Complete wetting

There are several features to note about Figure 4.7. While water will bead on a surface prepared with PTFE or an FA, it will wet a nylon-6,6 surface. For the case of hexadecane, botlr PTFE and FA surfaces will show appreciable contact angles, while a nylon-6,6 surface will be wetted completely (0 = 0). This is the reason that oily soils are relatively difficult to remove from materials made from nylon-6,6. The surface of a material prepared with a FA using perfluoroalkyl chains often has a lower surface tension than PTFE. For comparison, the surface tensions of nylon-6,6, PTFE " and FAs are estimated to be about 46, 24, and 10-20 mN/m, respectively. 

A small contact angle implies that the drop spreads over the surface if the contact angle is zero, the surface will be wetted completely (Figure C2-8). This happens when the solid/vapour tension is much larger than the solid/liquid tension the system then avoids any solid/vapour interface. If the contact angle is equal to Jt, there is no wetting. This happens when the solid/liquid tension is much higher than the solid/vapour tension. The system then minimizes the liquid/vapour interface, as with a drop of mercury on paper. 

In sufficiently fine porous media the effect of gravity is not important (Figure C2-11). You would then expect the solid either not to wet at all (the left figure) or to wet completely (the right figure). 

Similar to tray columns, packed columns operated at high gas velocities causes backmixing, and low gas velocities reduce the mass transfer rate. If the gas velocity is too high, the column will flood. In addition, at low liquid flow rates the packing will not wet completely, resulting in a reduction in mass-transfer. Another problem is the tendency for the liquid to channel. To minimize this effect, redistributors have to be installed every 5 to 10 m (16.4 to 30.5 ft) [23] to even out the liquid flow. 

Spray the surface to be treated, miking sure to wet completely. Let air dry. Repeat at weekly intervals or when mildew reappears. 

Spray surface to be treated making sure to wet completely. 

For density to be determined according to the flotation process, of course, the sample must not dissolve or swell in the liquid, and it must wet completely. Make sure that no air bubbles appear on the surface of the sample for they may affect the measurement. Any bubbles must be completely removed. Carbon black, glass fibers, and other fillers can also influence the density measurements greatly. For example, the densities can vary depending on the filler content from 0.98 g/cm (polypropylene with 10% by weight of talcum) to 1.71 g/cm (polybutyleneterephthalate containing 50% glass fibers). Foams cannot be characterized by density determinations. 

Of more direct practical importance to textile processing is the fact that it becomes increasingly more difficult to remove the last traces of air from the fiber system. Fiber bundles in yarn can produce quite complex capillary systems that provide ample opportunity for air entrapment in very inaccessible nooks and crannies. It is found, for example, that yarns made of smooth essentially cylindrical fibers are much easier to wet completely than those eomposed of... 

Crawling n. (1) Defect in which a wet paint or varnish film recedes from small areas of the surface, leaving them apparently uncoated. British synonym is cissing. (2) The contraction of an ink film into drops after printing on a surface, which the ink does not wet completely. 

The method of processing viscosity enhancing substances in the aqueous phase depends on the type of substance. The general rule is The viscosity enhancer has to be wetted completely at first. Otherwise lumps may occur that cannot swell anymore because they are insulated by the outer, swollen part. Section 23.7.2 gives elaborate information on different preparation methods. 

When the oil layer is as thin as 0.9 nun (100 mL heavy oil used), the contact of exfoliated graphite inside the bag with the heavy oil was not sufficient, as shown in Figure 4.36a. A thin oil layer seems to be pushed away from exfoliated graphite, as schematically illustrated in Figure 4.36c. When the oil layer is thick enough, that is, thicker than about 4 mm (more than 500 mL of heavy oil used), exfoliated graphite was wetted completely, as shown in Figure 4.36b. 

The polymeric resins are substantially more hydrophobic than activated carbon. The non-wetting types are subjected to the pre-wetting procedure described above (i.e., wetting wi a solvent, such as methanol, followed by aqueous solution). The pores are presumably wetted (completely) upon this treatment. Undoubtedly, the mesopores (i.e., voids between the microspheres within each bead) are wetted. It is not clear, however, whether the micropores within each microsphere are completely wetted by this procedure. 

