with different properties to flow in opposite directions 鈥� even if one of those directions is uphill.
Araucaria is a genus of evergreen trees 鈥� including some known as monkey puzzles 鈥� with spiky, cylindrical leaves made up of smaller, scale-like segments called ratchets. at City University of Hong Kong and his colleagues examined these leaves after noticing them in a park and bringing some back to the lab.
They found out that the shapes of these layers of ratchets give the leaves a special property. When placed on an Araucaria leaf, liquids with a low surface tension 鈥� the degree to which the particles in the surface layer of the liquid stick together 鈥� flow along the direction that the ratchets point, towards the tip of the leaf. Liquids with a high surface tension flow in the opposite direction.
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The researchers tested this with ethanol, which has a low surface tension, and water, which has a high one. Each flowed in the expected direction, and when the two were mixed together, the speed and direction of the flow changed based on how much of each liquid there was in the mixture.
They then 3D printed a strip of plastic with the same texture as the leaf to investigate these properties in more detail. They found that even when they tilted their artificial leaf vertically, liquids still flowed in the expected direction, although the distance that they flowed decreased based on how inclined the strip was.
When they stirred together water and oil and placed the mixture on the strip, the two separated, with the lower surface tension oil flowing along the ratchets and the higher surface tension water flowing against them.
This textured material may be useful for transporting liquids without using up any energy, which could be helpful in computer cooling or microfluidics experiments, says Wang.
鈥淭he liquid-steering behaviour can also be utilised to either promote or suppress a certain liquid movement, which can help accelerate desired processes, such as textile dying, while slowing down unwanted ones,鈥� says at the University of Rochester in New York. It could also be used for separating different liquids that have been mixed together, such as in an oil spill.
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