Sessile Microdrop Coalescence on Partial Wetting Surfaces : Effects of Surface Wettability and Stiffness
We experimentally investigated the coalescence of two sessile microdrops on rigid surfaces with diverse wettability (macroscopic apparent water contact angles of θapp ≈ 13-110°) and on hydrophobic surfaces (θapp ≈ 110-124°) with very different stiffness properties (Young's moduli of E ≈ 1.1 MPa...
| Veröffentlicht in: | Langmuir : the ACS journal of surfaces and colloids. - 1992. - 35(2019), 40 vom: 08. Okt., Seite 12955-12961 |
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| Format: | Online-Aufsatz |
| Sprache: | English |
| Veröffentlicht: |
2019
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| Zugriff auf das übergeordnete Werk: | Langmuir : the ACS journal of surfaces and colloids |
| Schlagworte: | Journal Article |
| Zusammenfassung: | We experimentally investigated the coalescence of two sessile microdrops on rigid surfaces with diverse wettability (macroscopic apparent water contact angles of θapp ≈ 13-110°) and on hydrophobic surfaces (θapp ≈ 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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| Beschreibung: | Date Revised 04.03.2020 published: Print-Electronic Citation Status PubMed-not-MEDLINE |
| ISSN: | 1520-5827 |
| DOI: | 10.1021/acs.langmuir.9b02294 |