Computer simulation of macromolecular crystals and their defects
- Oak Ridge National Lab., TN (United States)
Computational results on dynamics of polyethylene, are reviewed and connected to experiment. It can be demonstrated that conformational defects can be created at temperatures as much as 100 K below the melting point and that the concentration continues to increase exponentially with temperature, ultimately leading to disordered crystals along the polymer chains (high temperature CONDIS crystals). Although rate of formation of these defects is high, approximately 1 {times} 10{sup 10} s{sup {minus}1} at 350 K, the defects do not, by themselves, lead at low temperature to lamellar thickening or deformation. Diffusion mechanisms involve coupling of large-amplitude torsional motion with transverse and longitudinal vibrations of the crystal, which lead to formation of disclinations, dispirations, and twists. Such defects can, move towards the end of the crystal, thereby causing a chain diffusion process leading to lamellar thickening and deformation processes. Collective twisting of the chains without major influence of conformational defects leads to hexagonal or pseudo-hexagonal structures of the asymmetric motifs, involving dynamic multidomain arrangements of the chains. The especially efficient molecular dynamics simulation-code produces reasonable agreement with experiment on density, defect concentration, heat capacity, vibrational spectra (including stress-induced frequency shifts), melting temperature, and speed of sound. The simulations produced data on crystals of up to 30,000 atoms for times of up to 100 picoseconds (10{sup {minus}10} s). Total simulation efforts needed 8,000 hours of supercomputer CPU time between 1988 and 1993.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States); National Science Foundation, Washington, DC (United States)
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 10169093
- Report Number(s):
- DOE/OR/21400-T475; ON: DE93015213; CNN: Grant DMR-92-00520
- Resource Relation:
- Other Information: PBD: [1993]
- Country of Publication:
- United States
- Language:
- English
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