Molecular Dynamics Simulation of Thermal Motion and Elasticity of a Polymer Chain

• Published in: KOBUNSHI RONBUNSHU 1994/06/25, Vol.51(6), pp.365-370
• Main Authors: YAMAMOTO, Satoru, MATSUOKA, Takaaki, FUKUMORI, Kenzo, TAKAHASHI, Hideroh, KURAUCHI, Toshio
• Format: Article
• Language: Japanese
• Subjects: Elasticity; Glass Transition; Molecular Dynamics; Polybutadiene; Polymer Chain
• ISSN: 0386-2186; 1881-5685
• DOI: 10.1295/koron.51.365

A molecular dynamics simulation was done to analyze the glass transition temperature and the elasticity of polybutadiene using a single polymer chain. The radius of gyration of a free polymer chain without constraint was calculated at various temperatures to decide the glass transition temperature. When the end-to-end distance of a single polymer chain is constrained, a shrinkage force exerts on both ends. This constrained force was calculated for various end-to-end distances at 300K, by using POLYGRAF. The constrained force was estimated in two different ways for an average during 200ps calculations for each distance. One estimate came by calculating directly the force exerted between the end atoms, and the other came by estimating from the free energy expression of the system. The constrained force was compared with that of the Gaussian chain model. For the free polymer chain, a bend was found in the line relating radius of gyration and temperature, and its temperature was almost the same the an experimental glass transition temperature. The simulated force was in agreement with that of the Gaussian chain model before reaching a straight conformation, however, it increased rapidly when the polymer chain was further extended to a large end-to-end distance. An energetic force due to the van der Waals interaction among non-bonding atoms affected the elasticity of the polymer chain when it was in the random-coiling conformation at a small end-to-end distance.