Molecular Dynamic Simulations of Amorphous Systems under Stress

聚合物晶体中的无定形畴：我们改进了为研究橡胶弹性而开发的分子动力学程序，以计算凝聚缠结体系的化学势μ和刚性G。结果表明，由于缠结在无定形区中凝聚，它变得硬化，其G约为普通橡胶的几倍。自由链中元素的化学势μ_f大于固定在层片上的链的化学势μ_t。μ_f与μ_t之差随非晶畴内纠缠态浓度x的增加而增大。这表明在结晶过程中，自由链和悬挂链被迅速地从非晶畴中排出。有人建议，这可能会使期间的堆叠片层结构不稳定和铅形成spherite.Amorphous二氧化硅系统：分子动力学模拟的硅酸盐草Feuston和Garofalini提出的三体相互作用势。系统的温度从9000K逐步降至室温，每200K一次，在每个温度下退火0.1nsec。结果表明，随着温度的升高，系统的体积V在一定温度下增大，高于一定温度时，体积V开始减小，最后又增大。V的这种复杂行为与实验相符。同时还发现，在本模拟计算的等温压缩性定性地同意由斋藤和Ikushima实验确定。

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.