Measurement Technique - Malvern Zetasizer Nano Series Accessories Manual

Surface zeta potential cell

Measurement technique

A surface zeta potential measurement consists of attaching a sample to a mount or
holder that is then held in place between two electrodes. The sample is then
immersed in an appropriate aqueous solution, containing tracer particles.
The apparent tracer mobility is now measured at a number of different distances
from the sample surface. The electro-osmotic flow at the sample surface will tend
to fall off with increasing distance hence; close to the surface the tracer mobility
will be dominated by the electro-osmotic surface flow, while at distances further
from the surface it will be dominated by the electrophoretic motion of the tracer
itself.
The graph below shows a typical plot of reported zeta displacement from the sur-
face.
The zeta potential at the surface is then calculated by extrapolating the graph to
zero displacement and applying the following formula;
where the tracer zeta potential is recorded far from the wall, where the electro-
osmotic flow can be taken as zero.
In the displacement graph above, the blue circles represent the reported zeta
potential of the tracer particles, while the red squares represent the zeta potential
of the tracer particles measured far from the sample surface and also independent
from any electro-osmotic effects.
Zetasizer Nano accessories guide
Surface zeta potential =
–
intercept + tracer zeta potential
Chapter 3
ill 8694
Page 3-3