diffusionsresistans

Diffusionsresistans, or diffusion resistance, is a property of a material or barrier that quantifies how much it opposes the diffusive transport of species such as gases, liquids, or ions across it. It is a key concept in the study of membranes, coatings, and barrier layers, influencing how well a material protects or separates substances.

In a simple, steady-state model for a homogeneous layer of thickness L with diffusion coefficient D and a sorption (partition) coefficient K between the two phases, the permeation flux J is given by J = (D K / L) ΔC, where ΔC is the concentration difference across the layer. The diffusion resistance is defined as R = ΔC / J = L / (D K). For a stack of layers, the total resistance is the sum of the individual resistances: R_total = Σ L_i / (D_i K_i). A higher resistance corresponds to lower diffusive transport.

Measurement methods commonly used to determine diffusion resistance include time-lag techniques, where the lag time in the receiving side yields information about resistance and diffusivity, and steady-state permeation tests that measure flux under a maintained concentration difference. Gravimetric or volumetric methods can be employed for liquids and gases, respectively.

Several factors influence diffusion resistance, including layer thickness, diffusivity, solubility (partitioning) of the diffusing species, and the microstructure of the material (porosity, tortuosity, crystallinity). Temperature, aging, and chemical interactions at interfaces also affect resistance.

Applications of diffusion resistance concepts span packaging and barrier films, membranes for gas separation, protective coatings, geotechnical barriers, and electrochemical devices, where controlling diffusive transport is essential for performance and safety.