Wetting

Surfactants ◽  
2019 ◽  
pp. 427-464
Author(s):  
Bob Aveyard
Keyword(s):  
Contact Angle ◽  
Solid Surface ◽  
Contact Angles ◽  
Surface Forces ◽  
Solid Surfaces ◽  
Surface Topology ◽  
Spreading Coefficient ◽  
Surfactant Solutions ◽  
Receding Contact ◽  
Solid Liquid

Wetting of one liquid by another can be understood in terms of the spreading coefficient; the relevance of surface forces to wetting is also explained. If a small liquid drop does not spread, it forms a lens whose shape is determined by the various interfacial tensions. The wetting of solids is characterized by the contact angle θ‎ of the liquid with the solid surface; θ‎ usually depends on how a configuration is reached and advancing and receding contact angles are defined. It is often useful notionally to split solid/liquid tensions into polar and nonpolar contributions in the treatment of wetting. Effects of surfactant on the wetting of both hydrophobic and hydrophilic solids by water are explored. Surface topology can greatly influence wettability, and superhydrophobic solid surfaces exist widely in nature. Finally some dynamic aspects of wetting of solid surfaces by surfactant solutions are described briefly.

The Effect of Solid Surface Roughness on Dynamic Contact Angles in Solid-Liquid-Liquid Systems

2002 ◽  
Author(s):  
Dandina N. Rao ◽  
Hussain H. Radwani
Keyword(s):  
Surface Roughness ◽  
Contact Angle ◽  
Solid Surface ◽  
Water System ◽  
Dynamic Contact ◽  
Contact Angles ◽  
Solid Surfaces ◽  
Liquid Systems ◽  
L Systems ◽  
Solid Liquid

The engineering applications of spreading and adhesion phenomena involving fluids on solids are numerous. The adhesive and spreading interactions at the solid-fluid interfaces are well characterized by dynamic contact angles. This study reports on the results of an experimental investigation into the effect of solid surface roughness on dynamic contact angles in solid-liquid-liquid (S-L-L) systems. The experiment involved the use of Wilhelmy Plate apparatus to measure adhesion tension (which is the product of interfacial tension and cosine of the contact angle between the liquid-liquid interface and the solid surface), the DuNuoy tensiometer to measure the liquid-liquid interfacial tension, and a profilometer to characterize the roughness of the solid surfaces used. The components of the solid-liquid-liquid systems studied consisted of: (i) smooth glass, roughened quartz and an actual rock surface for the solid phase, (ii) normal-hexane and deionized water as the two immiscible liquid phases. The dynamic contact angles (advancing and receding angles) of the three-phase (rock-oil-water) system provide essential information about the wettability of petroleum resrvoirs. The wettability of a reservoir is an important parameter that affects oil recovery in primary, secondary, and enhanced recovery operations [1]. Contact angle measurements on smooth surfaces are generally used to characterize reservoir wettability. However pore surfaces within reservoir rocks are essentially rough and hence it is important to determine the effect of such roughness on measured contact angles. There is very little information in the open literature on the effect of surface roughness on dynamic contact angles in S-L-L systems. In the present work, four levels of roughness of solid surfaces of similar mineralogy (quartz and glass) were tested in hexane-deionized water fluid pair. The advancing and receding contact angles measured at ambient conditions were analyzed for wettability effects. It was found that as surface roughness increased, the dynamic contact angles also increased. The wettability of the rock-oil-water system shifted from weakly water-wet for the smooth glass to intermediate-wet for the roughened surface. The general trends observed in our study were found to be in good agreement with other published results. However, the generally held notion of increasing contact angle hysteresis with increasing roughness appears to be incorrect in solid-liquid-liquid systems.

The Measurement of Solid-Liquid Contact Angles

1992 ◽  
Vol 114 (3) ◽  
pp. 460-463 ◽  
Author(s):  
Kenji Katoh ◽  
Hideomi Fujita ◽  
Hideharu Sasaki ◽  
Koichi Miyashita
Keyword(s):  
Contact Angle ◽  
Theoretical Model ◽  
Solid Surface ◽  
Contact Angles ◽  
Solid Surfaces ◽  
Critical Height ◽  
Liquid Meniscus ◽  
Angle Measurements ◽  
Contact Angle Measurements ◽  
Solid Liquid

A new method is proposed for measuring solid-liquid contact angles. The well-known phenomenon where the liquid meniscus formed under a downward facing solid surface spontaneously breaks at a certain height is utilized in the contact angle measurements. The relation between the contact angle and the critical height of the solid surface where the instability occurs was derived theoretically from the solid-liquid wetting behavior using a thermodynamic approach. From the theoretical model the contact angles can be obtained by measuring the critical height of the solid. The validity of the analysis and the usefulness of the method were experimentally confirmed for various solid surfaces and test liquids.

scholarly journals Some problems of characterization of a solid surface via the surface free energy changes

