MIT engineers created a new type of elastic material that is coated with microscopic "hair-like" structures that respond to magnetic fields.
The field's orientation determines which way the microhairs tilt, creating a path for water to flow. The new material also has the ability to move water upwards against gravity. Each individual microhair is one-fourth the diameter of an actual human hair.
In experiments the material proved to be able to not only direct the flow of water, but light as well. The innovation could help lead to new waterproofing and anti-glare applications.
"You could coat this on your car windshield to manipulate rain or sunlight," said Yangying Zhu, a graduate student in MIT's Department of Mechanical Engineering. "So you could filter how much solar radiation you want coming in, and also shed raindrops. This is an opportunity for the future."
The material could also be implemented in "lab-on-a-chip" devices to direct the flow of cells or other material through microchannels.
The material was, in part, inspired from nature. Human nasal passages are lined with fine hairs called cilia; these hairs sway back and forth to remove dust or other irritants.
"We see these dynamic structures a lot in nature," Zhu said. "So we thought, 'What if we could engineer microstructures, and make them dynamic?' This would expand the functionality of surfaces."
The team manufactured the material using microscopic pillars that tilt in response to a magnetic field. The pillars are created using molds electroplated with nickel. These molds are stripped away and the pillars are bonded with a soft layer of silicone.
To test the material the team piped a water solution through a syringe and onto the array of microhairs. The liquid moved in the direction in which the pillars tilted. A combination of surface tension and tilitng pillars allowed the water to climb vertically up the array.
Since the array's silicone layer is transparent, researchers also played with light. The researchers shone a laser through the material while tilting the pillars at various angles, and found they could control how much light passed through.
"A nice thing about this substrate is that you can attach it to something with interesting contours," said Evelyn Wang, an associate professor of mechanical engineering. "Or, depending on how you design the magnetic field, you could get the pillars to close in like a flower. You could do a lot of things with the same platform."
The findings were published in this month's edition of Advanced Materials.
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