Lotus leaf bumps the secret to smooth surfaces?
How do you make a surface smooth? Paradoxically, you add bumps to it, Ohio State University researchers find.
The lotus plant, otherwise known as the water lily, has been a source of inspiration for centuries. But this time, people are mostly interested in the bumps on the surface of its leaves.
Bharat Bhushan
Engineering professor,
Ohio State University
Researchers at Ohio State University have created computer models of materials that, arrayed with tiny bumps, will repel water or allow microscopic machines to operate with far less friction. In a few years, the development could lead to far cheaper wide-screen televisions, chips that can analyze blood samples or windshields that clean themselves.
The project was inspired by lotus leaves' deceiving looks. Although they appear waxy and smooth to the naked eye, the leaves are actually covered with a series of microscopic bumps that prevent water drops from touching their surface.
In computer simulations, Bharat Bhushan, the Howard Winbigler professor of mechanical engineering at OSU, is studying the pitch, spacing and size of the bumps for different results. By placing bumps a few nanometers apart (a nanometer is a billionth of a meter), water droplets will balance above a surface. Changing the pitch a bit will then make the droplets cascade off. The bumps are so small that they would not be detected by the naked eye.
Conceivably, this could lead to windows that stay dry in the rain, but Bhushan said he is mostly interested in improving the performance of microelectromechanical systems, or MEMS, tiny chips with moving parts that perform complex functions. Ultrasound-imaging company Sensant, for instance, has created a MEMS with microscopic drums that could one day help doctors get more accurate MRI scans, while another start-up, Pria Diagnostics, has created a chip for measuring sperm samples.
The idea is to use surfaces to eliminate friction between moving parts that can't be oiled.
"When you introduce bumps, you reduce the contact area and reduce the friction," Bhushan said in an interview.
Properly deployed bumps could also reduce the impact of ambient water from interfering with the operation of MEMS, which, in turn, could reduce the cost of these devices. Nearly half of the cost of a micromirror, made up of the MEMS chips inside rear projection TVs, goes toward hermetically sealing these chips.
Texas Instruments, whose digital light processing systems is one of the most commercially successful micromirror MEMS, is one of the key sponsors of the research, Bhushan said.
Similarly, redesigning the surface of chip parts could help improve the performance of microfluidic chips, which are MEMS that prepare fluid samples.
Bhushan has created computer models of different surfaces and has filed patent applications for the technology. The next step will involve creating prototype surfaces, though he added that companies could license the technology now.