NG在聚氨酯中扩散性能的分子动力学模拟

为研究二异氰酸酯类型、温度、硝化甘油（ NG）含量等因素对NG在聚氨酯弹性体内扩散性能的影响，用分子动力学方法，在COMPASS力场下对NG和聚氨酯弹性体混合体系进行了模拟。构建NG与不同聚氨酯弹性体的混合体系模型，并进行结构优化，先后进行恒温恒压系综（ NPT）和恒温恒容系综（ NVT）的分子动力学模拟，得到NG在混合体系中的均方位移，通过爱因斯坦方程计算得到其扩散系数。结果表明：NG在聚氨酯弹性体内扩散系数的数量级为10-8 cm2· s-1，与实验数据一致；扩散系数随聚氨酯弹性体链的柔顺性增加而上升；随温度的不断升高，扩散系数先缓慢上升，当超过308 K后，扩散系数急剧增加。随NG含量的不断升高，扩散系数先缓慢下降，当超过14％后，扩散系数急剧下降。

Molecular Dynamics Simulation of the Diffusion Behaviors of NG in Polyurethane

The influences of temperature, content of nitroglycerin(NG), structure of diisocyanate on the diffusion behaviors of NG in elastomeric polyurethane were investigated by the molecular dynamics method with COMPASS(Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies) force field. The mixed models of NG and different elastomeric polyurethane were also constructed and optimized. The mean square displacement of NG in mixtures was obtained by the molecular dynamics simulation of NPT(constant-temperature, constant-pressure ensemble) and NVT(constant-temperature, constant-volume ensemble). The diffusion coefficients were obtained by the Einstein equation. The results show that the order of magnitude of diffusion coefficients of NG in elastomeric polyurethane reaches 10^-8 cm²·s^-1, which is in agreement with experiment. The diffusion coefficients increase with the increasing of chain flexibility, and increase slowly when the temperature belows 308 K and then increase quickly. At meanwhile, the diffusion coefficients decrease slowly at first, and quickly when the content of NG exceeds 14%.