13.1e. The adjectivepartialsignifies that the globules do not coalesce into
one drop, although there is oil–oil contact between them.
The mechanismof partial coalescence is illustrated in Figure 13.20a. A
fat crystal protruding from the globule surface may pierce the film between
close globules (or between a globule and a true droplet). If there is attraction
between the globules, or if they are pressed together, the sharpness of the
crystal causes considerable stress concentration, facilitating the piercing of
the film and, if needed, of the adsorption layer on the globule. The contact
angle water–oil–crystal, as measured in the water phase, tends to be obtuse
(Figure 13.20a), which means that the crystal is preferentially wetted by the
oil. This then leads to a junction between the globules, consisting of an oil
FIGURE13.20 Illustration of the onset of partial coalescence. (a) Protruding
crystal piercing the film between approaching globules. (b) Enhanced probability for
piercing of the film when globules roll around each other in a shear field.