Calculation of unstirred layer thickness in membrane transport experiments: a survey

It has long been recognized that measurements of the permeability characteristics of membranes (and of epithelia) may be strongly influenced by the presence of unstirred, or diffusion, layers adjacent to the membranes: see Dainty (1963) for the first systematic discussion of the subject in a biological context and Barry & Diamond (1983) for an important recent review. Consider a homogeneous, plane, uncharged membrane separating two solutions of the same solute at different bulk concentrations C b+ and C b- (Fig. 1), but at the same hydrostatic pressure and electrostatic potential (note that in this paper subscripts + and − refer to the two sides of the membrane, not to cation and anion parameters; electroneutrality is assumed throughout).