interface then compensates for its dilution by expansion of the surface.
Moreover, the conformation of macromolecular surfactants should be
constant.
Invariably,gdynis larger for a faster expansion rate within a certain
range ofxvalues. At highx, the value of the pure solventg 0 is reached, at
very lowx, the equilibrium value. Some examples are in Figure 10.18, and it
is seen that, as expected,gdynis smaller for a larger surfactant concentration,
even if the plateau value ofgis the same. Figure 10.18 relates to A–W
interfaces; measurements at O–W interfaces can also be done, although not
as easily. Unfortunately, very high expansion rates cannot be obtained,
especially not at an O–W interface (because of the high viscosity of the oil).
As mentioned, changes inprotein conformationreadily occur upon
adsorption. Results as, for instance, given in Figure 10.14 relate to
FIGURE10.17 Adsorption of ovalbumin at the A–W interface; pH¼6.4, ionic
strength¼0.02 M. (a) Surface load (G). (b) surface pressure (P) as a function of the
square root of adsorption time (t). The numbers near the curves denote the protein
concentration in ppm. (From results by J. de Feijter, J. Benjamins. In: Food
Emulsions and Foams, ed. E. Dickinson. Roy. Soc. Chem., 1987, p. 74.)