Permeate

Permeate is a term with both verb and noun uses. As a verb, permeate means to spread through or to pass through a barrier or substance, often gradually or completely. The word derives from Latin permeare, through + via; entered English in the 17th century. As a noun, especially in science and engineering, permeate refers to the portion of a mixture that passes through a membrane or barrier during filtration or separation.

In biology and chemistry, permeability describes how easily a substance crosses a membrane. Factors include molecule size, polarity, solubility in the membrane, and the presence of transport proteins. Permeation and diffusion are related processes; Fick's laws describe the rate of transport. In membrane technology, permeate is the liquid or gas that has passed through the membrane, while the remaining portion is called retentate or concentrate. The permeate's composition depends on membrane selectivity, operating conditions (pressure, temperature), and feed composition.

In everyday usage, permeate is used figuratively: a smell or aroma can permeate a room; moisture can permeate fabric or leather, indicating widespread diffusion.

Examples: In desalination by reverse osmosis, the permeate is the purified water; in gas separation, the permeate is the desired product gas. The term emphasizes the movement of material across a barrier rather than the barrier itself.