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What Is Zeta Potential?
The term "Zeta Potential" applies to the electrical charges existing in liquid emulsions or dispersions of a colloidal nature.
A particle (or dispersed liquid) suspended in a fluid is surrounded by a dense layer of ions having a specific electrical charge. This layer is surrounded by another layer, more diffuse than the first, that has an electrical charge of its own. The bulk of the suspended liquid also has its own electrical charge. The difference in electrical charge between the dense layer of ions surrounding the particle and the bulk of the suspended fluid is the "Zeta Potential", usually measured in millivolts. |
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How is Zeta Potential Used?
When ions or polymers are absorbed on a particle in a colloidal system, or by the dispersed liquid in an emulsion, the charge of the layer surrounding the particle is altered. This results in a change in the potential difference between the surrounding layer of ions and the bulk of the suspending fluid. This, by definition, is a change in the zeta potential. The stability of a colloidal system is dependent upon the degree of ion absorption, and, therefore, on the zeta potential. Thus, measurement of zeta potential makes possible the control of processes wherein dispersion or agglomeration is important.
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Practically all aqueous colloids are electronegative, with the general range of zeta potential being -14 to -30 millivolts. As the zeta potential is made more negative, the stability of the system is increased. This can be accomplished by the addition of an anionic electrolyte or polyelectrolyte. Zeta potential values more electronegative than -30 mv generally represent sufficient mutual repulsion to result in stability. Stability is assured within a zeta potential range of -45 to -70 millivolts.
When agglomeration is desired, it is necessary to bring the zeta potential closer to zero. This can be achieved by the addition of cationic electrolytes or polyelectrolytes, such as alum or cationic polymers. If the zeta potential is already near zero, agglomeration can be improved further by the addition of long chain polymers capable of producing mechanical bridging between particles.
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