HAN基ECSP凝胶模型的构建与分子动力学模拟

目的 从微观分子的角度对硝酸羟胺(HAN)基电控固体推进剂(Electrically Controlled Solid Propellants，ECSP)的性能参数进行模拟与计算。方法 利用分子表面静电势(ESP)对HAN分子2种可能的构型进行优化和稳定性分析。通过真空非周期性分子动力学模拟得到聚乙烯醇(PVA)分子稳定构型，并以HAN基ECSP的主要成分按一定比例构建凝胶模型。基于RESP(Restrained Electrostatic Potential)电荷生成更准确的凝胶模型拓扑文件，并进行凝胶模型的分子动力学模拟、模型稳定分析以及模型参数计算。结果 凝胶模型总能量相对平均值的周期性波动不超过7%。由于三维PVA链的包裹，H2O分子的扩散系数被大幅削弱。氢键分析和径向分布函数表明氢键键长主要分布在0.282 6 nm附近，PVA与H2O间的氢键较少，H2O与HAN、H2O与H2O之间的氢键较多。模型密度为1.405 g/cm³，与实验值吻合度高。在283、293、303 K下，HAN基ECSP凝胶模型的拉伸模量依次降低，剪切模量先增后减。在15 K/600 ps冷却速率下，HAN基ECSP凝胶模型的拉伸模量和剪切模量均增大。结论 ECSP制备结束后，冷却过程中的环境温度不宜过高，否则容易造成ECSP力学性能的快速下降，快速冷却可以提高ECSP的力学性能。

Structure and Molecular Dynamics Simulation of HAN Based ECSP Gel Model

The work aims to simulate and calculate the performance parameters of hydroxylamine nitrate (HAN) based electrically controlled solid propellants (ECSP) from a microscopic molecular perspective. Optimization and stability analysis were carried out to the two possible configurations of HAN molecules with molecular surface electrostatic potential (ESP). The stable molecular configuration of polyvinyl alcohol (PVA) was obtained through vacuum aperiodic molecular dynamics simulation, and the gel model was constructed with the main components of HAN based ECSP in a certain proportion. More accurate gel model topology file was generated based on Restrained Electrostatic Potential (RESP) charge, and molecular dynamics simulation, model stability analysis and model parameter calculation of gel model were carried out. The periodic fluctuation of the relative average value of the total energy of the gel model did not exceed 7%. Due to the significant weakening of the diffusion coefficient of H2O molecules encapsulated in the three-dimensional PVA chain, hydrogen bond analysis and radial distribution function indicated that hydrogen bond lengths were mainly distributed around 0.282 6 nm, with fewer hydrogen bonds between PVA and H2O, and more hydrogen bonds between H2O and HAN, H2O and H2O. The model density was 1.405 g/cm3, which was highly consistent with the experimental values. At 283 K, 293 K and 303 K, the tensile modulus of ECSP gel model decreased in turn, and the shear modulus firstly increased and then decreased. The tensile modulus and shear modulus of ECSP gel model increased at 15 K/600 ps cooling rate. The ambient temperature during the cooling process after the preparation of ECSP should not be too high, as it can easily cause a rapid decline in the mechanical properties of ECSP. Rapid cooling after ECSP preparation can improve the mechanical properties of ECSP.