TY - JOUR
T1 - Dewetting of Thin Liquid Films Surrounding Air Bubbles in Microchannels
AU - Khodaparast, S.
AU - Atasi, O.
AU - Deblais, A.
AU - Scheid, B.
AU - Stone, Howard A.
N1 - Funding Information:
S.K. thanks the Swiss National Science Foundation (P2ELP2-158896) for the partial funding of this project. We thank the NSF for support from grant CBET-1702693. We thank M. Kreutzer and colleagues for sharing a preprint of their work. O.A. and B.S. thank the F.R.S-FNRS for financial support.
Publisher Copyright:
© 2017 American Chemical Society.
PY - 2018/1/30
Y1 - 2018/1/30
N2 - As an air bubble translates in a microchannel, a thin film of liquid is formed on the bounding walls. In a microchannel with a rectangular cross-section, the liquid in the film leaks toward the low-pressure corners of the geometry, which leads to the appearance of local minima in the film thickness in the cross-sectional plane. In such a configuration, theory suggests that the minimum film thickness scales with Ca and Ca4/3 depending on the distance from the nose of the bubble, where Ca = μUb/γ is the flow capillary number based on the bubble velocity Ub, liquid viscosity μ, and surface tension γ, and Ca ≤ 1. We show that the film of a partially wetting liquid dewets on the channel wall at the sites of the local minima in the film thickness as it acquires thicknesses around and below 100 nm. Our experiments show that the distance Lw between the nose of the bubble and the initial dewetting location is a function of Ca and surface wettability. For channels of different wettability, Lw always scales proportional to Caα, where 1.7 < α < 2 for the range of 10-5 < Ca < 10-2. Moreover, Lw increases up to 10 times by enhancing the wettability of the surface at a given Ca. Our present measurements of Lw provide a design constraint on the lengths of bubbles to maintain a liquid wet channel without dry patches on the wall.
AB - As an air bubble translates in a microchannel, a thin film of liquid is formed on the bounding walls. In a microchannel with a rectangular cross-section, the liquid in the film leaks toward the low-pressure corners of the geometry, which leads to the appearance of local minima in the film thickness in the cross-sectional plane. In such a configuration, theory suggests that the minimum film thickness scales with Ca and Ca4/3 depending on the distance from the nose of the bubble, where Ca = μUb/γ is the flow capillary number based on the bubble velocity Ub, liquid viscosity μ, and surface tension γ, and Ca ≤ 1. We show that the film of a partially wetting liquid dewets on the channel wall at the sites of the local minima in the film thickness as it acquires thicknesses around and below 100 nm. Our experiments show that the distance Lw between the nose of the bubble and the initial dewetting location is a function of Ca and surface wettability. For channels of different wettability, Lw always scales proportional to Caα, where 1.7 < α < 2 for the range of 10-5 < Ca < 10-2. Moreover, Lw increases up to 10 times by enhancing the wettability of the surface at a given Ca. Our present measurements of Lw provide a design constraint on the lengths of bubbles to maintain a liquid wet channel without dry patches on the wall.
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U2 - 10.1021/acs.langmuir.7b03839
DO - 10.1021/acs.langmuir.7b03839
M3 - Article
C2 - 29239613
AN - SCOPUS:85041431056
SN - 0743-7463
VL - 34
SP - 1363
EP - 1370
JO - Langmuir
JF - Langmuir
IS - 4
ER -