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One example is capillary electrophoresis, [10] [12] 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.
For example, in capillary sequencing of DNA, the sieving polymer (typically polydimethylacrylamide) suppresses electroosmotic flow to very low levels. [10] Besides modulating electroosmotic flow, capillary wall coatings can also serve the purpose of reducing interactions between "sticky" analytes (such as proteins) and the capillary wall.
Electroosmosis is the motion of liquid induced by an applied potential across a porous material, capillary tube, membrane or any other fluid conduit. Electroosmotic flow is caused by the Coulomb force induced by an electric field on net mobile electric charge in a solution.
Electroosmotic pumps are fabricated from silica nanospheres [6] [7] or hydrophilic porous glass, the pumping mechanism is generated by an external electric field applied on an electric double layer (EDL), generates high pressures (e.g., more than 340 atm (34 MPa) at 12 kV applied potentials) and high flow rates (e.g., 40 ml/min at 100 V in a pumping structure less than 1 cm 3 in volume).
Capillary electrophoresis is a separation technique which uses high electric field to produce electroosmotic flow for separation of ions. Analytes migrate from one end of capillary to other based on their charge, viscosity and size. Higher the electric field, greater is the mobility.
The potential flow approach occurs in the modeling of both stationary as well as nonstationary flows. Applications of potential flow include: the outer flow field for aerofoils, water waves, electroosmotic flow, and groundwater flow. For flows (or parts thereof) with strong vorticity effects, the potential flow approximation is not applicable.
Continuous flow microfluidics rely on the control of a steady state liquid flow through narrow channels or porous media predominantly by accelerating or hindering fluid flow in capillary elements. [28] In paper based microfluidics, capillary elements can be achieved through the simple variation of section geometry.
The equation is derived for capillary flow in a cylindrical tube in the absence of a gravitational field, but is sufficiently accurate in many cases when the capillary force is still significantly greater than the gravitational force. In his paper from 1921 Washburn applies Poiseuille's Law for fluid motion in a circular tube.