Anomalous Contact Angle Hysteresis of a Captive Bubble: Advancing Contact Line Pinning

Langmuir ◽  
2011 ◽  
Vol 27 (11) ◽  
pp. 6890-6896 ◽  
Author(s):  
Siang-Jie Hong ◽  
Feng-Ming Chang ◽  
Tung-He Chou ◽  
Seong Heng Chan ◽  
Yu-Jane Sheng ◽  
...  
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Contact Angle Hysteresis ◽  
Contact Line Pinning

LATTICE BOLTZMANN SIMULATIONS OF CONTACT LINE PINNING

2007 ◽  
Vol 18 (04) ◽  
pp. 595-601 ◽  
Author(s):  
XINLI JIA ◽  
J. B. MCLAUGHLIN ◽  
G. AHMADI ◽  
K. KONTOMARIS
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Lattice Boltzmann ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Contact Lines ◽  
Lattice Boltzmann Simulations ◽  
Spatially Periodic ◽  
Contact Line Pinning ◽  
Geometrical Defects

Contact angle hysteresis is caused by contact line pinning by geometrical and/or chemical non-uniformities on a solid surface. For small contact angles, theories have been developed for the pinning of contact angles, and an analogy between geometrical and chemical defects has been established. This paper presents LBM results for the interaction of a contact line with a spatially periodic array of chemical defects. The results are for finite contact angles. Qualitative comparisons with existing theories for chemical defects and experimental results for geometrical defects are made for pinned contact lines.

Simulation of Spreading Dynamics of a EWOD Droplet With Dynamic Contact Angle and Contact Angle Hysteresis

2009 ◽  
Author(s):  
Fangjun Hong ◽  
Ping Cheng ◽  
Zhen Sun ◽  
Huiying Wu
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Low Voltage ◽  
Contact Angle Hysteresis ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Dielectric Surface ◽  
Contact Radius ◽  
Droplet Spreading ◽  
Spreading Dynamics

In this paper, the electrowetting dynamics of a droplet on a dielectric surface was investigated numerically by a mathematical model including dynamic contact angle and contact angle hysteresis. The fluid flow is described by laminar N-S equation, the free surface of the droplet is modeled by the Volume of Fluid (VOF) method, and the electrowetting force is incorporated by exerting an electrical force on the cells at the contact line. The Kilster’s model that can deal with both receding and advancing contact angle is adopted. Numerical results indicate that there is overshooting and oscillation of contact radius in droplet spreading process before it ceases the movement when the excitation voltage is high; while the overshooting is not observed for low voltage. The explanation for the contact line overshooting and some special characteristics of variation of contact radius with time were also conducted.

Shear flow over a liquid drop adhering to a solid surface

1996 ◽  
Vol 307 ◽  
pp. 167-190 ◽  
Author(s):  
Xiaofan Li ◽  
C. Pozrikidis
Keyword(s):  
Contact Angle ◽  
Shear Flow ◽  
Contact Line ◽  
Simple Shear ◽  
Liquid Drop ◽  
Contact Angle Hysteresis ◽  
Boundary Integral ◽  
Simple Shear Flow ◽  
Contact Lines ◽  
Transient Deformation

The hydrostatic shape, transient deformation, and asymptotic shape of a small liquid drop with uniform surface tension adhering to a planar wall subject to an overpassing simple shear flow are studied under conditions of Stokes flow. The effects of gravity are considered to be negligible, and the contact line is assumed to have a stationary circular or elliptical shape. In the absence of shear flow, the drop assumes a hydrostatic shape with constant mean curvature. Families of hydrostatic shapes, parameterized by the drop volume and aspect ratio of the contact line, are computed using an iterative finite-difference method. The results illustrate the effect of the shape of the contact line on the distribution of the contact angle around the base, and are discussed with reference to contact-angle hysteresis and stability of stationary shapes. The transient deformation of a drop whose viscosity is equal to that of the ambient fluid, subject to a suddenly applied simple shear flow, is computed for a range of capillary numbers using a boundary-integral method that incorporates global parameterization of the interface and interfacial regriding at large deformations. Critical capillary numbers above which the drop exhibits continued deformation, or the contact angle increases beyond or decreases below the limits tolerated by contact angle hysteresis are established. It is shown that the geometry of the contact line plays an important role in the transient and asymptotic behaviour at long times, quantified in terms of the critical capillary numbers for continued elongation. Drops with elliptical contact lines are likely to dislodge or break off before drops with circular contact lines. The numerical results validate the assumptions of lubrication theory for flat drops, even in cases where the height of the drop is equal to one fifth the radius of the contact line.

