oil treatment로 coffee ring effect 약화시키기

The coffee-stain effect is a well-known effect in physics and daily life in which a dark-colored edge remains when a fluid containing particles evaporates. This is caused by an "avalanche" of particles moving to the outer edge, University of Twente scientists showed in a past study. In inkjet and 3-D printing, this is an undesired effect. Now, researchers have demonstrated that the effect can be suppressed by modifying the surface using an oily layer

Earlier work of the UT research group showed that if a particle-laden droplet evaporates, the particles start moving to the edge of the droplet. At first, this is a slow and regular movement, but as soon as the droplet loses height by evaporation, the particles rush to the edge in a disorderly fashion, like in an avalanche.

In this case as well, the droplet has an edge, but it is limited by a layer of oil that does not evaporate. It also prevents the water at the droplet's edge from evaporating quickly This in turn prevents particles from moving to the edge. They even move the other way, from the edge to the inside of the droplet. Once all water is evaporated, the particles uniformly cover the surface instead of forming a ring.

reference

Yaxing Li et al. Evaporating droplets on oil-wetted surfaces: Suppression of the coffee-stain effect, Proceedings of the National Academy of Sciences (2020). DOI: 10.1073/pnas.2006153117