Assessment of ζ-potential in TiO2 aqueous suspensions: A comparative study based on thermodynamic and rheological methods

It is widely demonstrated that the distinct electrokinetic techniques lead to different values of ζ-potential despite what should be expected from the classical theory. Electrophoresis and conductivity measurements were used to estimate the ζ-potential and the electrical double layer parameters of TiO2 aqueous suspensions. An assessment of the results was made following thermodynamic and rheological methods. In the first case, the Gibbs free energy increment was compared. In the second one, the yield stress/ζ-potential plots were used. In spite of the ζ-potentials obtained from conductivity, electrophoresis and electrophoresis-conductivity combined techniques are different, the Gibbs free energy increment values do not discriminate the best ζ-potential value. Moreover, the correlation between the yield stress and the square of the ζ-potential has shown that all the ζ-potentials can physically be acceptable. Therefore, the only reasonably conclusion from this study is that the use of combined techniques, like electrophoresis-conductivity, should always be taken as the more cautious approach of evaluating ζ-potentials.