My watch list
my.chemeurope.com  
Login  

Bacterium counteracts coffee ring effect

16-May-2013

Ever notice how a dried coffee stain has a thicker outer rim, while the middle of the stain remains almost unsoiled? This 'coffee ring effect' also occurs in other materials. Researchers from the Departments of Chemical Engineering and Chemistry at KU Leuven have now discovered how to counteract coffee rings with 'surfactants', i.e. soap. The key to the discovery was not a kitchen towel, but a bacterium that counteracts the coffee ring effect at the microscopic level.

When a coffee ring dries, its edges become noticeably darker and thicker. This occurs because the coffee particles move toward the edge of the stain while the water in the liquid evaporates. At a microscopic level, this coffee ring effect can also be seen in liquids with particles of other materials such as plastic and wood.

In various industrial applications – applying an even coat of paint or varnish, for example – the coffee ring effect can be particularly troublesome and scientists have long been seeking ways to counteract it. Raf De Dier and Wouter Sempels (Departments of Chemical Engineering and Chemistry) have now described a solution based on examples found in nature. De Dier and Sempels carried out experiments and calculations on nanomaterials as well as on a particularly promising bacterium, Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a dangerous bacterium that can cause infections in open wounds. “A Pseudomonas aeruginosa bacteria colony wants to find as large a breeding ground as possible. To avoid overconcentration on the edges of a wound when spreading itself during the drying-out process, the bacterium produces substances that counteract the coffee ring effect.”

These surface-tension-disrupting substances are called surfactants. Detergents such as soap are also surfactants. “Add soap to a stain – a coffee stain or any other stain –and you will still get a coffee ring effect. But at the same time the soap causes a counterflow from the edge back towards the centre of the stain in such a way that the small particles – material or bacteria – end up in a kind of whirlwind. In this way, you get a more uniform distribution of particles as evaporation occurs."

"If we genetically modify the bacteria so they can no longer produce surfactants, the coffee ring effect remains fully intact. Our findings on Pseudomonas aeruginosa also apply to other bacteria. For the biomedical sector, this study contributes primarily to our understanding of a biological system.” But surfactants could also potentially be added to nanomaterials, and that makes De Dier and Sempels' findings interesting for industry. “Surfactants are inexpensive. It won't be long before we start seeing them turn up in industrial applications.”

Original publication:

Wouter Sempels, Raf De Dier, et al., “Auto-production of biosurfactants reverses the coffee ring effect in a bacterial system”, Nature Communications, 2013

Facts, background information, dossiers
  • Katholieke Universi…
More about Katholieke Universiteit Leuven
  • News

    Electronic nose smells pesticides and nerve gas

    Detecting pesticides and nerve gas in very low concentrations. An international team of researchers led by Ivo Stassen and Rob Ameloot from KU Leuven, Belgium, have made it possible. The best-known electronic nose is the breathalyser. As drivers breathe into the device, a chemical sensor me ... more

    Designer crystals for next-gen electronics

    Liquid is often seen as the kryptonite of electronics, known for damaging and corroding components. That's why a new process that uses vapour- rather than liquid - to grow designer crystals could lead to a new breed of faster, more powerful electronic devices. The method, invented by an int ... more

    Scientists develop diesel that emits far less CO2

    Researchers from KU Leuven and Utrecht University have discovered a new approach to the production of fuels. Their new method can be used to produce much cleaner diesel. It can quickly be scaled up for industrial use. In 5 to 10 years, we may see the first cars driven by this new clean dies ... more

Your browser is not current. Microsoft Internet Explorer 6.0 does not support some functions on Chemie.DE