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.
In this work, structural and active corrosion inhibition effects induced by lithium ion addition in organic-inorganic coatings based on polymethyl methacrylate (PMMA)-silica solgel coatings have been investigated. The addition of increasing amounts of lithium carbonate (0, 500, 1000 and 2000 ppm), yielded homogeneous hybrid coatings with increased connectivity of nanometric silica cross-link nodes, covalently linked to the PMMA matrix, and improved adhesion to the aluminum substrate (AA7075). Electrochemical impedance spectroscopy (EIS), performed in 3.5% NaCl aqueous solution, showed that the improved structural properties of
In this work, we report the effects of incorporation of variable amounts (1-20 wt %) of sodium montmorillonite (MMT) into a siloxane-poly(ethylene oxide) hybrid hydrogel prepared by the sol-gel route. The aim was to control the nanostructural features of the nanocomposite, improve the release profile of the sodium diclofenac (SDCF) drug, and optimize the swelling behavior of the hydrophilic matrix. The nanoscopic characteristics of the siloxane-cross-linked poly(ethylene oxide) network, the semicrystallinity of the hybrid, and the intercalated or exfoliated structure of the clay were investigated by X-ray diffraction, small-angle X-ray scattering, and differential scanning calorimetry. The correlation between the nanoscopic features of nanocomposites containing different amounts of MMT and the swelling behavior revealed the key role of exfoliated silicate in controlling the water uptake by means of a flow barrier effect. The release of the drug from the nanocomposite displayed a stepped pattern kinetically controlled by the diffusion of SDCF molecules through the mass transport barrier created by the exfoliated silicate. The sustained SDCF release provided by the hybrid hydrogel nanocomposite could be useful for the prolonged treatment of painful conditions, such as arthritis, sprains and strains, gout, migraine, and pain after surgical procedures.
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