Environmental Engineering Reference
In-Depth Information
Stern layer
diffuse layer
bulk solution
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Ψ
Ψ
Ψ s
Ψ s
ζ
ζ
Ψ s / e
Ψ s / e
x s
x s
x
x
1/ κ
1/ κ
Figure 4.5 Schematic diagram of the diffuse double layer (DDL) forming from the surface
of a colloidal particle into the bulk solution. Abbreviations: zeta potential (
ζ
), electrostatic
potential (
S), Euler's number (e), Boltzmann
constant (k). X is a distance from the surface, Xs is the shear plane, the distance from where
ions and molecules are mobile and can be sheared off. (With kind permission from Springer
Science
Ψ
), electrostatic potential at the stern layer (
Ψ
Business Media: Ecotoxicology , 17 , 2008, 287-314, The ecotoxicology and
chemistry of manufactured nanoparticles, R. D. Handy, F. von der Kammer, J. R. Lead,
M. Hassellöv, R. Owen and M. Crane, Figure 2.)
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trophoresis). Under conditions of very low ionic strength, the decay of the potential
between the Stern layer and the shear plane is negligible and the zeta potential can
be seen as an approximate of the Stern potential. For more details about the dif-
ferent models describing the double layer, the reader is referred to the literature
(Elimelech et al. , 1995a ).
4.4.3
Surface Coating by Natural Organic Matter
Natural organic matter (NOM) molecules form surface fi lms of several nanometres
on macroscopic surfaces (Lead et al. , 2005), manufactured nanoparticles (Baalousha
et al. , 2008) and natural particles (Baalousha and Lead, 2007; Hunter and Liss, 1982;
Loder and Liss, 1985; Wilkinson et al. , 1997b), hence the similarity in surface charge
of colloidal particles in aquatic environment. Almost all environmental particles,
regardless of chemical composition, are negatively charged due to the dissociation
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