Membrane transport explained with a colloidal interaction-based framework

Understanding, modeling, and predicting transfer in membrane processes remain major challenges, as they involve several coupled phenomena occurring in concentrated, non-ideal phases. Current models often treat hydrodynamic, colloidal, and interfacial effects separately, making it difficult to link microscopic interactions to macroscopic behavior such as permeation, selectivity, and fouling. This work proposes an interaction-based framework that describes membrane transport through the fundamental couplings between the fluid, colloid, and membrane phases. By reformulating transport equations in terms of these interactions, the approach reveals the minimal set of ingredients and interactions required to capture the essence of membrane transfer phenomena — the ultimate reduction before losing physical meaning. The resulting framework provides a continuous description from dilute dispersions to concentrated or consolidated states, bridging thermodynamic and mechanical regimes. Finally, the framework is applied to three representative cases illustrating how interaction complexity shapes separation. Beyond offering a new way to model transfer, this perspective helps recover the physical sense of membrane separation: connecting intuition, equations, and mechanisms into a coherent view of how membranes actually operate. Finally, controlling interactions in three dimensions — within and across the membrane structure — emerges as a promising route toward the next generation of selective and energy-efficient membranes. • A physical recipe explains membrane transfer through key interactions. • Connects intuition, equations, and mechanisms into a coherent picture. • The membrane–fluid–colloid ternary defines the core of separation. • Interactions control selectivity, osmosis, clogging and fouling. • Controlling interactions opens new paths for membrane processes.