Definitions

# Electro-osmosis

[ih-lek-troh-oz-moh-sis, -os-]
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 non-macroporous materials which have ionic sites and allow for water uptake, the latter sometimes referred to as "chemical porosity" ) under the influence of an applied electric field. Electro-osmosis was first described by F.F. Reuss in 1809, and has growing applications in microfluidics.

## Applications

### Vascular plant biology

In vascular plant biology, electro-osmosis is also used as an alternative or supplemental explanation for the movement of polar liquids via the phloem that differs from the cohesion-tension theory supplied in the mass flow hypothesis and others, such as cytoplasmic streaming. Principally, companion cells are involved in the "cyclic" withdrawal of ions ($K^+$) from sieve tubes, and their secretion parallel to their position of withdrawal between sieve plates, resulting in polarisation of sieve plate elements alongside potential difference in pressure, and results in polar water molecules and other solutes present being moved upwards through the phloem.

In 2003, St Petersburg University graduates based an experiment on the electro-osmosis hypothesis through the application of direct electric current to 10mm segments of mesocotyls of maize seedlings alongside one-year linden shoots used with normal conducting systems and without vascular bundles; electrolyte solutions present in the tissues moved towards the cathode that was in place, suggesting that electro-osmosis may play a role in solution transport through conductive plant tissues.

### Physics

In fuel cells, electro-osomosis causes protons moving through a proton exchange membrane (PEM) to drag water molecules from one side (anode) to the other (cathode).