Applications of Electrokinetic Phenomena

Many practical applications using dispersed systems are related to colloidal stability. In some cases, one prefers to have the system aggregated as much as possible in other cases aggregation must be prevented. Whatever the desired situation, the zeta potential may serve as a useful parameter to indicate colloid stability. All other factors kept constant, the higher the the more stable the system. 

For instance, industrial and domestic wastewater contains a variety of solid and liquid particles that are colloidally stable, often becanse they are covered with charged (biological) surface-active substances. For most of these particles, H+ and 

OH are the charge-determining ions, and, hence, the colloidal stability is sensitive to the pH. By adjusting the pH, low C values for most of the materials may be reached so that aggregation readily occurs and the materials can be removed by sedimentation or filtration. In fact, for aggregation to occur, it would be most favorable if some components have a positive value for and others a negative. The aggregation of colloidal particles is discussed in more detail in Chapter 16. 

In some fruit juices, such as orange or tomato juice, colloid stability contributes to the desired cloudiness. This may be improved by additives that increase of the dispersed particles. Also, in shampoos and hair conditioners, addition of macroions having a high may help to increase the hair volume by adsorbing to the hairs. 

Streaming potentials should be prevented in the transport of (apolar) liquids, for example, oil, through pipelines. In particular, in systems with low K p, such a transport may lead to large streaming potentials causing a real danger of explosions. A similar situation exists when grains are transported in elevators. 

Throughout most of this chapter the emphasis has been on the evaluation of zeta potentials from electrokinetic measurements. This emphasis is entirely fitting in view of the important role played by the potential in the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability. From a theoretical point of view, a fairly complete picture of the stability of dilute dispersions can be built up from a knowledge of potential, electrolyte content, Hamaker constants, and particle geometry, as we discuss in Chapter 13. From this perspective the fundamental importance of the f potential is evident. Below we present a brief list of some of the applications of electrokinetic measurements. 

Numerous other applications could be listed in which electrokinetic characterization provides a convenient experimental way of judging the relative stability of a system to coagulation. Paints, printing inks, drilling muds, and soils are examples of additional systems with properties that are extensively studied and controlled by means of the f potential. 

14 The use of electroosmosis in environmental remediation (known as the lasagna process). (Redrawn with permission of Ho et al. 1993.) 

15 Crossed immunoelectrophoresis of human serum with rabbit antihuman serum. (Redrawn with permission from B. Weeke, in A Manual of Quantitative Immunoelectrophoresis Methods and Applications (N. H. Axelsen, J. Kroll, and B. Weeke, Eds.), Universitetsforlaget, Oslo, Norway, 1973.) 

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Finally, a number of examples of applications of electrokinetic phenomena are described briefly in Section 12.11. 

Masliyah, J. H., Electrokinetic Transport Phenomena, Alberta Oil Sands Technology and Research Authority, Edmonton, Alberta, Canada, 1994. (Graduate and undergraduate levels. An excellent introduction to transport processes relevant to applications of electrokinetic phenomena. Most of the material is accessible to undergraduate students. Chapter 12 presents some very practical applications of electrokinetic phenomena of interest to engineers.)... 

APPLICATION OF ELECTROKINETIC PHENOMENA TO THE REMOVAL OF ORGANIC AND INORGANIC CONTAMINANTS FROM SOILS... 

A last application of electrokinetic phenomena is the concentration of industrial muds. Here also, with a small expanse in energy, elimination of water by electroosmosis allows to concentrate muds from 70% of water (a liquid like mud), to 20% of water (a solid, clay rock like). 

When one thinks of electrokinetic phenomena in the context of a first-level course on colloid and surface chemistry, the first thought that probably comes to mind is the use of such phenomena to measure zeta potentials and charges of colloidal species. But, as we have already seen in Chapter 1 and as we see later in this chapter, electrokinetic phenomena play a significant role in many other applications. We take a look at one such application here and see why the topics we consider in this chapter and in others are important in that context. 

