The science of the ‘coffee ring effect’
Have you noticed how coffee stains are rather peculiar? It produces a special mark – a clear stain with a dark ring encircling it.
This occurrence has bothered some so much, that they have been plugging away at the problem, wondering why this happens.
Robert D. Deegan of the University of Chicago and his team of researchers took this ‘problem’ head on and have found some intriguing results.
Their findings may allow the special quality of coffee to be used in strange new ways.
So what’s the deal? Well, coffee is made up of spherical particles and one of their properties means that as the liquid dries, the particles are pushed towards the edge to form a thick line or ring.
This is how the iconic thick brown line appears around the edge of a coffee stain.
However, when scientists tested liquids with non-spherical, elongated particles, something different happened: the particles did not gravitate towards the edge to create the ‘ring’ but rather spread out evenly over the liquid. As such, it seems that it’s the shape of the particle that leads to the coffee ring effect.
This finding can be taken one step further. Scientists then discovered that they could deform the drop of liquid to prevent the ‘coffee ring effect’. By using elliptically shaped particles, the scientists prevented the creation of the line around the edge of the drop.
How is this significant? There are many scenarios when you would prefer a liquid to dry in a uniform way, rather than with a dark ring around the edges. For example, imagine the use of ink in a printer –the ink should be uniformly dark, not with an emphasis towards the edge of the letters.
To be honest when we see a coffee ring stain, we instantly think: ‘Why doesn’t this person replace their cups?’…
Make sure you check out our wide range of cups and saucers to refresh those coffee stained cups that are becoming the bane of your business.