文档介绍：11 Stability of Dispersions
The ulation of dispersions is a consequence of attractive forces holding parti-
cles together when they collide. If the particles repel each other sufficiently
strongly, they bounce apart on collision and the dispersion is free from coagula-
tion and stable. The quantitative theory for the stability was independently devel-
oped by Derjaguin and Landau in the . and Verwey and Overbeek in the
Netherlands and is called the DLVO theory. This theory provides a fundamental
framework, with which to discuss the stability of dispersions. However, we must
note that this theory works best for ideal model materials since ions treated in the
theory are considered as point charges which do not readily form -
plexes (MatijevicÂ, 1973). The hydration forces observed, for instance, between
mica surfaces are caused by adsorption of hydrated species (ions) rather than by
the inherent nature of the surface (Pashley and Quirk, 1984). In particular, an ap-
plication of the DLVO theory to the stability of emulsions is questionable, since
there are usually emulsifying agents at the interfaces.
DLVO Theory
Particles dispersed in an electrolyte solution are usually surrounded by diffuse
electric double layers. If they approach each other, the double layers overlap and
particles repel each other as discussed in Chapt. 10. Thus, the significant proper-
ties of the interactions are the f-potentials and the thickness of the double layers
(the inverse of the Debye-HuÈckel screening parameter, Eq. ). The f-poten-
tials are measured in terms of ic phenomena (see Sec. ).
The electrostatic repulsive interactions between charged spheres are discussed
in Sec. . The attractive dispersion forces have been treated in Chapt. 8. As
shown in Eq. , the total interaction free energy is given by
DGT DGR DGA DGS 11:1
In the DLVO theory, however, the solvent mediated term, DGS, is ignored.
220 11 Stability of Dispersio