On the ability of drops to stick to surfaces of solids. Part 3. The influences of the motion of the surrounding fluid on dislodging drops

1987 ◽  
Vol 174 ◽  
pp. 381-397 ◽  
Author(s):  
E. B. Dussan V.
Keyword(s):  
Contact Angle ◽  
Solid Surface ◽  
Specific Problem ◽  
Contact Angle Hysteresis ◽  
Immiscible Fluid ◽  
Planar Surface ◽  
Fixed Position ◽  
Constant Rate ◽  
Advancing Contact Angle ◽  
Surrounding Fluid

The ability of a drop to stick to a solid surface is investigated when the surrounding fluid is in motion. The specific problem analysed consists of a small drop on a planar surface immersed in a second immiscible fluid which is flowing parallel to the solid surface at a constant rate of strain. An expression is obtained, in terms of experimentally measurable quantities, for the value of the rate of strain beyond which the drop cannot maintain contact with a fixed position on the solid. The most limiting restrictions assumed in the analysis are that both the advancing contact angle and the contact angle hysteresis must be small.

scholarly journals Is contact angle a cause or an effect? – A cautionary tale

2020 ◽  
Vol 146 ◽  
pp. 03004
Author(s):  
Douglas Ruth
Keyword(s):  
Contact Angle ◽  
Solid Surface ◽  
Contact Angles ◽  
Two Dimensions ◽  
Experimental Results ◽  
Flow In Porous Media ◽  
Two Dimensional ◽  
Wide Range ◽  
Fluid Drop ◽  
Surrounding Fluid

The most influential parameter on the behavior of two-component flow in porous media is “wettability”. When wettability is being characterized, the most frequently used parameter is the “contact angle”. When a fluid-drop is placed on a solid surface, in the presence of a second, surrounding fluid, the fluid-fluid surface contacts the solid-surface at an angle that is typically measured through the fluid-drop. If this angle is less than 90°, the fluid in the drop is said to “wet” the surface. If this angle is greater than 90°, the surrounding fluid is said to “wet” the surface. This definition is universally accepted and appears to be scientifically justifiable, at least for a static situation where the solid surface is horizontal. Recently, this concept has been extended to characterize wettability in non-static situations using high-resolution, two-dimensional digital images of multi-component systems. Using simple thought experiments and published experimental results, many of them decades old, it will be demonstrated that contact angles are not primary parameters – their values depend on many other parameters. Using these arguments, it will be demonstrated that contact angles are not the cause of wettability behavior but the effect of wettability behavior and other parameters. The result of this is that the contact angle cannot be used as a primary indicator of wettability except in very restricted situations. Furthermore, it will be demonstrated that even for the simple case of a capillary interface in a vertical tube, attempting to use simply a two-dimensional image to determine the contact angle can result in a wide range of measured values. This observation is consistent with some published experimental results. It follows that contact angles measured in two-dimensions cannot be trusted to provide accurate values and these values should not be used to characterize the wettability of the system.

Understanding contact angle hysteresis on an ambient solid surface

2016 ◽  
Vol 93 (5) ◽  
Author(s):  
Yong Jian Wang ◽  
Shuo Guo ◽  
Hsuan-Yi Chen ◽  
Penger Tong
Keyword(s):  
Contact Angle ◽  
Solid Surface ◽  
Contact Angle Hysteresis

scholarly journals Leaf surface structures enable the endemic Namib desert grass Stipagrostis sabulicola to irrigate itself with fog water

2012 ◽  
Vol 9 (73) ◽  
pp. 1965-1974 ◽  
Author(s):  
A. Roth-Nebelsick ◽  
M. Ebner ◽  
T. Miranda ◽  
V. Gottschalk ◽  
D. Voigt ◽  
...  
Keyword(s):  
Contact Angle ◽  
Leaf Surface ◽  
Contact Angle Hysteresis ◽  
Maximum Size ◽  
Large Degree ◽  
Namib Desert ◽  
Fog Water ◽  
Water Conduction ◽  
Key Factor ◽  
Advancing Contact Angle

The Namib grass Stipagrostis sabulicola relies, to a large degree, upon fog for its water supply and is able to guide collected water towards the plant base. This directed irrigation of the plant base allows an efficient and rapid uptake of the fog water by the shallow roots. In this contribution, the mechanisms for this directed water flow are analysed. Stipagrostis sabulicola has a highly irregular surface. Advancing contact angle is 98° ± 5° and the receding angle is 56° ± 9°, with a mean of both values of approximately 77°. The surface is thus not hydrophobic, shows a substantial contact angle hysteresis and therefore, allows the development of pinned drops of a substantial size. The key factor for the water conduction is the presence of grooves within the leaf surface that run parallel to the long axis of the plant. These grooves provide a guided downslide of drops that have exceeded the maximum size for attachment. It also leads to a minimum of inefficient drop scattering around the plant. The combination of these surface traits together with the tall and upright stature of S. sabulicola contributes to a highly efficient natural fog-collecting system that enables this species to thrive in a hyperarid environment.

scholarly journals The Possibility of Changing the Wettability of Material Surface by Adjusting Gravity

Research ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-11 ◽  
Author(s):  
Yong-Ming Liu ◽  
Zi-Qing Wu ◽  
Sheng Bao ◽  
Wei-Hong Guo ◽  
Da-Wei Li ◽  
...  
Keyword(s):  
Contact Angle ◽  
Solid Surface ◽  
Contact Region ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Angle Measurement ◽  
Measured Parameter ◽  
Material Surface ◽  
Vapor Interface ◽  
Liquid Vapor

The contact angle, as a vital measured parameter of wettability of material surface, has long been in dispute whether it is affected by gravity. Herein, we measured the advancing and receding contact angles on extremely low contact angle hysteresis surfaces under different gravities (1-8G) and found that both of them decrease with the increase of the gravity. The underlying mechanism is revealed to be the contact angle hysteresis and the deformation of the liquid-vapor interface away from the solid surface caused by gradient distribution of the hydrostatic pressure. The real contact angle is not affected by gravity and cannot measured by an optical method. The measured apparent contact angles are angles of inclination of the liquid-vapor interface away from the solid surface. Furthermore, a new equation is proposed based on the balance of forces acting on the three-phase contact region, which quantitatively reveals the relation of the apparent contact angle with the interfacial tensions and gravity. This finding can provide new horizons for solving the debate on whether gravity affects the contact angle and may be useful for the accurate measurement of the contact angle and the development of a new contact angle measurement system.

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.

A NEW APPROACH TO INVESTIGATE CONTACT ANGLE HYSTERESIS

2018 ◽  
Author(s):  
Qiao Liu ◽  
Abbasali Abouei Mehrizi ◽  
Hao Wang
Keyword(s):  
Contact Angle ◽  
Contact Angle Hysteresis ◽  
New Approach

Drop impact on solids: contact-angle hysteresis filters impact energy into modal vibrations

2021 ◽  
Vol 923 ◽  
Author(s):  
Vanessa R. Kern ◽  
Joshua B. Bostwick ◽  
Paul H. Steen
Keyword(s):  
Contact Angle ◽  
Impact Energy ◽  
Contact Angle Hysteresis ◽  
Drop Impact

Abstract

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