Electro-endosmosis

As the permeability of the membrane for ions of different charge signs largely varies, salt diffusion through a membrane is accompanied by the establishment of a membrane potential. These concentration or dialysis potentials play an important part in the study of membrane phenomena. With the above described model, the phenomenon of electro-endosmosis i.e. the transport of solvent across a membrane under the influence of an electric field, can easily be explained also. 

If a membrane separates two identical liquids or solutions and a potential difference is applied across the membrane, there results a flow of liquid through the pores of the membrane. This phenomenon is known as electro-endosmosis, or as electro-osmosis. A simplified version of the theory is as follows. 

The movement of a liquid, when in contact with a charged surface, situated in a strong electric field is called electro-endosmosis. The flow of liquid through a silica tube under electro-endosmosis is of plug form, and does not exhibit the parabolic velocity profile that normally occurs in Newtonian flow. As a result of this, there is little, or no, resistance to mass transfer similar to that in open tubular columns. It follows, that there is very little band dispersion when the flow is electrosmotically driven and consequently extremely high efficiencies can be attained. 

Unfortunately, most chiral substances are not ionic and so are not appropriate for electrophoretic separation. However, it has been shown that neutral, uncharged substances can be separated by partitioning the solutes between an ionic phase and miscelles containing long aliphatic chains. In effect, this is replacing an electrophoretic technique by a chromatographic system, where the mobile phase is driven by electro endosmosis. 

Cf. Rutgers and coworkers on streaming potential and electro-endosmosis, and Overbeek on electro-phoresis. 

Faitbrother, F. Stubbs, A. E. (1935). 119. Studies in electro-endosmosis. Part VI. The bubble-tube method of measurement. Journal of the Chemical Society (Resumed), 527-529. Fang, W.-F., Ting, S.-C., Hsu, C.-W., Chen, Y.-T., Yang, J.-T. (2012). Locally enhanced concentration and detection of oligonucleotides in a plug-based microfluidic device. Lab on a Chip, 12, 923-931. 

Fairbrother E, Stubbs AE. Studies in electro-endosmosis, part VI The Bubble-tube method of measurement. J. Chem. Soc. 1935 1 527-529. 

In our previous discussion we studied in brief the movement of the colloidal particles under the influence of an electric field. If the particles are now forcibly stopped from moving, we will see that the dispersion medium now starts moving. This movement of fluid in an electric field is called electro-endosmosis or electro-osmosis. 

Fairbrother F, Stubb J. (1935) Studies in electro-endosmosis. Part VI. The bubble-mbe method of measurement./ CAera Soc 1 527—529. 

Electro-osmosis (also called electro-endosmosis) is the movement of a liquid with respect to a solid wall as the result of an applied potential gradient It can be observed in an arrangement shown diagrammatically in Fig. i. 

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