Electrokinetic phenomena applications

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

Observation of this electrokinetic phenomenon involves the application of a spatially nonhomoge-neous electric field to the suspension this provoking the migration (or dielectrophoresis) of the polarized particles [48,49]. The particles will move toward the high-field region if they are more polarizable than the dispersion medium, or will be repelled toward the low-field region otherwise. 

Let us mention that dielectrophoresis has also found wide application in manipulation and sorting of particles and biological cells. Together with standard electrophoresis, it is perhaps the most often used electrokinetic phenomenon with practical applications in mind. Even particle separation can be achieved by using microelectrode arrays [55]. Based on the dielectrophoresis phenomenon, a new technique has recently become available for particle or cell separation, namely the dielectrophoresis/gravitational field-flow fractionation (DEP/G-FFF). In DEP/ G-FFF, the relative positions and velocities of unequal particles or cells are controlled by the dielectric properties of the colloid and the frequency of the applied field. The method has been applied to model polystyrene beads, but, most interestingly, to suspensions of different biological cells [56]. 

Another very important issue in this respect is the way to account for the surface conductivity. The formula of Bikerman (Equation 5.359), the correction factor to the electrophoretic mobility of Henry 3 (Equation 5.368), and the formula of O Brien and Hunter (Equation 5.371), quoted above are derived under the assumption that only the ions in the movable part (x > x Figure 5.67) of the EDL contribute to the surface conductivity, Xs- Moreover, the ions in the EDL are taken to have the same mobility as that in the bulk electrolyte solution. A variety of experimental data ° suggest, however, that the ions behind the shear plane (x < x ) and even those adsorbed in the Stem layer may contribute to Xs- Th term anomalous surface conductance was coined for this phenomenon. Such an effect can be taken into account theoretically, but new parameters (such as the ion mobility in the Stem layer) must be included in the consideration. Hence, the interpretation of data by these more complex models usually requires the application of two or more electrokinetic techniques which provide complementary information. Dukhin and van de Ven specify three major (and relatively simple) types of models as being most suitable for data interpretation. These models differ in the way they consider the surface conductivity and the connection between i and "Q. 

Electrokinetic and electrohydrodynamic instability mixing in microsystems is a complex phenomenon which researchers are only beginning to exploit and understand. Future work requires a further development of experimental models and expansion of computational simulations to better understand how the instabilities form and grow. Specific applications of electrokinetic and electrohydrodynamic instabilities are still limited. The application of these instabilities to improve mixing between components should be explored. One example is through the use of multiphase systems where electrohydrodynamic instabilities are utilized to improve component partitioning for liquid extraction devices. 

Electrokinetic remediation of groundwater and soil usually involves the use of electroosmosis and electromigration. Electroosmosis describes the phenomenon of water flow induced by application of an electrical field on porous media (14). Electromigration describes the transport of ions under the influence of an electrical field (75). The electroosmotic flux, qeo, can be written as... 

The Electrokinetic Sonic Amplitude (ESA) effect in this context refers to the generation of ultrasound by the application of an alternating electric field to a colloid. Previous reviews on the ESA have mainly focused on the determination of particle size and zeta potential from the ESA. While this is certainly a very important application of the ESA phenomenon, there is more information in the ESA spectmm than just particle size and zeta. It can be used, for instance, to determine the thickness of adsorbed polymer layers or the surface conductance under the shear plane. It is these other applications that will be our main interest here. To begin we will give an alternative explanation for the ESA phenomenon, one that allows a deeper understanding of the underlying physics. 

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