Study of Microdroplet Growth on Homogeneous and Patterned Surfaces Using Lattice Boltzmann Modeling

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Nilesh D. Pawar ◽  
Sunil R. Kale ◽  
Supreet Singh Bahga ◽  
Hassan Farhat ◽  
Sasidhar Kondaraju
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Lattice Boltzmann ◽  
Growth Dynamics ◽  
Hydrophobic Surface ◽  
Droplet Growth ◽  
Patterned Surfaces ◽  
Hydrophobic Region ◽  
Hydrophilic Region ◽  
Contact Line Pinning

We present droplet growth dynamics on homogeneous and patterned surfaces (surface with hydrophilic and hydrophobic region) using two-dimensional thermal lattice Boltzmann method (LBM). In the first part, we performed 2D simulations on homogeneous hydrophobic surfaces. The result shows that the droplet grows at higher rate on a surface with higher wettability which is attributed to low conduction resistance and high solid–liquid contact area. In the later part, we performed simulations on patterned surface and observed that droplet preferentially nucleates on the hydrophilic region due to lower energy barrier and grows in constant contact line (CCL) mode because of contact line pinning at the interface of hydrophilic–hydrophobic region. As the contact angle reaches the maximum value of hydrophobic surface, contact line depins and droplet shows constant contact angle (CCA) growth mode. We also discuss the effect of characteristic width of hydrophilic region on growth of droplet. We show that contact angle of the droplet increases rapidly and reaches the contact angle of hydrophobic region on a surface with a lower width of the hydrophilic surface.

scholarly journals Wetting of doubly periodic rough surfaces in Wenzel’s regime

2018 ◽  
Vol 145 ◽  
pp. 03006
Author(s):  
Stanimir Iliev ◽  
Nina Pesheva ◽  
Pavel Iliev
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Numerical Study ◽  
Rough Surfaces ◽  
Contact Angle Hysteresis ◽  
Stick Slip ◽  
Liquid Meniscus ◽  
Three Phase ◽  
Mutual Disposition ◽  
Physical Defects

In this work we present preliminary results from our numerical study of the shapes of a liquid meniscus in contact with doubly sinusoidal rough surfaces in Wenzel’s wetting regime. Using the full capillary model we obtain the advancing and the receding equilibrium meniscus shapes for a broad interval of surface roughness factors. The contact angle hysteresis is obtained when the three-phase contact line is located on one row (block case) or several rows (kink case) of physical defects. We find that depending on the mutual disposition of the contact line and the lattice of periodic defects, different stick-slip behaviors of the contact line depinning mechanism appear, leading to different values of the contact angle hysteresis.

On the ability of drops or bubbles to stick to non-horizontal surfaces of solids

1983 ◽  
Vol 137 ◽  
pp. 1-29 ◽  
Author(s):  
E. B. Dussan V. ◽  
Robert Tao-Ping Chow
Keyword(s):  
Contact Angle ◽  
Solid Surface ◽  
Contact Line ◽  
Common Knowledge ◽  
Contact Angle Hysteresis ◽  
Point Of View ◽  
Fluid Interface ◽  
Mathematical Point

It is common knowledge that relatively small drops or bubbles have a tendency to stick to the surfaces of solids. Two specific problems are investigated: the shape of the largest drop or bubble that can remain attached to an inclined solid surface; and the shape and speed at which it moves along the surface when these conditions are exceeded. The slope of the fluid-fluid interface relative to the surface of the solid is assumed to be small, making it possible to obtain results using analytic techniques. It is shown that from both a physical and mathematical point of view contact-angle hysteresis, i.e. the ability of the position of the contact line to remain fixed as long as the value of the contact angle θ lies within the interval θR [les ] θ [les ] θA, where θA [nequiv ] θR, emerges as the single most important characteristic of the system.

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