Biomedical Engineering Reference
In-Depth Information
Figure 4.50
Principle of three-phase flow reactions: spacer plugs of immiscible liquid prevent co-
alescence of droplets.
plugs separated, Chen et al. [51] use spacer plugs constituted by a third immiscible
liquid.
Obviously a first condition for the efficiency of spacer plugs is that the liquid
plugs do not engulf each other. Figure 4.51 shows the satisfactory arrangement of
the plugs (a), and engulfment (b). The condition for the stability of plugs in contact
is given by the balance of the surface tension forces at the triple line (Neumann's
construction)
� � �
γ γ γ
+
+
=
0
(4.74)
ct
tr
rc
Equation (4.74) can be satisfied only if the magnitude of every force is smaller
than the sum of the magnitudes of the other two forces. This statement can be easily
Figure 4.51
Sketch of two plugs in contact. (a) Plugs stay distinct; (b) spacer liquid plug engulfing
reagent liquid; (c) Neumann's construction for the equilibrium of the interfaces.
