Malvern Zetasizer Nano Series, Руководство пользователя

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Electrophoresis
When an electric field is applied across an electrolyte, charged particles suspended
in the electrolyte are attracted towards the electrode of opposite charge. Viscous
forces acting on the particles tend to oppose this movement. When equilibrium is
reached between these two opposing forces, the particles move with constant
velocity .
The velocity of the particle is dependent on the following factors :
.
Strength of electric field or voltage gradient.
.
The Dielectric constant of the medium.
.
The Viscosity of the medium.
.
The Zeta potential.
The velocity of a particle in an electric field is commonly referred to as its
Electrophoretic mobility .
With this knowledge we can obtain the zeta potential of the particle by application
of the
Henry equation .
The Henry equation is :
.
z : Zeta potential.
.
U
E
: Electrophoretic mobility.
. e
: Dielectric constant.
.
h
: Viscosity.
.
ƒ(Ka) : Henrys function.
Two values are generally used as approximations for the
f
(Ka) determina-
tion - either 1.5 or 1.0 .
Electrophoretic determinations of zeta potential are most commonly made
in aqueous media and moderate electrolyte concentration.
f
(Ka) in this
case is 1.5 , and is referred to as the Smoluchowski approximation.
Therefore calculation of zeta potential from the mobility is straightforward
for systems that fit the Smoluchowski model, i.e. particles larger than about
0.2 microns dispersed in electrolytes containing more that 10
-3
molar salt.
The Smoluchowski approximation is used for the folded capillary cell and
the universal dip cell when used with aqueous samples.
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