Field-flow fractionation for colloids, macromolecules and particles

4 Field-flow fractionation for colloids, macromolecules and particles 

If the flow in the channel is laminar and fully developed, then i/,y = 0 and 

If there are two macromolecular species a and b, the characteristic thicknesses of their profiles extending fi om the wall out are and db, respectively. Species subjected to a lower Uiy and possessing a higher Dj, will have a larger d,-. Therefore the larger species, whose diffusion coefficient at infinite dilution may be described by the Stokes-Einstein equation (3.3.90c) 

This field induced macromolecular migration velocity Uiy normal to the channel wall and toward the wall at y = 0 

Field-flow fractionation exploits this difference in the distance of the mean of the species profile from the channel wall hy coupling it with the velocity profile in the channel. In laminar channel flow with a parabolic velocity profile (equation (6.1.2h)), the larger molecules are then concentrated in the slower axial velocity zones closer to the 

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