Electrokinetic forces Electroosmosis

Four different electrokinetic processes are known. Two of them, electroosmosis and electrophoresis, were described in 1809 by Ferdinand Friedrich Renss, a professor at the University of Moscow. The schematic of a cell appropriate for realizing and studying electroosmosis is shown in Fig. 31.1a. An electrolyte solution in a U-shaped cell is divided in two parts by a porous diaphragm. Auxiliary electrodes are placed in each of the half-cells to set up an electric held in the solution. Under the inhuence of this held, the solution starts to how through the diaphragm in the direction of one of the electrodes. The how continues until a hydrostahc pressure differential (height of liquid column) has been built up between the two cell parts which is such as to compensate the electroosmotic force. 

An innovative technology called the "lasagna" process is based on the electrokinetic phenomenon called electroosmosis. The lasagna process was created to treat difficult wastes in low permeability, silt- and day-laden soils (40). The lasagna process is so named because it consists of a number of layered subsurface electrodes and treatment zones. These layers can be constmcted either horizontally where contaminants are forced to more upward or in vertical position where lateral contaminant movement is desired. 

In the presence of an external electric field, the nanoparticle mainly moves due to electrophoresis and electroosmosis (the electrokinetic effects). Here, it should mention that the Brownian motion is one of the main signatures of the nanoparticle motion. However, it was shown previously that the effect of the Brownian force on the nanoparticle is negligible compared with the electrokinetic effects (the electrophoretic and the electroosmotic forces) [5]. In the presence of the external electric field, the nanoparticles are mainly manipulated by the electrokinetic effects, and the Brownian force has negligible effect on the nanoparticle motion. 

The motion of electrically charged particles or molecules in a stationary medium under the influence of an electric field is called electrophoresis. In such transport the electric force is applied through a potential difference between electrodes. Selective use of the Lorentz force by applying a magnetic field can also induce such movement. Electrophoresis and electroosmosis are two key modaUties of electrokinetic transport which are very useful in micro- and nanofluidics for a variety of apphcations including biomedical (bio-NEMS, etc.), fuel cell, and micro total analysis systems (/r-TASs). In electroosmosis the bulk fluid moves due to the existence of a charged double layer at the solid-hquid interface. While one-dimensional electrophoresis is more commonly used, two-dimensional electrophoresis may also become a useful tool for the separation of gel proteins based on isoelectric property. 

Electrokinetic phenomena refers to dynamic processes that occur when viscous or electrical forces are applied to a charged interface. The most common of these phenomena are electrophoresis, electroosmosis, streaming potential and sedimentation potential. 

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