Surface Morphology of Drying Latex Films: Multiple Ring Formation

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Reference

Surface morphology of drying latex films: multiple ring formation

Shmuylovich L, Shen AQ, Stone HA

Langmuir 18: 3441-3445 (2002)

Summary

Rings formed by the evaporation of a solution containing 0.88 um particles. The drop volume is written below each image, while the outer ring diameter is written above.

The experiment was simple: a small drop of a monodisperse solution of particles (either 0.008% (w/w) solution of 0.88 um diameter particles, or 0.01% solution of 3.15 um particles) was placed on a glass microscope slide. The drying process was then captured on camera. As the solution evaporated it formed concentric rings of particle arrays.

The "pinning" and "un-pinning" of the contact line of the solution with 0.88 um particles. Insets show two histograms: one of the distances traversed between "sticking events", and one of the time between pinning events.

It was observed that a larger drops size produced more rings that covered a wider area. Using solutions of larger particles decreased the number of rings, but did not have a significant effect on the diameter of the outer rings. Studying the dynamics of the contact line during liquid evaporation revealed that the motion is not continuous. Rather, the contact line became "pinned" and unable to move for periods of time, with different parts of the same ring being able to be pinned and unpinned at the same time.