Abstract
Computer experiments using the molecular dynamics method have been carried out in order to investigate the formation and motion of defects in polymer crystals. The simulations were carried out on a crystal of 12.6-nm-long chains consisting of 3700 CH2 groups over times of 20 ps, and preliminary results for crystals containing up to 30 000 atoms that include the hydrogens explicitly are discussed. Chain diffusion through the crystal is shown to involve sharply defined thermal conformational defects and longer-range soft twists. An activation energy for the formation of conformational defects is found to be on the order of 16 kJ/mol and an additional “activation” energy gradient of 4 kJ/mol is determined to be necessary to cause directed motion of a chain through the crystal. At 350 K the rate of conformational defect formation is about 1010 s-1, causing doubling of a crystal in thickness on a time scale of 0.1 ns. Both structural and dynamical details of defect generation and motion are extracted from the extensive simulations, and the results are discussed in context to currently existing theories for lamellar thickening and relaxation behavior in polymer crystals.
Original language | English |
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Pages (from-to) | 7247-7255 |
Number of pages | 9 |
Journal | Macromolecules |
Volume | 25 |
Issue number | 26 |
DOIs | |
State | Published - Dec 1 1992 |