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What is micro and nano fluidics?

 

Micro and nano fluidics deals with the behavior, control and manipulation of fluids that are geometrically constrained to micro and/or nanoscale. As dimensions shrink, forces at interfaces become more important due to the increasing ratio of interfacial area and volume. Electrical force offers advantages relative to the conventional pressure-driven flows in macroscale. Our research focuses on understanding the electrokinetic transport phenomena in micro and nano scale channels and pores.

Electrokinetic phenomena includes: Electroosmosis, Electrophoresis, Streaming Potential and Sedimentation Potential.

Electroosmosis

When in contact with electrolytes, many solid substrates acquire a surface charge and attract oppositely charged ions, creating thin layers of charges next to it, called electrical double layers (shown below). Under an external electric field, the fluid in these electrical double layers acquires a momentum and drags the fluid in the bulk by virtue of its viscosity. The resulting fluid motion is calledas electro-osmotic flow (Probstein, 2003).

Electrical double layer

Electrophoresis

Electrophoresis is the most known electrokinetic phenomena. It refers to the motion of charged particles related to the fluid under the influence of an applied electric field.

Electrophoresis

Streaming Potential

When an electrically conducting fluid is passed through a channel or tube under an imposed pressure drop, there is an electrical potential difference set up as a result since the net current in the channel must vanish(i.e. there are no upstream and downstream electrodes). This potential is called streaming potential. The streaming potential is usually very small and it tends to oppose the fluid flow.

Streaming potential

Sedimentation Potential

The sedimentation potential also called the Dorn effect is the potential induced by the fall of a charged particle under an external force field. It is analogous to electrophoresis in the sense that a local electric field is induced as a result of its motion. Just as in electroosmotic flow the fall ofa particle induces a streaming current caused by the distortion of the electric double layer and is similar to that described in the section on electrophoresis.

Sedimentation Potential

Reference

Probstein RF (2003), Physicochemical Hydrodynamics: An Introduction, 2nd edn. Wiley-Interscience.