10-Jun-2022 - Friedrich-Alexander-Universität Erlangen-Nürnberg

More than a coffee ring

Researchers develop method that promotes uniform drying of particle-containing liquids

What do coffee, red wine and ink have in common? The stubborn stains they leave behind. Anyone who has ever knocked over a cup of coffee will know that coffee dries in an unusual pattern, the stain is lighter at the center but it gets darker around the perimeter, an effect known as the coffee ring. Prof. Dr. Nicolas Vogel and his team of researchers from the Department of Chemical and Biological Engineering at FAU and their colleagues in Edinburgh are investigating a strategy to tackle the coffee ring effect and produce a consistent drying pattern. Their findings have been published in the journal Nature Communications.

When a droplet of coffee dries, the liquid evaporates faster at the edges than in the center Small, solid particles are present in the coffee when it is brewed. They are drawn to the edge of the droplet by different drying speeds and separate there, forming the characteristic pattern of a coffee ring. This is a universal phenomenon which occurs when liquids containing particles dry, so-called dispersions, for example ink, paint or red wine. Ring patterns are just as undesirable in technical processes as when we spill our coffee. They lead to irregular print images, defects and performance degradation in various coating methods and printing processes.

Researchers have discovered that the trick to achieving consistent drying patterns is modifying the surfaces of the particles with polymer chains so that they efficiently repel each other while being strongly attracted to the surface of the droplet. Spatial repulsion prevents particle accumulation at the edge of the droplet, while particle attachment to the droplet surface results in a homogeneous particle film. When they are combined both effects prevent the formation of a coffee ring.

Importantly, this method not only allows coffee droplets to dry evenly: it can be used with a wide range of commercially available pigment particles and different liquids. As the method is easy to implement and versatile, the new method paves the way to reliable coating processes and inkjet-printed electronic devices in a wide range of advanced technologies, for example, solar cells, transistors or biosensors.

Facts, background information, dossiers

  • particles
  • coating processes

More about Friedrich-Alexander-Universität Erlangen-Nürnberg

  • News

    Nano-Rust: Smart Additive for Autonomous Temperature Control

    The right temperature matters – whether in technical processes, for the quality of food and medicines, or the lifetime of electronic components and batteries. For this purpose, temperature indicators record (un)desired temperature increases that can be read out later. Researchers in the gro ... more

    By capsule through the bloodstream

    Bacteria in the intestine pack a wide spectrum of their biomolecules into small capsules. These are transported via the bloodstream to various organs in the body and even absorbed and processed by nerve cells in the brain. This has now been shown for the first time by a team of researchers ... more

    How Cells Correctly Choose Active Genes

    It is essential for cells to control precisely which of the many genes of their genetic material they use. This is done in so-called transcription factories, molecular clusters in the nucleus. Researchers of Karlsruhe Institute of Technology (KIT), Friedrich-Alexander-Universität Erlangen-N ... more

  • q&more articles

    Transfer of aroma compounds into breast milk

    “We are what we eat.” In a way, this quote by the German philosopher Ludwig Feuerbach (1804–1872) also applies to what we feed our offspring: the aroma profile of breast milk reflects a mother's eating habits [1, 2] and can thus influence the preferences of her children ... more

    Colorful off-odors in artists’ paints

    Acrylic-based paints are among the most frequently used by artists. Although they can be produced on a water basis and with low levels of volatile substances, they often still possess a strong inherent smell. However, no targeted studies have as yet been conducted to identify odor-active su ... more

    New Trends in Computer-Aided Drug Design

    Computer-Aided Drug design (CADD) is not new. The Journal of Computer-Aided Molecular Design (Springer) was founded in 1987, when computers in the worldwide top 500 were slower than today’s smart phones. This makes the field a quarter of a century old. Generally, scientific disciplines of t ... more

  • Authors

    Dr. Helene M. Loos

    Helene Loos studied food technology at the University of Hohenheim and completed her doctorate in food chemistry at the Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) in 2015. During her doctoral studies, she investigated the aroma composition of breast milk and the behavioral resp ... more

    Diana Owsienko

    Diana Owsienko, born in 1994, studied food chemistry at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) in Erlangen from 2013 to 2017 and worked on her final scientific thesis at the Fraunhofer Institute for Process Engineering and Packaging (IVV) in Freising from 2017 to 2018. In 2 ... more

    Nadine I. Goldenstein

    Nadine Goldenstein studied Marine Environmental Sciences at the University of Bremen, Germany. Subsequently she worked as a scientist in Organic Biogeochemistry at MARUM, Bremen, where she concentrated her research activities on the investigation of microbial metabolic processes, with a foc ... more

q&more – the networking platform for quality excellence in lab and process

The q&more concept is to increase the visibility of recent research and innovative solutions, and support the exchange of knowledge. In the broad spectrum of subjects covered, the focus is on achieving maximum quality in highly innovative sectors. As a modern knowledge platform, q&more offers market participants one-of-a-kind networking opportunities. Cutting-edge research is presented by authors of international repute. Attractively presented in a high-quality context, and published in German and English, the original articles introduce new concepts and highlight unconventional solution strategies.

> more about q&more

q&more is supported by: