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Effect of Polydispersity on the Evolution of Density Fluctuations to Lamellar Crystals in Linear Polyethylene

Published

Author(s)

Y A. Akpalu, Eric J. Amis

Abstract

The effect of polydispersity on structure development in linear polyethylenes is studied by simultaneous real time small-angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS). Our measurements show that below 128 degrees C, changes in the SAXS and WAXS intensity profiles for a broad molecular-weight distributed sample occur simultaneously as previously reported for a narrow molecular-weight distributed sample. We demonstrate that variations in the SAXS profile can be correlated to the morphological changes associated with the evolution of single chainfolded crystal lamella to lamellar aggregates as is the case for a narrow molecular-weight distributed sample. At 128 degrees C and higher temperatures, changes in SAXS and WAXS also occur simultaneously for the narrow molecular-weight distributed sample while for the broad molecular-weight distributed sample changes in the SAXS intensity profile occur much earlier than the onset of lamellar crystal growth as evidenced in the WAXS profile. We show that these differences are consistent with what one would expect on the basis of the dependence of the crystallization rate on chain length and hence its distribution. On the other hand, the temperature dependence of the variation in the average crystal thickness during isothermal crystal growth is a function of the relative rates of primary crystallization and thickening at a given temperature. We discuss the effect of a broad distribution in chain length on the various stages in the development of the morphology.
Citation
Journal of Chemical Physics
Volume
113
Issue
No. 1

Keywords

crystallization, polydispersity, polyethylene, SAXS/WAXS

Citation

Akpalu, Y. and Amis, E. (2000), Effect of Polydispersity on the Evolution of Density Fluctuations to Lamellar Crystals in Linear Polyethylene, Journal of Chemical Physics, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=851658 (Accessed March 3, 2024)
Created June 30, 2000, Updated October 12, 2021