Electro-osmosis in a capillary

Electro-osmosis in a capillary. In the local model of the previous section we assumed for the flow rate v the phenomenological generalized Darcy s law (6.3.3a) with constant coefficients. 

Figure 2.8 Electro-osmosis in a capillary. The double-layer ion sheath migrates, and this brings...

The electro-osmotic mobility b is the coefficient of linear response. This ubiquitous approximation, which can be justified in the limits of thin double layers and/or weak fields, greatly limits possible flows and particle motions. With constant zeta and thin double layers, for example, electro-osmosis in a capillary is irrotational (free of vortices), and particles of different shapes and sizes have the same electrophoretic mobility b = U/E and thus cannot be separated. 

---