Activation energy of permeability

Activation Energies of Permeability Afp, diffusion Eo, as well as Heat of Penetrant Sorption AHs for C3H6 and C3H8 in Polyimides... 

When using the microporous zeolite membrane (curve 3) the N2 permeance decreases when the pressure increases such a behaviour can be accounted for by activated diffusion mechanisms [21], which are typical of zeolite microporous systems. In such systems the difflisivity depends on the nature and on the concentration of the diffusing molecule which interacts with the surface of the pore. For gases with low activation energies of diffusion, a decrease of the permeability can be observed [22]. 

The temperature dependence of the water permeability of radiation crossllnked PVA membranes Is shown In Figure 5. From this dependence an activation energy of 6.0i0.2 kcal/mole can be derived, In good agreement with data reported earlier by Peter and Mlttelstadt (7) and by PaulW. ... 

Using a similar approach, Notman et al. [81], determined the free energy for pore formation in bilayers composed of ceramide, as a model for the stratum corneum of the skin, both in the presence and in the absence of DMSO. Without DMSO, the bilayer was in the gel phase, and interestingly, a hydrophobic pore was observed with a high free-energy barrier ( 60 kj/mol). In the presence of DMSO, the bilayer was more fluid, and the more typical hydrophilic pore was observed, with a much smaller activation energy of 20kJ/mol. This work provided a thermodynamic and structural explanation for the enhanced permeability of skin by DMSO. 

Table 1. Activation energies and permeability ratia for permeation of different gases in a silicalit-1 membrane on a alumina support (pore size 0.15 pm).

Permeation of the blowing agent through a plastic membrane can usually be treated as an activated process with an activation energy and permeability at the standard or room temperature... 

Additionally, the temperature dependence of the permeability of a dense metal membrane is observed to follow an Arrhenius-type expression, Eq. 10.8. Ep and ko represent the activation energy of permeation and the pre-exponential constant respectively. 

Probably the most systematic and complete study on the influence of temperature on water transfer has been performed on mammalian red cells [10,20,28]. The dependence on temperature of both the tracer diffusional permeability coefficient (cotho) 3 nd the hydraulic conductivity (Lp) of water in human and dog red-cell membranes have been studied. The apparent activation energies calculated from these results for both processes are given in Table 2. The values for the apparent activation energies for water self-diffusion and for water transport in a lipid bilayer are also included in the table. For dog red cells, the value of 4.9 kcal/mol is not significantly different from that of 4.6-4.8 kcal/mol for the apparent activation energy of the water diffusion coefficient ( >,) in free solution. Furthermore, it can be shown that the product L — THOV )rt, where is the partial molar volume of water and the viscosity of water remains virtually independent of temperature for dog, hut not for the human red-cell membrane [20]. The similarity of the transmembrane diffusion with bulk water diffusion and the invariance of the... 

A feature of highly permeable polyacetylenes is a low (sometimes negative) value of activation energy of permeation. Since... 

Already a qualitative analysis of Figure 3.2 indieates that the activation energies of carbon dioxide and ethane are negative, while those of other gases have relatively small valnes (see also Table 3.6). This is one more feature that explains solubility controlled permeation in PTMSN and its large gas permeability. 

The temperature dependence of a diffusion coefficient is determined by the activation energy of diffusion. The temperature dependence of the solubility coefficient is given by the enthalpy of solution AH. Hence, the temperature dependence of the permeability coefficient is given by... 

From these data, the effect of mole-% of MD in PMLG-MD on the oxygen permeability and the activation energy of the oxygen permeation is shown in Figure 9. The interesting phenomena of the permeability... 

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