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Calculation of the temperature dependence of the negative thermal expansion of polyethylene chains by means of the self-consistent harmonic approximation

✍ Scribed by Rainer A. Stobbe; Peter C. Hägele

Publisher
John Wiley and Sons
Year
1996
Tongue
English
Weight
389 KB
Volume
34
Category
Article
ISSN
0887-6266

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✦ Synopsis

A parameter-free model based on molecular mechanics with zero Kelvin potentials is developed to describe quantitatively the shortening of the unit cell of polyethylene crystals in chain direction with increasing temperature. Based on the well-known conception that an increase of the amplitudes of the torsional vibrations will cause the thermal shrinkage, we introduce a self-consistent phonon approach to calculate the temperature dependence of the angular displacement correlation function taking into account the anharmonicity of the potential. By means of these functions, we calculate the mean value of the length of a representative chain segment and compare the results with those obtained from x-ray diffraction measurements.

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