© United Soybean Board
© United Soybean Board

New understanding into how coatings dry

Researchers in the UK and France have described a new physical mechanism that separates particles according to their size during the drying of wet coatings.

Their discovery could help to improve the performance of a wide variety of everyday goods.

When coatings with different sized particles, e.g. paints, dry, the smaller particles come together to push away larger ones, creating ‘self-layering’ coatings, researchers at the University of Surrey, UK, and Université Claude Bernard, Lyon, France, found.

This mechanism can be used to control the properties at the top and bottom of coatings independently, which could help to improve the performance of coatings across industries as diverse as beauty and pharmaceuticals.

“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,” explains lead author Dr Andrea Fortini of the University of Surrey.

“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.”

He adds that this type of self-layering could be used in sunscreen to make most of the sunlight-blocking particles push their way to the top, leaving particles that can adhere to the skin near the bottom of the coating.

The researchers are now working to understand how to control the width of the layers by changing the type and amount of small particles in a coating. They also hope to explore the use of layers in industrial products such as paints, inks and adhesives.

The funding for this work comes from BARRIERPLUS, a Seventh Framework Programme aimed at the reduction of environmentally damaging volatile organic compounds in paints. The research has been published in the journal Physical Review Letters.