Drying Droplets

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Science  26 Apr 2002:
Vol. 296, Issue 5568, pp. 619
DOI: 10.1126/science.296.5568.619d

When a drop of liquid evaporates from a substrate, entrained particles will accumulate at the drying front, a phenomenon observed in coffee spills. In addition to the thick ring at the outer edge, a series of thinner concentric rings will sometimes form within. Shmuylovich et al. studied the evaporation of two sizes of latex particles suspended in water. The larger latex particles required a larger minimum drop volume for inner ring formation to occur, and, for the same drop size, fewer rings were observed. The authors propose that these rings are produced by slip-stick motion of the evaporation front as it passes over particles that are pinned to the substrate from the outset and that the process is essentially stochastic, in contrast to previous theories.—MSL

Langmuir, 10.1021/la011484v (2002).

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