Colloidal systems coagulated

Smoluchowski, M.V., 1916. Three lectures on diffusion. Brownian movement and coagulation of colloidal systems. Physik Zeitung, 17, 557. 

Smoluchowski, M.V., 1917. Mathematical theory of the kinetics of coagulation of colloidal systems. Zeitschrift fur Physikalische Chemie, 92, 129-168. 

The hydrogen ion concentration at which a colloidal system is electrically neutral the addition of acidic substances to, for example, rubber latex causes the pH value to move towards the isoelectric point, which is the region of minimum stability, and coagulation may take place. 

We need to understand under which conditions a colloidal system will remain dispersed (and under which it will become unstable). Knowing how colloidal particles interact with one another makes possible an appreciation of the experimental results for phase transitions in such systems as found in various industrial processes. It is also necessary to know under which conditions a given dispersion will become unstable (coagulation). For example, one needs to apply coagulation in wastewater treatment so that most of the solid particles in suspension can be removed. Any two particles coming close to each other, will produce different forces. 

Fig. 9.4.23 Dispersibility of colloidal systems of a kind of metals in various organic liquids. er. Relative dielectric constant of liquids A, electron affinity disp, dispersion (O) floe, flocculation ( ) upon stirring, the suspension becomes turbid then particles slowly sediment) coag, coagulation ( immediately after stirring of the suspension, particles aggregate again to sediment). ( ) Boundary between disp and floe ( ) boundary between Hoc and coag. Broken lines divide each region, (a) Hexane, (b) benzene, (c) diethyl ether, (d) ethyl acetate, (e) letrahydrofuran. (0 dichloroethane. (g) benzyl alcohol, (h) 2-butanol, (i) butanol, (j) acetone, (k) ethanol. (From Ref, 23.)...

As noted above, dilute colloidal systems display Newtonian behavior that is, their apparent viscosity is independent of the rate of shear. Accordingly, the capability to measure 77 under conditions of variable shear is relatively superfluous in these systems. However, non-Newtonian behavior is commonplace in charged colloids and coagulated colloids (see Section 4.8). 

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. 

It has been established experimentally that whereas mutual coagulation takes place in certain quantitative relationships when various oppositely charged colloidal systems—hydrophile and hydrophobe—interact, quite a different process can take place in the case of other interrelationships the addition of a small amount of a hydrophile colloid to a hydrophobe system... 

Other factors also affect the stability of eolloidal solutions, in particular the pH of the environment. The surface molecules of the nucleus of the micelles of different colloidal systems can have acid, basic, or amphoteric properties. Colloids characterized by this feature are called, respectively, acidosid, basoids, and ampholitoids (Marchenko, 1965). It has been established that the coagulation threshold of acidoids (sols of weak acids) increases and that of basoids decreases when the pH is increased. 

Use of Ultrasonic Vibration Potential To Monitor Coalescence. The complex chemical nature of crude oils makes it difficult to relate the dispersion behavior to the physicochemical properties at the crude-oil-water interface. In addition, the nonpolar and nontransparent nature of the oleic phase provides significant obstacles for studies of the interactions of the suspended water droplets in real systems. Recent development (28, 29) of electroacoustical techniques has shown considerable promise for electrokinetic measurements of colloidal systems and the direct monitoring of the rate and extent of coagulation (flocculation and coalescence) of water droplets in nontransparent water-in-oil media. The electroacoustic measurement for colloidal systems in nonpolar media is based on the ultrasound vibration potential (UVP) mode, which involves the applica-... 

Colloidal particles are usually too small to be extracted by filtration however, heating a colloid or adding an electrolyte may cause the particles to coagulate. The larger particles produced by coagulation will settle out or can be extracted by filtration. Colloidal systems can also be separated by a semipermeable membrane, a process called dialysis. 

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