Particle Interactions in Suspensions

As discussed below, a dispersion that has been somehow stabilized can also be made to flocculate by adding to the suspension a nonadsorbing polymer, which induces depletion flocculation (Asakura and Qosawa 1954, 1958 Vrij 1976 Fleer and Scheutjens 1982 Li- 

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Particle-Particle Interaction and Hindered Settling. At solids concentrations of <0.5% by volume, the individual particles are on average so far apart they do not affect each other (i.e., no particle-particle interaction) as they move through the fluid (i.e., laminar flow). For practical purposes, there is no particle-particle interaction in suspensions where the ratio of particle diameter to interparticle distance is <0.1. 

In principle, SAXS is suitable for determining the structure factor S(q) from experimental results. It will become apparent, however, that the influence of particle interaction in suspensions of latex particles is restricted to very small q-val-... 

Further discussion of clay hydration and its relation with unit-layer interaction in swelling clay particles, and particle interaction in suspension... 

Further Discussion of Clay Hydration and Its Relation with Unit-Layer Interaction in Swelling Clay Particles, and Particle Interaction in Suspensions... 

Relaxation studies have shown that the attachment of an ion to a surface is very fast, but the establishment of equilibrium in wel1-dispersed suspensions of colloidal particles is much slower. Adsorption of cations by hydrous oxides may approach equilibrium within a matter of minutes in some systems (39-40). However, cation and anion sorption processes often exhibit a rapid initial stage of adsorption that is followed by a much slower rate of uptake (24,41-43). Several studies of short-term isotopic exchange of phosphate ions between aqueous solutions and oxide surfaces have demonstrated that the kinetics of phosphate desorption are very slow (43-45). Numerous hypotheses have been suggested for this slow attainment of equilibrium including 1) the formation of binuclear complexes on the surface (44) 2) dynamic particle-particle interactions in which an adsorbing ion enhances contact adhesion between particles (43,45-46) 3) diffusion of ions into adsorbents (47) and 4) surface precipitation (48-50). 

In practice, thinking of small-particle interactions in terms of dilute-suspension or dilute-solution dielectrics liberates us from having to theorize about the added a. We can simply measure... 

The structure of secondary particles of nanosilicas is random and loose with an empty volume V, = pbx - pbx > 10 cm3/g.6"9 Changes in synthesis conditions allow one to vary the structure of contacts between adjacent primary particles in aggregates6,7, which affect the properties of powders and dispersions. Different treatments of the powders and suspensions result in changes in particle-particle interactions in aggregates, that leads to variation of the adsorption capacity for various adsorbates.1 16 From the textural characteristics (Table 1 and Figure 1) one can surmise that the structures of... 

In all but the most basic cases of very dilute systems, with microstructural elements such as rigid particles whose properties can be described simply, the development of a theory in a continuum context to describe the dynamical interactions between structure and flow must involve some degree of modeling. For some systems, such as polymeric solutions, we require modeling to describe both polymer-solvent and polymer-polymer interactions, whereas for suspensions or emulsions we may have an exact basis for describing particle-fluid interactions but require modeling via averaging to describe particle-particle interactions. In any case, the successful development of useful theories of microstructured fluids clearly requires experimental input and a comparison between experimental data and model... 

Staniforth JN. Particle interactions in dry-powder formulation of aerocolloida suspensions. In Proceedings of the Second Respiratory Drug Delivery Symposium, College of Pharmacy, The University of Kentucky,... 

Hinch, E.J. (1977) An averaged-equation approach to particle interactions in a fluid suspension, J. Fluid Mech. 83, 695-720. 

Powders, Suspensions, and Emulsions - One of the most signi-ficant articles in recent years is that by Hiestand on particle-particle interaction in powders. The author has brought together much information from pharmaceutical research and from other disciplines and has perspectively assembled a rational treatise. The importance of plasticity and the true area of contact is clearly described. In addition, several novel methods for evaluating cohesion and adhesion of powder particles are described in this paper. 

Rand, B. and Melton. I.E., Particle interactions in aqueous kaolinite suspensions. I. Effect of pH and electrolyte upon the mode of particle interaction in homoionic sodium kaolinite suspensions, J. Colloid Interf. Sci.. 60. 308. 1977. 

A conceptual and mechanistic model of particle interactions in silica-iron binary oxide suspensions is described. The model is consistent with a process involving partial Si02 dissolution and sorption of silicate onto Fe(OH)3. The constant capacitance model is used to test the mechanistic model and estimate the effect of particle interactions on adsorbate distribution. The model results, in agreement with experimental results, indicate that the presence of soluble silica interferes with the adsorption of anionic adsorbates but has little effect on cationic adsorbates. 

PARTICLES AND suspensions of many kinds play an important role in our interaction with the physical environment. They abound in earth, soil, water, and air. They are also present in chemicals and many other industrial products. If particles were spherical or cubical, characterization would be easy. Unfortunately, most of the particles present in the environment are of irregular size and shape. In many industrial processes, size characterization is a critical aspect of understanding particle behavior in suspension, the bulk properties of suspensions, and their bulk behavior. Therefore, it is important to understand the strengths and limitations of techniques used to characterize particles and suspensions. 

Interfacial phenomena at metal oxide/water interfaces are fundamental to various phenomena in ceramic suspensions, such as dispersion, coagulation, coating, and viscous flow. The behavior of suspensions depends in large part on the electrical forces acting between particles, which in turn are affected directly by surface electrochemical reactions. Therefore, this chapter first reviews fundamental concepts and knowledge pertaining to electrochemical processes at metal oxide powder (ceramic powder)/aqueous solution interfaces. Colloidal stability and powder dispersion and packing are then discussed in terms of surface electrochemical properties and the particle-particle interaction in a ceramic suspension. Finally, several recent examples of colloid interfacial methods applied to the fabrication of advanced ceramic composites are introduced. 

Similarly to the shear stress ramp tests, the yield stress tests produced results which suggest particle-particle interactions in the grease structure. The yield results are also similar to that of polymer suspensions [38]. 

The process of particle interaction in an electric field can be evaluated quantitatively. Such an evaluation was performed in [207] for suspensions of a methyl methacrylate-styrene copolymer and titanium in butyl alcohol and heptane. The rate and extent of particle aggregation were monitored by determining the average radius of the resulting aggregates. 

Information on interparticle forces can be obtained from rheological studies. As the shear rate is increased, the particles rearrange, or floes distort in a flocculated system, and eventually the system starts to flow. The magnitude of the Bingham yield stress, Tg, reflects maximum rearrangement of the particles in an unflocculated system deformation of the floes in a flocculated system before flow. The shear moduli, G, G and G effectively probe the unperturbed system at very low shear rates and reflect the particle-particle interactions in a pure clay suspension the intraparticle structure of the floes in a flocculated suspension. 

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