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.

scholarly journals Thick drops climbing uphill on an oscillating substrate

2018 ◽  
Vol 840 ◽  
pp. 131-153 ◽  
Author(s):  
J. T. Bradshaw ◽  
J. Billingham
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Boundary Integral ◽  
Static Contact Angle ◽  
Rise Velocity ◽  
Contact Lines ◽  
Weakly Nonlinear ◽  
Static Contact

Experiments have shown that a liquid droplet on an inclined plane can be made to move uphill by sufficiently strong, vertical oscillations (Brunet et al., Phys. Rev. Lett., vol. 99, 2007, 144501). In this paper, we study a two-dimensional, inviscid, irrotational model of this flow, with the velocity of the contact lines a function of contact angle. We use asymptotic analysis to show that, for forcing of sufficiently small amplitude, the motion of the droplet can be separated into an odd and an even mode, and that the weakly nonlinear interaction between these modes determines whether the droplet climbs up or slides down the plane, consistent with earlier work in the limit of small contact angles (Benilov and Billingham, J. Fluid Mech. vol. 674, 2011, pp. 93–119). In this weakly nonlinear limit, we find that, as the static contact angle approaches $\unicode[STIX]{x03C0}$ (the non-wetting limit), the rise velocity of the droplet (specifically the velocity of the droplet averaged over one period of the motion) becomes a highly oscillatory function of static contact angle due to a high frequency mode that is excited by the forcing. We also solve the full nonlinear moving boundary problem numerically using a boundary integral method. We use this to study the effect of contact angle hysteresis, which we find can increase the rise velocity of the droplet, provided that it is not so large as to completely fix the contact lines. We also study a time-dependent modification of the contact line law in an attempt to reproduce the unsteady contact line dynamics observed in experiments, where the apparent contact angle is not a single-valued function of contact line velocity. After adding lag into the contact line model, we find that the rise velocity of the droplet is significantly affected, and that larger rise velocities are possible.

scholarly journals Superhydrophobicity and Contact-Line Issues

MRS Bulletin ◽  
2008 ◽  
Vol 33 (8) ◽  
pp. 747-751 ◽  
Author(s):  
Lichao Gao ◽  
Alexander Y. Fadeev ◽  
Thomas J. McCarthy
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Contact Angle Hysteresis ◽  
Water Repellency ◽  
Contact Angles ◽  
Single Step ◽  
Contact Lines ◽  
Lotus Effect ◽  
Three Phase ◽  
Solid Liquid

AbstractThe wettability of several superhydrophobic surfaces that were prepared recently by simple, mostly single-step methods is described and compared with the wettability of surfaces that are less hydrophobic. We explain why two length scales of topography can be important for controlling the hydrophobicity of some surfaces (the lotus effect). Contact-angle hysteresis (difference between the advancing, θA, and receding, θR, contact angles) is discussed and explained, particularly with regard to its contribution to water repellency. Perfect hydrophobicity (θA/θR = 180°/180°) and a method for distinguishing perfectly hydrophobic surfaces from those that are almost perfectly hydrophobic are described and discussed. The Wenzel and Cassie theories, both of which involve analysis of interfacial (solid/liquid) areas and not contact lines, are criticized. Each of these related topics is addressed from the perspective of the three-phase (solid/liquid/vapor) contact line and its dynamics. The energy barriers for movement of the three-phase contact line from one metastable state to another control contact-angle hysteresis and, thus, water repellency.

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

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 Lattice Boltzmann Modeling of Drying of Porous Media Considering Contact Angle Hysteresis

2021 ◽  
Author(s):  
Feifei Qin ◽  
Jianlin Zhao ◽  
Qinjun Kang ◽  
Dominique Derome ◽  
Jan Carmeliet
Keyword(s):  
Contact Angle ◽  
Porous Media ◽  
Lattice Boltzmann ◽  
Phase Distribution ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Contact Radius ◽  
Curved Surfaces ◽  
Hysteresis Model ◽  
Droplet Drying

