What is zeta potential?

When a voltage is applied to a solution in which colloidal particles are dispersed, particles are attracted to the electrode of the opposite polarity.  The actual particle migrates to the electrode as a part of the system which includes the charged particle, and layers of solvent and ions that are bound with varying degrees of strength to the particle.  At a certain distance from the surface of the particle there is a layer of ions that are mobile and are removed as the particle system moves through the solvent as a result of the electrostatic attraction to the electrode.  This layer is called the “sliding surface.”

Zeta potential is considered to be the electric potential of this inner area including this conceptual "sliding surface". As this electric potential approaches zero, particles tend to aggregate due to Van der Waals force overcoming electrostatic repulsion.  Higher zeta potentials will cause colloidal systems to remain stable and dispersed.

Dispersed particles

Aggregated particles

As this electric potential approaches zero, particles tend to aggregate.  Higher zeta potentials will cause particles to repel due to like charges.

The static layer is computed using the following formula (which is embedded in the Zeecom software).

The static layer is computed using the following formula (which is embedded in the Zeecom software).

Zeta Potential (Smoluchowski’s Formula)

The Zeecom unit uses a microscope to observe particle electrophoresis migration on a monitor while performing image processing to determine the particle migration speed, which is then converted into the zeta potential value.

To eliminate errors due to electroosmotic flow caused by any electrostatic charge on the measurement cell, the zeta potential is measured at the static layer, whose position can be calculated from the width and depth of the cell (the software performs this calculation automatically).

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