May 092012
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Every morning it’s the same: A few drops of coffee end up on your table. And once they dry, they form ring-shaped stains. But why? This problem is related to the question how to build tomorrow’s communication systems.

Some of you might remember your grandma’s coffee pot, which had a sponge attached to the spout. This was done to avoid coffee stains. These stains – black on the outside, white on the inside and always round in shape – are also interesting for science, especially for nanotechnology.

Physicists might use the coffee stains as a model to design better communication systems in the future. This is why the question of the month reads:

“Why does coffee always form ring-shaped stains and not a chaotic splash?” asked Leonie Anna Mueck, Editor of the Journal of Unsolved Questions.

Listen to the podcast here.

Read more about self-assembly in colloidal dispersions here: A. Marin et al. “Order-to-disorder transition in ring-shaped colloidal stains”, Phys. Rev. Lett. 107, 085502 (2011)

  2 Responses to “Question of the Month: Why does coffee form ring-shaped stains?”

  1. It’s a well-known phenomenon and there are many publications about it. For instance, there are two Nature papers from 1997 and 2011.

  2. Thanks for the comment.

    This is true, it is a well-known and well-explained effect. Our questions of the month have the goal to explain some scientific phenomena, which ideally have a relation to every-day life, to the broad public. This is done in collaboration with the internet radio station We used the example with the coffee stain to explain order-to-disorder transitions and self-assembly in general. And I am sure you agree that there are still a lot of unsolved questions regarding self-assembly!

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