Colloids

At very short distances, the interpenetration of electron shells leads to the strong repulsive force known as the Born repulsion. The corresponding interaction energy is given as

(50)

for a sphere-plate where ).

DLVO Theory of Colloidal Stability

The theory of colloidal stability was developed by Deryaguin, Landau (1941), Verway, and Overbeak (1948) and is now known as the DLVO theory.

The interaction potential between particles is composed as the sum of van der Waals, , i.e.

(51)

Depending on the magnitude of van der Waals and electrical double layer potential energies, the suspension could be stable or could rapidly aggregate.

Figure (a) shows a stable suspension where a strong energy barrier (EB) is formed. There is a deep primary minimum (SM). The secondary minimum could lead to weak aggregation which will break easily.

(Diagram Here)

Figure (b) shows the total potential for a colloidal system for which the electrical double layer is weak or absent. The particles will attract each other and the suspension will aggregate quickly.

(Diagram Here)

Steric Interaction

A colloidal suspension could remain stable when the particles absorb polymetric chains.

Hydrophobic Interaction

There is an attraction between hydrophobic surfaces as a result of water molecules migrating from the gap to the bulk.

Hydration Effects

At very short distances, hydrophilic surfaces may experience hydration repulsion. This is because of the need for the surfaces to become dehydrated for the particles to come in contact.