In this work, a set of experimental
electrophoretic mobility (μe) data was used to show
how inappropriate selection of the
electrokinetic model used to calculate the zeta potential (ζ-potential)
can compromise the interpretation of the results for nanoparticles
(NPs). The main consequences of using ζ-potential values as
criteria to indicate the colloidal stability of NP dispersions are
discussed based on DLVO interaction energy predictions. For this,
magnetite (Fe3O4) NPs were synthesized and characterized
as a model system for performing electrokinetic experiments. The results
showed that the Fe3O4 NPs formed mass fractal
aggregates in solution, so the ζ-potential could not be determined
under ideal conditions when μe depends on the NP
radius. In addition, the Dukhin number (Du) estimated from potentiometric
titration results indicated that stagnant layer conduction (SLC) could
not be neglected for this system. The electrokinetic models that do
not consider SLC grossly underestimated the ζ-potential values
for the Fe3O4 NPs. The DLVO interaction energy
predictions for the colloidal stability of the Fe3O4 NP dispersions also depended on the electrokinetic model
used to calculate the ζ-potential. The results obtained for
the Fe3O4 NP dispersions also suggested that,
contrary to many reports in the literature, high ζ-potential
values do not necessarily reflect high colloidal stability for charge-stabilized
NP dispersions.
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