It’s a technicolour dreamcoat for your crisp packet –
The natural version, also called nacre, is found on the inner shell of some molluscs, where it is built up of layers of the mineral aragonite separated by organic polymers such as chitin. It is remarkably strong, without being brittle or dense.
We would like to use nacre and similar materials as a protective coating in many situations. However, making them is a slow and delicate process that is difficult to recreate at any useful scale. Artificial nacre-like materials are usually painstakingly built up layer by layer, but Luyi Sun at the University of Connecticut in Storrs and his colleagues found a way to do it all in one go.
With their quick method, they were able to make their thin film coating 60 per cent stronger than stainless steel. A plastic sheet covered in the material was over 13,000 times less permeable to air and other gases than it was on its own. When the team tried to set it on fire, it became scorched where the flame directly touched the coated sheet, but would not ignite.
To form the film, the researchers mixed a type of clay that sheds layers when exposed to ultrasonic pulses with water and a polymer to stick the layers together. They then dipped strips of plastic the size of standard sheets of paper in the mixture to coat them.
When the coated sheets of plastic are hung up like drying laundry, the thin liquid layer flows towards the ground, pulling the nanometre-thick sheets of clay into alignment with one another like neatly laid bricks. This is crucial for keeping the coating strong and airtight.
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