Comments on expressing the permeability of polymers to gases

Abstract

The fundamentals of permeability and diffusivity are presented briefly to demonstrate the possible dimensional forms available in principle for expressing the coefficients of permeability (P,) and diffusion (D,). The interrelation between P, and D, is discussed and two recent experimental methods specific to the permeation of oxygen are summarised. Twenty-nine units appearing for P, in the literature are discussed and corrected where necessary. On the basis of its convenience, one particular unit is recommended and conversion factors to it are tabulated. ZUSAMMENFASSUNG :Die Grundlagen der Begriffe ,,Permeabilitat" und ,,Diffusion" werden kurz beschrieben, um die prinzipiell mbglichen Formen aufzuzeigen, in denen die Koeffizienten der ,,Permeabilitat" (P,) und ,,Diffusion" (D,) erhalten werden kbnnen. Der Zusammenhang zwischen P, und D, wird diskutiert, und zwei experimentelle Methoden, die fur die Sauerstoffdiffusion spezifisch sind, werden zusammengefaBt. 29 Einheiten fur P,, die in der Literatur vorkommen, werden diskutiert undwenn nbtig korrigiert. Auf Grund ihrer ZweckmMigkeit wird eine Einheit empfohlen, und Umrechnungsfaktoren, mit denen man andere Einheiten in die empfohlene umrechnen kann, werden aufgelistet. 0 1983 Huthig & Wepf Verlag, Base1 0003-3146/83/$03.00the units. Although some of these are merely unconventional, others are ambiguous or even incorrect. In this respect the following observations of Hwang and KammermeyerZ seem appropriate: " --permeability is used in so many different disciplines and research fields. It seems, at times, that there is hardly any communication among investigators in different fields of study. Numerous publications report all sorts of permeability-* * * -"Existing interconversion tables 1,3*J covering only ca. seven different permeability units are rather inadequate in view of the much larger number of units appearing in the scientific and patent literature (see later). In the present communication an attempt is made to rationalise the situation for the practical convenience of others, and a proposal is made for the adoption of a single recommended unit. In view of their essential complimentarity, both permeability and diffusivity are discussed together. Permeability and Diffusivity DefinitionsP,, which is termed permeability, permeability coefficient or permeability constant, is defined by eq. (1) * STP = standard temperature and pressure.

A Model for Adsorption and Diffusion in Water Vapor Barrier Films

“…For the steady state of diffusion in a single polymer layer, the flux of the substance through the monolayer polymer film can be expressed bywhere D (cm 2 s −1 ) is the diffusion coefficient, and p 1 and p 2 are the ambient pressure on the two sides of the film with thickness d, respectively. The product of the solubility and diffusion coefficient is defined as the permeation coefficient ( P = S × D ) with the unit of [ 31 ] …”

“…where D (cm 2 s À1 ) is the diffusion coefficient, and p 1 and p 2 are the ambient pressure on the two sides of the film with thickness d, respectively. The product of the solubility and diffusion coefficient is defined as the permeation coefficient (P ¼ S  D) with the unit of [31] P ¼ ðamount of gas under stated conditionsÞðfilm thicknessÞ ðfilm areaÞðtimeÞðdriving pressureÞ (3) Note that the amount n w (atoms) can be expressed in terms of the molar mass and density of the water, i.e., mass m ¼ n w  M/N A , where N A is the Avogadro constant and M is the molar mass of water M ¼ 18 g mol À1 , and volume…”

Temperature dependence of the leak rate and permeability of helium gas through Kapton foils

“…Actually none of the listed sources use the unit barrer, therefore all values were converted to this unit using the conversion factors presented in Table 2 of [13]. Furthermore, it has to be noted that the publications [15,17] use a different definition of the permeability, which needs an additional conversion factor (see Table 1 for details).…”

“…And finally in Table 1 Literature values for the permeability constant P and the activation energy E P . Unless otherwise stated, the permeability constants are indicated at T ¼296 K, and were converted by us to units of barrer using the conversion factors given in Table 2 of [13] [19] Activation energy (kJ/mol) Source 18:2 7 0:3 g [20] a Official Datasheet by DuPont. Indicate "permeance" which is P=d.…”