Title Sessile microdrop coalescence on partial wetting surfaces: Effects of surface wettability and stiffness
Date 16.09.2019
Number 57249
Abstract 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.
Publisher Langmuir
Citation Langmuir 35 (2019) 12955-12961
Authors Jiang, X. ; Zhao, B. ; Chen, L.

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