scholarly journals An undamped oscillation model with two different contact angles for a spherical droplet impacting on solid surface

2020 ◽  
Vol 24 (2) ◽  
pp. 390-400
Author(s):  
Shi Chen ◽  
Bozhong Cong ◽  
Dongqi Zhang ◽  
Xiaohua Liu ◽  
Shengqiang Shen
Keyword(s):  
Solid Surface ◽  
Contact Angles ◽  
Spherical Droplet ◽  
Undamped Oscillation ◽  
Oscillation Model

Предложен нелинейный подход описания колебания сферической капли на твердой поверхности. Интегрирование уравнений движений осуществляется без использования линеаризации тригонометрических функций, зависящих от угла контакта. Иными словами, угол контакта является произвольной конечной величиной. Проведено исследование влияние силы тяжести на угол контакта и радиус распространения капли по твердой поверхности. Таким образом, было найдено нелинейное уравнение, описывающее изменение радиуса распространения капли в зависимости от времени. Данное уравнение было численно проинтегрировано. Исследование численной сходимости осуществлялось посредством сравнения с известными модельными точными решениями и известными экспериментальными данными. На основании исследования методами численного интегрирования полученного в статье уравнения можно сделать вывод о целесообразности использования математической модели для описания и исследования новых физических эффектов при колебании капель.

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.

Contact Angles and Solid Surface Tensions

2010 ◽  
pp. 491-554 ◽  
Author(s):  
Robert David ◽  
Jan Spelt ◽  
Junfeng Zhang ◽  
Daniel Kwok
Keyword(s):  
Solid Surface ◽  
Contact Angles ◽  
Surface Tensions

Macroscopic Wetting Behavior and a Method for Measuring Contact Angles

1990 ◽  
Vol 112 (3) ◽  
pp. 289-295 ◽  
Author(s):  
K. Katoh ◽  
H. Fujita ◽  
H. Sasaki
Keyword(s):  
Contact Angle ◽  
Solid Surface ◽  
Liquid Surface ◽  
Contact Angles ◽  
Critical Height ◽  
Solid Cone ◽  
Wetting Behavior ◽  
Conventional View ◽  
The Subject ◽  
Thermodynamic Instability

Macroscopic wetting behavior is investigated theoretically from a thermodynamic viewpoint. The axisymmetric liquid meniscus formed under a conical solid surface is chosen as the subject of the theoretical analysis. Using the meniscus configuration obtained by the Laplace equation, the total free energy of the system is calculated. In the case of the half vertical angle of the cone φ = 90 deg (horizontal plate), the system shows thermodynamic instability when the meniscus attaches to the solid surface at the contact angle. This result, unlike the conventional view, agrees well with the practical wetting behavior observed in this study. On the other hand, when 0 deg < φ < 90 deg, the system shows thermodynamic stability at the contact angle. However, when the solid cone is held at a position higher than the critical height from a stationary liquid surface, the system becomes unstable. It is possible to measure the contact angle easily using this unstable phenomenon.

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.

scholarly journals COMPARATIVE CHARACTERISTICS OF COATINGS WITH SiO AND GeO ON LEUCOSAPPHIRE

2021 ◽  
Vol 26 (2(78)) ◽  
pp. 14-21
Author(s):  
V.F. Zinchenko ◽  
I. R. Magunov ◽  
O. V. Mozkova ◽  
B. A. Gorshtein ◽  
V. P. Sobol’ ◽  
...  
Keyword(s):  
Solid Surface ◽  
Multilayer Coating ◽  
Contact Angles ◽  
Qualitative Assessment ◽  
Condensed State ◽  
Multilayer Coatings ◽  
Gaseous State ◽  
Film Forming ◽  
Spectral Ranges ◽  
First Moment

