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Lineshape Analysis of X-ray Diffraction Profiles: Polyethylene and Model Copolymers

Published online by Cambridge University Press:  06 March 2019

Buckley Crist and
Paul R. Howard
Buckley Crist
Affiliation:
Dept. of Materials Science & Engineering and Materials Research Center Northwestern University Evanston, IL 60208
Paul R. Howard
Affiliation:
Dept. of Materials Science & Engineering and Materials Research Center Northwestern University Evanston, IL 60208
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Studies of the shapes of X-ray diffraction peaks from synthetic polymers are still rather uncommon. One probable cause of this situation is the small peak-to-background ratio in most polymer diffraction experiments; it is difficult to achieve precise line profiles for quantitative analysis. Increased utilization of automated data collection/analysis systems and more intense X-ray sources should alleviate this restriction. We suspect, furthermore, that confusion about nomenclature has impeded the acceptance of lineshape analysis for polymers. The peak broadening mechanisms which are generally considered are finite coherence length or crystal size, lattice parameter fluctuation, and displacement disorder of the second kind. Both latter mechanisms have, unfortunately, been referred to as “strains” or “microstrains”. Metallurgists have traditionally expressed displacement disorder as a (length dependent) “microstrain”, and this convention has been adopted in some studies of polymer diffraction. Other work on polymers, however, has termed lattice parameter fluctuation as “microstrain“. The inconsistent use of this term can imply a nonexistent relation between two distinct phenomena.

Information

Type
X. Crystallite Size/Strain Analysis
Information
Advances in X-Ray Analysis , Volume 34: Thirty-Ninth Annual Conference on Applications of X-ray Analysis, July 30 - August 3, 1990 , 1990, pp. 519 - 529
Copyright
Copyright © International Centre for Diffraction Data 1990

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