AbstractDrying of porous media is governed by a combination of evaporation and movement of the liquid phase within the porous structure. Contact angle hysteresis induced by surface roughness is shown to influence multi-phase flows, such as contact line motion of droplet, phase distribution during drainage and coffee ring formed after droplet drying in constant contact radius mode. However, the influence of contact angle hysteresis on liquid drying in porous media is still an unanswered question. Lattice Boltzmann model (LBM) is an advanced numerical approach increasingly used to study phase change problems including drying. In this paper, based on a geometric formulation scheme to prescribe contact angle, we implement a contact angle hysteresis model within the framework of a two-phase pseudopotential LBM. The capability and accuracy of prescribing and automatically measuring contact angles over a large range are tested and validated by simulating droplets sitting on flat and curved surfaces. Afterward, the proposed contact angle hysteresis model is validated by modeling droplet drying on flat and curved surfaces. Then, drying of two connected capillary tubes is studied, considering the influence of different contact angle hysteresis ranges on drying dynamics. Finally, the model is applied to study drying of a dual-porosity porous medium, where phase distribution and drying rate are compared with and without contact angle hysteresis. The proposed model is shown to be capable of dealing with different contact angle hysteresis ranges accurately and of capturing the physical mechanisms during drying in different porous media including flat and curved geometries.

scholarly journals Dependency of Contact Angles on Three-Phase Contact Line: A Review

2021 ◽  
Vol 5 (1) ◽  
pp. 8
Author(s):  
H. Yildirim Erbil
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Contact Radius ◽  
Phase Contact ◽  
Sessile Droplet ◽  
Line Energy ◽  
Three Phase ◽  
Tension Term

The wetted area of a sessile droplet on a practical substrate is limited by the three-phase contact line and characterized by contact angle, contact radius and drop height. Although, contact angles of droplets have been studied for more than two hundred years, there are still some unanswered questions. In the last two decades, it was experimentally proven that the advancing and receding contact angles, and the contact angle hysteresis of rough and chemically heterogeneous surfaces, are determined by interactions of the liquid and the solid at the three-phase contact line alone, and the interfacial area within the contact perimeter is irrelevant. However, confusion and misunderstanding still exist in this field regarding the relationship between contact angle and surface roughness and chemical heterogeneity. An extensive review was published on the debate for the dependence of apparent contact angles on drop contact area or the three-phase contact line in 2014. Following this old review, several new articles were published on the same subject. This article presents a review of the novel articles (mostly published after 2014 to present) on the dependency of contact angles on the three-phase contact line, after a short summary is given for this long-lasting debate. Recently, some improvements have been made; for example, a relationship of the apparent contact angle with the properties of the three-phase line was obtained by replacing the solid–vapor interfacial tension term, γSV, with a string tension term containing the edge energy, γSLV, and curvature of the triple contact line, km, terms. In addition, a novel Gibbsian thermodynamics composite system was developed for a liquid drop resting on a heterogeneous multiphase and also on a homogeneous rough solid substrate at equilibrium conditions, and this approach led to the same conclusions given above. Moreover, some publications on the line energy concept along the three-phase contact line, and on the “modified” Cassie equations were also examined in this review.

Studying of Contact Angle Friction and Contact Angle Hysteresis (CAH) Though Force Measurements

2012 ◽  
Author(s):  
Qi Ni ◽  
Timo Marschke ◽  
Samuel Steele ◽  
Najafi Seyed ◽  
Nathan B. Crane
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Force Measurements ◽  
Droplet Motion ◽  
Characterization Methods ◽  
Receding Contact ◽  
Novel Method ◽  
Contact Line Friction

A novel method of measuring contact line friction and contact angle hysteresis is described. In this method, a droplet is constrained between two surfaces while the surface of interest initiates motion. The results are compared to conventional characterization methods such as measuring the angle of inclined plane for droplet motion and measuring advancing and receding contact angles by infusing/withdrawing liquid from the substrate. At slow speeds, the proposed method provides a measure of the hysteresis but can also capture information about the contact line friction and viscous affects. Droplet force dependence on droplet size (height/width) is also investigated.

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