the same extent to the triglyceride oil–water interface as to the crystal–water
interface, giving the same decrease in interfacial tension.
If the concentration of SDS is about 35 mmolar (i.e., well above the
CMC), the solid becomes even completely wetted by the aqueous phase.
Although most fat crystals are not nearly spherical, and the geometrical
relations thus become more complicated, complete wetting can also be
achieved in practice. In the so-called Lanza process fat crystals are separated
from a dispersion in oil by washing with an aqueous solution of a suitable
amphiphile.
For other systems, the relations may be quite different. Often, the plots
ofgOWcosyversusgOWare linear, but of a slope>1. Moreover, many of
such plots go almost through the origin, which implies that the contact angle
will remain about the same, unlessgOWbecomes very small. Such a situation
FIGURE10.25 Effect of the concentration (c, in mol?m^3 ) of a surfactant on the
contact angle (y) of spherical particles of a solid S at the O–W interface.gis
interfacial tension in mN?m^1. (a) Configuration of the particles and some
quantitative data. (b) State diagram ofgOWcosyversusgOWand plot of the data
for W–O–S systems. The numbered points correspond to the numbers near the
particles at left. The broken line refers to another system, wherey& 1508.