Motion of Liquid Drops on Surfaces Induced by Asymmetric Vibration: Role of Contact Angle Hysteresis

In this study, a thermodynamic analysis is conducted to investigate the chemical effect, in terms of intrinsic contact angle (CA), on the superhydrophobic behavior. It is theoretically revealed that the essential effect of intrinsic CA is to promote the composite transition. In particular, a large intrinsic CA more than 90° is necessary for such transition. Furthermore, for a pillar system with an intrinsic CA smaller than 90°, composite states are not impossible but is thermodynamically unstable. Once composite states are achieved, the advancing or maximum CA always approaches 180° whether an intrinsic CA is larger or smaller than 90°. In addition, the role of intrinsic CA in the water-repellent or self-cleaning behavior such as contact angle hysteresis (CAH) and equilibrium CA has been discussed in detail.

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The role of contact angles and contact angle hysteresis in dropwise condensation heat transfer

International Journal of Heat and Mass Transfer ◽

10.1016/0017-9310(78)90186-2 ◽

1978 ◽

Vol 21 (7) ◽

pp. 947-953 ◽

Cited By ~ 33

Author(s):

A.W. Neumann ◽

A.H. Abdelmessih ◽

A. Hameed

Keyword(s):

Heat Transfer ◽

Contact Angle ◽

Contact Angle Hysteresis ◽

Contact Angles ◽

Condensation Heat Transfer ◽

Dropwise Condensation

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Motion of Newtonian drops deposited on liquid-impregnated surfaces induced by vertical vibrations

Journal of Fluid Mechanics ◽

10.1017/jfm.2019.600 ◽

2019 ◽

Vol 876 ◽

Cited By ~ 8

Author(s):

Paolo Sartori ◽

Elia Guglielmin ◽

Davide Ferraro ◽

Daniele Filippi ◽

Annamaria Zaltron ◽

...

Keyword(s):

Phase Diagram ◽

Contact Angle ◽

Fast Rate ◽

Contact Angle Hysteresis ◽

Solid Surfaces ◽

Distilled Water ◽

Liquid Drops ◽

Dynamical Phase ◽

Viscous Drops ◽

Vertical Vibrations

We have studied the motion of drops on inclined liquid-impregnated surfaces (LISs) subject to vertical vibrations. The liquid drops comprise distilled water and different aqueous solutions of glycerol of increasing viscosity. The use of weak pinning LISs strongly affects the dynamical phase diagram. First of all, there is no trace of the dominant static region at low oscillating amplitudes reported for oscillating solid surfaces characterized by contact angle hysteresis. On the contrary, at sufficiently low oscillating amplitudes, the drops always move downwards with a velocity that depends only on the drop viscosity. Further increasing the oscillating amplitude may drive the drop upwards against gravity, as reported for dry surfaces. The use of more viscous drops widens this climbing region. Arguably, the main novelty of this work concerns the observation of two distinct descending regimes where the downhill speed differs by a factor of five or more. Fast-rate videos show that the evolution of the drop profile is diverse in the two regimes, likely because the vertical oscillations reduce the effect of the oil meniscus surrounding the drop at high accelerations.

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