DLVO theory

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Final Project for AP225 Fall 2011, written by Hyerim Hwang

Definition

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The DLVO theory is named after Derjaguin, Landau, Verwey, and Overbeek. It is the explanation of the stability of colloidal suspension. It describes the balance between two forces, electrostatic repulsion and van der Waals attraction. Electrostatic repulsion becomes significant when two colloids approach each other and their electrical double layers begin to interfere. Some energy is required to overcome this repulsive force, so that the repulsion curve in the figure indicates the energy that must overcome if the particles are forced together. It has a maximum value which is related to the surface potential when they almost touch and decrease to zero outside the double layer. Van der Waals attraction is the results of forces between molecules in each colloidal particle. One molecule of the colloid has a van der Waals attraction to each molecule in the other colloid which means additive force. The curve which represents an attractive energy indicates the variation in van der Waals force between colloidal particles. The DLVO theory explains the tendency of colloids to agglomerate or separate by combining two curves of electrostatic repulsion and van der Waals attraction. At each distance, the smaller value is subtracted from the larger value to obtain the net energy. In the regime where there is repulsion, energy can be thought to be a energy barrier. We can increase or decrease the energy barrier by changing the ionic or pH environment or adding surfactants to affect the surface charge of the colloid. In this case, zeta potential can be measured to know the stability of dispersion. There are many other effects we should consider for sure, but steric stabilization is the most important thing. Adsorbed layer on each particle prevents the particles from coming close enough for van der Waals attraction to cause flocculation. There are no long range repulsive forces unlike electrostatic stabilization and the particles are subject to attractive forces until the outer regions of the molecules

DLVO Theory

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The DLVO theory has number of parameters: proper description of van der Waals force, surface charge density, surface potentials, Debye length, etc.

References

1. Israelachvili, Jacob N. (2011). Intermolecular and Surface Forces. Academic Press. ISBN 9780123919274.

2. "DLVO Theory". Wikipedia.

Additional Readings

1. Mayers, Drew. (2002), Surfaces, Interfaces, and Colloids: Principles and Applications, Second Edition. ISBN 9780471330608.

2. Verwey, E. J. W.; Overbeek, J. Th. G. (1948), Theory of the stability of lyophobic colloids, Amsterdam: Elsevier.

3. Russel, W. B.; Saville, D. A.; Schowalter, W. R. (1989), Colloidal Dispersions, New York: Cambridge University Press.

4. See also: DLVO theory in Thin "soft" films and colloidal stability from Lectures for AP225.

Keyword in references:

Dispersion of Silica Fines in Water-Ethanol Suspensions