Capillarity contact angle

Wetting and capillarity can be expressed in terms of dielectric polarisabilities when van der Waals forces dominate the interface interaction (no chemical bond or charge transfer) [37]. For an arbitrary material, polarisabilities can be derived from the dielectric constants (e) using the Clausius-Mossotti expression [38]. Within this approximation, the contact angle can be expressed as ... 

The next two chapters are concerned with wetting and capillarity. Wetting phenomena are still poorly understood contact angles, for example, are simply an empirical parameter to quantify wettability. Chapter 6 reviews the use of scanning polarization force... 

Figure 2.1 (a) A schematic representation of the apparatus employed in an electrocapillarity experiment, (b) A schematic representation of the mercury /electrolyte interface in an electro-capillarity experiment. The height of the mercury column, of mass m and density p. is h, the radius of the capillary is r, and the contact angle between the mercury and the capillary wall is 0. (c) A simplified schematic representation of the potential distribution across the metal/ electrolyte interface and across the platinum/electrolyte interface of an NHE reference electrode, (d) A plot of the surface tension of a mercury drop electrode in contact with I M HCI as a function of potential. The surface charge density, pM, on the mercury at any potential can be obtained as the slope of the curve at that potential. After Modern Electrochemistry, J O M. 

Surface tension and contact angle, wetting phenomena, effects of the curvature of the surface on capillarity and phase equilibria, and porosimetry (Chapter 6)... 

Fig. 47 clearly shows that the contact angle, , is satisfactorily taken into account by the function Ku x sin =/(Bd). Only now it is also obvious that the capillarity-buoyancy number CB exerts no influence on the hanging film. The liquid viscosity, 11, proves to be irrelevant. This is not surprising because of the fact that the respective measurement were executed in the turbulent flow range, Re = 4.15 x 103-1.42 x 10s. 

This equation has been known for over a century it was given by Young2 (without proof ) and by Dupre 3 it can be deduced also from Laplace s theory of Capillarity, or indeed from any theory of the cohesive forces, since it can be obtained from consideration of energies only. Until recent years it has been little noticed, which is unfortunate, as the meaning of the contact angles is much clarified when the work of adhesion is introduced, and the surface tensions of the solid surfaces, which are not measurable, are eliminated. Most authors are now, however, expressing their results in terms of the work of adhesion or of closely related expressions. 

Figure 10 presents the interface shape of the rivulet for wall superheat as 0.5 K and Re = 2.5. Here also presented the data on pressure in liquid and heat flux density in rivulet cross-section. The intensive liquid evaporation in near contact line region causes the interface deformation. As a result the transversal pressure gradient creates the capillarity induced liquid cross flow in direction to contact line. Finally the balance of evaporated liquid and been bring by capillarity is established. This balance defines the interface shape and apparent contact angle value.For the inertia flow model, the solution is obtained from a non-stationary system of equations, i.e., it is time-dependable. In this case the disturbances in flow interface can create the wave flow patterns. The solutions of unsteady state liquid spreading on heat transfer surface without and with evaporation are presented on Fig. 11. When the evaporation is not included (for zero wall superheat) the wave pattern appears on the interface. When the evaporation includes, the apparent contact angle increase immediately and deform the interface. It causes the wave suppression due to increasing of the film curvature.

Finally, floating lenses of liquids offer a pabulum for the development of theory to describe the involved curvatures mathematically. Comparison with experiments allows the establishment of the three contact angles, see for Instance refs. 2 3). Aveyard and Clint" ) reviewed the stability and capillarity of floating droplets in the presence of surfactants. 

Capillarity may be defined as the phenomena resulting from the fact that a free liquid surface has a finite or zero contact angle with a solid wall and will attain this angle when placed in contact with the wall. It is commonly thought of as the rise (or fall) of liquids in small tubes or finely porous media. More generally, capillary motion can be said to be any flow that is governed in some measure by the forces associated with surface tension. Ordinary capillarity is observed in a fine tube open at both ends that is placed vertically in a pool of liquid exposed to the atmosphere, with the liquid seen to attain a level in the tube above the level of the pool. The actual rise velocity of the free surface of the liquid in the tube from the level of the pool is one simple example of capillary motion. ... 

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