Molecular dynamics study of the rate of melting of a crystalline polyethylene molecule: Effect of chain folding

Journal Article · Mon Jan 01 00:00:00 EST 1990 · Macromolecules; (United States)

DOI:https://doi.org/10.1021/ma00223a027· OSTI ID:6841702

Sumpter, B G; Noid, D W; Wunderlich, B ^[1]; Cheng, S Z.D. ^[2]

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1. Oak Ridge National Lab., TN (United States). Chemistry Division Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemistry
2. Univ. of Akron, OH (United States). Dept. of Polymer Science

Molecular dynamics is used to study the melting on the surface of a polyethylene-like crystal. The rate constant for melting of a crystalline molecule without and with one to four folds is determined at several different temperatures and molecular lengths. The results show a strong dependence of the transition rate on the number of folds. For a constant lamellar thickness, the transition rate decreases with increasing number of folds for temperatures near the equilibrium melting temperature, as expected from analogy with experimental melting temperatures. In contrast, the transition rate increases with increasing number of folds for temperatures that exceed the equilibrium melting temperature, as expected from analogy with experimental melting temperatures. In contrast, the transition rate increases with increasing number of folds for temperatures that exceed the equilibrium melting temperature by more than 100 K. Two melting paths are suggested to explain the simulation data. One pathway involves a competition between melting and crystallization. This pathway leads to a decreasing transition rate as a function of increasing folding. The second pathway exhibits dominating melting. In this case, the rate of transition tends to increase with increasing number of folds. Diffusion coefficients of segments at different locations along the chain show that motion of the ends of a polymer chain or of the folds is faster than in the center of the stem. The overall effect of increasing temperatures is to increase the diffusion coefficients.

• DOE Contract Number: AC05-84OR21400
• OSTI ID: 6841702
• Journal Information: Macromolecules; (United States), Vol. 23:21; ISSN 0024-9297
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
POLYETHYLENES
MELTING
EXPERIMENTAL DATA
MELTING POINTS
MOLECULAR STRUCTURE
RECRYSTALLIZATION
DATA
INFORMATION
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
POLYMERS
POLYOLEFINS
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE
360602* - Other Materials- Structure & Phase Studies