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Atomistic Details Of Disordering Processes in Superheated Polymethylene Crystals II. Effects of Surface Constraints

Published online by Cambridge University Press:  15 February 2011

B. Wunderlich ,
G. L. Liang ,
B. G. Sumpter  and
D. W. Noid
B. Wunderlich
Affiliation:
Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, and Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6197.
G. L. Liang
Affiliation:
Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, and Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6197.
B. G. Sumpter
Affiliation:
Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, and Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6197.
D. W. Noid
Affiliation:
Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, and Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6197.
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Abstract

Atomistic details of disordering in superheated polymethylene crystals have been studied using full molecular dynamics simulations of crystals containing 9600 CH2-groups. The crystal size was about 227 nm3 Simulations were carried out for up to 100 ps, starting at temperatures about 100 K above the melting temperature. Typically 1.5 h of CPU time on a Cray X-MP were necessary per ps simulation. Superheating causes a quick development of large-scale disorder throughout the crystal, including reorientation, translation, and the destruction of crystal symmetry. This is followed ultimately by surface Melting. Crystallization centers with hexagonal packing are found in superheated, unconstrained crystals. On cooling during the simulation, recrystallization processes compete with the disordering, resulting in a reorientation of the molecular chains and reorganization of the crystal. Neither the fully amorphous phase nor the ordered crystal are reached during these short-time simulations using an instantaneous temperature increase to above the melting temperature, followed by a slow cooling into the crystallization temperature region.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 321: Symposium E – Crystallization and Related Phenomena in Amorphous Materials—Ceramics, Metals, Polymers, and Semiconductors , 1993 , 93
Copyright
Copyright © Materials Research Society 1994

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