Confined colloidal droplets dry to form circular mazes

TL;DR

This paper demonstrates that confined colloidal droplets evaporate to form intricate circular maze patterns instead of coffee rings, revealing new pattern formation behavior under confinement conditions.

Contribution

It introduces the novel observation of maze-like pattern formation in confined colloidal droplets during slow evaporation, expanding understanding of drying phenomena.

Findings

Confined droplets form circular maze patterns upon drying.

Pattern formation depends on confinement and evaporation rate.

Natural occurrences of such patterns are likely but previously unreported.

Abstract

During drying, particle-laden sessile droplets will leave so-called coffee-stain rings behind. This phenomenon is well-known and well-understood (Deegan et al., Nature 389, 827-829 (1997)). Here we show that when particle-laden droplets confined in a slit are allowed to evaporate very slowly, they do not deposit coffee rings, but form a surprisingly intricate, circular maze-like pattern. We present experiments that illustrate this pattern formation and discuss the factors that determine when such patterns can form. We are not aware of reports of natural examples of the formation of such beautiful patterns under confinement, although it seems likely that they exist.