Coagulation stabilization

Small amounts of modified methylcellulose and mono-substituted sodium phosphate (both 0.1%), may be added to plugging cement [1766]. The mono-substituted sodium phosphate weakens the effect of calcium ions on modified methylcellulose and prevents its coagulation. Stabilization of the plugging solution and increased strength of the cement rock result. 

Stumm and Sigg (1979) predicted the coagulation stability domains of goethite based on surface chemistry and surface potential estimates (Fig. 7.9). 

C. Kinetic Aspects of Suspension Coagulation Stability Ratio 179... 

Nowadays, catalytic properties of metal nanoparticles are the subject of extensive studies. It has been found recently [1,2] that not only the particle size but also a distance between supported particles affects the properties of nanostmctured catalytic systems. This effect opened up a new way to improve the catalytic properties of supported metal particles by the formation of coatings with the optinial surface particle density. However, most of the known preparative methods are unsuitable for fabrication of dense nanostmctures because closely located crystalhne particles coagulate into larger aggregates. For this reason, a search for methods that can enhance the coagulation stability of the metallic nanoparticles is the task whose accomplishment governs the development of new promising areas in catalysis. 

The repulsion between two double layers is important in determining the stability of colloidal particles against coagulation and in setting the thickness of a soap film (see Section VI-5B). The situation for two planar surfaces, separated by a distance 2d, is illustrated in Fig. V-4, where two versus x curves are shown along with the actual potential. 

For a more complete understanding of colloid stability, we need to address the kinetics of aggregation. The theory discussed here was developed to describe coagulation of charged colloids, but it does apply to other cases as well. First, we consider the case of so-called rapid coagulation, which means that two particles will aggregate as soon as they meet (at high salt concentration, for instance). This was considered by von Smoluchowski 1561 here we follow [39, 57]. 

In slow coagulation, particles have to diffuse over an energy barrier (see the previous section) in order to aggregate. As a result, not all Brownian particle encounters result in aggregation. This is expressed using the stability ratio IV, defined as... 

Reerink H and Overbeek J Th G 1954 The rate of coagulation as a measure of the stability of silver iodide sols Discuss. Faraday Soc. 18 74-84... 

Despite the anhydride stmcture, it is remarkably stable, surviving addition to the highly alkaline viscose, the acidic coagulating bath, and also resisting multiple laundering of the rayon fabric. The unusual stability may be attributed to the sulfur atoms, which enhance hydrophobicity, and to the stericaHy hindering neopentyl groups that retard hydrolysis. 

The development of freeze-drying for the production of blood derivatives was pioneered during World War II (96,97). It is used for the stabilization of coagulation factor (98,99) and intravenous immunoglobulin (IgG iv) products, and also for the removal of ethanol from intramuscular immunoglobulin (IgG im) solutions prior to their final formulation (Fig. 2). 

The product of an emulsion polymerization is a latex ie, polymer particles on the order of 0.5—0.15 p.m stabilized by the soap. These form the basis for the popular latex paints. SoHd mbber is recovered by coagulating the latex with ionic salts and acids (see Latex technology). 

In dipping generally, but particularly with the anode process, it is desirable to use tanks that circulate the coagulant and latex compound, particularly the latter. Use of circulation keeps the Hquid surface clean and free from lumps, scum, or bubbles. Mechanical circulation can cause mbber particle instabihty, however, and eventually coagulate the compound. Therefore, tanks should be designed to minimize friction or shear action, and the compound stabilized to maintain mechanical stabiUty. 

Cure Characteristics. Methods of natural rubber production and raw material properties vary from factory to factory and area to area. Consequentiy, the cure characteristics of natural mbber can vary, even within a particular grade. Factors such as maturation, method and pH of coagulation, preservatives, dry mbber content and viscosity-stabilizing agents, eg, hydroxylamine-neutral sulfate, influence the cure characteristics of natural mbber. Therefore the consistency of cure for different grades of mbber is determined from compounds mixed to the ACSl formulation (27). The ACSl formulation is as follows natural mbber, 100 stearic acid, 0.5 zinc oxide, 6.0 sulfur, 3.5 and 2-mercaptobenzothiazole (MBT), 0.5. 

P. C. Hiemen2, Principles of Colloid and Suf ace Chemisty, 2nd ed., Marcel Dekker, Inc., New York, 1986 R. D. Void and M. J. Void, Colloid and Inteface Chemisty, Addison-Wesley, Reading, Mass., 1983 H. Sonntag and K. Strenge, Coagulation and Stability of Disperse Systems, Halsted, New York, 1972 D. J. Shaw, Introduction to Colloid and Suf ace Chemisty, 3rd ed., Butterworth, London, 1980. 

There are two general theories of the stabUity of lyophobic coUoids, or, more precisely, two general mechanisms controlling the dispersion and flocculation of these coUoids. Both theories regard adsorption of dissolved species as a key process in stabilization. However, one theory is based on a consideration of ionic forces near the interface, whereas the other is based on steric forces. The two theories complement each other and are in no sense contradictory. In some systems, one mechanism may be predominant, and in others both mechanisms may operate simultaneously. The fundamental kinetic considerations common to both theories are based on Smoluchowski s classical theory of the coagulation of coUoids. 

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