Electro-kinetic phenomenon

In their study of the effects of hydrolyzable cations on electro kinetic phenomena (see Problem 4), James and Healy compared the electrophoretic behavior of colloidal silica with the streaming potential through a silica capillary. In both sets of experiments the solution was 10-3 M KN03 and 10 4 M Co(N03)2. The following results were obtained ... 

After S.S. Dukhin who explicitly introduced this parameter in his analyses of electro-kinetic phenomena. See e.g. S.S. Dukhin. Non-equilibrium electric surface phenomena. Ado. Colloid Interface ScL 44 (1993) 1. where older references can be found. The very idea that the ratio K /aK plays an Important role in electrokinetics is much older and can be found for example in J.J. Bikerman. Trans. Faraday Soc. 36 (1940) 154. In sec. 4.5c we shall Indicate how K can be measured. 

The third category concerns autonomous applications of one of the electro-kinetic phenomena to solve a practical problem. 

The electrokinetic potential (zeta potential, f) is the potential drop across the mobile part of the double layer (Figure 9.19c) that is responsible for electro-kinetic phenomena, for example, electrophoresis (motion of colloidal particles in an electric field). It is assumed that the liquid adhering to the solid (particle) surface and the mobile liquid are separated by a shear plane (slipping plane). The electrokinetic charge is the charge on the shear plane. 

Capture by interception assumes that the center of a small nondiffusing spherical particle follows an undisturbed fluid streamline near a larger collector until the particle and collector touch, whereupon the particle is retained by adhesion. We have illustrated this for the case of a cylinder in Fig. 8.3.2, taken from Spielman (1977). This simple model neglects any lubrication effects between the particle and the collector, as well as surface attraction. Electro-kinetic phenomena would also need to be considered if the particles and collector were charged. 

The zeta potential of a particle is calculated from electro kinetic phenomena such as electrophoresis, streaming potential, electro-osmosis and sedimentation potential. Each of these phenomena and the determination of zeta potential by using each technique will be discussed briefly in this section. 

On the other hand, investigat ions of later years made it pretty clear that the evaluation of the C -potential from electro-kinetic phenomena presents more difficulties than was originally supposed. There are practically no cases standing the test of even moderate criticism in which determinations of s for one system with different methods give concordant results. This may be explained partly by the difficulties of getting really comparable surfaces for the different experiments, partly by the difficulties in the interpretation of electro-kinetic phenomena. And in all interpretations of electrokinetics we always retain the fundamental difficulty that even if C could be calculated exactly, the place of the slipping plane is by no means self-evident, so that farther-reaching conclusions remain open to doubt. 

Synergistic effects were observed when electric and acoustic fields were appfied simultaneously. The coupling mechanism is befieved to be due to a combination of effects induced by cavitation and electro-kinetic phenomena. 

The theoretical description of nonlinear electro-kinetic phenomena is challenging and not yet... 

Dukhin SS, Deryaguin BV (1974) Electro-kinetic phenomena. In Matijevic E (ed) Surface and colloid science. Wiley, New York... 

There are many applications of nonlinear electro-kinetic phenomena in microfluidics. For example, the dielectrophoretic motion of particles and cells is used for separating and concentrating biological samples. Electrokinetic flow instability and electrothermal effects can be used for microfluidic mixing. 

Chapter 3 deals with theoretical and experimental studies of thermo-osmosis of liquids and gases along with thermo-osmotic concentration differences. Correlation with kinetic theory has also been attempted. Chapter 4 is concerned with experimental and theoretical studies of electro-kinetic phenomena, e.g. electro-osmosis and streaming in a system containing two subsystems separated by a membrane. Relationship with Helmholtz double layer theory has been examined with a view to provide physical interpretation of phenomenological coefficients. Theory and experiment have been compared to assess the range of validity of thermodynamic theory. Chapters 3 and 4 are concerned with discontinuous systems involving a membrane as barrier. 

In spite of the above difficulties, a simple theory [26-28] based on Helmholtz model yields a microscopic picture which is useful in understanding the role of pore size and channel length along with the electrical characteristics of this interface in electro-kinetic phenomena. Whereas the macroscopic theory based on irreversible thermodynamics does not depend on any model, the theory discussed below would be valid provided the situation conforms to the model. Both approaches are complementary in understanding the phenomena. 

The efficiency of energy conversion may also be estimated in view of the interest in the engineering applications of electro-kinetic phenomena during recent years [58-61]. One may define the efficiencies of energy conversion and E, which are related to coupling in electro-osmosis and streaming potential, as follows ... 

H.A. Abramson, Electro-kinetic Phenomena and Their Application to Biology and Medicine, American Chemical Society Monograph, Chemical Co. Inc., New York, 1934. 

Steady-state thermodynamics in the linear range provides a good glimpse of the non-equilibrium region close to equilibrium. The utility of steady-state thermodynamics is illustrated in the case of electro-kinetic phenomena in Parts Two and Three in the regions more and more distant from equilibrium (non-linear steady state, bistability, oscillations, pattern formation) including complexity and complex phenomena. 

Non-linear flux equations in electro-kinetic phenomena... 

