Dispersion of Solid Particles

As an example of the forces acting on a particle in a flowing melt, consider the shear flow. In shear flow, the following relationship exists 

In a shear field, a particle experiences rotation because of velocity differences in addition to the load created by the shear forces. This produces cyclical loading. The cyclical application of a load promotes dispersion, since solid particles often undergo fatigue fracture [1], 

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For preparing lakes, a solution of aluminium sulfate (or chloride) is mixed with sodium carbonate, forming fresh alumina Al(OH)3. The colorant is then added and adsorbed on the surface of alumina. Usually the content of colorant in the lake ranges from 10 to 40%." The product is filtered, washed with water, dried, and milled. The product is allowed to contain unreacted alumina but must not contain more than 0.5% HCl-insoluble matter and not more than 0.2 % ether-extractable matter. - Lakes are insoluble in most solvents used for pure dyes, and they have high opacity and better stability to light and heat. Lakes impart their color by dispersion of solid particles in the food. The coloring properties of lakes depend on particles, crystal structures, concentrations of dye, etc. 

Because of the requirements of insolubility in water, in organic solvents and in the medium that it is being used to colour, the application processes for using pigments are quite different from those for dyes. Coloration with pigments is essentially a process of dispersion of solid particles of the pigment in a semi-solid medium. 

Batch equilibrium tests are conducted on solid phase suspensions, prepared with previously air-dried solids, ground to uniform powdery texture for mixing with various concentrations of the pollutants of interest in solution. The concentrations of these pollutants or the COMs leachate in the solution are designed to evaluate the capability of the suspended solids to adsorb all the pollutants possible with increasing amounts of available pollutants, consistent with interaction characteristics dictated by the surface properties of the solids and the pollutants [1,16,22-26,66,67,71]. For a successful and proper study of solid particle sorption of pollutants, the requirement for complete dispersion of solid particles in solution is absolute [143 -145]. Common practice is to use a solution to solid ratio of 10 1 [1], together with efficient sample agitation at a constant temperature (e.g.,48 h at 20 °C). 

Colloid chemistry investigates substance mixtures. These substance mixtures can be heterogenous, such as emulsions (in which tiny droplets of one liquid are dispersed in another), suspensions (consisting of a fine dispersion of solid particles in a liquid volume phase), and aerosols (in which liquid droplets are dispersed in the gas phase). However, there are also homogenous mixtures in which the solute is present in larger, supermolecular aggregates. These homogenous mixtures include micellar solutions and liquid crystalline... 

In the food industry it has often been difficult to obtain true viscosity measurements (unithj.j) of complex fluid foods such as coarse fruit suspensions. These are usually non-Newtonian suspensions. Fruit concentrates are dispersions of solid particles (pulp) in aqueous media (serum). Their rheological properties are of interest in practical applications related to processing, storage stability, and sensory properties. Expensive rheometers are often not available in quality control and product development laboratories. However, viscosity is nonetheless an important quality factor of these products. 

SN1 and reactions Two varieties of nucleophilic substitution, with unimolecular and bimolecular ratedetermining stages, respectively, sol A colloidal dispersion of solid particles in a liquid, solid A rigid form of matter that maintains the same shape whatever the shape of its container, solid emulsion A colloidal dispersion of a liquid in a solid. Example butter, an emulsion of water in butterfat. solid solution A solid homogeneous mixture of two or more substances. 

The work was planned on the basis of a model of a dispersed solid particle onto which one type of sequences of a BG copolymer is adsorbed selectively while the other type sequence is dissolved in the dispersion medium. A sketch of this model is shown in Figure 1. The model is the result of applying the same arguments which had been advanced (12) in discussing the mechanism of stabilization of polymeric oil-in-oil emulsions by BG copolymers to the problem of stabilization of dispersions of solid particles in organic media. Previously, essentially the same arguments had led to the demonstration of micelle formation of styrene-butadiene block copolymers in organic media under certain conditions (15). 

It has to be kept in mind that particulate materials are dispersions. In fact, the classical powder is a concentrated dispersion of solid particles in air. At a very low concentration, very Lne particles (micron, submicron size) can form an aerosol. In such a case-ewing to the large interparticulate distance-fhe particle-particle interactions can be neglected. In general, a particle can exhibit a substructure, that is, a particle may have external and internal pores. An external pore can be related to the roughness of the surface of a particle. 

