Colloidal Aggregation

What is Coagulation and Flocculation?

Flocculation is the process by which particles overcome their apparent charge in the dispersant (Zeta potential or ζ-potential) to contact and adhere to each other to form large clusters. The terms coagulation and flocculation are often used interchangeably, however, coagulation is generally considered to be irreversible and to form denser aggregates that sediment. On the other hand flocculation products, or flocs, tend to be less dense aggregates, may float and can be re-dispersed by the application of a force. For emulsions, flocculation describes the way droplets cluster together but do not lose their individual identity. It is, therefore the first phase of the separation of the emulsion into its components.

Zeta Potential

Zeta Potential (ζ-potential) is used to assess the likelihood of flocculation of a dispersion. This can be measured by the Malvern Zetasizer Nano series.

Dispersions with high ζ-potential will repel each other and resist flocculation whereas those with lower ζ-potential can overcome the repulsive charge to become strongly and irreversibly joined. Accumulation results in flocculation as the material comes out of solution.

Applications

Parenteral Nutrition
An example of studying zeta potential for maintaining dispersion stability is parenteral nutrition where surgery patients are fed intravenously.  

Emulsions
Emulsions are kept on shelves for long periods and the dispersion stability must be assured.  

Waste Water
Users may wish to stimulate flocculation in order to remove material from waste water. A number of factors can alter the ability of water to change the state of flocculation, such as pH or the addition of chemical flocculants to the dispersant. For more information please register for free to view application notes on ζ-potential, flocculation and water treatment.