Electro-osmosis zeta potential measurement

Particle charge plays a major role on the stabilization of colloidal systems. Especially when nanoparticles are stabilized by an adsorption layer of polyelectrolytes, zeta potential measurements are very useful. The stabilization of the nanoparticles results from a combination of ionic and steric contributions. The zeta potential can be detected by means of electro-osmosis, electrophoresis, streaming potential, and sedimentation potential measmements. The potential drop across the mobile part of electric donble layer can be determined experimentally, whenever one phase is made... 

With electro-osmosis data, on the other hand, interpretation is not subject to the complexities of the electrophoretic measurement. Analysis of zeta potential is straightforward, and a wide range of pH can be employed. In this light it would be promising to characterize ceramic and mineral materials of a wide variety of compositions and forms, e.g., powders and processed plates. 

Electrophoresis The most familiar electrokinetic experiment consists of setting up an electric field, E, in a solution containing charged particles and determining their velocity. The particle velocity, V, is measured by direct microscopic observation at the stagnation point (i.e., zero velocity point for electro-osmosis at the radius 0.707i c) in a capillaiy as shown in Figure 9.19. The zeta potential is then computed... 

Electro-osmosis and streaming potential measurements of aqueous D-glucose solutions across testosterone-plug membranes have been used to determine zeta potentials and to examine the Influence of H-bonding between water molecules and those of D-glucosa. 

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. 

The above relationship shows that zeta potenticd is a little lower than the Stem potential and this is because it Is located further out from the surface of the macromolecule. The zeta potential of any colloidal solution can be calculated by electrokinetic measurements like electrophoresis, electro-osmosis and streaming potential. Though the methods are different, all lead to the same calculated value of the zeta potential for any particular system. All the methods involve the relative motion of the two surfaces in contact. 

The average velocity of the liquid during electro-osmosis is determined by Eq. (28). Using the measured average velocity data, the method described earlier can be used to calculate the zeta potential The measured total current for single-concentration systems is required to determine the specific surface conductivity Xs according to... 

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... 

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