Niels P. Ryde

Kinetics of heterocoagulation. Part.2—The effect of the discreteness of surface charge

Coagulation rates in dispersions of uniform spherical particles of surfactant-free sulfate latices, silica and cerium (hydrous) oxide were measured as a function of the ionic strength by a low-angle scattering technique. The results were used to interpret the significant discrepancies between theoretical predictions and experimental results of slow coagulation kinetics. The variations in values of all usual parameters in the accepted theoretical models were tested in order to eliminate the disagreements, but the task proved unsuccessful. However, the assumption of the segregated surface charge on the smooth spherical particles has led to the concordance between the measured and calculated stability ratios. In the model employed, the heterocoagulation theory is required even though one deals with systems of identical particles.

Particle adhesion in model systems. Part 13.—Theory of multilayer deposition

A model is developed to describe multilayer deposition in packed-bed systems. The multilayer deposition is significant for colloid suspensions which are near or beyond the critical coagulation conditions. Packed-bed deposition studies of such suspensions are possible in experiments with short residence times. Our model is formulated along the lines of the existing monolayer theories and involves one new parameter which characterizes the multilayer adhesion probability.

Kinetics of heterocoagulation 1. A comparison of theory and experiment

Abstract Experimentally determined stability coefficients for the coagulation of hematite dispersions consisting of uniform spherical particles, and for the deposition of the same solids on glass beads, are compared with theoretically predicted values by the Hogg, Healy and Fuerstenau (HHF) approximation and the recently developed Overbeek formulation. Significant discrepancies are found between the measured coefficients for slow processes and those calculated by either the HHF or the Overbeek expressions. The effect of the linearization incorporated in the HHF approximation on the computation of stability coefficients is also assessed by the comparison with the Overbeek treatment. It is found that considerable deviations are generated when Ψ S1 ≈ Ψ S2 > 25 mV, where Ψ S1 and Ψ S2 are the Stern potentials for surfaces 1 and 2 respectively, whereas good agreements ensue when Ψ S1 ⪡ Ψ S2 , even though Ψ S2 is as high as 100 mV.

Particle adhesion in model systems. Part 14.—Experimental evaluation of multilayer deposition

The deposition of uniform, spherical colloidal haematite particles on glass beads was studied as a function of the ionic strength using the packed column technique. The data were interpreted in terms of a recently developed multilayer adhesion model, which is of particular interest for systems at high ionic strength. The evaluated parameters suggest that the adhesion behaviour can be explained in terms of colloid stability and particle to particle interaction energies.

Kinetics of heterocoagulation. Part 4.—Evaluation of absolute coagulation rate constants using a classical light scattering technique

The rate of coagulation in systems of identical and unlike colloids in aqueous media has been studied by a simultaneous multi-angle static light scattering technique. The mixed dispersions consisted of polystyrene latex particles of different radii and of opposite sign of charge. A procedure based on the Rayleigh–Gans–Debye approximation permits one to estimate the absolute rate constant either for homo- or hetero-coagulation. The absolute coagulation rate constants were compared to those calculated theoretically, using the Smoluchowski theory. In homosystems, the fast coagulation rate corresponded to ca. 55–60% of the Smoluchowski value. In the heterosystem, the coagulation rates exceeded the calculated values based on the diffusion-controlled process at a low ionic strength. An increase in the electrolyte content led to a decrease of the coagulation rate, which at high concentrations corresponded to ca. 85% of the Smoluchowski value.

Color effects of uniform colloidal particles of different morphologies packed into films

The experimentally determined chromaticities and reflectance spectra of films consisting of uniform ellipsoidal or spherical colloidal hematite particles are compared with calculated values and are found to be in good agreement. The theoretical treatment of the light-scattering problem involves the Mie theory for the spheres and the T-matrix method for the ellipsoids. The reflectance spectra for the pigment films are calculated through the use of the Kubelka-Munk analysis.

Deposition and detachment studies of fine particles by the packed column technique

Abstract The use of the packed column technique for the study of deposition of colloidal particles from dispersions in liquids onto collector beads is described. The technique also allows to investigate the removal of adhered particles, by rinsing the loaded column with solutions of different compositions. A number of examples are described illustrating the effects of various experimental conditions, including the surface and intrinsic properties of reactants, the nature and the ionic strength of the liquid phase, the effects of various additives, and of superimposed external magnetic fields, etc. The results are presented in terms of breakthrough curves and interpreted by means of three phenomenological parameters, which are related to interaction forces between colloidal particles and the collector. This approach makes it possible to distinguish between monolayer and multilayer depositions.

Kinetics of particle deposition and detachment

Abstract The packed column technique serves as a useful tool in the investigations of the deposition and removal mechanisms of particles dispersed in a liquid in contact with a solid substrate. A model is presented which can be used to estimate explicitly the effects of multilayer deposition, which is based on three phenomenological parameters: two mass transfer coefficients, and one blocking parameter. The latter accounts for the area occupied by each adhered particle. The method can be used to evaluate the experimental results in terms of the particle-collector and particle-particle interactions. The former are related to heterocoagulation, and the latter to homocoagulation. It is shown that the rate of deposition of hematite particles onto glass beads, in the absence of a repulsion barrier, is governed by a convective diffusion mechanism. If a repulsion barrier exists, the deposition rate depends on the ionic strength in a manner consistent with colloid stability. The adhered particles can be removed b...