Soap film drainage

Although stable diluted bitumen films are more complex than soap films, they appear to follow a classical film-drainage pattern without demulsifier as shown in a study by Angle et al. (82) and reproduced in Fig 21, 22. 

The drainage of a liquid between two stationary soap films may take several hours. Assuming a liquid viscosity 17 = 10 P (c.g.s.), a film thickness d = 10 cm, a liquid density p = 1 g cm, and g (gravity constant) = 1000 cm s , show that such a time frame is not unreasonable. 

A rigid soap film created in an enclosure is prevented from thinning by evaporation. If it is allowed to drain in a saturated, vibrationless, clean, environment the film will not rupture. In such circumstances the drainage will be by viscous flow alone. The fluid will flow between the rigid, or plastic surfaces of the soap film (Fig. 2.7(a)). The profile of the film will be parabolic as indicated in Fig. 2.7(b). The parabolic cross-section is joined at its highest point to avertical black film (Fig. 2.7(b)). The black film will have a constant... 

As we have seen in the previous example of the vertical soap film (Figure 2.10), thick film surfaces can be curved. However, as the films lose water (drainage), they progressively flatten due to interactions between the sinfaces. 

This chapter discusses the relation between foam behavior, properties of the soap films that separate the bubbles, and properties of the surfactant mono-layers that cover the film surfaces. Different aspects are taken into account —foaming, ripening, drainage and bubble coalescence—and are illustrated with experimental results. We show, in particular, that the relation between foam properties and foam films and monolayers is far from obvious in mixed surfactant-polymer solutions. 

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