The effects of glassy microstructure on small molecule transport in amorphous poly (ethylene terephthalate)

• Published in: Journal of membrane science 1992-09, Vol.72 (2), p.119-136
• Main Authors: Vieth, Wolf R., Laird, Scott P.
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; conformational structure; diffusion; Exact sciences and technology; General and physical chemistry; glass membranes; Membranes
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/0376-7388(92)80193-N

Transport of carbon dioxide in amorphous poly (ethylene terephthalate) is found to vary with the conformational structure of the polymer. Analysis of transient CO 2 discharge from the polymer film into a finite penetrant bath volume demonstrates that the mobilities of the individual Henrian and Langmuirian sorbed species are dependent upon polymer conformation as well. The increase in Henrian diffusivity with increasing gauche fraction is suspected to result from an increase in the excess free volume of those polymer regions associated with Henrian dissolution. The concurrent decrease in Langmuirian diffusivity appears to result from increased diffusional resistance arising from additional Langmuirian sorption capacity. Transient sorption data yields penetrant sorption and transport parameters from a single experiment and insures that these parameters reflect an isotropic polymer microstructure. A computer model incorporating the effects of isomerization on CO 2 sorption and transport has been developed which simulates the onset of microstructural anisotropy during steady-state permeation trials and illustrates how such permeation data can result in inaccurate parameter estimations.