involves hundreds of such bonds. These bonds may even be of various kinds.
Consequently, it may be advisable to speak of ajunctionbetween particles as
a general term.
Alsobridges, as depicted in Figure 12.8, are a form of junction. Some
additional mechanisms will be mentioned. Figure 12.8c shows bridging of
large fluid particles by small solid ones. An example is partially solid
emulsion droplets bridging air bubbles, as in whipped cream; or compact
protein aggregates bridging oil droplets, if insufficient protein is present to
cover fully the O–W interface.
Figure 12.8d shows a liquid neck between solid particles in a fluid,
which holds the particles together by capillary forces (see Section 10.6); the
attractive interaction energy can be very large. An example is bridging of
various particles in cocoa mass (&melted chocolate)—where oil is the
continuous phase—induced by tiny water droplets; this then gives the cocoa
mass a greatly enhanced viscosity.
Finally, it has been observed that air bubbles or oil droplets in water
can be bridged by layers of ana-gel of a suitable small-molecule surfactant
(see Section 10.3.1), if sufficient surfactant is present. This is used to lend
stiffness and stability to some whipped toppings.
FIGURE12.11 Illustration of some bond strengthening mechanisms. See text.