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Lotus plants inspire Brookhaven Lab development of new water-repellent materials

Physicists Charles Black, Antonio Checco and Atikur Rahman

Physicists Charles Black, Antonio Checco and Atikur Rahman demonstrate their discovery of ultra-water repellant nano materials on Friday, Oct. 9, 2015 at Brookhaven National Lab. Credit: Joseph D. Sullivan

When it comes to industrial design, perhaps no one is better than Mother Nature. From the pigeons that inspired the Wright Brothers to the woodland burrs that gave rise to Velcro, flora and fauna have long fueled the creativity of inventors and entrepreneurs.

Now researchers at Brookhaven National Laboratory have developed technology -- borrowed from lotus plants -- to make ultra-water-repellent materials that could pave the way for a new generation of self-cleaning eyeglasses, solar panels, medical devices, car windshields and more.

The materials are equipped with infinitesimal spikes that mimic the texture of lotus leaves, creating a virtual force field to stop water from wetting the surface. Without moisture, dust and other grime have nothing to stick to, making it nearly impossible for the materials to get dirty.

"You can understand why the Egyptians thought lotus leaves were sacred," said Antonio Checco, a Brookhaven scientist who has spearheaded the research.

The idea of patterning ultra-water-resistant materials (which scientists call superhydrophobic) after the lotus is not new. There are scads of superhydrophobic products already available that can be brushed or sprayed onto surfaces. Yet, scientists say these coatings are temporary and prone to failing under high speed and pressure.

Instead of applying a coating, Checco and his team figured out how to etch the tiny water-repellent spikes directly into the material. That makes the technology superior to anything else available, the scientists said. Plus, they say their process is ready for mass production. "You could manufacture this today," said Charles Black, who leads Brookhaven's materials synthesis and characterization group.

The potential, scientists say, could be significant. Imagine surgical gloves that repel liquids and curb the spread of bacteria. Superhydrophobic solar panels could soak up every bit of sun without having to be cleaned. Airplane wings would de-ice themselves. And windshield wiper fluid could go the way of carburetors.

The trick, however, is that the process developed at Brookhaven is complex and would add a costly step to manufacturing. "It's a matter of finding the application where the complexity is worth it," Black said.

The Brookhaven team developed the process at the lab's Center for Functional Nanomaterials, where scientists use powerful microscopes and other equipment to study matter on the smallest of scales. For the sake of context, the period at the end of this sentence is more than 1 million nanometers wide.

The scientists created their super-water-resistant surfaces by etching nanoscale spikes into silicon and glass.

First, they coat the surfaces with a material called a block copolymer. When heated, it forms a honeycomb pattern, with holes 20,000 times smaller than grains of sand.

The pattern of tiny holes functions as a stencil, allowing researchers to use a gas to burn away the exposed panel, leaving behind a forest of spikes.

Brookhaven researchers have used the same process to etch similar texture into solar panels, creating a non-reflective coating that allows the devices to soak up more light. That technology mimics the pattern found on the eyes of a moth, helping the insects see in the dark.

And once again, the design was care of Mother Nature.

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