Interactions and Colloid Stability

FIGURE 6.1 Colloids in suspension are in the dispersed or peptized state shown at left. Eventually the particles would aggregate into larger entities, which will sediment. The reverse process is possible, which can lead to landslides. 

FIG U RE 6.2 (a) Idealized illustration of the contact or adhesion between two surfaces 1 and 

should, in general, be affected by all these contributions, which are usually assumed to be independent (i.e., can be calculated independently of each other). However, except at short distances, only the two first terms in the right-hand side of Equation 6.5 are important image forces are present only for metal surfaces and the remainder act only at very short distances. 

As it will be seen in the next sections, there are basically two approaches analysis of interaction forces and analysis of interaction energies. In the second view, the interaction energy (7(d) of two particles at a distance d apart can be found from the 

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Two nucleation processes important to many people (including some surface scientists ) occur in the formation of gallstones in human bile and kidney stones in urine. Cholesterol crystallization in bile causes the formation of gallstones. Cryotransmission microscopy (Chapter VIII) studies of human bile reveal vesicles, micelles, and potential early crystallites indicating that the cholesterol crystallization in bile is not cooperative and the true nucleation time may be much shorter than that found by standard clinical analysis by light microscopy [75]. Kidney stones often form from crystals of calcium oxalates in urine. Inhibitors can prevent nucleation and influence the solid phase and intercrystallite interactions [76, 77]. Citrate, for example, is an important physiological inhibitor to the formation of calcium renal stones. Electrokinetic studies (see Section V-6) have shown the effect of various inhibitors on the surface potential and colloidal stability of micrometer-sized dispersions of calcium oxalate crystals formed in synthetic urine [78, 79]. 

Our objective in this chapter is to establish the quantitative connections between interparticle forces and colloid stability. Before we consider this it is instructive to look at the role of interaction forces in a larger context, that is, the relation between interparticle forces and the microstructure of dispersions and the factors that determine such a relation. These aid us in appreciating the underlying theme of this chapter, namely, the manipulation of interparticle forces to control the properties of dispersions. 

Discuss polymer-colloid interactions and steric stability from a thermodynamic perspective. What is enthalpic stabilization What is entropic stabilization What is the critical flocculation temperature (CFT) ... 

Chapters 11-13 of the second edition, which discussed van der Waals forces (old Chapter 11), electrical double layers (old Chapter 12), electrokinetic phenomena (old Chapter 13), and colloid stability (old Chapters 11 and 12), have been restructured and new materials on colloid stability and polymer/colloid interactions have been added. For example ... 

In more applied veins, -potentials are not measured for their own sake, but to assess particle interaction, as is for instance required in rheology and colloid stability. These measurements have to be carried out for particles that are often ill-defined the shapes may be known from electron microscopy, but they may be heterodisperse and heterogeneous and the surface composition may be unknown. For those cases the following summary may be helpful. 

Smoluchowski was the first to recognize that the interactions responsible for electrokinetic phenomena and colloid stability can be rationalized in terms of this potential potential), which must not be identified with the surface potential. In absence of strongly adsorbing species C potential has the same sign as the surface potential, but the absolute value of the potential is lower, especially at high ionic... 

Ringenbach, E., Chauveteau, G., and Pefferkom, E.. Effect of soluble aluminum ions on polyelectrolyte-alumina interaction. Kinetics of polymer adsorption and colloid stabilization. Colloids Surf. A, 99, 161, 1995. 

The first useful theory of colloidal interaction forces and colloid stability (against aggregation) was developed independently by Deryagin and Landau and by Verwey and Overbeek. Hence it is called the DLVO theory. It takes into account the combined effects of van der Waals attraction and electrostatic repulsion. 

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