By Sunil Bhardwaj

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The charged colloidal particles move under the influence of an electric field during electrophoresis. If electrophoresis is avoided by maintaining the particles stationary, the dispersion medium will move under the influence of an electric field. This movement of dispersion medium under the influence of an electric field is called electro-osmosis.

The colloidal solution is placed in compartment X. The compartments Y and Z are filled with the dispersion medium. X is separated from Y and Z by using porous partitions P and P'. The levels of the dispersion media in the capillary tubes T and T' are noted. When a potential is applied at the electrodes, there will be flow of dispersion medium from one side to the other.

This can be observed by looking at the levels of dispersion medium in the capillary tubes T and T’. The level of dispersion medium is observed to fall on one side and rise on the other. If colloidal particles carry negative charge, the diffused layer has a resultant positive charge. Therefore, the dispersion medium will move towards negative electrode and if the particles are positively charged, the dispersion medium will move towards positive electrode since it has now resultant negative charge. In this method, the electroosmosis pressure is related to zeta potential by the equation $$ \xi = \frac { P\pi { r }^{ 2 } }{ 2DF } $$ where, P = electroosmosis pressure in Nm2 ; r = radius of the capillary in cm; E = applied potential in e.s.u. and D = dielectric constant of the medium.