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Team Eyes Self-Cleaning AR Coating

Thursday, February 27, 2014

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Inspired by the eyes of nocturnal insects, University of Cambridge researchers have developed a new self-cleaning, anti-reflective coating for glass and plastics.

moth eye

Scyrene / Flickr

Moth eyes have inspired coating developments over the past decade, however issues with dirt have made the signature anti-reflective properties less effective. The University of Cambridge team has figured out a way to make the moth eye-inspired coatings self-cleaning.

The coating could be used on building glass and solar cells, according to the researchers.

Details of the discovery were recently published online in the journal Nano Letters.

Moth Coatings Research

Anti-reflective coatings need to refract as little light as possible in order to be effective, but it is extremely difficult to produce them as a single layer, the university explained in a research announcement.

Over the past decade, researchers have developed coatings that resolve this by mimicking the structure of moth eyes.

The anti-reflective properties of the insects’ eyes do not come from a single layer, but from a hexagonal pattern of tiny bumps.  

“The spaces between these bumps are so small that incoming beams of light see the eye’s surface as a single layer, essentially removing the interface between the air and the surface, allowing moths to see at night and be less visible to predators,” the researchers said.

The problem with synthetic versions of moth eye-inspired coatings is that the tiny spaces that make the coating anti-reflective can also very quickly become clogged with dirt, inhibiting the anti-reflective effect, according to the university.

TiO2 Incorporated

Physics and Materials Professor Ulli Steiner and colleagues from the Cavendish Laboratory say they have come up with a solution.

The team made layers of plastic with very well-defined small pores, similar to moth eyes.

University of Cambridge

Physics and Materials Professor Ulli Steiner and colleagues from the Cavendish Laboratory developed the coating technology.

“But by making the pores larger than they are in most other types of moth-eye coatings, they were able to incorporate titanium dioxide nanocrystals into the structure,” the announcement said.

These nanocrystals are photocatalytic: When light falls on them, they start to break down the dirt clogging the pores, until all that is left is carbon dioxide and water that evaporates off the surface, rendering the material self-cleaning, the team explained.

‘Breakthrough’ Coating

In early tests of the material, the TiO2 nanoparticles were able to break down all of the oils contained in a fingerprint within 90 minutes, according to the research announcement.

The resulting coating is capable of breaking down most of the standard hydrocarbons that clog most porous antireflective coatings.

The "breakthrough research" marks the first time that these nanoparticles have been effectively incorporated into antireflective coatings, raising the possibility of antireflective, self-cleaning glass or plastic, the university said.

“The coating adheres to the substrate through sol-gel chemistry, resulting in a durable bond and a coating which will not flake off,” according to the team.

Potential Developments

The team says the coating is currently suitable only for outdoor applications, as it requires ultraviolet light for photocatalysis to occur. 

However, the researchers are planning more tests to see if the material could be adapted for indoor light, which would open up a wider range of potential applications.

Cambridge Enterprise, the university’s commercialization arm, is currently looking for commercial partners to help develop this material.


Tagged categories: Biomimicry; Coating chemistry; Coatings manufacturers; Coatings technology; Nanotechnology; Research; Self-cleaning coatings

Comment from Catherine Brooks, (2/27/2014, 11:28 AM)

I am in awe of scientists who look to nature for inspiration on how to solve technological challenges.

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