Coagulation of dispersions

Even allowing for the fact that the Debye-Hiickel approximation applies only for low potentials, the above analysis reveals some features of the electrical double layer that are general and of great importance as far as stability with respect to coagulation of dispersions and electrokinetic phenomena are concerned. In summary, three specific items might be noted ... 

Roughly 60 years ago Derjaguin, Landau, Verwey, and Overbeek developed a theory to explain the aggregation of aqueous dispersions quantitatively [66,157,158], This theory is called DLVO theory. In DLVO theory, coagulation of dispersed particles is explained by the interplay between two forces the attractive van der Waals force and the repulsive electrostatic double-layer force. These forces are sometimes referred to as DLVO forces. Van der Waals forces promote coagulation while the double layer-force stabilizes dispersions. Taking into account both components we can approximate the energy per unit area between two infinitely extended solids which are separated by a gap x ... 

Structure formation that takes place in disperse systems is the result of spontaneous thermodynamically favorable processes of particle aggregation that lead to a decrease in free energy of the system. These processes include coagulation of dispersed phase or condensation of substance in the zones of direct particle contact. The development of spacial networks (disperse structures) of different kinds defines the ability of disperse system to be converted into a material with particular mechanical properties. Such system becomes qualitatively different from its initial, unstructured state. 

Critical Coagulation Concentration (CCC) The electrolyte concentration that marks the onset of coagulation of dispersed species. The... 

Heterocoagulation The coagulation of dispersed species of different types or having different states of surface electric charge. 

Comparison of 0-point flocculation with weak coagulation of dispersions... 

Critical Coagulation Concentration. (CCC) The electrolyte concentration that marks the onset of coagulation of dispersed species. The CCC is very system-specific, although the variation in CCC with electrolyte composition has been empirically generalized. See also Schulze-Hardy Rule. 

Higashitani K and Matsuno Y 1979 Rapid Brownian coagulation of colloidal dispersions J. Chem. Eng. Japan 12 460-5... 

Poly etrafluoroethylene is manufactured and sold in three forms granular, fine powder, and aqueous dispersion each requires a different fabrication technique. Granular resins are manufactured in a wide variety of grades to obtain a different balance between powder flows and end use properties (Pig. 1). Pine powders that are made by coagulating aqueous dispersions also are available in various grades. Differences in fine powder grades correspond to their usefulness in specific appHcations and to the ease of fabrication. Aqueous dispersions are sold in latex form and are available in different grades. A variety of formulation techniques are used to tailor these dispersions for specific appHcations. 

Dispersions to be added to latex must have good storage stabiHty and be compatible with the latex the pH of each should be similar to that of the latex, eg, pH 8.5—11 for ammonia-preserved latex and pH 3.5 for cationic-preserved concentrates. Addition of low pH materials to high pH latex or vice versa generally results in mutual precipitation and coagulation of the suspended mbber particles. 

The appheation of coagulation for removal of dispersed and coUoidal soUds of several industrial wastewaters is shown in Table 9. 

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. 

Dispersion polymer obtained by coagulation of a dispersion. It consists of agglomerates with an average diameter of 450 pm made up of primary particles 0.1 pm in diameter. 

Rubber is obtained from the juice of various tropical trees, mainly the tree Hevea brasiliensis. The juice is a latex consisting of a dispersion of polymer phase at a concentration of about 35% by mass, together with traces of proteins, sterols, fats, and salts. The rubber is obtained either by coagulation of the latex with acid, either ethanoic or methanoic, or by evaporation in air or over a flame. The material that results from this process is a crumbly, cheeselike substance, sometimes called raw rubber or caoutchouc. In order to... 

Evaporation of volatile byproducts and solvents is often used to obtain the solid metal nanoparticles. The residue may contain metal nanoparticles and protective reagents. When the nanoparticles are well protected by ligands or polymers, then the solid residues can be dispersed again without coagulation of the particles. When the nanoparticles are not well protected, however, the evaporation often results in aggregation of the nano-particles. 

In rubber latex, the process whereby the dispersed rubber globules separate out from the watery serum the globules clot together to form a jelly-like mass, the coagulum. In the preparation of natural rubber, coagulation of the latex is... 

In a number of recent publications (1, 2) microcrystailine cellulose dispersions (MCC) have been used as models to study different aspects of the papermaking process, especially with regard to its stability. One of the central points in the well established DLVO theory of colloidal stability is the critical coagulation concentration (CCC). In practice, it represents the minimum salt concentration that causes rapid coagulation of a dispersion and is an intimate part of the theoretical framework of the DLVO theory (3). Kratohvil et al (A) have studied this aspect of the DLVO theory with MCC and given values for the CCC for many salts, cationic... 

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