Applications dispersion viscosity

Furthermore, dispersions of a-lactalbumin nanotubes could have promising industrial application as viscosity enhancing agents or gelling agents. 

Many kinds of native and modified starches are being used on the size press.207 The governing factors are dispersion viscosity, film formation and resistance to retrogra-dation. For low-cost applications, native corn starch is depolymerized in the paper mill by enzymic or thermal-chemical conversion. In-plant converted starches are... 

All the above formulas are one-parameter equations, i.e. they relate the dispersion viscosity only to the volume fraction of particles contained in it. This limits the range of applicability of the equations to not very high dispersion concentrations. To take account of the influence of the structure of concentrated dispersions on their rheological behavior, Robinson [12] suggested that the viscosity of dispersions is not only propertional to the volume fraction of solid phase, but is also inversely proportional to the fraction of voids in it. (At about the same time Mooney [40], who proceeded from a hydrodynamic model, arrived, using theoretical methods, at the same conclusion). Robinson s equation contains the relative sedimentation volume value — S, which depends on the particle size distribution of the dispersion... 

Suspension—polymerization of monomers dispersed in an inert phase with monomer-soluble initiator Low dispersion viscosity compared to bulk good heat transfer high polymerization rate and high molecular weight direct application of the latex Smaller reactor capacity than bulk reactor wall fouling wastewater problems Polystyrene, PVC, polypropylene... 

This work will describe a series of magnetic colloidal systems that were specifically developed for an application in ink jet printing technology. This application imposes a certain set of requirements such as particle size 100 + 50A, magnetic moment of 25 emu/g or 35%w Fe O in colloidal dispersion, viscosity of 8-10 cps, non-toxic aqueous system, shelf life of a few years, freeze-thaw stability, fast drying (2 msec) and high optical density of magnetic ink on various papers. 

The physical interpretation of the load factors is that a liquid flow should be transported through the interface, and this transport is augmented by the density difference and decreased by the continuous phase viscosity. The liquid load factor accounts for transport of both phases through the interface, while the other two only transport the applicable dispersed phase. Flence, the liquid load factor is in line with the new separator design philosophy proposed by Polderman et al. (12, 15), while the oil and water load factors are in line with the dispersion layer theory developed by Jeelani and Flartland (16-20) (for the corresponding dispersed phase). 

A major advantage of suspension polymerization over bulk techniques is that the polymer separation is much more facile (Dawkins, 1989), however, the application of this technique is somewhat limited as few monomers are completely water insoluble. In addition, suspension polymerization is limited to radical polymerization systems and the nature of the agitation of the system is key, as is the viscosity in determining the size, stability and nature of the polymer particles formed. Of interest is the synthesis of porous particles via this technique that can be readily achieved by the inclusion of an inert porogen into the monomer phase, which can be readily removed after polymerization (Seidl et al, 1967). Suspension polymerization has a number of advantages including the ease of heat removal, low dispersion viscosity, low levels of impurities in the resultant particle, low separation costs and the final product is in particle form. On the other hand, the disadvantages of this technique are primarily wastewater problems, lower productivity compared to bulk and a continuous process has to date not been achieved industrially. 

Colloidal dispersions often display non-Newtonian behaviour, where the proportionality in equation (02.6.2) does not hold. This is particularly important for concentrated dispersions, which tend to be used in practice. Equation (02.6.2) can be used to define an apparent viscosity, happ, at a given shear rate. If q pp decreases witli increasing shear rate, tire dispersion is called shear tliinning (pseudoplastic) if it increases, tliis is known as shear tliickening (dilatant). The latter behaviour is typical of concentrated suspensions. If a finite shear stress has to be applied before tire suspension begins to flow, tliis is known as tire yield stress. The apparent viscosity may also change as a function of time, upon application of a fixed shear rate, related to tire fonnation or breakup of particle networks. Thixotropic dispersions show a decrease in q, pp with time, whereas an increase witli time is called rheopexy. 

