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Membranes 2018, 8(1), 8;

Gas Transport in Glassy Polymers: Prediction of Diffusional Time Lag

Department of Civil, Chemical, Environmental and Materials Engineering (DICAM), Alma Mater Studiorum-University of Bologna, Via Terracini, 28, 40131 Bologna, Italy
Author to whom correspondence should be addressed.
Received: 29 December 2017 / Revised: 26 January 2018 / Accepted: 1 February 2018 / Published: 3 February 2018
(This article belongs to the Special Issue Advances in Liquid Membrane-Based Separation)
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The transport of gases in glassy polymeric membranes has been analyzed by means of a fundamental approach based on the nonequilibrium thermodynamic model for glassy polymers (NET-GP) that considers the penetrant chemical potential gradient as the actual driving force of the diffusional process. The diffusivity of a penetrant is thus described as the product of a purely kinetic quantity, the penetrant mobility, and a thermodynamic factor, accounting for the chemical potential dependence on its concentration in the polymer. The NET-GP approach, and the nonequilibrium lattice fluid (NELF) model in particular, describes the thermodynamic behavior of penetrant/polymer mixtures in the glassy state, at each pressure or composition. Moreover, the mobility is considered to follow a simple exponential dependence on penetrant concentration, as typically observed experimentally, using only two adjustable parameters, the infinite dilution penetrant mobility L10 and the plasticization factor β, both determined from the analysis of the dependence of steady state permeability on upstream pressure. The available literature data of diffusional time lag as a function of penetrant upstream pressure has been reviewed and compared with model predictions, obtained after the values of the two model parameters (L10 and β), have been conveniently determined from steady state permeability data. The model is shown to be able to describe very accurately the experimental time lag behaviors for all penetrant/polymer pairs inspected, including those presenting an increasing permeability with increasing upstream pressure. The model is thus more appropriate than the one based on Dual Mode Sorption, which usually provides an unsatisfactory description of time lag and required an ad hoc modification. View Full-Text
Keywords: gas permeability; diffusion; thermodynamics; NELF model; glassy polymers gas permeability; diffusion; thermodynamics; NELF model; glassy polymers

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Minelli, M.; Sarti, G.C. Gas Transport in Glassy Polymers: Prediction of Diffusional Time Lag. Membranes 2018, 8, 8.

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