Zeta Potential Analysis

The zeta potential describes the electrokinetic potential of colloidal dispersions composed of liquids or solids. When subjected to an electric field, charged particles will demonstrate specific electrokinetic effects such as electrophoresis, electroosmosis, streaming potential, or sedimentation potential.

Zeta potential is assessed at Infinita Lab using either a Litesizer 500 (Anton Paar) system or a Zetasizer Nano ZS (Malvern Panalytical) device. Both use the electrophoresis concept to determine zeta potential.

When charged colloidal dispersions are introduced into a zeta cell for a zeta potential analysis, the particles move towards the electrode with the opposite charge to the particle when an external electric field is applied. LASER Doppler velocimetry determines their velocity, or electrophoretic mobility, when subjected to an electric field.  The Henry equation is then used to compute the zeta potential: 

Zeta potential is frequently useful in excluding possible product batches from stability testing, saving time and resources. Large charges on the suspended particles will likely cause them to repel one another and have less of a tendency to flocculate, indicating stability and long shelf life. On the other hand, there are times when low zeta potential is preferred, such as for water purification systems. Reduced inter-particle repulsion will increase flocculation and aid in appropriate filtration. 

The stern layer, which forms tightly around a particle’s surface where its attractive forces are strongest, comprises counter ions (in this case, cations). Since the interactive force between two charged particles is proportional to their charges’ magnitudes and inversely proportional to the distance separating them, cations in the diffuse layer are also attracted by the negatively charged particle, albeit to a lesser extent.  The diffuse layer also contains anions that are attracted by stern layer cations and simultaneously repelled by negatively charged particles. The slip plane (shear plane), which is a boundary within the diffuse layer, is where the zeta potential of the particle is determined. Ions within the slip plane move with a moving particle due to their strong attraction to it. Still, ions outside the slip plane do not move with the particle because the force of the applied electric field and the ensuing particle velocity overcomes any bonding they may have with it, resulting in a shear plane.

Advantages

Zeta Potential is designed to shed light on a suspension’s stability.

Considerations

Results are pH and conductivity-dependent.

High conductivity might not be suitable, i.e. samples in isotonic saline or PBS.

Carrier viscosity: Electrophoretic mobility, which is proportional to zeta potential, is inhibited by Viscous media. Ideal viscosity is no more than 10cP.

Video 01: Zeta Potential Analysis