Molly Ayala
Electro-osmosis, also known as electro-osmotic flow (EOF), is the movement of liquid through a capillary tube, membrane, or microchannel under the influence of an electric field. It was first reported in 1807 by Ferdinand Friedrich Reuss in an unpublished lecture and was later discovered independently in 1814 by English chemist Robert Porrett Jr. Electro-osmosis is commonly used in chemical analysis, soil analysis, and microfluidic devices, and plays a role in the transport of solutions through conductive plant tissues. The technique is also used in controlling rising damp in buildings, although its effectiveness in this application is controversial.
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What You'll Learn
Electro-osmosis is the movement of liquid through a porous membrane
Electro-osmosis is a process that involves the movement of liquid through a porous membrane. It is a phenomenon that has been exploited by humans for various applications, including food preservation and chemical analysis. This process is driven by the application of an electric field or potential difference across the membrane, resulting in the migration of water and dissolved substances through the pores. The size of the pores is not a limiting factor, as electro-osmotic velocities are independent of conduit size.
In chemistry, electro-osmosis is described as the motion of liquid induced by an applied potential across a porous material, membrane, or any other fluid conduit. This motion is caused by the Coulomb force, which acts on the net mobile electric charge within the solution when an electric field is applied. The resulting flow is termed electroosmotic flow, and it plays a crucial role in chemical separation techniques such as capillary electrophoresis.
Electro-osmosis is particularly significant in small channels, where it can be utilized for self-pumping pores powered by chemical reactions. This principle has been applied in fuel cells, where electro-osmosis causes protons to drag water molecules from the anode to the cathode through a proton exchange membrane (PEM). This movement of water molecules is essential for the functioning of the fuel cell.
In vascular plant biology, electro-osmosis provides an alternative explanation for the movement of polar liquids through the phloem. Companion cells contribute to the cyclic withdrawal of ions (K+) from sieve tubes, leading to the polarisation of sieve plate elements and the subsequent upward movement of water molecules and solutes. This understanding of electro-osmosis has been supported by experiments conducted by St. Petersburg University graduates, who observed the movement of electrolyte solutions in plant tissues toward a cathode when direct electric current was applied.
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It is caused by an electric field applied to a fluid
Electro-osmosis is the movement of liquid through a porous material in response to an electric field. It is caused by an electric field applied to a fluid, usually via electrodes placed at inlets and outlets. The flow of liquid is induced by an applied potential across a porous material, capillary tube, membrane, microchannel, or any other fluid conduit.
The electric field applied to the fluid induces a net charge in the electrical double layer to move by the resulting Coulomb force. This results in what is known as an electroosmotic flow. This flow is a plug flow, which means that its velocity profile is approximately planar, with slight variation near the electric double layer.
Electro-osmotic flow is most significant when in small channels and is an essential component in chemical separation techniques, notably capillary electrophoresis. It can occur in natural unfiltered water, as well as buffered solutions. It was first reported in 1807 by Ferdinand Friedrich Reuss in an unpublished lecture before the Physical-Medical Society of Moscow.
Electro-osmosis can also be used for self-pumping pores powered by chemical reactions rather than electric fields. This approach, using H2O2, has been demonstrated and modeled with the Nernst-Planck-Stokes equations.
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It is used in controlling rising damp
Electro-osmosis is a scientific theory that has been proposed as a method of controlling rising damp in buildings. Rising damp is the process by which moisture rises from the earth into walls through capillary action. Electro-osmosis involves the application of a small electric current to the damp wall, which is thought to interfere with the natural electrical potential that develops between the wall and the earth, thereby depressing the rise of moisture.
The electro-osmosis system involves drilling a series of holes into the outside brickwork just above ground level and inserting titanium anodes into the holes. These anodes are then linked by a connecting wire, and a small electric current is passed through them. The charge created by this process repels the rising moisture molecules, pushing them back down the walls and into the ground. As long as this positive charge is maintained, the walls will remain dry.
The Timberwise electro-osmosis system is one such system that operates on this principle. It is designed to work in all types of masonry, including brick, stone, composite walls, and concrete. The system features a control unit that automatically adjusts to the level of dampness in the wall. After the titanium damp course is fitted, a small voltage is applied to it, causing the titanium wire in contact with the wall and anode sections to conduct electricity. Over time, an insoluble film of titanium dioxide builds up at the titanium-wall interface, reducing further electrical conduction from the wire. The anodes continue to conduct electricity, maintaining the wall potential.
