Malvern Zetasizer Nano Series, User Manual

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Measurement position in the cell
The M3 method performs the measurement in the middle of the cell, rather than
at the stationary layer. In principle the M3 measurement could be done at any
position in the cell, however there are a number of reasons for choosing to work
at the
centre .
.
The measurement zone is further from the cell wall, so reduces the chance
of flare from the nearby surface.
.
The alignment of the cell is less critical.
.
The charge on the cell wall can be calculated.
Reversal of the applied field
All systems that measure mobilities using LDV (Laser Doppler Velocimetry)
reverse the applied field periodically during the measurement. This is normally
just the slow field reversal mentioned below.
However, M3 consists of two measurements for each Zeta potential
measurement, one with the applied field being reversed slowly - the SFR
measurement; and a second with a rapidly reversing applied field - the FFR
measurement stage.
Slow Field Reversal (SFR)
This reversal is applied to reduce the polarisation of the electrodes that is
inevitable in a conductive solution. The field is usually reversed about every 1
second to allow the fluid flow to stabilise.
Fast Field Reversal (FFR)
If the field is reversed much more rapidly, it is possible to show that the particles
reach terminal velocity, while the fluid flow due to electroosmosis is insignificant.
(The residual flow in this diagram below is exaggerated).
This means that the mobility measured during this period is due to the
electrophoresis of the particles only, and is not affected by electroosmosis.
C H A P T E R 1 5 Z e t a s i z e r N a n o S e r i e s
P a g e 1 5 . 8
M A N 0 3 1 7
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Stationary
Layer
Significant fluid flow
ILL
6753