Shear-Induced Migration and Flow Chromatography

Abstract

The presence of inhomogeneities in the flow velocity is an ubiquitous feature in nature and laboratory, from flow in tubes to motion in rivers and oceans; in contrast with an uniform velocity profile, which simply adds a displacement to the usual Fickian diffusion, inhomogeneities in the velocity profile exert a deep influence on the behaviour of diffusion whose consequences have practical interest in many situations ranging from microfluidic chromatographic flows to pollutant transport in oceans and atmosphere. Some of these influences are purely dynamical; others, however, modify the equations of state and their analysis requires the use of non-equilibrium thermodynamics. In this chapter, we consider several examples of the modification of the usual diffusion behaviour in the presence of a velocity gradient.