Scientists found that if they changed a particle's shape, they could change the way it dries.
A phenomenon known as the "coffee-ring effect" has been put under the microscope.
Findings from the research could revolutionize printing, paints and coatings.
Ever noticed that if you spill coffee onto a table and let it dry, the color will be concentrated at the edges of the stain?
The intriguing phenomenon has been put under the microscope, and scientists believe their findings may encourage a revolution in printing, paints and product coatings.
The "coffee-ring effect", they report, derives from two factors: the shape of the particles in the liquid and the way these particles respond to surface tension.
"Particles" mean the molecules of coffee, ink or dye or whatever that are in suspension in the liquid.
Round particles tend to gather at the perimeter of the drop, which explains why they remain in a ring once it has dried, according to the research.
But particles that are elongated or ellipsoid distribute themselves in looser clumps, which makes it easier to smooth them across the entire surface.