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.

Crystal patterns formed by evaporation play important roles in industrial technologies. Recently, it was found that a concentric pattern and an orchid pattern may be seen when a pinned sessile droplet dries. Due to complex coupling between evaporation and crystallization, the mechanism behind this unique recrystallization phenomenon is yet to be determined. Here, we investigate the formation of these macroscopic patterns using microscopy. Then we show that diffusion-limited aggregation, absorption, and dewetting from the substrate all play a role in its development. In addition, it is found that anisotropy of the core is a key parameter for the pattern formation on a long length scale.