Plug, electro-osmosis through

The method can also be applied to the electro-osmosis through a plug (without surface conductance) ... 

It may be necessary to correct the experimental data for effects such as electro-osmosis in the measuring capillary tube and electro-osmotic leak back through the plug. 

In electro-osmosis (Fig. 5), when an externally applied electric field gradient operates across the wet clay, water is moved from the anode (the positive electrode) to the cathode (the negative electrode) that is, there is a movement of the liquid phase through the stationary solid phase (a clay, soil, capillary, or porous plug, etc.) in response to an applied electric field, as shown schematically in Fig. 6, taken from Probstein. ... 

Electro osmosis This technique involves the movement of a liquid relative to a stationary charged surface (e.g. a capillary or porous plug) by the application of an electric field. Experimentally, zeta potentials may be measured by this method by means of an apparatus such as that shown in Figure 10.10. The potential is supplied by electrodes, as shown in the schematic, and the transport of liquid across the tube is observed through the motion of an air bubble in the capillary providing the return flow. For water at 25°C, a field of about 1500 V/cm is needed to produce a velocity of 1 cm/s if the surface potential (xjro) is 100 mV. 

In electro-osmosis, the volume flow rate (dV/df) is measured through a capillary or a porous plug which can be treated as a series of capillaries. Using the Smoluchowski equation (Eq. 3.15), this is related to the zeta potential. For flow in a capillary of cross-sectional area A, we obtain... 

Electro-osmosis is one of the electrokinetic effects (q.v.). If a potential difference is applied between the ends of a capillary tube containing electrolyte, or across a plug of finely divided material (which can be regarded as a bundle of capillaries), a movement of the liquid is observed. This is the reverse effect of electrophoresis (q.v.), where particles move through a liquid which is stationary. The effect can be studied in an apparatus such as that sketched in figure E.IO. A plug of the finely divided material is in the centre of the tube, which is completely filled with liquid, and a potential of, say, 200 V is applied between the two calomel electrodes. An air-bubble trapped in the capillary measures the rate of movement of the liquid. 

The streaming potential effect is the reverse of electro-osmosis (q.v.) when liquid flows through a capillary tube or through a plug of finely divided material, a potential difference arises between the two ends of the material (figure S.2). The hydrostatic pressure is measured by the difference of level maintained by the reservoirs, and a plug of the material under study is contained between the two platinum gauze electrodes, which are connected to a valve potentiometer. 

The apparatus used for measuring electro-osmosis can also be used for obsendng streaming potentials. When the liquid is forced through the porous plug by an external pressure, a potential difference (the streaming-potential) can be measured betv/een the... 

Although a direct measurement of the electro-osmotic velocity (ve) is possible it is more usual to determine the volume of liquid displaced through a capillary or porous plug by electro-osmosis If we consider a capillary with a constant cross-section Of the volume displaced per sec is given by... 

Another method of determination of the electro-osmosis consists in the measurement of the counter pressure generated by the electro-osmotic displacement of the liquid Th counter pressure causes the liquid to flow back through the capillary or plug In the stationary state the electro-osmotic flow is just counterbalanced by the backflow. 

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