F. Dumont

Influence of the point of zero charge of titanium dioxide hydrosols on the ionic adsorption sequences

Abstract Several TiO2 hydrosols with point of zero charge (pzc) ranging from 2.8 to 6 were prepared depending on the method of synthesis. The ionic adsorption sequences at the different interfaces were deduced from the critical coagulation concentrations of the corresponding hydrosols. The general behavior can be summarized as follows: on positively charged surfaces, the structure-maker anions are always more adsorbed than the structure-breakers; on negatively charged surfaces, for “high pzc” hydrosols, the cationic sequence is the same as that observed for the anions, whereas, for “low pzc” hydrosols, the reverse sequence is found. The model based on the generalization to the ion-surface interactions of the Gurney concept of the ion-ion interactions, as proposed by Gierst, is used to explain the observed properties of the different hydrosols.

Stability of ferric oxide hydrosols

Ferric oxide hydrosols are composed of a haematite core surrounded by an hydrated oxide shell. Interactions have been studied, on both sides of the p.z.c., between ferric oxide surface and a series of anions and cations having characteristics ranging from structure promoters to structure breakers. Although ferric oxide has a moderate crystalline field, the observed adsorption sequences show that the interface acts as a structure promoter for water molecules. The large spreading of the measured adsorption sequences, especially at extreme pH values, proved the coagulation technique to be a good tool for the study of ion-surface interactions. A new type of behaviour has been observed; at low surface potentials the ions behave as indifferent but at higher surface potentials they are specifically adsorbed.

Study of ferric oxide hydrosols from electrophoresis, coagulation, and peptization measurements☆

Abstract Coagulation values, electrokinetic potentials and peptization properties of ferric oxide hydrosols were measured in the pH range 2–12 in the presence of various monovalent ions. The observed ionic adsorption sequences are explained in terms of the Gurney concept of the ion-ion interactions extended to the ion surface interactions. From stability and peptization measurements, it is shown that the water structure near the interface changes through the p.z.c. The conclusions deduced from the haematite surface study are extended to other interfaces.

Effect of particle size on stability of monodisperse selenium hydrosols

Abstract Monodisperse spherical selenium hydrosols were prepared in a large range of particle radii. Stability was measured as a function of the particle dimension at a fixed pH. For each particle size, the electrophoretic mobilities were determined in the coagulation concentration domain, and the calculated electrokinetic potentials were found to be radius-independent at the Clim. This set of experimental data was interpreted in terms of the DLVO theory. The interaction energy curves were computed under both conditions of constant potential and constant charge; the correcting term taking into account the viscous interactions was incorporated into the classical Fuchs integral. The calculated Clim/particle size relationship is discussed. In comparing these computations with experimental data, it is shown (1) that the elaborated theories could not explain the size effect on stability, (2) that the coagulation of small particles, occurring in the primary minimum, is well described by using the simple model of a critical barrier height, and (3) that, for large particles, excellent agreement with experiment is obtained when considering a constant secondary minimum.

Heterocoagulation between small and large colloidal particles. Part I. Equilibrium aspects

Abstract Heterocoagulation between small positive (Fe 2 O 3 , silica, polystyrene) and large negative polystyrene particles was experimentally studied by a counting technique. The formation and the structure of the resulting heteroparticles were particularly investigated. This study led to the conclusion that, when dealing with mixtures of oppositively charged hydrosols, which are individually stable, the size ratio and the relative number of the interacting units are the only parameters which govern the structure of the resulting heteroparticles. The chemical nature of the partner does not play any role except in determining the pH range at which each one bears the required opposite electrical charge.

Effect of urea on the stability of ferric oxide hydrosols

The effect of urea on the stability of α-haematite hydrosols was studied in the presence of various monovalents ions on each side of the point of zero charge (PZC) (pH 8.2). It was observed that for pHs lower than the PZC, the presence of urea stabilizes the hydrosols by increasing the critical coagulation concentration values for all anions used in this study. However, for pHs higher than the PZC, an inversion of the cationic adsorption sequence was observed. This behaviour is in agreement with the well known action of urea on the structure of water and also with the general properties of the α-haematite water/interface.

Stability of TiO2 hydrosols synthesized by hydrolysis of titanium tetraethoxide

Abstract The TiO2 hydrosols studied in this work were synthesized by hydrolysis of titanium tetraethoxide according to Zukoskis method. Critical coagulation concentrations (CCC) were measured for pH values ranging from 2 to 12 in the presence of various monovalent ions. The observed ionic adsorption sequences are explained in terms of an extension of the Gurney concept of ion-ion interactions. The influence of the volume fraction of the solid is also reported and explained by the coagulation-repeptization theory.

Optical properties of rod-shaped selenium hydrosols

Rod-shaped selenium hydrosols have been synthesized by heterogenous nucleation of selenium on silver nuclei containing dislocations. These hydrosols have been characterized initially by electron microscopy. Comparison between theoretical and experimental turbidity spectra provided the mean diameter of the rods. Experiments have also been carried out in a flow cell, where the hydrodynamic gradient orientated the rods and induced significant changes in the turbidity spectra.

Comparison Between Theoretical and Experimental Turbidity Spectra of Medium and Large Size Monodisperse Polystyrene Latexes

The particle size determination of dispersed materials by optical methods is largely used; the general trend consists in using angular light scattering and intensity fluctuation spectroscopy (1) methods, the analysis of turbidity spectra (2–7) receiving less attention. Nevertheless the latter method may also be worthwhile, but needs the knowledge of the refractive index of the dispersed material in the wavelength range 200–800 nm. If the refractive index values of bulk polystyrene are well known for λ > 400 nm, the literature data below 400 nm are not very reliable (8–11). In this paper, new measurements (20) of the refractive index of polystyrene are reported and tested by comparing calculated and experimental turbidity spectra of several PS hydrosols. It was then possible to describe the general behaviour from the U.V. to the near I. R. regions and to draw conclusions concerning the use of these results to determine the particle size of PS hydrosols.