Abstract
Macroscopic patterns in nature formed during crystal growth e.g. snow crystals have a significant influence on many material properties, such as macroscopic heat conduction, electrical conduction, and mechanical properties, even with the same microscopic crystal structure. Although crystal morphology has been extensively studied in bulk, the formation of patterns induced by re-crystallization during evaporation is still unclear. Here, we find a way to obtain concentric circles, a dendritic pattern, and a lattice pattern by pinning the edge of droplets using the coffee ring effect; only aggregates of crystallites are seen in the absence of pinning. Our systematic study shows that the macroscopic patterns depend both on initial concentration and evaporation rate. In addition, our qualitative analysis suggests that the local concentration of solute at the center of the pattern is related to the macroscopic patterns.
Highlights
We investigate macroscopic crystal patterns formed by evaporation of solution droplets
We put latex particles in the solution such that the edge of the droplet is pinned by the coffee ring effect
Our systematic study shows that the CC pattern is formed for larger evaporation rate and lower initial concentration, while the DD pattern is formed for lower evaporation rate and larger initial concentration
Summary
We discuss the effect of dewetting from the substrate. CC or DD patterns are formed at the center when the solution macroscopically wets the substrate. It was reported that a DD pattern is formed by dewetting in a colloidal suspension[29]. The crystallization is different in nature from the aggregation of the colloidal particles, the effect of dewetting seems crucial for pattern formation.
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