Temperature dependence permeability

Permeability is an essential property of the materials that constitute the membrane and is independent of membrane thickness [23], Additionally, permeability can be described as the product of the diffusion coefficient and the solubility constant (see Equation 10.3) and is temperature dependent. Permeability can then be represented by the following Arrhenius-type expression (see Section 5.6.1)... 

The temperature-dependent permeability, as in the case of dense organic polymeric membranes, can be expressed in the form of a solubility term multiplied by a diffusivity term as follows ... 

Temperature-dependent permeability to moisture could even be provided by polyurethane-based shape memory polymer (SMP). Better comfort is also provided by moving humidity and sweat away from the surface of the skin, either with hydrophilic linings or by the use of channelled cross-section fibres with reinforced wicking properties. 

Molecular modification of ozone-pretreated PVDF via thermally induced graft copolymerization with V-isopropylacrylamide (NIPAM) was carried out in NMP solution to produce the PVDF-g-PNIPAM copolymers [63]. The synthetic route is shown in Scheme 8.1. Microporous membranes were fabricated from the PVDF-g-PNIPAM graft copolymers by phase inversion in aqueous media. The surface composition and morphology of the resulting PVDF-g-PNIPAM membranes can be adjusted by the casting temperature, while the flux through the membrane exhibits temperature-responsive behavior. In addition to pure water flux, the copolymer membranes also exhibited reversible temperature-dependent permeability to calcein and... 

CHEOPS is based on the method of atomic constants, which uses atom contributions and an anharmonic oscillator model. Unlike other similar programs, this allows the prediction of polymer network and copolymer properties. A list of 39 properties could be computed. These include permeability, solubility, thermodynamic, microscopic, physical and optical properties. It also predicts the temperature dependence of some of the properties. The program supports common organic functionality as well as halides. As, B, P, Pb, S, Si, and Sn. Files can be saved with individual structures or a database of structures. 

The temperature dependence of the permeability arises from the temperature dependencies of the diffusion coefficient and the solubility coefficient. Equations 13 and 14 express these dependencies where and are constants, is the activation energy for diffusion, and is the heat of solution... 

Structure of the medium. It is temperature-dependent, since the properties of the fluid (density and viscosity) are temperature-dependent. Hydraulic conductivity can be written more specifically in terms of the intrinsic permeability and the properties of the fluid. 

All packing materials produced at PSS are tested for all relevant properties. This includes physical tests (e.g., pressure stability, temperature stability, permeability, particle size distribution, porosity) as well as chromatographic tests using packed columns (plate count, resolution, peak symmetry, calibration curves). PSS uses inverse SEC methodology (26,27) to determine chromatographic-active sorbent properties such as surface area, pore volume, average pore size, and pore size distribution. Table 9.10 shows details on inverse SEC tests on PSS SDV sorbent as an example. Pig. 9.10 shows the dependence... 

Mazur, P., Rail, W.F., Leibo, S.P. (1984). Kinetics of water loss and the likelihood of intracellular freezing in mouse ova Influence of the method of calculating the temperature dependence of water permeability. Cell Biophy. 6, 197-214. 

In accordance with observed data, this model shows that water flux increases linearly with applied pressure AP, decreases with higher salt concentration through its impact on osmotic pressure Jt, increases with a smaller membrane thickness I, and increases with temperature through the temperature dependence of the water permeability P . The model also demonstrates that the solute or salt flux J, increases linearly with applied pressure AP, increases with higher salt concentration c , increases with a smaller membrane thickness I, and increases with temperature through the temperature dependence of the solute permeability Pj. Polarization, as described early in this section, causes the wall concentration c to exceed the bulk concentration ci,. 

Diffusion-mediated release of root exudates is likely to be affected by root zone temperature due to temperature-dependent changes in the speed of diffusion processes and modifications of membrane permeability (259,260). This might explain the stimulation of root exudation in tomato and clover at high temperatures, reported by Rovira (261), and also the increase in exudation of. sugars and amino acids in maize, cucumber, and strawberry exposed to low-temperature treatments (5-10°C), which was mainly attributed to a disturbance in membrane permeability (259,262). A decrease of exudation rates at low temperatures may be predicted for exudation processes that depend on metabolic energy. This assumption is supported by the continuous decrease of phytosiderophore release in Fe-deficient barley by decreasing the temperature from 30 to 5°C (67). 

The temperature dependence of the x-metal permeability is not well known, although it decreases at low temperatures. Another material, cryo-perm, seems to retain large permeability even at liquid helium temperatures. 

The membrane performance for separations is characterized by the flux of a feed component across the membrane. This flux can be expressed as a quantity called the permeability (P), which is a pressure- and thickness-normalized flux of a given component. The separation of a feed mixture is achieved by a membrane material that permits a faster permeation rate for one component (i.e., higher permeability) over that of another component. The efficiency of the membrane in enriching a component over another component in the permeate stream can be expressed as a quantity called selectivity or separation factor. Selectivity (0 can be defined as the ratio of the permeabilities of the feed components across the membrane (i.e., a/b = Ta/Tb, where A and B are the two components). The permeability and selectivity of a membrane are material properties of the membrane material itself, and thus these properties are ideally constant with feed pressure, flow rate and other process conditions. However, permeability and selectivity are both temperature-dependent... 

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. ... 

Figure 5. Temperature dependence of the water permeability of radiation cross-linked PVA membranes under various pressure differentials ( ) AP = 200 psi ...

Study of the temperature dependence of the salt and water permeabilities through heat treated PVA membranes indicates that the heat treatment effect is expressed mainly in changes in permeability activation energies. The activation parameters for water and salt permeability of PVA membranes following various treatments are presented in Table IV. It is evident that the salt permeability activation energy is increasing about 2-3 times as... 

Temperature dependence of water and salt permeabilities of heat treated PVA membranes -E /RT P=P e ... 

Fever/External heat Serum fentanyl concentrations may increase by approximately one third for patients with a body temperature of 40°C (104°F) because of temperature-dependent increases in fentanyl release from the transdermal system and increased skin permeability. 

Figure 29 Temperature dependence of the permeability of p-nitrophenol for A-ProOMe grafted films. The permeability (P) was calculated from the equation, P = KVjAC, where k, V, A, and C are the slope of the permeation-time curve, the volume of the receiver chamber, the surface area of the membrane, and the concentration of p-nitropenol in the donor chamber, respectively.

Figure 30 Temperature dependence of the permeability (P) of polyethylene glycol molecules for A-isopropylacrylamide (NIPAAm) grafted films. Polyethylene glycol with four kinds of masses (1 x 10, 1x10, 2x10, 7x10" ) are contained in the solution.

On the Energy of Activation. The temperature dependence of many processes, such as diffusion, permeability, and partition coefficients, has been represented often in terms of the Arrhenius plots (52). It would appear that ki in Equation 14 also could be treated in this manner by defining... 

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