2017 ◽  
Vol 35 (7-8) ◽  
pp. 647-659 ◽  
Author(s):  
Emil Chibowski
Keyword(s):  
Contact Angle ◽  
Free Energy ◽  
Experimental Determination ◽  
Surface Free Energy ◽  
Solid Surface ◽  
Contact Angles ◽  
Absolute Value ◽  
Receding Contact

During the processes occurring at a solid surface, the changes in the surface free energy take place. The knowledge about surface free energy is very helpful for understanding the processes taking place on the surface. However, experimental determination of solid surface free energy is still not a fully solved problem. In this paper, some problems dealing with calculation of solid surface free energy from contact angle are discussed based on literature values of advancing and receding contact angles measured on four different fluoropolymers surface. The four approaches most often used for the calculation are described and especial focus on the approach in which both the advancing and receding contact angles is paid. It is concluded that using probing liquids the absolute value of solid surface free energy cannot be determined. However, the determined apparent values of the energy are very helpful to understand the conditions necessary for a given process to occur.

The Properties of Liquid Phase Embryos at the Intersections of Plane Solid Surfaces

1952 ◽  
Vol 5 (4) ◽  
pp. 618
Author(s):  
RG Wylie
Keyword(s):  
Contact Angle ◽  
Solid Surface ◽  
Contact Angles ◽  
Solid Surfaces ◽  
Boundary Line ◽  
Pure Liquid ◽  
Liquid Droplets ◽  
Free Energies ◽  
Different Types ◽  
Kinetics Of

In order to calculate the probabilities of nucleation of liquid droplets at different types of site on a solid surface, the properties of embryonic droplets which may exist in complete thermodynamic equilibrium at those sites must be known. The general properties of liquid embryos formed on a plane solid surface, or at lines or points of intersection of plane solid surfaces, are considered. It is shown that, although an edge free energy associated with the boundary line may substantially affect the properties -of embryos at small contact angles, the effect is probably not large, for embryos of the sizes of interest, when the contact angle is larger than about π/4. The areas, volumes, total surface free energies, and free energies of formation are found for embryos at these sites as functions of the contact angle, any edge free energies being neglected. The extension to the formation of bubbles at plane solid surfaces in a pure liquid is indicated. The results are applied in a following paper to the kinetics of condensation of a vapour at an imperfect crystalline surface.

scholarly journals Free Energy Balance of Polyamide, Polyester and Polypropylene Surfaces

2012 ◽  
Vol 7 (4) ◽  
pp. 155892501200700 ◽  
Author(s):  
Marcela Bachurová ◽  
Jakub Wiener
Keyword(s):  
Contact Angle ◽  
Free Energy ◽  
Energy Balance ◽  
Surface Energy ◽  
Solid Surface ◽  
Contact Angles ◽  
Surface Energies ◽  
Receding Contact ◽  
Smooth Plate

The wettability of a solid surface is often characterized by the contact angle of liquid on the solid surface. The wettability is pertinent to surface energy, which is an important parameter. The wettability can be affected, for example, by the roughness of the solid surface. In our work textiles are used as macroscopic roughness surfaces, and smooth plate surfaces are used as well to determine surface energies. For the calculation of surface energies it is fundamental to know the contact angle. The advancing and receding contact angles are measured, and the relation between the hysteresis and surface energy is monitored.

Contact Angle Hysteresis – Advantages and Disadvantages: A Critical Review

2020 ◽  
Vol 8 (1) ◽  
pp. 47-67
Author(s):  
Andrew Terhemen Tyowua ◽  
Stephen Gbaoron Yiase
Keyword(s):  
Contact Angle ◽  
Contact Angle Hysteresis ◽  
Theoretical Models ◽  
Contact Angles ◽  
Solid Surfaces ◽  
Advantages And Disadvantages ◽  
Volatile Liquid ◽  
Receding Contact ◽  
Rain Drops ◽  
The Difference

The existence of contact angle hysteresis – the difference between the values of the advancing and receding contact angles – is evident in nature (e.g. sticking of rain drops to car windscreens and window panes) and many industrial processes (e.g. surface coating, spraying, and dyeing of fabrics). This phenomenon is often viewed as a nuisance, but it is advantageous in many processes including dip and spin coating, spraying, and painting. With the early theoretical framework of Thomas Young, Robert Wenzel, and A. B. D. Cassie and S. Baxter, describing the wettability of solid surfaces and by extension contact angle, contact angle hysteresis has been deeply investigated. We review here the various ways of measuring contact angle and, consequently, contact angle hysteresis as well as related theoretical models. The successes and limitations of these models are highlighted. We conclude with the advantages and disadvantages of contact angle hysteresis whose presence in many processes is often considered as a nuisance, especially when "coffee stain" forms from the evaporation of a volatile liquid drop containing nonvolatile components.

