When a coffee mug leaves a ring, the outer edges of that ring are darker than the inside of the ring. That's because the solute is separated from the liquid during the evaporation process — the coffee ring effect. This same effect can happen with printers. When printing a text document, the text itself consists of an outline of the letters and the inside of the letters. While it may not be visible to the untrained eye, the outlines are actually darker than the inside. This happens during the drying process, just like the coffee ring effect. Efforts have been made to find a way to remove this difference in pigmentation.

(a) There is particle transport to the apex of the target droplet and a dense center deposit is formed. (b) The final mapped deposit is more uniform.

The flow inside and on the surface of drying droplets was studied to understand more about the coffee ring effect and how to avoid it. Using a unique technique called electrospray, a high voltage was applied to a liquid to produce an aerosol to add nanoparticles to the droplets. Nanoparticles are often useful due to their small size and large surface area. This technique allowed for a more even dispersal of ink and stopped the coffee ring effect.

While this difference in quality may not affect the standard user's print job, it will have a substantial effect on the capabilities of additive manufacturing and biotechnology in which printing films in a uniform way is extremely important.

For more information, contact Ryan Yarosh at This email address is being protected from spambots. You need JavaScript enabled to view it.; 607-777-2180.

Tech Briefs Magazine

This article first appeared in the February, 2019 issue of Tech Briefs Magazine.

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