PEG/N-100中增塑剂扩散性能的微观与介观模拟

Micro and Mesoscopic Simulations on Diffusion Behaviors of Plasticizers in PEG/N-100

为探究含能钝感增塑剂三羟甲基乙烷三硝酸酯(TMETN)在硝酸酯增塑聚醚(NEPE)推进剂黏合剂中的扩散性能,采用分子模拟(MD)法比较了硝化甘油(NG)、1,2,4-丁三醇三硝酸酯(BTTN)及TMETN在聚乙二醇/固化剂(PEG/N-100)中的扩散系数、分析了扩散机理,并讨论了温度及增塑比对TMETN扩散性能的影响。结果表明:增塑剂扩散系数的大小顺序为NG>BTTN>TMETN,这说明TMETN的扩散能力较弱;从微观角度分析扩散的机理为:增塑剂与预聚体的分子间相互作用越强、体系的自由体积分数越小、增塑剂分子的尺寸越大,则增塑剂越难发生扩散;在三种增塑体系中,TMETN与PEG/N-100的结合能力最强、原子间氢键作用最强、该体系中PEG/N-100的自聚集能力最弱,且TMETN分子尺寸最大,故而TMETN最难发生扩散;随着温度升高,TMETN扩散系数的增加先缓慢后剧烈,这与高温加速老化的规律保持一致,分析温度对扩散机理的影响为:高温使原子间氢键作用峰值减小、位置后移,即增塑剂与黏合剂的相互作用减弱,并且体系的自由体积分数也变大;随着增塑比的增加(2.5、2.8、3),TMETN扩散系数减小,介观研究表明体系的相容性变好是其中的原因之一。

The diffusion coefficients and mechanisms of NG(nitroglycerin),BTTN(1,2,4-butanetriol trinitrate)and TMETN(trimethylolethane trinitrate)in PEG/N-100(polyethylene glycol/curing agent)were studied by molecular simulations. The order of diffusion coefficients is NG > BTTN > TMETN. By comparing the three systems,the weakest diffusion of TMETN was attributed to the following two aspects:firstly,the strongest binding force between TMETN and PEG/N-100 as well as the weakest self aggregation ability of PEG/N-100 in the system;secondly,the largest size of TMETN among the three plasicizer systems. The effects of temperature and plasticization ratio on the diffusion properties of TMETN were investigated. With the increasing temperature,the diffusion coefficient of TMETN increased slowly at first and then sharply,which was consistent with the law of accelerated aging at high temperature;the position of hydrogen bond moved backward and the peak value decreased owing to the high temperature,suggesting the weakened interaction between plasticizer and binder;meanwhile,the fractional free volume of system increased. With the increase of plasticization ratio(2.5,2.8,3),the diffusion coefficient of TMETN decreased. Mesoscopic studies showed that the improvement of compatibility was one of the reasons.