It is obvious that ORR is obeyed. Thus, in case of chemical reactions, linear and non-linear flux equations similar to the case of electro-kinetic phenomena are predicted and ORR between first-order cross-coefficients is also obeyed. However, experimental studies so far have not been made, although triangular reaction of the above type for isomerisation of Aa - pentenoic acid has been investigated from a different viewpoint [25]. 

Since electro-kinetic systems can be maintained in the far-from-equilibrium region to any desired extent by controlling the variables, they constitute a very good system for the study of dynamic instability from experimental angle. A brief discussion of bistability and oscillations in electro-kinetic phenomena from an experimental point of view is given below. 

In electro-kinetic phenomena, bistability was studied by several groups in a system of following type [35-38] the system was as follows. The plots of / (current) versus A were found to be typical N-shaped curves (Fig. 8.6). These N-shaped curves have been referred to as flip-flop type. 

A typical example of bistability in electro-kinetic phenomena [35-38] is demonstrated in Fig. 8.6, which is essentially the current-voltage curve obtained when solutions of different concentrations of the electrolyte are kept on the two sides of the membrane. Current is passed and the transmembrane potential A4> is recorded. 

Recent experiments have shown that bistability is not always observed in electro-kinetic phenomena. Whereas bistability is observed in the case of pyrex sinter, this is not so in the case of millipore filter [37]. In the case of pyrex sinter, the equation relating I and A(f) is non-linear and has cubic terms in A. Hence, bistability is expected in this case, whereas this is not so in the case of millipore filter, since I versus A equation is only quadratic in A(f). 

In the case of bistability of electro-kinetic phenomena, dependence of the transmembrane current on the applied potential difference is investigated when the pressure difference across the membrane is held constant [31, 33, 34] and a concentration difference is maintained on the two sides of the membrane. The current (/) increases with the transmembrane potential s4>. On attaining a certain value, it suddenly decreases (discontinuously) and then again increases linearly with slope much smaller than that found in the initial state. An N-shaped current-voltage curve [31, 39] is obtained, which is called the flip-flop type. 

In Chapters 3 and 4, it has been pointed out that on application of force in the form of temperature difference, potential difference or pressure difference, the development of steady thermo-osmotic pressure, electro-osmotic pressure or streaming potential takes some time. Similar situation occurs when these forces are withdrawn, resulting in the decay of steady state. Build-up and decay in the case of electro-kinetic phenomena have been found to be exponential (Section 4.6). Detailed analysis of the relaxation phenomena and co-relations between the relaxation time and membrane composition have been reported. 

For simpler phenomena such as thermo-osmosis, electro-kinetic phenomena, thermal diffusion and Dufour effect, the linear thermodynamics of irreversible processes is valid in a wide range as indicated by the experimental results discussed in Chapters 3-5. It may be noted that Onsager relations for thermal diffusion can be proved by ETT [2]. 

The complete mathematical expression for the double layer incorporating the Stern layer is quite complex and will not be given here. However, its existence and related effects are quite significant for practical studies of electro-kinetic phenomena discussed below because it is if/s that is actually being estimated in such procedures. When a charged particle moves relative to an electrolyte solution, or a solution moves relative to a charged surface, viscosity effects dictate that only that portion of the electrical double layer up to (approximately) the Stern layer will move. The ions in the Stern layer will remain with the surface. The dividing line between movement with the solution and that with the surface is referred to as the shear plane (Fig. 5.6). The exact... 

Flow pipes of 10-100-nm diameter attract attention [51] in part due to the development of new fabrication methods. Sensing based on nanofluidic devices is an emerging field [52,53], and electro-kinetic phenomena play a significant role [54,55]. Nanofluidic slippage phenomena have been observed [56], which in future may lead to nanoflow devices that are more effective when compared to theoretical prediction based on simply scaling microflow characteristics. 

In order to use the Fairbother-Mastin approximation for surface conductivity correction [36], measurements at a concentration high enough to neglect electro-kinetic phenomena (0.1 M NaCl) were also made and zeta potential was determined by means of Equation (9.11) [53] ... 

In response to a growing literature on the the subject of adsorption of gases onto solids (including physical adsorption, chemisorption and heterogeneous catalysis) this book was written to examine particularly some of the more fundamental properties of various liquid interfaces. Eight well-referenced chapters describe the physics of surfaces, electrostatic phenomena, electro-kinetic phenomena, adsorption at liquid interfaces, properties of monolayers, reactions at liquid surfaces, diffusion through interfaces, and disperse systems and adhesion. 

Because of the nonlinear (with respect to the applied field) nature of the electro-orientation effects, with the added difficulty of the nonspherical shape of the LPs, a quantitative explanation of the phenomenon is still lacking. However, these results have stimulated the investigation of electro-kinetic phenomena in bidisperse systems for cases where the quantitative evaluation and comparison with models are easier because of the sphericity and monodispersity of both the LPs and the SPs. 

A COMPARISON OF THE RESULTS OF DIFFERENT ELECTRO-KINETIC PHENOMENA. THE VALUE OF IN DIFFERENT CIRCUMSTANCES... 

A comparison of the results of different electro-kinetic phenomena. The... 

---