Viscosity colloidal suspensions

Bead Polymerization Bulk reaction proceeds in independent droplets of 10 to 1,000 [Lm diameter suspended in water or other medium and insulated from each other by some colloid. A typical suspending agent is polyvinyl alcohol dissolved in water. The polymerization can be done to high conversion. Temperature control is easy because of the moderating thermal effect of the water and its low viscosity. The suspensions sometimes are unstable and agitation may be critical. Only batch reaciors appear to be in industrial use polyvinyl acetate in methanol, copolymers of acrylates and methacrylates, polyacrylonitrile in aqueous ZnCh solution, and others. Bead polymerization of styrene takes 8 to 12 h. 

The viscosity of a fluid arises from the internal friction of the fluid, and it manifests itself externally as the resistance of the fluid to flow. With respect to viscosity there are two broad classes of fluids Newtonian and non-Newtonian. Newtonian fluids have a constant viscosity regardless of strain rate. Low-molecular-weight pure liquids are examples of Newtonian fluids. Non-Newtonian fluids do not have a constant viscosity and will either thicken or thin when strain is applied. Polymers, colloidal suspensions, and emulsions are examples of non-Newtonian fluids [1]. To date, researchers have treated ionic liquids as Newtonian fluids, and no data indicating that there are non-Newtonian ionic liquids have so far been published. However, no research effort has yet been specifically directed towards investigation of potential non-Newtonian behavior in these systems. 

Papell, S.S.Low viscosity magnetic fluid obtained by the colloidal suspension of magnetic particles. US Patent (1965) 3,215,572. 

The above model assumes that both components are dynamically symmetric, that they have same viscosities and densities, and that the deformations of the phase matrix is much slower than the internal rheological time [164], However, for a large class of systems, such as polymer solutions, colloidal suspension, and so on, these assumptions are not valid. To describe the phase separation in dynamically asymmetric mixtures, the model should treat the motion of each component separately ( two-fluid models [98]). Let Vi (r, t) and v2(r, t) be the velocities of components 1 and 2, respectively. Then, the basic equations for a viscoelastic model are [164—166]... 

From Equation 2.2, it can be seen that the viscosity of the slip plays an important role. It regulates the formation rate of the gel layer and helps to prevent the slip from penetrating the support pore system. In the colloidal suspension route the evolution of the viscosity during the solvent extraction is slow during the very first steps of the process and drastically increases just before gelling. With the polymeric gel route a more gradual increase of the viscosity is observed. In both cases the evolution of the viscosity can be modified by the addition of binders to the sol slip . Different kind of binders are chosen depending on the nature of the solvent, the compatibility with the precursors and the viscosity of the system. 

In various kinds of industrial production, materials need to be treated with charged colloidal particles. In such systems, the value of the zeta-potential analyses are needed to control production. For example, in paper, adhesive, and synthetic plastics, colloidal clay can be used as filler. In oil drilling, clay colloidal suspensions are used. The zeta potential is controlled so as to avoid clogging the pumping process in the oil well. It has been found that, for instance, the viscosity of a clay suspension shows a minimum when the zeta potential is changed (with the help of pH from 1 to 7) from 15 to 35 mV. Similar observations have been reported in coal slurry viscosity. The viscosity was controlled by the zeta potential. 

Frisch,H.L., Simha.R. The viscosity of colloidal suspensions and macromolecular solutions, Vol. 1, Chapter 14. In Eirich,F.R. (Ed.) Rheology. New York Academic Press 1956. 

This means that an aqueous salt solution should not be viewed as a homogeneous liquid with a modified inter-molecular interaction, but rather as a colloidal suspension of inert particles in pure liquid water, with the particles formed by the ions and their first solvation shells. Following this view of an aqueous salt solution, the viscosity at low concentration can be described by the Einstein equation [19] ... 

At high neutralization levels with alkali metal ions, many ionomers spontaneously form colloidal suspensions in water when stirred vigorously at 100—150°C under pressure. Depending on solids content and acid level, the dispersions range in viscosity from water-like to paste-like. These provide convenient methods for applying thin coatings of ionomers to paper and other substrates. 

