Coagulation phenomena

Potential energy curves of the type shown in Figure 10.1 are thus seen to be useful constructs for understanding and describing coagulation phenomena. They also illustrate the role of the attractive van der Waals forces on the stability of colloids. 

To apply these ideas to coagulation phenomena, we must consider what happens to these distributions of potential when two similar surfaces approach one another (Section 11.7). To study coagulation phenomena, we need to compare the electrostatic effects of particle approach with the van der Waals effects discussed in the last chapter. This is done in terms of potential energy curves as discussed in Section 10.2. As we move through the chapter, our interest shifts from potential (volts) to potential energy (joules). It is important to keep track of the difference between the two as the development progresses. 

Coagulation Phenomena. Agglomeration and fragmentation calculations which bear direct kinship to the Fokker-Planck treatments but also include discussion of expectation of W-body systems for which the initial distribution function and dynamics cannot be or are not treated in the continuum limit. 

Mchedlov-Petrossyan et al. [138] studied the interaction of cationic dyes such as indopolycarbocyanine and methylene blue with the CggFWSs, and demonstrated the occurrence of a strong interaction between the cationic dyes and the dispersed phase of the Cgg hydrosol, which resulted in adsorption at the surface of the coUoid particles and finaUy in the coagulation of the sol [131, 134] Such adsorption processes are accompanied by the neutrahzation and hydrophobization of the Cgg/water interface and play a decisive role in coagulation phenomena. 

Double layers are also important in colloid chemistry. When a colloid particle is composed of an ionic crystal, it often preferentially adsorbs one of its component ions, thereby acquiring a charge. As a result the colloid particle is surrounded by a double layer. The interfacial properties are very important in determining a variety of colloidal properties, including electrophoresis and electroosmosis. It also plays a role in colloid stability and coagulation phenomena. The effects of the electrical properties of the interface are well known in colloid chemistry. The description of colloid phenomena is a well-developed area of physical chemistry which is often important in industrial processes. 

Other species can compete with OH for coordination sites on Al(III). As evidence that such competition takes place, it can be shown that the amount of OH which must be added to a solution to bring about the formation of Al(OH)3(s) is less when phosphates are present in solution than when they are not. Competitive effects probably cause a difference in coagulation phenomena based on a difference in the ligand concentrations in the water being treated. 

The behavior of montmorillonite suspension on the addition of sodium, on a cationic, and on an anionic detergent could be directly observed with x-ray microscopy. The internal structures of the aggregates formed by the addition of the surfactants could be clearly visualized. Therefore, it can be expected that x-ray microscopy will become a very useful tool in the investigation of coagulation phenomena. 

A. Rende (1972), A new approach to coagulation phenomena in wet-spinning , Journal of Applied Polymer Science, 16(3), 585-594. 

The calcium pectate coagulation phenomenon as a result of pectinesterase action improves the pressing characteristics of ground citrus peel and lowers costs when the peel has to be dried for cattle feed. When the pomace has to be dried for pectin manufacture pectin de-esterification must be prevented since otherwise calcium sensitive pectin is obtained. This is achieved by immediate blanching (8). 

In the previous sections, we described the overall features of the heat-induced phase transition of neutral polymers in water and placed the phenomenon within the context of the general understanding of the temperature dependence of polymer solutions. We emphasised one of the characteristic features of thermally responsive polymers in water, namely their increased hydropho-bicity at elevated temperature, which can, in turn, cause coagulation and macroscopic phase separation. We noted also, that in order to circumvent this macroscopic event, polymer chemists have devised a number of routes to enhance the colloidal stability of neutral globules at elevated temperature by adjusting the properties of the particle-water interface. 

The coagulation cascade is at first a protein adsorption phenomenon. One approach we suggested was to make the surface sufficiently hydrophilic to prevent adsorption of the proteins. This is not always possible, however. If the goal of research is to devise a vascular graft, certain physical requirements preclude hydrophilic polymers. An alternative would be a composite material, but that is problematic. Another approach — the one most researchers have followed — is interrupting the coagulation cascade at a point further along the process. 

A related phenomenon is the repeat of a domain along the same polypeptide chain, as found in the immunoglobulins. Such repeats could have evolved by the fusion of two copies of the same gene. The proteases of coagulation, fibrinolysis, and complement activation appear to have arisen in a modular manner.31... 

COACERVATION. An important equilibrium state of colloidal or macromolecular systems. It may be defined as the partial miscibility of two or more optically isotropic liquids, at least one of which is in Ihe colloidal state. For example, gum arabic shows the phenomenon of coarcrvalion when mixed with gelatin. It also may be defined as the production, hy coagulation of a hydrophilic sol, of a liquid phase, which... 

In 1861. Thomas Graham first used the term syneresis to describe the phenomenon of exuding small quantities of liquid hy gels. By definition, syneresis is the spontaneous separation of an initially homogeneous colloid system into lwo phases—a coherent gel and a liquid. The liquid is actually a dilute solution whose composition depends upon the original gel. When the liquid appears, the gel contracts, but there is no net volume change. Syneresis is reversible if the colloid particles do not become ton coagulated immediately after their formation. 

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