TY - JOUR
T1 - Influence of gravity on the sliding angle of water drops on nanopillared superhydrophobic surfaces
AU - Li, Hao
AU - Yan, Tianyu
AU - Fichthorn, Kristen A.
N1 - Funding Information:
This work was supported by the National Natural Science Foundation of China (51905315), the Shandong Provincial Natural Science Foundation (ZR2019BEM012), the Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents (2019RCJJ001), the Fundamental Research Funds for the Central Universities (20CX02316A), and the Opening Fund of National Engineering Laboratory of Offshore Geophysical and Exploration Equipment. In addition, H.L. thanks the China Scholarship Council for providing her with a living fee during her stay in the United States.
Publisher Copyright:
Copyright © 2020 American Chemical Society.
PY - 2020/8/25
Y1 - 2020/8/25
N2 - Molecular dynamics (MD) simulations were used to study the effects of gravity, solid surface energy, and the fraction of water-solid interface area on the water droplet sliding angles on nanopillared surfaces. To effectively simulate the influence of gravity on drop sliding, we developed a protocol in which we scale the value of gravitational acceleration used in our simulations according to the Bond number (Bo). In this way, we approximate the behavior of drops larger than we can effectively simulate using MD. The sliding angle decreased with an increase in Bo, while it increased with an increase in the liquid-solid surface interaction. The sliding angles exhibit a minimum with an increase in the fraction of water-solid interface area, due to meniscus formation at high fractions. Trends predicted by our model are in agreement with experiment. Using our model, we investigated the mechanisms of droplet movement along nanopillared surfaces. Depending on the pinning state of the droplets at equilibrium, either the advancing or the receding contact angle initiates motion. Moreover, the minimum dynamic advancing and receding contact angles of drops with gravity are close to the static contact angle and the intrinsic contact angle, respectively, while the maxima of both angles are as large as 180°. We find that the drops move through a combination of sliding and rolling, in agreement with experiment. Our studies offer clarity to conflicting experimental reports and present new results awaiting experimental confirmation.
AB - Molecular dynamics (MD) simulations were used to study the effects of gravity, solid surface energy, and the fraction of water-solid interface area on the water droplet sliding angles on nanopillared surfaces. To effectively simulate the influence of gravity on drop sliding, we developed a protocol in which we scale the value of gravitational acceleration used in our simulations according to the Bond number (Bo). In this way, we approximate the behavior of drops larger than we can effectively simulate using MD. The sliding angle decreased with an increase in Bo, while it increased with an increase in the liquid-solid surface interaction. The sliding angles exhibit a minimum with an increase in the fraction of water-solid interface area, due to meniscus formation at high fractions. Trends predicted by our model are in agreement with experiment. Using our model, we investigated the mechanisms of droplet movement along nanopillared surfaces. Depending on the pinning state of the droplets at equilibrium, either the advancing or the receding contact angle initiates motion. Moreover, the minimum dynamic advancing and receding contact angles of drops with gravity are close to the static contact angle and the intrinsic contact angle, respectively, while the maxima of both angles are as large as 180°. We find that the drops move through a combination of sliding and rolling, in agreement with experiment. Our studies offer clarity to conflicting experimental reports and present new results awaiting experimental confirmation.
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U2 - 10.1021/acs.langmuir.0c01597
DO - 10.1021/acs.langmuir.0c01597
M3 - Article
C2 - 32787051
AN - SCOPUS:85089922483
SN - 0743-7463
VL - 36
SP - 9916
EP - 9925
JO - Langmuir
JF - Langmuir
IS - 33
ER -