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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Adjustments of the curing temperature and silica content were used to improve the corrosion protection properties of an organic−inorganic hybrid (OIH) coating based on a polyurethane-silica (SPU) system. Fourier transform infrared and nuclear magnetic resonance ( 13 C and 29 Si NMR) spectroscopy analyses revealed the conversion of urethane groups to secondary amines, with concomitant condensation of Si−R to Si−O−Si, when the curing temperature was increased, while small-angle Xray scattering analysis showed the formation of denser and less branched aggregates of the inorganic framework. The silica content influenced the roughness and thickness of the coatings, with values in the ranges 1.6−9.6 nm and 1.7−6.5 μm, respectively. All the hybrid coatings deposited on steel presented impedance modulus at the lowest frequency (|Z 5 |) above 0.1 GΩ cm 2 throughout the 28 days of analysis. The SPU coating prepared using a TEOS/ APTES ratio of 1 and a curing temperature of 167 °C presented the best performance as a corrosion protection barrier, characterized by predominant capacitive behavior and the invariance of |Z 5 | over 10 GΩ cm 2 .

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