What Is Electro-Osmosis?

Andrew Kirmayer

In a phenomenon called electro-osmosis, fluids can be moved through tiny spaces in a barrier when there is an electrical charge. It occurs in natural substances such as soil as well as in masonry products like brick and cement. Analysis of electro-osmosis physics is conducted by modeling small tubes called microchannels. The wall of a channel within soil or concrete has positively charged ions. The inner surface is negatively charged, creating the electrical double layer that causes the fluid to move.

Capillary action is responsible for moving water through the xylem of a vascular plant.
Capillary action is responsible for moving water through the xylem of a vascular plant.

Electro-osmosis is also affected by the type of material lining the space, as well as the fluid moving through it such as water or chemicals used in industrial processes. Fluids typically move at the same speed through the width of the tube or space, but at the microscopic level, a layer of slower moving liquid is found where the positive charge is. In biology, this can explain how fluid is moved through the small vesicles within plants, which is known as electro-osmosis vascular plant biology. Water drawn from the soil must be drawn through the stems and branches of trees and plants for nutrients to reach everywhere.

Other processes occur along with this type of osmosis, such as the motion of charged particles in a fluid, or electrophoresis, and the actual movement of this fluid within the electrical field, which is called electroendosmosis. The characteristics of these processes can be measured and modeled scientifically. This has enabled engineers to create ways to use electro-osmosis as an advantage rather than it being a burden on homes and civil engineering projects.

Humans have made use of this to decontaminate water, and in creating barriers which make soil on hills more stable. Soil characteristics can be altered naturally by adjusting how thick the electrical double layer is, which can affect the acidity of the soil. The change in moisture content also allows for more efficient ways to change the volume and adherence of different soil types. These changes can be modeled to scale in the laboratory, so engineers know how to best utilize electro-osmosis physics in the real world.

Several ways have been devised in keeping water out of basements, and electro-osmosis is an efficient way to keep moisture out of walls. Water can be kept out of wall cavities using an electro-osmosis damp proofing system which adds an electrical voltage, via titanium anodes, to prevent fluids in the ground from entering in the first place. The moisture then flows back harmlessly into the ground.

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