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arXiv · 2402.17452

Non-monotonic surface tension leads to spontaneous symmetry breaking in a binary evaporating drop

Christian Diddens·Pim J. Dekker·Detlef Lohse
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Abstract

The evaporation of water/1,2-hexanediol binary drops shows remarkable segregation dynamics, with hexanediol-rich spots forming at the rim, thus breaking axisymmetry. While the segregation of hexanediol near the rim can be attributed to the preferential evaporation of water, the symmetry-breaking and spot formation could not yet be successfully explained. With three-dimensional simulations and azimuthal stability analysis of a minimal model, we investigate the flow and composition in the drop. We show that a slightly non-monotonic surface tension causes the emergence of a counter-rotating Marangoni vortex in the hexanediol-rich rim region, which subsequently becomes azimuthally unstable and forms the observed spots. Accurate measurements with several different methods reveal that the surface tension is indeed non-monotonic. This work provides valuable insight for applications like inkjet printing or spray cooling.

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Christian Diddens, Pim J. Dekker, Detlef Lohse. 2024-02-27. Non-monotonic surface tension leads to spontaneous symmetry breaking in a binary evaporating drop. https://arxiv.org/abs/2402.17452

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