Binary Diffusion and Bulk Flow through a Potential-Energy Profile: A Kinetic Basis for the Thermodynamic Equations of Flow through Membranes

The flow of a two‐component solution through a potential‐energy profile is analyzed in detail. The thermodynamic flow equations of Kedem and Katchalsky are derived, along with the Onsager reciprocal relation—the equality of the osmotic‐flow coefficient and the ultrafiltration coefficient. Expressions are obtained for the solute permeability $\omega$ and the Staverman reflection coefficient $\sigma$ . It is demonstrated that contributions from equilibrium partitioning and “frictional” effects both arise from the characteristics of the energy profile. The role of the pressure gradient as the driving force for osmotic flow is stressed.