On Diffusion and Permeation

Stephen S. L. Peppin 1
  • 1 OCCAM, Mathematical Institute, Oxford University, OX1 3LB, UK


Diffusion and permeation are discussed within the context of irreversible thermodynamics. A new expression for the generalized Stokes–Einstein equation is obtained which links the permeability to the diffusivity of a two-component solution and contains the poroelastic Biot–Willis coefficient. The theory is illustrated by predicting the concentration and pressure profiles during the filtration of a protein solution. At low concentrations the proteins diffuse independently while at higher concentrations they form a nearly rigid porous glass through which the fluid permeates. The theoretically determined pressure drop is nonlinear in the diffusion regime and linear in the permeation regime, in quantitative agreement with experimental measurements.

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The Journal of Non-Equilibrium Thermodynamics serves as an international publication organ for new ideas, insights and results on non-equilibrium phenomena in science, engineering and related natural systems. The central aim of the journal is to provide a bridge between science and engineering and to promote scientific exchange on non-equilibrium phenomena and on analytic or numeric modeling for their interpretation.