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.

The Surface Modification with Fluorocarbon Thin Films for the Prevention of Stiction in Mems

1998 ◽  
Vol 518 ◽  
Author(s):  
Sang-Ho Lee ◽  
Myong-Jong Kwon ◽  
Jin-Goo Park ◽  
Yong-Kweon Kim ◽  
Hyung-Jae Shin
Keyword(s):  
Contact Angle ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Fluorocarbon Films ◽  
Perfluorodecanoic Acid ◽  
Large Hysteresis ◽  
Static Contact ◽  
Receding Contact ◽  
Highly Hydrophobic ◽  
Receding Contact Angle

AbstractHighly hydrophobic fluorocarbon films were prepared by the vapor phase (VP) deposition method in a vacuum chamber using both liquid (3M's FC40, FC722) and solid sources (perfluorodecanoic acid (CF3(CF2)8COOH), perfluorododecane (C12F26)) on Al, Si and oxide coated wafers. The highest static contact angles of water were measured on films deposited on aluminum substrate. But relatively lower contact angles were obtained on the films on Si and oxide wafers. The advancing and receding contact angle analysis using a captive drop method showed a large contact angle hysteresis (ΔH) on the VP deposited fluorocarbon films. AFM study showed poor film coverage on the surface with large hysteresis. FTIR-ATR analysis positively revealed the stretching band of CF2 groups on the VP deposited substrates. The thermal stability of films was measured at 150°C in air and nitrogen atmospheres as a function of time. The rapid decrease of contact angles was observed on VP deposited FC and PFDA films in air. However, no decrease of contact angle on them was observed in N2.

Surface Topography Induced Ultrahydrophobic Behavior: Effect of Three-Phase Contact Line Topology

2006 ◽  
Author(s):  
Neeharika Anantharaju ◽  
Mahesh Panchagnula ◽  
Wayne Kimsey ◽  
Sudhakar Neti ◽  
Svetlana Tatic-Lucic
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Anomalous Behavior ◽  
Contact Angles ◽  
Wet Etching ◽  
Surface Geometry ◽  
Wetting Behavior ◽  
Void Fractions ◽  
Three Phase ◽  
Receding Contact

The wettability of silicon surface hydrophobized using silanization reagents was studied. The advancing and receding contact angles were measured with the captive needle approach. In this approach, a drop under study was held on the hydrophobized surface with a fine needle immersed in it. The asymptotic advancing and receding angles were obtained by incrementally increasing the volume added and removed, respectively, until no change in angles was observed. The values were compared with the previously published results. Further, the wetting behavior of water droplets on periodically structured hydrophobic surfaces was investigated. The surfaces were prepared with the wet etching process and contain posts and holes of different sizes and void fractions. The surface geometry brought up a scope to study the Wenzel (filling of surface grooves) and Cassie (non filling of the surface grooves) theories and effects of surface geometry and roughness on the contact angle. Experimental data point to an anomalous behavior where the data does not obey either Wenzel or Cassie type phenomenology. This behavior is explained by an understanding of the contact line topography. The effect of contact line topography on the contact angle was thus parametrically studied. It was also inferred that, the contact angle increased with the increase in void fraction. The observations may serve as guidelines in designing surfaces with the desired wetting behavior.

scholarly journals Sessile droplets on deformable substrates

2018 ◽  
Author(s):  
Gulraiz Ahmed ◽  
Nektaria Koursari ◽  
Anna Trybala ◽  
Victor M. Starov
Keyword(s):  
Liquid Droplet ◽  
Contact Angles ◽  
Surface Forces ◽  
Interfacial Behavior ◽  
Equilibrium Conditions ◽  
The Past ◽  
Technological Advances ◽  
Three Phase ◽  
Significant Interest ◽  
Receding Contact

Wetting of deformable substrates has gained significant interest over the past decade due to its extensive applications and uses. This interest has developed due to technological advances which are able to capture interfacial behavior taking place when a liquid droplet is placed on a deformable substrate. Researchers have developed different theories to explain processes taking place in the process of wetting of deformable/soft substrates. For the scope of this review, we will consider the fluid to be Newtonian, partially wetting, and surface forces are incorporated with the help of disjoining/conjoining pressure acting in the vicinity of the apparent, three-phase contact line. The following subjects are briefly reviewed: (i) Equilibrium of droplets on soft substrates. It is shown that properties of the disjoining/conjoining pressure isotherm and properties of the deformable substrate determine both the shape of the liquid droplet and deformation of the substrate; (ii) Equilibrium conditions of droplets on deformable substrates. It is shown that for a droplet to be at equilibrium on a deformable substrate under consideration, Jacobi’s sufficient condition is satisfied; (iii) Hysteresis of contact angle of sessile droplets on deformable substrates. It is shown that as the elasticity of the deformable substrate is increased, both advancing and receding contact angles are reduced.

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