Bridging membrane transport models

Analysis of transport processes in swollen polymer networks bridges two classical models The movement of small molecules (e.g., water, organic solvents, gases) through polymeric membrane materials is critical for a wide range of applications including water desalination and filtration, crude oil refining, and some controlled-release devices ( 1 – 4 ). For decades, researchers have used two classical models to describe fluid passage through membranes: solution diffusion and pore flow ( 1 ). Although each model is generally accepted to describe certain materials, the mechanism of how solvent passes through materials whose structure falls between the two models, such as swollen polymers, has been debated since the 1960s. On page 186 of this issue, Hegde et al. ( 5 ) present a two-phase fluid-solid model and perturbation analysis to demonstrate that both the solution-diffusion model and the pore-flow model ultimately describe the same driving force for solvent passage in swollen polymers.