Just as with emulsions and foams, suspensions can exist with additional dispersed phases present. They may contain, in addition to solid particles and a continuous liquid phase (and possibly a stabilizing agent), emulsified droplets and/or gas bubbles. Figure 2.4 (in Section 2.2.1) shows photomicrographs of a practical suspension that contains suspended oil droplets in addition to the particles. The terminology used to describe such systems can become confusing. Consider an aqueous dispersion of solid particles and emulsion droplets. If the solid particles are adsorbed on the emulsion droplets then it is an emulsion that also contains solids. If, however, the particles and droplets are not mutually associated then the system is at once a suspension and an emulsion. Which term is used becomes a matter of choosing the most appropriate context frequently one or the other is considered to be the primary dispersion while the other phase is considered to be an additive or a contaminant. 

Sedimentation potential— (also called electrophoretic or Dorn potential) Potential difference established during sedimentation (caused, e.g., by gravitation or centrifugation) of small charged particles (suspended in solution dispersion of solid particles or emulsion of immiscible liquid droplets). 

Figure 1 shows a comparison, published by Mori and Ototake [13], of the experimental dependences of viscosity on concentration of dispersions of solid particles based on the data of Vand [34], Robinson [12], Orr and Blocker [5], Dalla Valle and Orr [17] with the theoretical equations based on the hydrodynamic approach used by Einstein (1), Simha (30), Vand (31), Roscoe (44) and the phenomenological equation of Mori and Ototake (14). A more complicated form of the theoretical dependence, naturally makes it possible to describe experimental results over a wider range, but for concentrated dispersions most of theoretical equations remain inapplicable. 

Sengun and Probstein [70] drew the same conclusion when they analyzed the flow of concentrated monomodal dispersions of solid particles at extremely high shear... 

Glawe, D. D., and M. Samimy. 1993. Dispersion of solid particles in compressible mixing layers. J. Propulsion Power 9(l) 83-89. 

A dispersion Is a system made of discrete objects separated by a homogeneous medium In colloidal dispersions the objects are very small In at least one dimension. Colloidal sizes range from 1 to 100 nm however these limits are somewhat arbitrary, and It Is more useful to define colloids as dispersions where surface forces are large compared to bulk forces. Here we are concerned with systems where the dispersion medium Is a liquid examples are droplets In emulsions or mlcroemulslons (oll/water or water/oll), aggregates of amphiphilic molecules (surfactant micelles), foams, and all the dispersions of solid particles which are used as Intermediates In the manufacture of ceramics. At this stage we are not too concerned with the nature of the constituents, but rather with the structures which they form this Is a geometrical problem, where the system Is characterized by Its surface area A, by the shapes of Its Interfaces (curvatures - b ), and by the distances between opposing surfaces (d — concentration parameter). 

Suspensions are dispersions of solid particles in a liquid. The amount of solid material suspended occupies a certain fraction of space in the total volume of... 

Pharmaceutical suspensions are dispersions of solid particles in a suspending medium or vehicle (usually aqueous in nature). When the suspended solids are less than 1 pm, the system is referred to as a colloidal suspension. When the particle sizes are greater than about 1 pm, the system is called a coarse suspension. The practical upper limit for particles in a coarse suspension is approximately 50-75 pm. Depending on the affinity or interaction between the dispersed phase and the dispersion medium, a colloidal dispersion can be classified as lyophilic (hydrophilic) or lyophobic (hydrophobic). ... 

Several investigations have been made on the flow characteristics in multistaged fluid beds. Nishinaka et al. (N6, N8, N9) have measured the average bubble holdup, the lateral distribution of bubble holdup, and the longitudinal dispersion of solid particles in four- and eight-stage fluid beds installed with various horizontal baffles. As shown in Fig. 25 the average bubble holdup (except for beds baffled with tube plates) is correlated by the equation of Nishinaka et al., (N8) ... 

A suspension is a dispersion of solid particles in a liquid. A colloidal suspension is a sol. Colloidal properties become significant when the size of the parhcles is of the order of a few micrometer or less. In suspensions of large particles, for example, of some 10 pm or higher, hydrod5mamic interactions dominate the suspension flow properties emd particle packing behaviour. In colloidal suspensions interaction forces between the particles as well as hydro-dynamic interactions play a role in determining the flow and particle packing properties. 

Dispersion of solid particles in a polymeric matrix is another target that can be reached successfully using a purposely tailored diblock copolymer. 

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