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)
- 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)
- 김만호; Glinka, Charles J.
- in situ vapor soprtion small angle neutron scattering; iVSANS; semicrystalline polymers; nano-swelling; sorption kinetics; Effective Diffusion Coefficient; Crystallinity; Fickian; Correlation; Lamellae
- Issue Date
- VOL 42, NO 7, 2618-2625
- 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.
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