Electroosmotic flow

Electroosmotic flow

Electroosmotic flow (or Electro-osmotic flow, often abbreviated EOF) is the motion of liquid induced by an applied potential across a capillary tube or microchannel. Electroosmotic flow is an essential component in chemical separation techniques, notably capillary electrophoresis. Electroosmotic flow can occur in natural unfiltered water, as well as buffered solutions.

Cause

The cause of electroosmotic flow is an electrical double layer that forms at the stationary/solution interface. In capillary electrophoresis, the narrow channels are made up of silica, and silanol groups form the inner surface of the capillary column. These silanol groups are ionized above pH3. Thus, the inner surface of the channel is negatively charged. In solutions containing ions, the cations will migrate to the negatively charged wall. This forms the electric double layer. When an electrical potential is applied to the column, with an anode at one end of the column and a cathode at another, the cations will migrate towards the cathode. Since these cations are solvated and clustered at the walls of the channel, they drag the rest of the solution with them, even the anions. This results in an electroosmotic flow, not to be confused with the electrophoretic migration.

History

Electroosmotic flow was first reported in 1809 by F.F. Reuss in the Proceedings of the Imperial Society of Naturalists of Moscow. He showed that water could be made to flow through a plug of clay by applying an electric voltage. Clay is composed of closely packed particles of sand and other minerals, and water flows through the narrow spaces between particles just as it would through a narrow glass tube. Any combination of an electrolyte (a fluid containing dissolved ions) and insulating solid would generate electro-osmotic flow, though for water/silica (that is what glass or sand is, chemically) the effect is particularly large. Even so, flow speeds are typically only a few millimeters per second.

An early application of electroosmotic flow was in drying or decontaminating soil. There has been a great deal of interest and research in electroosmotic flow in the last decade, since it was realized that it provides a very efficient way to generate fluid flows in microfluidic devices, including electroosmotic pumps that can generate flow rates as large as a few milliliters per minute, and pressures as large as hundreds of atmospheres. Another reason for the increased interest in electroosmotic flow is its effect on capillary electrophoresis, where the flow tends to counteract the electric field used to drag the DNA molecule.

References

Skoog, et al. Principles of Instrumental Analysis.

Barz, D.P.J., Ehrhard. P., Model and verification of electrokinetic flow and transport in a micro-electrophoresis device, Lab Chip, 2005, 5, 949 - 958.


Wikimedia Foundation. 2010.

Игры ⚽ Поможем решить контрольную работу

Look at other dictionaries:

  • Electroosmotic pump — An electroosmotic pump (EOP), or EO pump, is used for removing liquid flooding water from channels and gas diffusion layers and direct hydration of the proton exchange membrane in the membrane electrode assembly (MEA) of the proton exchange… …   Wikipedia

  • Potential flow — streamlines around a NACA 0012 airfoil at 11° angle of attack, with upper and lower streamtubes identified. In fluid dynamics, potential flow describes the velocity field as the gradient of a scalar function: the velocity potential. As a result,… …   Wikipedia

  • Capillary electrophoresis — Infobox chemical analysis name = Capillary electrophoresis caption = acronym = CE classification =Electrophoresis analytes = Biomolecules Chiral molecules manufacturers = related = gel electrophoresis Two dimensional gel electrophoresis… …   Wikipedia

  • Glossary of fuel cell terms — The Glossary of fuel cell terms lists the definitions of many terms used within the fuel cell industry. The terms in this glossary may be used by fuel cell industry associations, in education material and fuel cell codes and standards to name but …   Wikipedia

  • Micellar electrokinetic chromatography — (MEKC), is a chromatography technique, used in analytical chemistry. It is a modification of capillary electrophoresis (CE), where the samples are separated by differential partitioning between micelles (pseudo stationary phase) and a surrounding …   Wikipedia

  • Electro-osmosis — In electrochemistry, physics and vascular plant biology, electro osmosis, also called electroendosmosis, is the motion of polar liquid through a membrane or other porous structure (generally, along charged surfaces of any shape and also through… …   Wikipedia

  • Membraneless Fuel Cells — convert stored chemical energy into electrical energy without the use of a conducting membrane as with other types of fuel cells. In Laminar Flow Fuel Cells (LFFC) this is achieved by exploiting the phenomenon of non mixing laminar flows where… …   Wikipedia

  • Microreactor — technologies developed at LLNL use micromachining techniques to miniaturize the reactor design. Applications include fuel processors for generating hydrogen, chemical synthesis, and bioreaction studies. A microreactor or microstructured reactor… …   Wikipedia

  • COMSOL Multiphysics — Developer(s) COMSOL Stable release 4.2a / October 14, 2011; 17 days ago (2011 10 14) …   Wikipedia

  • Double layer (interfacial) — A double layer (DL, also called an electrical double layer, EDL) is a structure that appears on the surface of an object when it is placed into a liquid. The object might be a solid particle, a gas bubble, a liquid droplet, or a porous body. The… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”