Authors
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Jiang, X. ; Zhao, B. ; Chen, L.
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Title
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Sessile microdrop coalescence on partial wetting surfaces: Effects of surface wettability and stiffness
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Date
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16.09.2019
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Number
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57249
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Abstract
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We experimentally investigated the coalescence of two sessile microdrops on rigid surfaces with diverse wettability (macroscopic apparent water contact angles of ·app ˜ 13–110°) and on hydrophobic surfaces (·app ˜ 110–124°) with very different stiffness properties (Young’s moduli of E ˜ 1.1 MPa to 130 GPa). We show that the coalescence contains two fast regimes, in which a liquid meniscus bridging the parent droplets rapidly grows, forming a hemi-ellipsoidal droplet, and a slow regime, in which the merged hemi-ellipsoidal droplet relaxes to the equilibrium hemispherical cap. Whereas the fast bridging regimes last less than 2 ms and are almost independent of surface wettability and stiffness, the relaxation regime, which was only observed on sufficiently hydrophobic and rigid surfaces with low wetting hysteresis, continues for a few tens to several hundreds of milliseconds depending on surface properties. We further demonstrate that the slow droplet relaxation can be described neither by the bulk hydrodynamics nor by a microscopic model concerning liquid evaporation near the droplet edge, but by the molecular kinetic theory for the motion of the three-phase contact line.
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Publisher
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Langmuir
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Wikidata
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Q90120237
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Citation
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Langmuir 35 (2019) 12955-12961
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DOI
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https://doi.org/10.1021/ACS.LANGMUIR.9B02294
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Tags
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