Evaporative deposition in receding drops

Abstract

We present a framework for calculating the surface density profile of a stain deposited by a drop with a receding contact line. Unlike a pinned drop, a receding drop pushes fluid towards its interior, continuously deposits mass across its substrate as it evaporates, and does not produce the usual “coffee ring.” For a thin, circular drop with a uniform evaporation rate, we find the surface density of the stain goes as η(r) ∝ ((r/a₀)^−1/2 − r/a₀), where r is the radius from the drop center and a₀ is the initial outer radius. Under these conditions, the deposited stain has a mountain-like morphology. Our framework can easily be extended to investigate new stain morphologies left by drying drops.