The focus of this chapter is to present the basics of electrokinetic phenomena and to provide a working knowledge of the subject. Some classical and some novel applications of these phenomena are also summarized at the end of the chapter. 

The field of electrokinetic phenomena has had a long history. For over a century, it has been recognized that ions in solution move in the presence of electric fields. It is also well known that bulk flow can occur when electric fields are applied and when the surfaces containing the fluid are charged (electroosmosis). These two phenomena, ion and bulk flow movement in the presence of electric fields, and their applications in both analytical chemistry and microfluidics are covered in depth in this book. 

The set of Eq. (10.85) is related to various classical studies of electrokinetic phenomena, since the equations describe the coupled processes and yield naturally a number of symmetry relationships, which have been observed experimentally. Therefore, they provide a practical application of the linear nonequilibrium thermodynamic approach. For example, we may consider studies with identical solutions at each surface of the membrane, so that An = Ans = 0. Then the system has only two degrees of freedom, and we have... 

Generalized theory of electrokinetic phenomena. Application to electrophoresis and experimental verification... 

Ishido, T. and Mizutani, H., Experimental and theoretical basis of electrokinetic phenomena in rock-water systems and its application to geophysics, J. Geophys. Res., 86, B3, 1763, 1981. 

There are two types of electrokinetic phenomena, namely those in which an electric potential is generated by the mechanical notion of a surface in a liquid and those in which a particle or liquid is caused to move by an electric potential. Classically there are four major effects, i.e., streaming potentials, sedimentation potentials, electrophoresis, and electroosmosis. (There are also several secondary effects that have been noted more recently such as acoustic potentials,K effect potentials, and U effect potentials.Each of the major effects has found a niche in physical chemistry, analytical chemistry, and chemical engineering. However, the application and understanding of electrokinetic phenomena in the biological sciences has been very spotty. 

In this chapter, we recall briefly some features of ionic transport in solutions [1]. Since the basic concepts of electrostatics and hydrodynamics have been presented before, we will directly present their application to electrokinetic phenomena after this first presentation. 

Quincke was probably the first to think of technical applications of electrokinetics, when he proposed to use the phenomena of streaming potentials as a source of electric energy ... 

Electrokinetic soil treatment is a commercially available in situ technology for the removal of metals and organic compounds. The application of direct current (DC) in a porous medium leads to two transport mechanisms electromigration and electro-osmosis. The combination of these two transport phenomena results in the movement of contaminant ions toward either the cathode or anode. Nonionic contaminants are transported by electro-osmosis alone. 

Chapters 11 and 12 in the present edition focus exclusively on the theories of electrical double layers and forces due to double-layer interactions (Chapter 11) and electrokinetic phenomena (Chapter 12). Chapter 11 includes expressions for interacting spherical double layers, and both chapters provide additional examples of applications of the concepts covered. 

Electrophoresis has the greatest practical applicability of these electrokinetic phenomena and has been studied extensively in its various forms, whereas electro-osmosis and streaming potential have been studied to a moderate extent and sedimentation potential rarely, owing to experimental difficulties. 

In this chapter, we extend the electrokinetic theory of soft particles (Chapter 21), which is applicable for dilute suspensions, to cover the case of concentrated suspensions [1-3] on the basis of Kuwabara s cell model [4], which has been applied to theoretical studies of various electrokinetic phenomena in concentrated suspensions of hard colloidal particles [5-23]. 

Distinction has to be made between the very first moments after the application of the external force and the stationary state, developing soon thereafter. Usually, such stationary states are considered, l.e. inertia is disregarded. This was also done in sec. 3.13. However, when electrokinetic phenomena are studied in alternating fields, various types of inertia start to play prominent roles, leading to additional dissipation. As a consequence, double layer characteristics like the Induced dipole moment, the dielectric... 

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