When the liquid, solution or lyophobic colloidal suspension contains asymmetric particles or when it is too concentrated, other methods must be applied to measure the viscosity. This is for instance the case with clay suspensions. In the past the viscosity of clay suspensions was measured by means of a bucket with a hole in it. The bucket was filled with clay suspension and after the stopper had been removed from the hole, the time required by the volume to drain was measured as a function of e.g. the volume and composition. Later mechanical methods were applied. One of them is based on the principle that a metal cylinder or disc, suspended from a torsion thread, is exposed to a certain resistance when you rotate it in the solution or suspension. Before the measurement the cylinder or disc is turned 360° anti-clockwise and then released. After having revolved over a certain angle, the cylinder or disc will change its direction of rotation. The rotation angle is a measure for the viscosity. 

Fig. 5.11 A possible relationship between the viscosity of a colloidal suspension and the mass percentage of the electrolyte.

According to the Einstein theory, the intrinsic viscosity of a spherical particle suspension is 2.5. However, for a colloidal suspension of nonspherical particles, [r ] > 2.5. Jeffery [112] obtained the viscosity of an ellipsoidal particle suspension under shear. Incorporating Jeffery s results of velocity fields around the particle, Simha [113] obtained expressions for two explicit limiting cases of ellipsoids. Kuhn and Kuhn [114] also obtained an expression for intrinsic viscosity for the full range of particle aspect ratio (p) by taking an approach similar to Simha s method. 

Self-supporting inorganic membranes can be formed with or without a substrate. In either case the precursor sol, consisting of either a colloidal suspension or a polymeric solution, must be formed. To produce a membrane supported on a substrate (i.e. a supported membrane), a preformed porous support is dipped in the precursor sol and a gel forms at the surface of the support typically by the slipcasting method [48]. Another approach is spin coating, in which an excess amount of liquid is deposited onto a substrate and then thinned uniformly by centrifugal force [12]. To produce a non-supported membrane, the liquid is simply poured into a mold of appropriate shape and allowed to dry. All these processes need to be done before the gel point which is accompanied by a large increase in viscosity. 

Frisch, H. L and R- Simha Viscosity of colloidal suspensions and macro-molecular solutions. In Rheology, Vol. I, pp. 525—-613. edited by F. Eirich, New York Academic Press 1956. 

The qualitative behavior of the viscosity of suspensions over a large range of shear rates is depicted in Fig. 7. This type of shear dependency is found, for example, for concentrated colloidal suspensions. These results cannot be immediately carried over to ceramic inks since the experiments are done with much higher concentrations of solids and at much lower shear rates than are applicable for the inkjet process. The suspended particles in these experiments are usually spherical at sizes of about 1 fim or smaller. But the shear dependency of the viscosity found for concentrated... 

Viscosity (dynamic) dispersions in water at the 1-2% w/v level are thin colloidal suspensions. At 3% w/v and above, dispersions are opaque. As the concentration is increased above 3% w/v, the viscosity of aqueous dispersions increases rapidly at 4-5% w/v, dispersions are thick, white colloidal sols, while at 10% w/v firm gels are formed. Dispersions are thixotropic at concentrations greater than 3% w/v. The viscosity of the suspension increases with heating or addition of electrolytes, and at higher concentrations with aging. 

Barium Sulfate. The many commercial preparations of barium sulfate differ in their density and their ability to coat the bowel wall. These ehuraeteristies arc deteniiined by the particle size of the harium suspension, its viscosity, and its pH. which in turn are determined by the addition of small amounts of flavoring agenks.. suspending agents, and so forth. The.se additives are the proprietary secret of the manufacturer and do improve the diagnostic properties of the bariutn colloidal suspension for Gl radiological studies. 

With increasing shear, Pe — the relative viscosity of suspensions — usually decreases (see Fig. 6.19). This shear thinning effect is quite moderate in colloidally stable suspensions, which actually can behave as nearly Newtonian up to... 

As discussed in Sect. 4, in the fluid, MCT-ITT flnds a linear or Newtonian regime in the limit y 0, where it recovers the standard MCT approximation for Newtonian viscosity rio of a viscoelastic fluid [2, 38]. Hence a yrio holds for Pe 1, as shown in Fig. 13, where Pe calculated with the structural relaxation time T is included. As discussed, the growth of T (asymptotically) dominates all transport coefficients of the colloidal suspension and causes a proportional increase in the viscosity j]. For Pe > 1, the non-linear viscosity shear thins, and a increases sublin-early with y. The stress vs strain rate plot in Fig. 13 clearly exhibits a broad crossover between the linear Newtonian and a much weaker (asymptotically) y-independent variation of the stress. In the fluid, the flow curve takes a S-shape in double logarithmic representation, while in the glass it is bent upward only. 

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