Emulsion polymerization also has the advantages of good heat transfer and low viscosity, which follow from the presence of the aqueous phase. The resulting aqueous dispersion of polymer is called a latex. The polymer can be subsequently separated from the aqueous portion of the latex or the latter can be used directly in eventual appUcations. For example, in coatings applications-such as paints, paper coatings, floor pohshes-soft polymer particles coalesce into a continuous film with the evaporation of water after the latex has been applied to the substrate. 

The type of solvent used depends on the binder. There is normally more than one type of solvent in paint, particularly for spray application. Highly volatile solvents are needed to reduce the viscosity during atomization and then disperse as quickly as possible, but lower volatile solvents are necessary to remain momentarily to ensure that there is sufficient flow to form a continuous film. 

Electrodeposition This method of paint application is basically a dipping process. The paint is water-based and is either an emulsion or a stabilised dispersion. The solids of the paint are usually very low and the viscosity lower than that used in conventional dipping. The workpiece is made one electrode, usually the cathode, in a d.c. circuit and the anode can be either the tank itself or suitably sized electrodes sited to give optimum coating conditions. The current is applied for a few minutes and after withdrawal and draining the article is rinsed with de-ionised water to remove the thin layer of dipped paint. The deposited film is firmly adherent and contains a minimum of water and can be stoved without any flash-off period. This process is used for metal fabrications, notably car bodies. Complete coverage of inaccessible areas can be achieved and the corrosion resistance of the coating is excellent (Fig. 14.1). 

Almost all urethane materials are synthesized without the use of solvents or water as diluents or earners and are referred to as being 100% solids. This is true of all foams and elastomers. There are many products, however, which do utilize solvents or water, and these are known as solvent-borne and waterborne systems, respectively. In the past, many coatings, adhesives, and binders were formulated using a solvent to reduce viscosity and/or ease application. However, the use of volatile solvents has been dramatically curtailed in favor of more environmentally friendly water (see Section 4.1.3), and now there are many aqueous coatings, adhesives, and associated raw materials. Hydrophilic raw materials capable of being dispersed in water are called water reducible (or water dispersible), meaning they are sufficiently hydrophilic so as to be readily emulsified in water to form stable colloidal dispersions. 

There are numerous applications where the development of high viscosity is necessary in a finished product. For example, thickeners, mainly based on poly(acrylic acid), are used to give body to so-called emulsion paints. Emulsion paints are not formulated from true emulsions (Le. stable dispersions of organic liquids in water), but are prepared from latexes, that is, dispersions of polymer in water. Since latexes do not contain soluble polymers, they have a viscosity almost the same as pure water. As such, they would not sustain a pigment dispersion, but would allow it to settle they would also fail to flow out adequately when painted on to a surface. Inclusion of a thickener in the formulation gives a paint in which the pigment does not settle out and which can readily be applied by brush to a surface. 

As suggested by Barrett (2), it is assumed that following the particle nucleation stage, the polymerization proceeds in the particle (monomer/polymer) phase with no mass transfer limitation. Therefore, the dispersion polymerization is similar to a mass or suspension polymerization, and kj can not be assumed to be constant even at isothermal conditions, since kp and even kp are dependent on the degree of polymerization because of a gel effect. (2., ,D However, since the application of the model is for a finishing step, with polymer molecular weight and viscosity fairly well established, further changes in kp and kp should be minimal. 

Modem oil spill-dispersant formulations are concentrated blends of surface-active agents (surfactants) in a solvent carrier system. Surfactants are effective for lowering the interfacial tension of the oil slick and promoting and stabilizing oil-in-water dispersions. The solvent system has two key functions (1) to reduce the viscosity of the surfactant blend to allow efficient dispersant application and (2) to promote mixing and diffusion of the surfactant blend into the oil film [601]. 

Dispersants are used in well cement slurries. For this application, the dispersant should be water soluble. The dispersants prevent high initial cement slurry viscosities and friction losses when the slurries are pumped. 

These humic acids are not dissolved because the pH of this slurry is in the range of 4 to 9. Small amounts of fulvic acids are formed, and these are soluble in the water of the slurry. The coal-derived humic acids find applications as drilling fluid dispersants and viscosity control agents, whereas the coal-derived fulvic acids may be used to produce plasticizers and petrochemicals. 

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