Researchers from the University of Surrey have revealed new physical mechanisms behind the processes of paint drying. This discovery could help improve a variety of consumer goods, including sunscreen, beauty products and pharmaceuticals.
Specifically, researchers were interested in learning more about how particle size affects the mechanics of drying paint and other coatings. Computer simulations and materials experiments showed that coatings with differently sized particles solidify spontaneously into two layers.
Paints are typically colloids, consisting of tiny particles suspended in a liquid. By manipulating the size of the particles in paint, Surrey researchers, alongside researchers from the Université Claude Bernard, Lyon, were able to change the qualities of each distinct layer.
"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," explained Andrea Fortini, lead author of the study from 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."
The idea is that this naturally occurring mechanism can be used to control the properties at the top and bottom of coatings independently, thus improving the performance of a wide variety of coatings.
"This type of 'self-layering' in a coating could be very useful. 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," Fortini added. "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."
In future studies the team hopes to learn more about how to control the width of the layer by changing the type and amount of small particles in the coating. The goal is to incorporate their findings into the advancement of industrial products such as paints, inks, and adhesives.
Their research was largely funded by the EU project BARRIERPLUS, which aims to reduce the use of environmentally damaging volatile organic compounds in paints.
Their study was recently published in the journal Physical Review Letters.