An anti-fog coating modeled on the nano-structure of a fly eye could one day be used on windows for cars, planes and buildings, say researchers. The coating could also protect electricity or telecommunication networks from freezing, suggests new research published in the journal Small.
Professor Shi Xue Dou and team at the University of Wollongong's Institute for Superconducting and Electronic Materials, together with colleagues from China have now been inspired by the eye of the common green bottle fly (Lucilia sercata) to make a new anti-fogging material.
The fly eyes can see clearly in moist environments without fogging up. Fogging occurs when moisture drops of larger than 190 nanometers in diameter form on surfaces, scattering light and making the surface more difficult to see through.
The researchers found that when the green bottle fly was put in a humid environment with droplets of less than 10 micrometers, condensation only occurred on its body, but not on its compound eyes. Looking more closely with microscopes, they found the 5 millimeter eyes were made up of thousands of repeating hexagonal units, each with a diameter of the order of 20 micrometers.
These units were, in turn, covered with numerous, near hexagonal bubble-like protuberances with diameters of around 100 nanometers.
"We suspect that these well-ordered, close packed, hierarchical hexagonal nanostructures are one of the origins of the superior superhydrophobicity and anti-fogging properties of the green bottle fly eyes," write the researchers.
The researchers used zinc nanoparticles to assemble small hexagonal structures to mimic the fly's eye.
"By investigating the surface structure of the compound eyes of the green bottle fly, we successfully synthesized hierarchically-mimicking bio-inspired inorganic nanostructures via a two-step molecular self-assembly method," they write.
After constructing the material, the researchers then tested it and found that it was superhydrophobic just like the insect's eye. Being superhydrophobic means water cannot wet the material and this paves the way for it being used for anti-fogging, and also anti-freezing, anti-corrosive and self-cleaning, say the researchers.
"This amazing superhydrophobic anti-fogging property is especially important in developing anti-freezing-fog materials for applications in some extreme and hazardous environments," write the researchers.
Freezing fog occurs when water vapor is super-cooled and forms a dense ice layer. This can cause havoc with electrical and telecommunication networks, and reduce the lift force that keeps airplanes in the air. The material could also be used as a transparent coating on the windows of cars, airplanes and buildings, add the researchers.
Mosquito eyes have previously inspired anti-fog materials, but the structure of their eyes are quite different, say the researchers. Also, the researchers say the system used to make previous bio-inspired anti-fogging inorganic nanostructures is not as suitable for mass production as the chemical synthesis they have used.
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