4πnEsin(
—
)
θ’
2
3η
ο
23
EQUATION
1
μ = Δωλ
0
Where :
μ = the electrophoretic mobility
ω =
the measured frequency shift
λ = the laser wavelength
n = the refractive index of the medium
θ’ contains the angular
light scattering information
After the electrophoretic mobility is determined using equation 1, the zeta
potential (ζ) is calculated using equation 2.
EQUATION
2
μ = 2ζε ƒ(κr)
Where:
µ
= the electrophoretic mobility
ζ
=
the zeta potential
ε
= the dielectric permittivity of the medium
η
o
= the viscosity
f=(κr) = a function describing the ratio of the particle
radius to the double layer
Zeta potential is often measured as a function of pH (or other additive property)
in order to determine the conditions at which there is zero zeta potential, also
known as the isoelectric point (IEP).
MOLECULAR WEIGHT
The SZ-100 can also be used to measure the molecular weight of proteins,
starch-
es, polymers, dendrimers and other large molecules. The data can be obtained by
two different methods: dynamic light
scattering and static light
scattering. Both methods are discussed below.
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