Permeationsrate

Permeationsrate, also referred to as permeation rate or permeation flux, is a measure of how quickly a substance passes through a barrier or membrane under defined conditions. It is typically expressed as a rate of mass transfer per unit area, for example grams per square meter per hour (g/m^2·h), but can also be given as moles, or as a change in partial pressure per area per time.

In steady-state diffusion through a solid barrier, the permeation rate J is often related to the barrier’s permeability P and the driving force across the barrier. A common relation is J = P Δp / l, where Δp is the partial pressure difference, and l is the barrier thickness. The permeability P itself is the product of diffusion and solubility properties of the barrier material (P = D × S). Depending on the context, P is reported in units such as Barrer in polymer science, while the flux J is expressed in mass per area per time.

Factors influencing the permeationsrate include the intrinsic properties of the barrier material (free volume, porosity, crystallinity, and glass transition temperature), the chemical nature of the permeant, temperature, humidity, pressure differential, and the thickness and orientation of the barrier. Materials can exhibit selective permeation, where certain substances pass more readily than others, making permeability and selectivity important for applications.

Measurement of the permeationsrate is performed with permeation tests using membranes or films, typically in constant-volume or constant-pressure setups. The equipment tracks changes in pressure or mass over time to derive flux and, from it, permeability. Standards exist for specific systems, including gas and liquid permeation tests, and results guide the design of packaging, protective gear, and membrane technologies.

Overall, the permeationsrate is a key parameter in assessing barrier performance and material suitability for controlling mass transfer of gases and liquids.