非晶性ポリマーの単軸引張り変形における自由エネルギの変化

概要

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Macroscopic deformation of a polymeric material is physically induced by collective evolution of orientation and alignment of its molecular chains. In the present work, we evaluate its deformation behavior from the molecular-level structure by the molecular dynamics simulations. Thermodynamic quantities such as free energy or entropy are key issues on considering the deformation of polymer because crystallization of the internal structure as deformation might produce entropy decrease. Therefore, we computationally calculate the thermodynamic values by the perturbation method within the MD scheme. First, the free energy difference on the structural change between the polyethylene (PE) and the syndiotactic polypropylene (st-PP) is examined. The results show the reasonable high energy barrier between them and the understandable entropy increase from PE to st-PP. Then, we apply it to amorphous polymer of PE constructed by the random walk method under the uniaxial tension. The entropy decrease due to decrease of the internal potential energy is obtained, which is one of the proper features of the polymer.
1999-01-25