While some sources claim that electro-osmosis systems are effective in controlling rising damp, particularly in structures with thick walls, others argue that there is little evidence to support these claims. Some have even gone as far as to call these systems a fraud, stating that independent research does not support their effectiveness.
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It can be used to dewater sludge cake
Electro-osmosis is a process that involves the movement of liquid through a porous material in response to an electric field. It is used to dewater sludge cake, which is a semi-solid colloid, by applying an electric current to drive a positively-charged liquid, such as water, through the sludge cake towards a negatively-charged cathode. This method of dewatering does not rely on mechanical force or evaporation by heat, but rather on electrical polarity differences between solids and liquids to efficiently pull water out of the sludge cake.
The Electro-Osmosis Dehydrator (ELODE) is a non-mechanical sludge dewatering machine that leverages electro-osmosis to dehydrate sludge cake. It is a compact machine that can easily be retrofitted in line with many existing presses. One of the main advantages of ELODE is its energy efficiency, as it consumes much less energy than thermal drying methods, helping operators save on operating costs. In just three minutes, the ELODE machine can reduce cake weight by 50% or more, consuming 300 kWh to remove one ton of water.
The process of electro-osmosis dewatering involves applying an electric field to the fluid between two electrode layers, inducing an electrostatic Coulomb force that makes the fluid flow. This technique is not limited to sludge cake dewatering and has applications in chemical analysis, soil analysis and processing, and microfluidic devices. For example, in soil analysis, the electricity applied to the soil results in heating, which increases the mobilization of volatile organics and enhances electro-osmotic permeability by lowering the viscosity of the pore water.
Electro-osmosis can also be used for self-pumping pores powered by chemical reactions rather than electric fields. This approach, using H2O2, has been demonstrated with the Nernst-Planck-Stokes equations. In vascular plant biology, electro-osmosis is offered as an alternative explanation for the movement of polar liquids via the phloem, differing from theories such as the mass flow hypothesis.
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It is an essential component in chemical separation techniques
Electro-osmosis is the migration of water and its contents through a porous membrane due to a potential difference. This potential difference is caused by the flow of electric charge through the membrane. The size of the pore does not matter, and the flow rate is primarily determined by the applied voltage. This technique is widely used in chemical analysis, soil analysis, and processing, as well as in microfluidic devices. Electro-osmosis is an essential component in chemical separation techniques, particularly capillary electrophoresis, where chemicals are separated according to their electrophoretic mobility.
In the context of chemical separation techniques, electro-osmosis plays a crucial role in several applications. For instance, it is used in the removal of organics and the dewatering of sludge cake, where it offers a more efficient alternative to mechanical force or evaporation. The ability to separate fluids on an atomic level through controlled electro-osmotic flow will also be valuable in drug discharge applications. Electro-osmosis is also relevant in ion-exchange membrane separation processes, specifically electrodialysis, where it influences the efficiency by facilitating the transport of water between the diluate and concentrate solutions.
Furthermore, electro-osmosis is employed in fuel cells, where it causes protons to move through a proton exchange membrane (PEM), simultaneously dragging water molecules from the anode to the cathode. This phenomenon has also been explored in vascular plant biology, where it provides an alternative explanation for the movement of polar liquids through the phloem, contrasting with theories such as the mass flow hypothesis.
Electro-osmotic flow is induced by applying an electric field to a fluid between two electrode layers, generating an electrostatic Coulomb force that propels the fluid. This flow is particularly significant in small channels, where it can be effectively utilized for chemical separation. The control of this flow is crucial but challenging due to the intricate factors involved, and it is typically managed through numerical methods and simulations.
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Frequently asked questions
Electro-osmosis is the movement of liquid through a porous material in response to an electric field.
Electro-osmotic flow is caused by the Coulomb force induced by an electric field on net mobile electric charge in a solution.
In fuel cells, electro-osmosis causes protons moving through a proton exchange membrane (PEM) to drag water molecules from the anode to the cathode.
Electro-endosmosis.
Electro-osmosis is used to dewater sludge cake, using an electric field rather than mechanical force or evaporation by heat.
