Transportation of gases and vapors

Saxena, V., and Stem, S.A., Concentration-Dependent Transport of Gases and Vapors in Glassy Polymers II. Organic Vapors in Ethyl Cellulose, J. Memb. Sci., 12, 65-85 (1982). 

Nonlinear, pressure-dependent sorption and transport of gases and vapors in glassy polymers have been observed frequently. The effect of pressure on the observable variables, solubility coefficient, permeability coefficient and diffusion timelag, is well documented (1, 2). Previous attempts to explain the pressure-dependent sorption and transport properties in glassy polymers can be classified as concentration-dependent and "dual-mode models. While the former deal mainly with vapor-polymer systems (1) the latter are unique for gas-glassy polymer systems (2). 

V. Saxean and S. A. Stem, Concentration-Dependent Transport of Gases and Vapors in Glassy... 

S. Matteucci, Y. Yampolskii, B.D. Freeman, I. Pinnau, Transport of gases and vapors in glassy and rubbery polymers, in Y. Yampolskii, I. Rnnau, B.D. Freeman (Eds.), Materials Science of Membranes for Gas and Vapor Separation, John Wiley Sons, Chichester, 2006, pp. 1 7. 

SAX Saxetia, V. and Stem, S.A., Concentration-dependent transport of gases and vapors in glassy polymers. II. Organic vapors in ethyl cellulose, J. Membrane Sci., 12,65,1982. 

Electrolytes diffuse in hydrophobic polymers with a mechanism similar to the transport of gases and vapors. Therefore, in the case of electrolytes with a high vapor pressure (for example, hydrochloric acid) the and D values are close to the corresponding values for water in the same polymers. For electrolytes with a low vapor pressure (for example, chlorides and phosphates) we found very low values of and D, i.e., hydrophobic polymers do not sorb these electrolytes to a significant extent. 

SA16 Advective transport of gases and vapor in soil pore-air... 

V.V.Volkov, Selective Transport of Gases and Vapors in Polymeric Glasses, TIPS, Moscow, 1992 (Russian). 

Stern and his co-workers were among the first to systematically study the transport and sorption of gases and vapors in high polymers at elevated pressures. 

The models most frequently used to describe the concentration dependence of diffusion and permeability coefficients of gases and vapors, including hydrocarbons, are transport model of dual-mode sorption (which is usually used to describe diffusion and permeation in polymer glasses) as well as its various modifications molecular models analyzing the relation of diffusion coefficients to the movement of penetrant molecules and the effect of intermolecular forces on these processes and free volume models describing the relation of diffusion coefficients and fractional free volume of the system. Molecular models and free volume models are commonly used to describe diffusion in rubbery polymers. However, some versions of these models that fall into both classification groups have been used for both mbbery and glassy polymers. These are the models by Pace-Datyner and Duda-Vrentas [7,29,30]. 

The permeation of gases and vapors through thin films is dependent on the molecular size, shape, wettability and soundness of the fabricated membrane. Since permeation in well-made products is a molecular transport phenomenon, it is affected by orientation, degree of crystallinity and temperature. Attempts have been made to relate permeation rates through thin films to absorption of thicker films, sheets, pipe, etc. This has been generally unsuccessful. Thicker films and sheets represent an average set of properties obtainable firom many thin films produced under a variety of conditions. To produce a thin film representative of this average is not practical. 

The ability of a plastic to protect and preserve products in storage and distribution depends in part upon the diffusion (i.e., transport) of gases, vapors, and other low-molecular-weight species through the materials. A substance s tendency to diffuse through the polymer bulk phase is its diffusivity or diffusion coefficient (D). The rate of diffusion is related to the resistance, within the polymer wall, to the movement of gases and vapors. Two important aspects of the transport process are permeability and the migration of... 

S A11 Molecular transport coefficients of gases and vapors in the soil pore-air SA12 Molecular transport coefficients for solutes in the soil pore-water... 

Differences in mass transport rates provide a potential means for discriminating between different gases and vapors. It is known, for example, that transport through molecular sieves can be a sensitive function of molecular size and shape [110]. For gases and vapors that have only weak physical interactions with a porous adsorbent layer, however, transport rates are often too high to allow... 

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