The reasons for the sharp difference in the adhesion of multilayer coatings containing SiO or GeO together with Ge on a leucosapphire (Al2O3) plate have been established. It should be mentioned that Silicon(II) and Germanium(II) oxides are quite stable in the gaseous state and, contrary, are metastable in condensed state; at high temperature they disproportionate into ultra-dispersed composites of amorphous nature. A comparison is made of the surface properties of ultramicroscopic droplets formed on solid surfaces – a substrate or the previous layer – upon condensation of SiO, GeO, or Ge vapors on leucosapphire. A qualitative assessment of the ratio of the corresponding contact angles of wetting by the indicated melts, formed at the first moment of contact, has been carried out. In assessing the surface tension of SiO and GeO melts (or Si – SiO2 and Ge – GeO2 composites), we proceeded from the corresponding values for SiO2 and GeO2, which are 296 and 248 mJ/m2 near the crystallization temperatures. On this basis, it was established that the smallest value of the contact angle, and hence the best wetting, is observed for the GeO melt (somewhat less for the SiO melt) on the solid surface of Al2O3 or Ge; the solid surface of SiO or GeO (especially, the first of them) with molten germanium should be much weaker wetted. Hence, it follows that thin-film multilayer coatings obtained from Ge and GeO on a leucosapphire substrate should have a significantly higher climatic resistance due to higher adhesion compared to multilayer coatings from SiO and Ge. Indeed, a multilayer coating containing SiO on a leucosapphire substrate with a large surface can withstand storage in air for no more than 2–3 months and begins to peel off; at the same time, the GeO coating remains intact after 4 years of storage. Thus, the GeO film-forming material is a promising one for use in multilayer coatings such as cut-off filters in interference optics of the near and mid-IR spectral ranges.

Macroscopic Wetting Behavior of a Two-Dimensional Meniscus Under a Horizontal Plate

1995 ◽  
Vol 117 (2) ◽  
pp. 303-308 ◽  
Author(s):  
Kenji Katoh ◽  
Hideomi Fujita ◽  
Hideharu Sasaki
Keyword(s):  
Solid Surface ◽  
Contact Angles ◽  
Two Dimensional ◽  
Horizontal Plate ◽  
Wetting Behavior ◽  
Made In

The purpose of this study is to investigate macroscopic wetting behavior and to verify the validity of the assumption made in the analysis of the preceding report that the complicated effects of the microscopic structures of the solid surface such as roughness or heterogeneity on the macroscopic wetting behavior are simply represented by the values of the apparent contact angles. The unstable phenomenon of a two-dimensional meniscus under a horizontal plate, in which the meniscus falls spontaneously at a certain height of the plate, is considered theoretically from a thermodynamic viewpoint. The results of the analysis based on the above assumption agree with those by an analysis in which the effect of microscopic structures of the solid surface, such as roughness and heterogeneity, are taken into consideration. Therefore, the validity of the assumption made in the preceding report is verified.

scholarly journals Derivation of Generalized Young’s Equation for Wetting of Cylindrical Droplets on Rough Solid Surface

2015 ◽  
Vol 5 (2) ◽  
pp. 17
Author(s):  
Xiao-Song Wang
Keyword(s):  
Surface Tension ◽  
Thermodynamic Equilibrium ◽  
Solid Surface ◽  
Line Tension ◽  
Contact Angles ◽  
Radius Of Curvature ◽  
Equilibrium Conditions ◽  
Vapor Interface ◽  
Curvature Effects ◽  
Young's Equation

<p class="1Body">The surface tension depends on the radius of curvature of the liquid-vapor interface. For nano-scale wetting phenomena of cylindrical droplets, we should consider the curvature effects of the surface tension and the line tension. However, previous works have not analyzed the influence of the curvature effects of the surface tension. In this paper, we discuss the influence of the curvature effects of the surface tension on the contact angles based the Kim-Lee-Han-Park equation. The hydrophilic wetting of cylindrical droplets on rough and chemically homogeneous non-deformable substrates were studied by methods of thermodynamics. A generalized Young’s equation for wetting of cylindrical droplets on chemically homogeneous and rough non-deformable substrates was derived based on the thermodynamic equilibrium conditions. This equation reduces to the Wenzel equation if we ignore the influence of line tension. For contact angles of cylindrical droplets with sufficiently large radii, a generalized Young’s equations were derived considering the curvature effects of the surface tension.</p>

The Effect of Drop Volume on Contact Angle

1991 ◽  
Vol 54 (3) ◽  
pp. 232-235 ◽  
Author(s):  
JOSEPH MCGUIRE ◽  
JIANGUO YANG
Keyword(s):  
Contact Angle ◽  
Surface Properties ◽  
Solid Surface ◽  
Contact Surface ◽  
Contact Angles ◽  
Equilibrium Contact Angle ◽  
Drop Volume ◽  
Food Contact ◽  
Food Contact Surface ◽  
Limiting Value

The effect of drop volume on the equilibrium contact angle, used in evaluation of food contact surface properties, was measured for liquids exhibiting both polar and nonpolar character on six different materials. Drop volumes used ranged from 2 to 40 μl. Contact angles were observed to increase with increasing drop volume in a range below some limiting value, identified as the critical drop volume (CDV). The CDV varied among materials and is explained with reference to surface energetic heterogeneities exhibited by each type of solid surface.

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