It turns out watching paint dry can be pretty exciting, at least if you are a physicist working in materials science. And what they discovered may have a big impact in how coatings including paint, ink, and even sunscreen, are applied.
When the paint is made up of different sizes of particles, the small ones team up to push the larger ones away. This leads to a mechanism in which the coating "self-layers", effectively making two coats.
This mechanism can be used to control the properties at the top and bottom of coatings independently, which could help increase performance of coatings across industries as diverse as beauty and pharmaceuticals, say researchers from the University of Surrey, who used computer simulation and materials experiments, to make the discovery.
"When coatings such as paint, ink or even outer layers on tablets are made, they work by spreading a liquid containing solid particles onto a surface, and allowing the liquid to evaporate," said Andrea Fortini, lead author of the paper published in the journal Physical Review Letters.
"This is nothing new, but what is exciting is that we've shown that during evaporation, the small particles push away the larger ones, remaining at the top surface whilst the larger are pushed to bottom. This happens naturally."
Fortini said the mechanism, now that we know it, could lead to a range of uses.
"For example, in a sunscreen, most of the sunlight-blocking particles could be designed to push their way to the top, leaving particles that can adhere to the skin near the bottom of the coating.
"Typically the particles used in coatings have sizes that are 1,000 times smaller than the width of a human hair so engineering these coatings takes place at a microscopic level. "
The team is continuing to work on such research to understand how to control the width of the layer by changing the type and amount of small particles in coatings and explore their industrial use.
Bill Condie is a science journalist based in Adelaide, Australia.
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