The combination of electrostatics with fluid mechanics results in the rich behavior exhibited by Plasmas (ionized gases). The role of electrostatics in the hydrodynamics of liquids is much less appreciated and has a much smaller community of devotees. The great strength of electrostatic forces makes liquids charge neutral on all length scales larger than the Debye length which is typically between 1 and 10 nm for typical electrolytes. Therefore charge separation takes place only in thin interfacial layers and the electrostatic force, like the force of surface tension is an interfacial force that scales as the area rather than the volume of a liquid drop. Electrostatic interactions start to play an important role in hydrodynamics typically on length scales of a 100 microns or less. For example, electrostatic forces can actually drive a fluid flow -- Electroosmotic flow -- that has some important practical applications. Electrophoresis -- the motion of charged macromolecules in water is at the heart of DNA sequencing technology, and is a favorite separation technique in the biologist's toolkit. The Brownian dynamics of charged polymers in ionic fluids determine how the machinery of biological systems function at the cellular and subcellular levels. In this talk I will first establish some fundamentals of the subject and then discuss several applications to the newly emerging fields of microfluidic systems and nanotechnology.
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