Electroosmotic flow (or electro-osmotic flow, often abbreviated EOF; synonymous with electroosmosis or electroendosmosis) is the motion of liquid induced by an applied potential across a porous material, capillary tube, membrane, microchannel, or any other fluid conduit. Because electroosmotic velocities are independent of conduit size, as long as the electrical double layer is much smaller than the characteristic length scale of the channel, electroosmotic flow will have little effect. Electroosmotic flow is most significant when in small channels. 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. Electroosmotic flow schematic Contents 1 History 2 Cause 3 Description 4 Applications 4.1 Physics 4.2 Vascular plant biology 5 Disadvantages 6 See also 7 References 8 Further reading History[edit]
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.
∇ ⋅ U = 0 displaystyle nabla cdot mathbf U =0 and momentum ρ D U D t = − ∇ p + μ ∇ 2 U + ρ e ∇ ( ψ + ϕ ) , displaystyle rho frac Dmathbf U Dt =-nabla p+mu nabla ^ 2 mathbf U +rho _ e nabla left(psi +phi right), where U is the velocity vector, ρ is the density of the fluid, D / D t displaystyle D/Dt is the material derivative, μ is the viscosity of the fluid, ρe is
the electric charge density, Φ is the applied electric field, and ψ
is the electric field due to the zeta potential at the walls.
∇ 2 ϕ = 0 , displaystyle nabla ^ 2 phi =0, while the potential within the electric double layer is governed by ∇ 2 ψ = − ρ e ϵ ϵ 0 , displaystyle nabla ^ 2 psi = frac -rho _ e epsilon epsilon _ 0 , where ε is the dielectric constant of the electrolyte solution and ε0 is the vacuum permittivity. This equation can be further simplified using the Debye-Hückel approximation ∇ 2 ψ = k 2 ψ , displaystyle nabla ^ 2 psi =k^ 2 psi , where 1 / k is the Debye Length, used to describe the characteristic thickness of the electric double layer. The equations for potential field within the double layer can be combined as ρ e = − ϵ ϵ 0 k 2 ψ . displaystyle rho _ e =-epsilon epsilon _ 0 k^ 2 psi . Applications[edit]
Electro-osmotic flow is commonly used in microfluidic devices,[2][3]
soil analysis and processing,[4] and chemical analysis,[5] all of
which routinely involve systems with highly charged surfaces, often of
oxides. One example is capillary electrophoresis,[3][5] in which
electric fields are used to separate chemicals according to their
electrophoretic mobility by applying an electric field to a narrow
capillary, usually made of silica. In electrophoretic separations, the
electroosmotic flow affects the elution time of the analytes.
Electro-osmotic flow is actuated in a
Wikimedia Commons has media related to Electro-osmosis. Surface charge Capillary electrophoresis Electrical double layer Streaming current Induced-charge Electrokinetics Streaming potential Zeta potential Electroosmotic pump electrical double layer microfluidics electrochemistry References[edit] ^ G. F. Yao, H. A Computational Model for Simulation of Electroosmotic
Flow in Microsystems.
^ Bruus, H. (2007). Theoretical Microfluidics.
ISBN 0-19-923509-0.
^ a b Kirby, B. J. (2010). Micro- and Nanoscale Fluid Mechanics:
Transport in
Further reading[edit] Bell, F.G. (2000). Engineering Properties of Soils and Rocks, 4th ed. Chang, H.C.; Yao, L. (2009). Electrokinetically Driven Microfluidics and Nanofluidics. Levich, V. (1962). Physicochemical Hydrodynamics. ISBN 0-903012-40-5. Probstein, R.F. (2003). Physicochemical Hydrodynamics: an introduct |