Equilibrium at intersections of surfaces wetting

The classical analysis of Young and Laplace of static wetting problems rests on the characterization of each interface by a macroscopic surface tension. At the intersection of three bulk phases, the three phase contact line is at rest only if the capillary forces represented by these surface tensions balance. When the three phases are a solid substrate S, a wetting liquid L and a vapor V, the mechanical equilibrium condition parallel to the solid gives the Young-Dupr6 equation for the contact angle Oq... 

Figure 12.3b depicts three thin films. The juncture of multiple thin films is called a Plateau border, after the Belgian physicist who first described the equilibrium structure of dry foams [24]. In three dimensions thin films define a surface, and Plateau borders are quasi-ID objects. The point of intersection of several Plateau borders is, in turn, known as a vertex or node. Increasing the liquid content causes the bubbles to become more rounded, ultimately attaining a circular/spherical shape. In the dry foam limit, the thin film thickness goes to zero and the radius of curvature R at each vertex vanishes. The liquid content in Figure 12.3 is therefore seen to be low—the foam is dry rather than wet. 

FIG. 24 Schematic depicting the pinning and depinning of the contact line on an oxide inhomogeneity. (a) Liquid wets the solid metal surface (a) with the equilibrium contact angle 0 - (b) The contact line pins at the intersection of the pure metal/metal oxide interface of the oxide until the contact angle increases to the value of (c) When this occurs, wetting commences over the oxide surface (/ ). 

Consider a flat, undeformable, perfectly smooth and chemically homogeneous solid surface in contact with a non-reactive liquid in the presence of a vapour phase. If the liquid does not completely cover the solid, the liquid surface will intersect the solid surface at a contact angle 9. The equilibrium value of 9, used to define the wetting behaviour of the liquid, obeys the classical equation of Young (1805) ... 

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