Evaporating a small drop of fluid on a surface will often result in formation of a ring-shape, as any particles or solutes within the drop get transported to the drop edge during evaporation. Alteration of different properties during this process can modify the shape of the resulting deposit, making evaporation of drops a useful tool for engineering at very small scales. In this video we show the spontaneous formation of a spiral pattern from a drop of calcium sulfate solution. The spiral forms due to a balance between contact angle hyseteresis causing propagation of pinning/depinning fronts and the evaporation rate.
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