Surface force nonwetting

The contact angle corresponds to the state where the different surface forces are at equihbrium. The magnitude of Yrock can be estimated if the value of contact angle, 0, and the 7, is known. The determination of surface tension of sohds (such as Yrock) has been extensively studied and its apphcation in real-world systans has been extensively delineated in the current hterature (Birdi, 1999,2010 Chattoraj and Birdi, 1984). If the contact angle is less than 90°, then the hquid is known to wet the sohd surface. However, if the contact angle is larger than 90°, then the surface is nonwetting. For example ... 

An alternate derivation of the Washburn equation can be pursued as follows. For a pore of circular cross-section with radius r the surface tension acts to force a nonwetting liquid out of the pore. The force developed due to interfacial tensions is the product of the surface tension y of the liquid and the circumference (2nr) of the pore, that is. 

Mercury is a nonwetting liquid that must be forced to enter a pore by application of external pressure. The surface tension of mercury causes mercury to bridge the openings of pores, cracks, and crevices until sufficient pressure is applied to force entry. For example, at atmospheric pressure, mercury will resist entering... 

Morrow, N.R., Songkran, B., 1981. Effect of viscous and buoyancy forces on nonwetting phase trapping in porous media. In Shah, D.O. (Ed.), Surface Phenomena in Enhanced Oil Recovery. Plenum Press, pp. 387 11. 

Surface tension. Assuming that a membrane stretches over each interface, the magnitudes of the interfacial tension between each pair of phases are the fluid-fluid interfacial tension Ogt, the wetting fluid-solid interfacial tension oft, and the nonwetting fluid-solid interfacial tension ogs. When in static equilibrium, the vectorial force balance at the line of contact (the law of Neumann triangle, Ref. 87) gives... 

When a liquid is placed on a solid surface, either it will spread and wet that surface (Fig. 10.22fl) or it will bead up (Fig. 10.22ft). The degree of wetting and whether a system is wetting or nonwetting are quantified by the equilibrium contact angle 9 that forms between the liquid and the solid and is defined in Fig. Q.22a and ft. A simple balance of forces indicates that at equilibrium... 

Adhesion of gas bubbles to solid particles. In the hydrometallurgical process, flotation, gas bubbles are attached to ore particles and carry them to the surface of the liquid phase. The attraction force is adhesion of circular line elements at the contact of a nonwetted solid phase (ore), liquid phase (aqueous solutions of flotation agents), and gas phase (air or hydrogen bubble). This system is presented in Figure 1.17. 

Thouzeau and Taylor [215] measured the adhesion of inert lime dusts of two types (nonwetting and ordinary) by a technique in which a dust-covered hydrophilic surface was inclined their work established that the force of adhe-... 

At a very low rate of penetration (curves 1 and 2), the concentration Cm does not differ appreciably from Cq due to the small Peclet number (Pe = v// D) and predominance of diffusion. At very high values of K, the concentration close to the meniscus tends to zero. This also takes place in the case of forced penetration under the action of an external pressure [19], when Pe > > 1. In this case, surfactant molecules cannot reach the meniscus and influence the contact angle. The effect of capillary radius is similar the smaller the values of r, the more pronounced is the influence of surfactant adsorption. An increase in Z)s2 values leads to some decrease in Cm due to the enhanced diffusion along the nonwetted capillary surface. 

Strictly speaking, the force is the molecular adhesive force in an atmosphere of saturated vapor. However, because the adsorption of vapors of a nonwetting liquid on solid surfaces is insignificant and does not influence adhesion between particles, one can nearly always assume that the value of the force Pss is ih same as that in air. 

It is thus evident that, within a first approximation. Equation 1.30 is valid for both wetting and nonwetting liquids, with a meniscus either present or absent. It is, however, worth pointing out that for macroscopic particles, this is valid only in the case of molecularly smooth surfaces. In this case, the equations for the molecular adhesive forces and for the capillary contraction force both contain the same macroscopic value of R. The situation is different for rough surfaces. Namely, the value of R in the expression for the molecular forces may be determined by the radii of microheterogeneities between which the contact is formed, while the value of R in the expression for the capillary adhesion force may be determined by the macroscopic radii of the particles. Consequently, particles with a microscopically... 

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