Liquid contact angle

The preceding definitions have been directed toward the treatment of the solid-liquid-gas contact angle. It is also quite possible to have a solid-liquid-liquid contact angle where two mutually immiscible liquids are involved. The same relationships apply, only now more care must be taken to specify the extent of mutual saturations. Thus for a solid and liquids A and B, Young s equation becomes... 

When a surface-active agent is present in a liquid droplet, it can adsorb to the surface, lower the surface energy, and cause the liquid contact angle to increase. This phenomenon, known as autophobicity, was postulated by Zisman many years ago [78, 79]. Autophobicity is quite striking in wetting films on clean... 

The first observation suggests that the results derived from the infinite dilution state are related to the most active adsorption sites which leads to a high surface free energy value. It is then not evident that a relationship exists between the results at infinite dilution and those of the classical liquid contact angle measurement as one of the wetting methods or the results at finite concentration. 

It is clear from Figure 3.12 that the amount of liquid penetration depends strongly on the liquid contact angle. In addition, since capillary pressures vary inversely with asperity size, the amount of liquid penetration also depends on the size of the asperity. These trends are shown in Figure 3.13 (page 65) where the volume fraction of the pore filled by liquid is plotted vs the contact angle for... 

Figure 3.13 Variation of liquid penetration into a sinusoidal surface feature (Figure 3.12) with liquid contact angle [14]. Different curves are obtained for different groove dimensions peak-to-peak amplitude is indicated in nanometers next to each. (Reprinted with pramission. See Ref. 114]. 1993 American Chemical Society.)...

Y. Tamai, T. Matsunaga and K. Horluchl, J. Colloid Interface Set 60 (1977) 112 comparison with data obtained with two-liquid contact angle method. 

Dynamic contact angles are the angles which can be measured if the three-phase boundary (liquid/solid/vapor) is in actual motion. A Wilhelmy plate is used in dynamic contact angle measurements, and this method is also called the tensiometric contact angle method. It has been extensively applied to solid-liquid contact angle determinations in recent years. In practice, a solid substrate is cut as a thin rectangular plate, otherwise a solid material is... 

In the pendular state, shown in Figure la, particles are held together by discrete lens-shaped rings at the points of contact or near-contact. For two uniformly sized spherical particles, the adhesive force in the pendular state for a wetting liquid (contact angle zero degree) can be calculated (19,23) and substituted for H in equation 1 to yield the following, where y is the liquid surface tension in N/m. 

TABLE I. Liquid Contact Angles on Roughest and Smoothest Wax Surfaces Available in This Study... 

Since the time that study was made, a large body of experimental data has accumulated which shows that regular and predictable changes in solid-liquid contact angles result from changes in the outermost layer of atoms in the solid surface. A "wettability spectrum" has been published [14],and the utility of the "critical surface tension of wetting" as an index of solid surface energy has been well established. 

Electrowetting is the electrostatically induced decrease of the liquid contact angle at a contact line formed at the intersection of a liquid, solid, and a third fluid that can be a gas or inuniscible liquid. The contact angle is measured within the droplet between the solid surface and the... 

The surface tension is calculated by using the Young-Dupre equation (Equation 2.10). In this equation, Ylv is the surface tension between the liquid and its vapour, and 0e is the solid/liquid contact angle measured at equilibrium . The critical surface tension, which is characteristic of a material surface, corresponds to 0e = 0 (or cos 0e = 1). As zero angles cannot be... 

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