利用反应分子动力学研究CL-20不同晶型热响应的构象转变和初始分解  

Revealing the Thermal Responses of CL-20 Polymorphs by Conformer Transformation and Initial Decomposition Using ReaxFF Molecular Dynamics Simulations

作　　者：任春醒 李晓霞[1,2,3] 牛诗尧 曲文刚 高红旭[4] REN Chun-xing;LI Xiao-xia;NIU Shi-yao;QU Wen-gang;GAO Hong-xu(State Key Laboratory of Multiphase Complex Systems,Institute of Process Engineering,Chinese Academy of Sciences,Beijing 100190,China;Innovation Academy for Green Manufacture,Chinese Academy of Sciences,Beijing 100190,China;University of Chinese Academy of Sciences,Beijing 100049,China;Science and Technology on Combustion and Explosion Laboratory,Xi′an Modern Chemistry Research Institute,Xi′an 710065,China)

机构地区：[1]中国科学院工程研究所多相复杂系统国家重点实验室,北京100190 [2]中国科学院绿色制造创新研究院,北京100190 [3]中国科学院大学,北京100049 [4]西安近代化学研究所燃烧与爆炸技术重点实验室,陕西西安710065

出　　处：《火炸药学报》2022年第6期793-806,共14页Chinese Journal of Explosives & Propellants

基　　金：The National Natural Science Foundation of China(No.21373227,91641102);Open Research Fund of State Key Laboratory of Multiphase Complex Systems(No.MPCS-2021-D-03)。

摘　　要：为探究不同晶型CL-20的热稳定性差异,采用接近热分析实验的600~900K低温条件,利用长时间反应分子动力学ReaxFF MD模拟研究了4种CL-20晶型(α-、β-、γ-和ε-CL-20)的热分解初始过程,从初始构象转变和热分解动力学性质两方面刻画了不同晶型CL-20热响应的动态过程。结果表明,在较为温和的热刺激条件下,构象转变主导着4种CL-20晶型的初始热响应过程;依据分子构象动态转变可知,分子构象稳定性由高到低依次为:γ>β≈α>ε。模拟发现,ε-CL-20晶型受热ε构象可转为γ或ζ-CL-20,γ-CL-20晶型受热则发生γ构象转变为ζ构象,这些构象转变现象均与Russell等实验得到的CL-20相图吻合。模拟结果表明,ε-CL-20晶型热响应过程中早期的构象转变会诱导其分解反应的快速引发;γ-CL-20晶型则相对较为稳定,其构象转变和分解引发均滞后于ε-CL-20晶型;分解反应一旦引发,γ-CL-20晶型热分解的整体反应速率会快于ε-CL-20晶型。从失重和主要化学键断裂的动力学性质来看,ε-CL-20晶型的热稳定性要高于γ-CL-20晶型,这与Nedelko的热重实验结果定性一致。所获得的对热刺激下不同晶型CL-20的动态响应微观机制的认识,表明ReaxFF MD有可能为预测含能材料晶型转变的温度相图提供一种计算方法。To explore the difference in thermal stability of different CL-20polymorphs,the initial thermal decomposition of four CL-20polymorphs(α-,β-,γ-,andε-)were depicted using longtime ReaxFF MD simulations at relative low temperatures of 600—900K,which are close to the conventional thermal analysis experiments.The dynamic responses of varied CL-20polymorphs under heating were characterized by the initial conformer transformation and thermal decomposition kinetics.The results show that under relative mild thermal stimulation contidions,conformer conversion dominates the initial responses of four CL-20polymorphs.The molecular conformer stability of varied CL-20polymorphs ranks asγ>β≈α>ε.Under heating conditions,ε-CL-20converts toγorζconformers,andγ-CL-20converts toζconformer.The above conformational transition phenomenons agree broadly with experimental phase diagram of Russell et al.Conformer conversion fromεtoγoccurring very early inε-CL-20polymorph induces its fast initiation of decomposition reactions.In contrast,γ-CL-20is rather stable,and its conformer transformation and decomposition lags behindε-CL-20.Once the decomposition initiates,the overall decomposition rate ofγ-CL-20polymorph is higher than that ofε-CL-20polymorphs with increasing of thermolysis duration or temperatures.In terms of the reaction kinetics of weight loss and major bond cleavage during the entire thermolysis process,the thermal stability ofε-CL-20polymorph is higher than that ofγ-CL-20,which agrees with Nedelko′s TG experiments.This work suggests that ReaxFF MD simulations may be served as a computational prediction method for temperature phase diagram of polymorph conversion of energetic materials.

关 键 词：物理化学 CL-20晶型 构象转变 热分解 反应分子动力学 

分 类 号：TJ55[兵器科学与技术—军事化学与烟火技术] O64[理学—物理化学]