The contact angle (0), another criterion for hydrophilicity and lipophilicity, is employed to evaluate the wettability of liquid to solid. Generally, the solid surface is considered to be wetted by liquid when 0 < 90° the solid surface is not considered to be wetted by liquid when 0 > 90° and the solid surface is wetted completely by liquid when 0 = 0°. As for inorganic whiskers, the bigger the contact angle between distilled water and whiskers, the better is the hydrophobicity of whiskers. 

One is free to choose which flow will be the continuous and which will be the dispersed phase. When the dispersed phase is lighter than the continuous phase, the separator is in the top of the column, and vice-versa. For a PPC a packing material should be selected that is wetted completely by the continuous phase. 

But there is also no doubt that the equilibrium configuration of three phases is sometimes— indeed, often— that of Fig. 8.3, where one of the phases, p, spreads at (wets completely) the interface between flie two others. In that case (8.9) holds, and with it Antonow s rule. That is not merely a limiting but unattainable case, and (8.8) is not merely an asymptotic law or an approximation. The case is attainable, and (8.8) is exact throughout the range of three-pbase- uilibrium states over whidi one of the phases spreads at the interface between the other two. 

In the cases first studied by Antonow, the two liquids p and y were formed from two incompletdy miscible, pure components not far from their consolute point (critical solution point). From our present knowledge we ate able to say that in just those drcumstances we would expect one of the liquid phases to wet completely the interface between the other liquid phase and the vapour. (We shall see why, in 8.5.) The picture in those cases would then be that of Rg. 8.3, so (8.8) would hold Antonow was right. But we can imagine a hypoflietical case, even of such a two-component liquid-liquid- apour system near the consolute point of the liquids, in which Antonow s rule must fail. Suppose the two components are an incompletely miscible enantiomeric pair, so that the two liquid phases p and y, ea slightly richer in one of the two components, are mirror images and suppose a is their common vapour. Then a =... 

Oil Absorption (Value) n Quantity of oil required to wet completely a definite weight of pigment to form a stiff paste when mechanically mixed. The oil absorption number or value of a pigment is the number of... 

Consider two types of mineral particles in an aqueous suspension. If air bubbles can be attached to one type of particle only, the latter will float to the surface of the suspension, due to reduced density, and can be separated from the other type of particles. Normally, mineral particles are wetted completely by water so that air bubbles cannot attach to them. However, if the particle surface can be made sufficiently hydrophobic to prevent wetting, air bubble attachment is possible. 

In Section 3.3.8, we observed that, in a gas-liquid-soUd system with a flat solid surface, there is either zero or a finite contact angle 9 (see Figure 3.3.16) the liquid attains this contact angle spontaneously without any other external force being present. If the contact angle is zero, the liquid spreads over the solid surface, displacing the gas/air the solid surface is said to be wetted completely by the wetting liquid. This phenomenon is routinely encountered and exploited when a porous medium, such as a porous membrane or porous bed or paper, comes into contact with a liquid which can wet the material of the porous medium. 

Which of the following liquids can wet completely PA-6 water (72.8), acetone (23.3), hexachloro butadiene (35.5), diethylene glycol (44.7) Explain briefly your answer. The values in parentheses are the surface tensions of the liquids, all in mN m ... 

The measured normalized wetting rates for various test liquids (for cellulose fibers Fig. 23) can be transformed into the cosine of the contact angle (cos0) and plotted as a function of the liquid surface tension (Fig. 24). The resulting linear relationship cos 0 = 1 — b(y — jc) was established empirically by Zisman and Fox [120] and found to hold for solid with low surface tensions. The critical surface tension 7c corresponds to the surface tension of the liquid that will just spread over/wet completely the solid. The constant C reflects the capillary geometry of the porous solid and may change in a non-predictable manner during the penetration process of different test liquids. It was concluded from the experiments performed [112] that there is no need to determine the constant C in order to obtain solid-surface tensions, because the position of the maximum in the C-7iv cos 0 vs. 7iv plot, which is expected to... 

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