How does the lotus stay dry even while growing in slime? This was a question that had intrigued scientists for ages. It took them an ultra high speed camera, a powerful microscope and an audio speaker to unlock the secret.
"We faced a tricky problem -- water droplets that fall on the leaf easily roll off, while condensate that grows from within the leaf's nooks and crannies is sticky and remains trapped," said Jonathan Boreyko, a third-year graduate student at Duke University Pratt School of Engineering (DUPSE), involved in the study.
"Scientists and engineers have long wondered how these sticky drops are eventually repelled from the leaf after their impalement into the tiny projections," Boreyko said.
"After bringing lotus leaves into the lab and watching the condensation as it formed, we were able to see how the sticky drops became unsticky."
The key was videotaping the process while the lotus leaf rested on top of the woofer portion of a stereo speaker at low frequency.
Condensation was created by cooling the leaf. It turned out that after being gently vibrated for a fraction of a second, the sticky droplets gradually unstuck themselves and jumped off the leaf.
"This solves a long-standing puzzle in the field," said DUPSE assistant professor Chuan-Hua Chen.
"People have observed that condensation forms every night on the lotus leaf. When they come back in the morning the water is gone and the leaf is dry."
"The speaker reproduced in the lab what happens every day in nature, which is full of subtle vibrations, especially for the lotus, which has large leaves atop long and slender stems," said Chen, according to a DUPSE release.
The results of these experiments will allow engineers to employ man-made surfaces much like the lotus leaf in settings where the removal of condensation and the transfer of heat are necessary.
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