semipermeerisen

Semipermeable membranes are barriers that allow certain substances to pass while blocking others. They are characterized by selective permeability, meaning transport depends on properties such as size, charge, polarity, and interactions with the membrane material.

Transport across these membranes occurs by diffusion of small, uncharged molecules; diffusion through transport proteins; and osmosis, the movement of solvent toward higher solute concentration.

Membrane pores and materials determine what passes. Biological membranes, such as the cell membrane, are lipid bilayers with embedded proteins that enable selective transport. Industrial and medical examples include dialysis membranes, ultrafiltration, nanofiltration, and reverse-osmosis membranes, with pore sizes spanning from submicrometer to subnanometer scales.

Common applications include desalination and water treatment, kidney dialysis, food and beverage clarification, and various biotechnology separations. In cells, semipermeable membranes maintain internal environments and enable signaling and transport processes.

Permeability is influenced by temperature, pressure differences, concentration gradients, membrane thickness, fouling, and the chemical nature of the membrane material (for example, polymer versus ceramic). There is often a trade-off between permeability and selectivity.

In engineering, permeability is described by flux and permeability coefficients, which help design and compare different membranes for specific separations.