Interfacial Tension, pages

Figure 11-18, page 336, Parachors of Heavy Fractions for Computing Interfacial Tension of Reservoir Fluids... 

It is well known that short-range forces of attraction exist between molecules (see page 215), and are responsible for the existence of the liquid state. The phenomena of surface and interfacial tension are readily explained in terms of these forces. The molecules which are located within the bulk of a liquid are, on average, subjected to equal forces of attraction in all directions, whereas those located at, for example, a liquid-air interface experience unbalanced attractive forces resulting in a net inward pull (Figure 4.1). As many molecules as possible will leave the liquid surface for the interior of the liquid the surface will therefore tend to contract spontaneously. For this reason, droplets of liquid and bubbles of gas tend to attain a spherical shape. 

If the interfacial tension between two liquids is reduced to a sufficiently low value on addition of a surfactant, emulsification will readily take place, because only a relatively small increase in the surface free energy of the system is involved. If tt y0, a microemulsion may form (see page 269). 

If Fowkes semiempirical interfacial tension theory (as described on pages 65-67) is applied to the solid-liquid interface, then... 

In equations describing rates of transport and equilibria between two phases (a and b) (see page 386), it has been assumed ihei the interfacial tension between them and water is the same for the two phases. In some cases this assumption may not hold, for instance, if the two phases have difTerent compositions. In these cases it would be more ajqiropiiale to include separate terms for the two phases, for example, y, and gj, for the interfacial tensions. 

A schematic of change in the type of microemulsion with the salinity is shown in Figure 7.8, and a volume fraction diagram of the data presented in Table 7.2 is shown in Figure 7.9. The volume fraction information can also be represented by a solubility plot, as shown in Figure 7.10 (see page 254). We will see later that the solubilization ratio is a very important parameter in interfacial tension calculation. 

Figure 4. The lowering of the interfacial tension at the air-water interface of meat juice in (0.2-7) at a concentration of 10" wt% (upper) and 10" (lower). Continued on next page.

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