Suspensions interparticle forces

Marlow and Rowell discuss the deviation from Eq. V-47 when electrostatic and hydrodynamic interactions between the particles must be considered [78]. In a suspension of glass spheres, beyond a volume fraction of 0.018, these interparticle forces cause nonlinearities in Eq. V-47, diminishing the induced potential E. 

Monovalent cations are good deflocculants for clay—water sHps and produce deflocculation by a cation exchange process, eg, Na" for Ca ". Low molecular weight polymer electrolytes and polyelectrolytes such as ammonium salts (see Ammonium compounds) are also good deflocculants for polar Hquids. Acids and bases can be used to control pH, surface charge, and the interparticle forces in most oxide ceramic—water suspensions. 

Dispersion is a term for systems containing various phases of at least one continuous and one finely dispersed. Referring to mineral slurries, this is typically a suspension of a mineral in water. This suspension normally contains some more additives for improved stability. One important additive in these systems is the dispersant. Interparticle forces hold the particles together and these interactions are reduced by the use of dispersants. This can be indicated by improved rheology profiles. 

Leong, Y.K., Scales, P.J., Healy, T.W., Boger, D.V. (1995). Interparticle forces arising from adsorbed polyelectrolytes in colloidal suspensions. Colloids and Surfaces A Physicochemical and Engineering Aspects, 95, 43-52. 

The DLVO-theory is named after Derjaguin, Landau, Verwey and Overbeek and predicts the stability of colloidal suspensions by calculating the sum of two interparticle forces, namely the Van der Waals force (usually attraction) and the electrostatic force (usually repulsion) [19],... 

Stabilising a colloidal suspension implies that the total interparticle potential decreases with increasing inter particle distance. The different kinds of stabilisation all use some of the above-mentioned interparticle forces. 

Normal stress differences do not exist in the absence of interparticle forces. Moreover, the relative viscosity of the suspension is a function of only particle densities approaching the maximum possible that still allow the suspension to flow, cluster size (and, as a result, the viscosity of the two-dimensional monolayer) appears to scale as... 

Repulsive interparticle forces cause the suspension to manifest non-Newtonian behavior. Detailed calculations reveal that the primary normal stress coefficient [cf. Eq. (8.7)] decreases like y 1. In contrast, the suspension viscosity displays shear-thickening behavior. This feature is again attributed to the enhanced formation of clusters at higher shear rates. 

Low, P.F., Interparticle forces in clay suspensions Flocculation, viscous flow and swelling, in CMC Workshop Lectures, Clay-Water Interface and Its Reological Implications, vol. 4, Giiven, N. and Polastro, R.M., Eds., Clay Mineral Society, Boulder, CO, 1992, p. 157. 

At very low shear rates (i.e., flow velocities), particles in a chemically stable suspension approximately follow the layers of constant velocities, as indicated in Fig. 2. But at higher shear rates hydro-dynamic forces drive particles out of layers of constant velocity. The competition between hydrodynamic forces that distort the microstructure of the suspension and drive particles together, and the Brownian motion and repulsive interparticle forces keeping particles apart, leads to a shear dependency of the viscosity of suspensions. These effects depend on the effective volume fraction of... 

In Chapter 12 of this book, the mechanical properties of ceramic suspensions, pastes, and diy ceramic powders are discussed. Ceramic suspension rheology is dependent on the viscosity of the solvent with polymeric additives, particle volume fraction, particle size distribution, particle morphology, and interparticle interaction energy. The interparticle forces play a veiy important role in determining the colloidal stability of the suspension. If a suspension... 

In this chapter, we described the fundamentals of suspension iheol-ogy from dilute suspensions to concentrated suspensions. Attention has been paid to interparticle forces and the structure of the suspension because these things drastically influence suspension iheology. In addition, visco-elastic properties of concentrated suspensions including ceramic pastes have been discussed. Finally, the mechanical properties of dry ceramic powders have been discussed in terms of the dJoulomb yield criterion, which gives the stress necessary for flow (or deformation) of the powder. These mechanical prc rties will be used in the next chapter to predict the ease with vdiich dry powders, pastes, and suspensions can be made into green bodies by various techniques. 

J. W. Goodwin, Rheological properties, interparticle forces and suspension structure, in D.M. Bloor and E. Wyn-Jones (Eds.), The Structure, Dynamics and Equilibrium Properties of Colloidal Systems. NATO ASI Series C 324, Kluwer, The Netherlands, 1990, pp. 659-679. 

Franks, G.V. et al.. Effect of interparticle forces on shear thickening of oxide suspensions, 7. Rheol., 44, 759, 2000. 

In the context of gas-solid suspensions, a cohesive powder may be defined as a powder in which the interparticle forces become so large that they exceed the aerodynamic drag which can be exerted by the gas. 

Flow or deformation involves the relative motion of adjacent elements of the material. As a consequence such processes are sensitive to interatomic or intermolecular forces. In the case of liquids containing dispersed particles, interparticle forces are also important. Because the rheological properties of colloidal suspensions exhibit such a rich variety of phenomena, rheological studies not only provide information on medium-particle and particle-particle interactions but also arc of immense technological importance. 

The thixotrqiic behavior of suspensions and emulsions is a rather difficult property to measure, and this is further cmnplicated by the contribution of viscoelastic behavior (see next section). The main reason for this difflculty lies in the nature of the phenomenon involved. Thixotropy arises because of the existence of interparticle forces that produce three-dimensional microsmictures called flocculates or aggregates (see Sec. III). Depending on the magnitude of these forces, these microstructures are more or less prone to destruction by shearing, in consequence, any manipulation of a thixotropic sample may induce structural breakdown, thereby changing, most often irreversibly, the viscosity and yield stress of the sample. 

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