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Evaporative Flux Reversal of Binary Droplets: From Edge to Apex

Minhyeok Kuk and Hyoungsoo Kim*

  • Department of Mechanical Engineering, KAIST, Daehak-ro 291, Yuseong-gu, Daejeon 34141, Korea

  • *Contact author: hshk@kaist.ac.kr
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Phys. Rev. Lett. 137, 084002 – Published 20 August, 2026

DOI: https://doi.org/10.1103/m739-56q7

Abstract

In this Letter, we directly measure the spatial variation of the saturation concentration along the interface of a binary droplet, showing that it is not uniform. This observation challenges the core assumption of classical evaporation theory, where a uniform interfacial saturation concentration leads to the edge-dominant evaporative flux responsible for the well-known coffee-ring effect in single-component droplets. Our interferometric measurements reveal that this assumption breaks down in multicomponent droplets, requiring a different framework to describe their evaporation behavior. By comparing the local evaporative flux with internal flow fields obtained using micro-particle image velocimetry, we show that changes in interfacial composition and flow pattern are closely coupled, leading the maximum evaporative flux to shift away from the contact line during evaporation. Recognizing that the maximum flux no longer resides at the edge is therefore essential for developing a correct and predictive understanding of evaporation in binary and more complex multicomponent droplets.

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Phys. Rev. Lett. 137, 084002– Published 20 August, 2026
  • Received 1 December 2025
  • Revised 20 March 2026
  • Accepted 23 June 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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