Evaluation of Activation Entropy and Activation Volume in Plastic Flow of Amorphous Polymers

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  • 無定形高分子の塑性流れにおける活性化エントロピーおよび活性化体積の評価

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Tensile and compressive plastic flows in glassy linear amorphous polymers have been investigated. The Eyring equation was applied to the lower yield value at which the stress becomes minimum after the yield point. This procedure allows to determine the variables such as the activation enthalpy, the activation entropy, and the activation volume for the plastic flow in the polymers as functions of temperature and stress. In previous papers it was already reported that experimental values of the activation enthalpy are explained well in terms of the Robertson theory when one assumes one-to-one correspondence between the molecular configuration and the activation enthalpy. In the present work, other Eyring coefficients, i. e., the activation entropy and the activation volume, were evaluated and discussed from the viewpoint of their relations to the polymer configurations. It was shown that the activation entropy for glassy polymers expressed as a function of Robertson's structural temperature θ1 was satisfactorily comparable with the activation entropy for polymer melts at temperature θ1. This means that the magnitude of the activation entropy depends to a considerable extent on the polymer configuration whether the polymer chain is in the state of glass or melt. By comparing the viscosity at θ1 calculated from the Eyring coefficients for the glasses with the viscosity measured for melts at temperature θ1, it was found that the magnitude of the activation volume was also closely associated with the polymer configuration.

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