Correlation between Structure and Vapor Sorption in Semicrystalline Linear Polyethylene: One Dimensional Nano-Swelling Measured Using in Situ Vapor Sorption Small Angle Neutron Scattering (iVSANS)

Title
Correlation between Structure and Vapor Sorption in Semicrystalline Linear Polyethylene: One Dimensional Nano-Swelling Measured Using in Situ Vapor Sorption Small Angle Neutron Scattering (iVSANS)
Authors
김만호Glinka, Charles J.
Keywords
in situ vapor soprtion small angle neutron scattering; iVSANS; semicrystalline polymers; nano-swelling; sorption kinetics; Effective Diffusion Coefficient; Crystallinity; Fickian; Correlation; Lamellae
Issue Date
2009-04
Publisher
Macromolecules
Citation
VOL 42, NO 7, 2618-2625
Abstract
Changes in the nanoscale structure of semicrystalline polyethylene (PE) resulting from the sorption/ diffusion of hexane-d14 vapor have been observed and quantified by in situ vapor sorption small-angle neutron scattering (iVSANS). We find a linear correlation between vapor sorption/diffusion and nanoexpansion of the amorphous phase within the lamellae confined in the spherulite domains. The expansion depends on the degree of crystallinity and spherulite perfection. We measured the structure-based sorption kinetics and isotherms of samples with two different crystalline volume fractions (φVc). The low crystalline polyethylene shows a larger expansion in the long period, L, than the high crystalline polyethylene. Low crystalline PE shows a Fickian-like diffusion profile with sorption time while the high crystalline PE (φVc ) 78%) shows a S-shape diffusion profile (non-Fickian) at P/P° ) 0.95. The diffusion coefficient increases with relative vapor pressure (P/P°) in both materials. The apparent diffusion coefficient in the low crystalline polymer is approximately a factor of 2 higher than that of the more crystalline polymer. On the other hand, effective diffusion coefficients, Deff’s, normalized with the amorphous volume fractions at each vapor activity are identical regardless of crystallinity. This indicates that amorphous volume fraction is the predominant factor that controls transport properties, at least for small diffusing molecules. Furthermore, the one-dimensional expansion is reversible during cyclic sorption and desorption processes, suggesting that the crystals were not destroyed unlike the inference of a previous study.
URI
http://pubs.kist.re.kr/handle/201004/45506
ISSN
0024-9297
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KIST Publication > Article
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