Zeta-Potential

The zeta potential ( potential well ) is the electrical potential ( also referred to as a coulombic potential) to the shear of a moving particle in a suspension. The electrical potential describes the ability of a ( caused by a charge ) field exert force on other charges.

Cause

Are charged particles in suspension, the potential is compensated by accumulation of ions in the suspension medium. On the particle surface is tightly bound ions accumulate in the so-called Helmholtz double layer. Other ions are deposited rather loosely bound in a diffuse, that is disordered, layer on. Thus, the particles from a distance appears electrically neutral because all particle charges are compensated by ions of the suspending medium.

When they observe a particle, part of the loosely bound diffuse layer is sheared off by friction and the particle will no longer electrically neutral, but again has a potential. This potential at the Abschergrenze is called zeta potential. So that it is a relative measure of the surface potential, and thus the charge of the particle, with the same medium. Can be measured by the zeta potential by using the charged particles being moved by an applied electric field. The resultant speed is then a measure of the zeta potential.

The difference in the electric potential at two locations, the electrical voltage.

Is the electrophoretic mobility, the dielectric constant of the sample, the zeta potential, the Henry function ( Hückel and Smoluchowski approximation), and η is the dynamic viscosity of the liquid.

Relationships

In connection with the zeta potential of the surface potential is referred to as the Nernst potential.

• Forming electrical charges at the interfaces can be made by friction or thermal movement
• Positively charged ions ( counter ions ) can be tightened (outer Helmholtz layer) and there are electric double layers
• Other ions have a loose arrangement, which extends into the liquid phase (diffused layer). Through molecular or thermal movement there is a diffuse distribution of positive and negative ions, with ions of the same charge repel each other. The total charge is balanced here.
• The shear forces that occur during movement of the particles in the liquid, do not affect the tightly bound to the surface tier of ions ( the shear plane ). Since the electrostatic attraction between the charged surface and the diffuse layer with increasing distance decreases, reducing the concentration of the initially present predominantly counterions with the distance and, finally, are in the neutral zone of negative and positive ions uniformly before.
• True charge of the particles ( the Nernst potential ) is characterized by the potential difference between the particle surface and the neutral area and therefore can not be determined experimentally.
• Electrokinetic potential = zeta potential ( ζ ) potential difference of the diffuse layer; characterized repulsion between the particles (dependent on the product of the distance and the reciprocal of the effective radius of the electrical double layer)
• Increase in zeta potential causes an increase in the interparticle repulsive force, so that aggregation is reduced or even prevented.