Langmuir-Henry’s law

It should be emphasized that permeation through a polymer involves three steps, as shown in Fig. 14.1 (1) the permeant dissolves at the polymer interface, (2) the permeant diffuses within the polymer film from the side of high concentration toward the low concentration side, and (3) the permeant diffuses out from the opposite polymer interface. These steps are always present in any system regardless of whether D and S follow Pick s and Henry s laws, respectively, or not. For instance, the solubility of CO2 in PET follows the Langmuir-Henry s law model, Equation 14.7, and P is given by,... 

In Equation 12.3, D is normally assumed to be independent of both penetrant concentration and polymer relaxations at low concentration, and x is the thickness of the membrane. This is especially true for gases such as oxygen (O2), carbon dioxide (CO2) at atmospheric pressure, and some organic compounds. Many theories have been proposed and many models have been developed to describe diffusion in polymers a detailed description of these models can be found elsewhere [7]. The diffusion processes through the membrane can generally be considered unidirectional and perpendicular to the flat surface, and solutions to the diffusion equations are obtained from the boundary conditions where the Henry s or Langmuir-Henry s law is applied. 

For glassy polymers and high-pressure penetrants, as in the cases of CO2 in PET, a nonlinear Langmuir-Henry s law model is followed. 

---

See also in sourсe #XX -- [ ]

---