DLVO theory of colloidal stability

In a number of recent publications (1, 2) microcrystailine cellulose dispersions (MCC) have been used as models to study different aspects of the papermaking process, especially with regard to its stability. One of the central points in the well established DLVO theory of colloidal stability is the critical coagulation concentration (CCC). In practice, it represents the minimum salt concentration that causes rapid coagulation of a dispersion and is an intimate part of the theoretical framework of the DLVO theory (3). Kratohvil et al (A) have studied this aspect of the DLVO theory with MCC and given values for the CCC for many salts, cationic... 

Derjaguin and Landau, and Verwey and Overbeek (1941-8) developed the DLVO theory of colloid stability. 

The well-known DLVO theory of colloid stability (10) attributes the state of flocculation to the balance between the van der Waals attractive forces and the repulsive electric double-layer forces at the liquid—solid interface. The potential at the double layer, called the zeta potential, is measured indirectly by electrophoretic mobility or streaming potential. The bridging flocculation by which polymer molecules are adsorbed on more than one particle results from charge effects, van der Waals forces, or hydrogen bonding (see COLLOIDS). 

Throughout most of this chapter the emphasis has been on the evaluation of zeta potentials from electrokinetic measurements. This emphasis is entirely fitting in view of the important role played by the potential in the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability. From a theoretical point of view, a fairly complete picture of the stability of dilute dispersions can be built up from a knowledge of potential, electrolyte content, Hamaker constants, and particle geometry, as we discuss in Chapter 13. From this perspective the fundamental importance of the f potential is evident. Below we present a brief list of some of the applications of electrokinetic measurements. 

A pair of polysaccharide molecules approaching each other in water exerts an interaction potential ( ) that is the algebraic sum of the competing attractive and repulsive forces. integrated over all pairs of molecules, is . This principle is embodied in the Deijaguin-Verwey-Landau-Overbeek (DLVO) theory of colloidal stability (Ross and Morrison, 1988). The equilibrium distance between the molecules is related to c, the volume of the hydrated particles, ionic strength, cosolute, nonsolvent additions, temperature, and shearing. 

Landau-Verwey-Overbeek (DLVO) theory of colloidal stability have been successful in qualitatively explaining microbial adhesion to solid substrata [8,13],... 

Latex stability will be determined by the combined effect of two factors the probability of collision between particles and the fraction of the encounters between particles which lead to permanent contact. Tha first factor, the collision frequency, will increase with increasing particle size and particle number. It will also increase with increasing shear rate. The influence of various test conditions on the second factor ought to be discussed on the basis of the DLVO theory of colloid stability. 

Very often, the microstructure and the macroscopic states of dispersions are determined by kinetic and thermodynamic considerations. While thermodynamics dictates what the equilibrium state will be, kinetics determine how fast that equilibrium state will be determined. While in thermodynamics the initial and final states must be determined, in kinetics the path and any energy barriers are important. The electrostatic and the electrical double-layer (the two charged portions of an inter cial region) play important roles in food emulsion stability. The Derjaguin-Landau-Verwey-Oveibeek (DLVO) theory of colloidal stability has been used to examine the factors affecting colloidal stability. 

Figure 4. DLVO theory of colloid stability. (Reproduced with permission from reference 10. Copyright 1988 Canadian Institute of Mining, Metallurgy, and...

Combination of the attractive van der Waals potential - -1/ and the repulsive double-layer potential ( gives rise to tiie famous DLVO theory of colloid stability. Depending on salt, the net potential can be such as to induce flocculation directly, pose a barrier to flocculation, or lead to a stable suspension. 

Consideration of the electrostatic repulsion and van der Waals forces of attraction by the Russians Deryagin and Landau and the Dutch scientists Verwey and Overbeek produced a satisfactory quantitative approach to the stability of hydrophobic suspensions. Their theory is known as the DLVO theory of colloid stability, the briefest outline of which is given here. 

Whether the colloidal particles encountering each other will flocculate (or coalesce) will generally depend on the net interaction resulting from the combined attractive van der Waals forces and repulsive electrostatic forces resulting from the overlap of the electric double layers. This theory of colloid stability, in considerably more detail than given here, is known as the Derjaguin, Landau, Verwey, Overbeek (DLVO) theory of colloid stability (Hiemenz 1986, Verwey c Overbeek 1948). 

On the hypothesis developed by Derjaguin, Landau, Verwey, and Overbeek (DLVO), a colloidal suspension becomes rapidly unstable if the maximum value of random thermal energy of the colloidal particles. This hypothesis forms the basis of the DLVO theory of colloidal stability. With the approximate expression for

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Clarke et al. (36) later explored the possibility of an electrical doublelayer contributing to the repulsion, thereby assisting in the stabilization of the film thickness. This double-layer repulsion is identical in origin to that in the DLVO theory of colloid stability (Chapter 4). Assuming that the grains have flat, parallel faces separated by a distance h, the expression for the doublelayer repulsion is... 

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