Wetting of solids by liquids

Surface and interfacial energy are important because of their controlling influence on such practical applications as spinning, polymer adhesion, and stability of dispersions and wetting of solids by liquids. 

The wetting of solid surfaces by liquids has been studied for many years, both theoretically and experimentally. Useful reviews of this work include those by de Gennes [1], Dietrich [2], Adamson (Chapters 10, 13, and 16 in [3]), and Sullivan and Telo de Gama [4]. Before beginning a discussion of this phenomenon in the case of vapors condensed onto solid carbons, it is helpful to summarize some general features of wetting. Thus, the characteristics of the wetting of solids by liquids will be briefly described in this introductory section, to be followed by a discussion of some of the experimental and simulation studies of vapors on carbon surfaces. 

Fowkes [47] later postulated that the interaction energy due to wetting of solids by liquids with dispersion force interactions only, could be described by a geometric mean equation as shown in Eq. (4) ... 

It is self-evident that the wetting of solids by liquids is strongly influenced by interactions at the solid-liquid and liquid-vapor interfaces. The Hamaker (1937)-deBoer (1936) theory of wetting is based on the assumption of pairwise van der Waals (dispersion) interactions between the molecules of the vapor, liquid, and the solid substrate. This model is reasonable for a collection of poorly polarizable, weakly interacting... 

The cohesion of liquids and solids, the condensation of vapours to liquids, the wetting of solids by liquids and many other simple properties of matter all pointed to the presence of forces of attraction many times stronger than gravity but acting only at very short separations of the molecules. Laplace said that the only condition imposed on these forces by the phenomena were that they were insensible at sensible distances. Little more could in fact be said until 1929. 

Figure 7.14 Wetting of solids by liquids = liquid-air surface tension, Ks, = solid surface energy, Kj, =solid-liquid surface tension, 9 = wetting angle.

Capillarity ka-po- lar-o-te n (1830) Force of attraction between like and dissimilar substances. It is exhibited, for example, by the rise of a liquid up a capillary tube, or by the wetting of solids by liquids. 

Mixing The reorientation of particles relative to one another to achieve uniformity or randomness. This process can include wetting of solids by a liquid phase, dispersion of discrete particles, or deagglomeration into a continuous phase. Heating and cooling via indirect conduction may be used in this operation to facilitate phase mixing or stabilization. 

These terms are evidently ambiguous for example, it is not always clear whether wet is confined to aqueous solutions—the wetting of solids by mercury indicates that liquid-metal corrosion should be classified as wet . Even if the term is restricted to aqueous solutions, the difficulty arises that the mechanism of growth of magnetite scale during the reaction of the interior of a boiler drum with dilute caustic soda at high temperatures and pressures is best interpreted in terms of a dry corrosion process. Similar considerations apply to the reactions of aluminium and zirconium with high-temperature water. 

A more accurate investigation of the heats of wetting of known areas of solids by various liquids over an extended temperature range is highly desirable since it offers a promising method of... 

The general usage of the terms lyophilic and lyophobic in describing colloidal systems is somewhat illogical. Lyophobic traditionally describes liquid dispersions of solid or liquid particles produced by mechanical or chemical action however, in these so-called lyophobic sols (e.g. dispersions of powdered alumina or silica in water) there is often a high affinity between the particles and the dispersion medium - i.e. the particles are really lyophilic. Indeed, if the term lyophobic is taken to imply no affinity between particles and dispersion medium (an unreal situation), then the particles would not be wetted and no dispersion could, in fact, be formed. Lyophilic ... 

Ishimov, V. I., Hlinov, V. V. and Esin, O. A. (1971) in Kinetics of Wetting of Solid Oxides by Liquid Metals / Physical Chemistry of Surface Phenomena in Melts, Kiev, Naukova Dumka, p. 213 (in Russian)... 

In chocolate coating, the liquid phase is an oil (cocoa butter). The addition of lecithin aids the wetting of solid cocoa particles by this oil, most probably by lowering This lowers the viscosity of the heterogenous mass as well as giving a smoother mouthfeel to the final product. 

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