How Colliodal Solution Is Stabilized

The long-term colloidal stability of a dispersion will be of great importance in a number of industries such as pharmaceutical, ceramic, paints and pigments. The term “stability” can have different connotations to different applications. When applied to colloids, a stable colloidal system is one in which the particles resist flocculation or aggregation and exhibits a long shelf-life. This will depend upon the balance of the repulsive and attractive forces that exist between particles as they approach one another. If all the particles have a mutual repulsion then the dispersion will remain stable. However, if the particles have little or no repulsive force then some instability mechanism will eventually take place e.g. flocculation, aggregation etc.

In certain circumstances, the particles in a colloidal disperson may adhere to one another and form aggregates of successively increasing size that may settle out under the influence of gravity. An initially formed aggregate is called a floc and the process of its formation flocculation. The floc may or may not separate out. If the aggregate changes to a much denser form, it is said to undergo coagulation. An aggregate usually separates out either by sedimentation (if it is more dense than the medium) or by creaming (if it less dense than the medium). The term’s flocculation and coagulation have often been used interchangeably. Usually coagulation is irreversible whereas flocculation can be reversed by the process of deflocculation. The following figure schematically represents some of these processes.

The scientists Derjaguin, Landau, Verwey and Overbeek developed a theory in the 1940s that dealt with the stability of colloidal systems.