Disjoining pressure apparatus

Figure 14. Schematic of a disjoining pressure apparatus. (Adapted from reference 38. Copyright 1987 Consultants Bureau.)...

Figure 10.3 Apparatus for measuring the disjoining pressure of free films as a function of their thickness225 (After B.V. Deryagin and A.S. Titijevskaya)...

Figure 5.7 illustrates how the disjoining pressure can be determined. A film is formed and liquid is withdrawn from it through a slit in the vertical wall of the apparatus. This produces a free liquid film (a), whose surface is under the same... 

We have constructed a new surface-force apparatus capable of measuring the capillary pressure and structural disjoining pressure of the thinning curved emulsion film as a function of time and film thickness (11-16). This apparatus is equipped with Max Zhender differential interferometry... 

Surface-induced layering corresponds to oscillations of the disjoining pressure in the molecular range of thickness (see also chapter 1). Well-known saw-tooth force profiles are obtained with surface forces apparatus (SFA) setups. In the case of microdroplets, where the thickness is free to adjust, an unstable part in the disjoining pressure behaves just like the usual pressure at three dimensions a Maxwell construction leads to a horizontal part in n(f), corresponding to the coexistence of films with different thickness (see chapter 3). 

The measurement of forces between surfaces at small separation is of great importance in gaining a fundamental understanding of the complex behaviour of colloidal systems. Interactions of solid surfaces (coated or uncoated) across a fluid medium have been made through development of both the surface forces apparatus (SFA) and the atomic force microscope. Interactions between liquid surfaces are generally discussed in terms of the variation of the disjoining pressure with surface separation, and the majority of studies relate to foam (i.e. vapour-liquid-vapour) Investigations of various aspects of emulsion (i.e. liquid-liquid-... 

A novel liquid surface forces apparatus (LSFA) developed at Hull has been used to study oil-water-oil films. An oil drop of radius a few microns is supported in an aqueous phase on the tip of a fine glass micropipette that is held initially below an oil-water interface. The other thick end of the micropipette is connected to a manometer containing the same oil. The radius of the oil drop is controlled by the balance of the Laplace pressure inside the drop and the applied pressure head. When the oil drop is moved up to the oil-water interface, a thin water film is formed between the apex of the drop and the interface the disjoining pressure in the film turns out to be simply one half of the pressure head since there are two... 

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