Zeta Potential represents a basic law of Nature, and it plays a vital role in all forms of plant and animal life.
Zeta potential is the charge a particle acquires in a particular medium. It is dependent upon the pH, ionic strength or concentration of a particular component.
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.
When agglomeration is desired, it is necessary to bring the zeta potential closer to zero. 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.
The shear plane (slipping plane) is an imaginary surface separating the thin layer of liquid bound to the solid surface and showing elastic behavior from the rest of liquid showing normal viscous behavior. The electric potential at the shear plane is called zeta potential. In the first, rough approximation, the electro-phoretic mobility (the ratio of the velocity of particles to the field strength), induced pressure difference in electro-osmosis, streaming potential and sedimentation potential are proportional to the zeta potential. The stability of hydrophobic colloids depends on the zeta potential: when the absolute value of zeta potential is above 50 mV the dispersions are very stable due to mutual electrostatic repulsion and when the zeta potential is close to zero the coagulation (formation of larger assemblies of particles) is very fast and this causes a fast sedimentation