Classic Entry and Spreading Coefficients

Here we are concerned with defining the conditions under which a drop of oil can anerge onto the gas-Uquid surface of a foaming liquid and subsequently spread on that surface to form a thin film (or layer) of oil. Haridns [16] identified three types of such layers  

Here we consider the particular case of oil-based antifoams in aqueous systems. The same arguments can of course be extended to other combinations of fluids as we will, for example, describe in Chapter 10. 

If an oil is to emerge into the air-water surface and subsequently spread, then there are certain requirements that must be satisfied concerning the so-called entry and spreading coefficients. If drops of oil dispersed in an aqueous phase are to emerge spontaneously into the air-liquid surface, the entry coefficient E defined by 

Selection of the appropriate values of the three surface tensions should, however, take account of the extent to which the antifoam and aqueous solution have been pre-equilibrated. Thus, we could follow Ross [4] and define three entry coefficients. First, the initial entry coefficient 

If the oil is also to spread at the surface of the aqueous phase to form a film, then the spreading coefficient S must also be positive. Here we may foUow Harkins [18] and define an initial spreading coefficient, 

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The definitions of the classic entry and spreading coefficients, given by Equations 3.1 through 3.12 in Section 3.2, and for the bridging coefficient, given by Equations 4.29 through 4.31 in Section 4.5.1, can be transformed to the present context if we make the substitutions... 

The classic semi-initial and equilibrium entry and spreading coefficients, together with equilibrium bridging coefficients and spreading pressures, Aa w. for this system are listed in Table 4.3. Up to and including undecane, the initial and equilibrium entry coefficients are positive. For higher alkanes, they are seen to be essentially... 

Classic Entry, Spreading, and Bridging Coefficients for n-Alkanes in 3.8 mM AOT Solutions in 0.03 M NaCI at 25°C... 

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