Permeation coefficient

Table 5-3 Permeation coefficients and rate of oxygen corrosion according to Eq. (5-21).

For gas and vapor systems, by combining the laws of sorption and diffusion in the sequence (l)-(3), general permeation equations are obtained. For sheet membrane samples of polymers above Tg, if the definition is made that permeation coefficient Q = Ds,... 

Increasing temperature permits greater thermal motion of diffusant and elastomer chains, thereby easing the passage of diffusant, and increasing rates Arrhenius-type expressions apply to the diffusion coefficient applying at each temperature," so that plots of the logarithm of D versus reciprocal temperature (K) are linear. A similar linear relationship also exists for solubUity coefficient s at different temperatures because Q = Ds, the same approach applies to permeation coefficient Q as well. 

In practical situations, if permeation through a hose lining, for example, is being considered, and the hose is exposed externally to a cold environment (such as the sea) while hot fluid passes through the hose (e.g., hot oil in the offshore production industry), a temperature gradient — Ti will apply across the lining. To cover this situation, for a representative permeation coefficient Campion and Thomas developed from Tick s laws... 

The interrelationships of the various coefficients associated with fluid uptake (Section 23.4.2) mean that it should be possible to estimate a rate for one of the uptake phenomena from test data for another of them. Campion proposed using this approach to estimate permeation coefficient Q from solubility coefficient s. The form of a liquid absorption plot (Figure 23.6, Section 23.4.4.1) is such that s should be obtainable from it, and inspection showed that this link was via Henry s law with concentration corrected by the polymer density p. The following expression was derived for s ... 

For gases, both permeation and diffusion data are best measured by permeation tests, many different types been described elsewhere. The same sheet membrane permeation test can quantify permeation coefficient Q, diffusion coefficient D, solubility coefficient s, and concentration c. The membrane, of known area and thickness, must be completely sealed to separate the high-pressure (initial) region from that containing the permeated gas it may need an open-grid support to withstand the pressure. The permeant must be suitably detected and quantified (e.g., by pressure or volume buildup, infrared (IR) spectroscopy, ultraviolet (UV), gas chromatography, etc.). 

When testing, the permeation equation shown for conical samples in Section 23.4.2 is used to provide permeation coefficient Q. Measured values showed that the more normal methods employed for high-pressure permeation testing at MERE and elsewhere, using a sample support sinter, are likely to give underestimates of true permeation rates by a factor of about three. 

The permeation profiles of the proteins through the polymer membrane can be approximated by two straight lines representing regions that were in the dark and under UV irradiation as shown in Figure 6. The permeation coefficients can be calculated from the slope of these straight lines by using the equation... 

Figure 7 Permeation coefficient of solute in HEMA-AEMA copolymer membrane vs. molecular weight of solute. ( ) In the dark (O) under UV irradiation. (From Ref. 28.)...

Kulkarni, A., Han, Y., and Hopfinger, A. J., Predicting Caco-2 cell permeation coefficients of organic molecules using membrane-interaction QSAR analysis, /. Chem. Inf. Comput. Sci., 2002, 42, 331-342. 

Fig. 2.8 Arrhenius plot of permeation coefficients (a) bare glass plate (b) glass plate with unpolymerized monolayer (c) glass plate with polymerized monolayer. Reprinted with permission from [46], K. Ariga and Y. Okahata, /. Am. Chem. Soc., 1989, J J J,...

The squares and full lines of Fig. 11 summarize their results. The scatter of the experimental points seems mainly due to the analysis of the transient behavior the diffusion coefficient D and hence the solubility s = P/D fluctuate much more than the steady-state permeation coefficient P. Their Arrhenius lines are described by ... 

PEN has excellent gas-barrier properties. The gas-permeation coefficients of unoriented cast film and biaxially oriented films for PEN and PET are given in Table 10.4. 

PEN has lower gas permeation coefficients than PET for carbon dioxide, oxygen and moisture for both film types. Although the gas-barrier properties of PEN are similar to those of poly(vinyl dichloride), it is not affected by moisture in the environment. Both oriented and unoriented PEN films restrict gas diffusion more... 

Figure 14. Solvent (water, methanol) diffusion coefficients of (a) Nafion 117 (EW =1100 g/equiv) and (b) sulfonated poly(arylene ether ketone)s, as a function of the solvent volume fraction. Self-diffusion data (AiaO. T eOi-i) are taken from refs 197, 224, 226, 255—263 and unpublished data from the laboratory of one of the authors) chemical diffusion coefficients (Z>h2o) are calculated from self-diffu-sion coefficients (see text), and permeation diffusion coefficients are determined from permeation coefficients. ...

Usually, the total permeation coefficient (FH20) is measured, and this, expressed as a permeation diffusion coefficient q, is given in the following data compilation. 

Figure 1. Permeation coefficient of PPHMDSO-Kapton, as function of T ( ), power (A) and dielectric heating effects (A) (from ref. 6).

The permeation coefficient of Kapton under test co itions similar to those used here has been reported as 4.47 x 10 (g.cm/cm. sec. cmHg),in close agreement with our own measurements. Thus, solving equation (4) for we find... 

The permeation coefficients of the two thin film materials differ by an order of magnitude. To the extent then, that water initiates and propagates the corrosion of metal substrates, plasma films of... 

S. Matsumoto and M. Kohda The Viscosity of W/OAV Emulsions An Attempt to Estimate the Water Permeation Coefficient of the Oil Layer from the Viscosity Changes in Diluted Systems on Aging under Osmotic Pressure Gradients. J. Colloid Interface Sci. 73,13 (1980). 

As a result of Internal concentration polarization, the effective osmotic pressure difference across the membrane can be significantly below the osmotic pressure difference between the bulk solutions. The effective osmotic pressure can be calculated from the salt permeation coefficient and the salt diffusion resistance in the porous membrane substrate. The highest power output for a membrane is obtained at an operating pressure equal to about one half of the effective osmotic pressure. 

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