Molekülendurch

Molekülendurch is a term used in physical chemistry and materials science to describe the transport of individual molecules across a barrier, such as a polymer membrane, porous ceramic, or layered solid. The concept separates the transit of molecules from macroscopic flow and focuses on the rate and mechanism by which molecules move from one side to the other under a driving force. In practice, molekülendurch encompasses diffusion, adsorption-desorption steps at interfaces, and, for light species, quantum tunneling.

Driving forces include concentration or chemical potential gradients, pressure differences, or electric fields in charged systems. Mechanisms vary with system and scale: solution-diffusion through polymer matrices, pore-dominated transport in porous media, surface hopping across adsorption sites, and, at very small scales, tunneling through narrow barriers. The resulting transport is often temperature-dependent and may show selectivity for specific molecules.

Quantification uses permeation flux J (moles per square meter per second) and permeability P, with measurements commonly performed by time-lag experiments, uptake sorption, or tracer studies. Activation energy Ea and selectivity factors further describe the process in multicomponent systems.

Applications include gas separation membranes, vapor barriers in packaging, and routes for drug delivery or sensor devices that rely on controlled molecular passage. The term molekülendurch remains less common than standard terms such as permeation or diffusion, and its use varies across subfields.

See also: diffusion, permeation, osmosis, transport phenomena.