Molecular Dynamic Simulations of Amorphous Systems under Stress

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Amorphous Domains in Polymer Crystals : The molecular dynamic program, which we have developed for the study of rubber elasticity, was modified to calculating chemical potentials μ and rigidity G of condensed entanglement systems. It is found that, as entanglements are condensed in the amorphous domain, it becomes harden and its G , ca.several times as large as ordinary rubbers. It is also found that chemical potential μ_f of elements in free chains is higher than μ_t of chains fixed to the lamella. The difference between μ_f and μ_t, increases with increase of concentration x of entanglements in the amorphous domain. This shows that free and dangling chains are expelled rapidly from the amorphous domain in the process of crystallization. It is suggested that this may make the period of stacking lamella structure unstable and lead formation of spherite.Amorphous Silica Systems : Molecular dynamic simulations are done for silicate grasses using the three-body interaction potential proposed by Feuston and Garofalini. The temperature of systems are lowered from 9000K to the room temperature, step-by-step, with an interval Of 200K.At each temperature, the system is annealed for 0.1 nsec. It is found that, as the temperate increases, volume V of the system increases up to a certain temperature, above it, V begins to decreases and finally it increases again. This complicated behavior of V agrees with experiments. It is also found that the isothermal compressibility computed in the present simulation agree qualitatively with that determined experimentally by Saito and Ikushima.