Molecular dynamics simulations on the structures and properties of ε-CL-20-based PBXs——Primary theoretical studies on HEDM formulation design

Five polymer bonded explosives (PBXs) with the base explosiveε-CL-20 (hexanitrohexaazaisowurtzitane), the most important high energy density compound (HEDC), and five polymer binders (Estane 5703, GAP, HTPB, PEG, and F2314) were constructed. Molecular dynamics (MD) method was employed to investigate their binding energies (Ebind), compatibility, safety, mechanical properties, and energetic properties. The information and rules were reported for choosing better binders and guiding formulation design of high energy density material (HEDM). According to the calculated binding energies, the ordering of compatibility and stability of the five PBXs was predicted as ε-CL-20/PEG ＞ ε-CL-20/ Estane5703 ≈ε-CL-20/GAP ＞ ε-CL-20/HTPB ＞ ε-CL-20/F2314. By pair correlation function g(r) analyses, hydrogen bonds and vdw are found to be the main interactions between the two components. The elasticity and isotropy of PBXs based ε-CL-20 can be obviously improved more than pure ε-CL-20 crystal. It is not by changing the molecular structures of ε-CL-20 for each binder to affect the sensitivity. The safety and energetic properties of these PBXs are mainly influenced by the thermal capability (C°p) and density (ρ) of binders, respectively.     

分子动力学模拟浓度和温度对TATB/PCTFE PBX力学性能的影响

为探讨高聚物粘结炸药(Polymer Bonded Explosive, PBX)的力学性能随温度和高聚物浓度而变化的规律, 用分子动力学(MD)方法和compass力场, 对著名高能炸药1,3,5-三氨基-2,4,6-三硝基苯(TATB)与常用高聚物粘结剂聚三氟氯乙烯(PCTFE)所构成的TATB/PCTFE PBX进行模拟计算. 结果表明, 在一定范围内, 随高聚物浓度的增加, PBX的弹性系数和模量减小, 表明其刚性减小、弹性增加; 而随温度的升高, PBX的刚性减小、弹性增强. 还发现PBX的结合能随浓度增高而增大, 随温度升高而减小.     

环四甲撑四硝胺/1,3,5-三氨基-2,4,6-三硝基苯共晶炸药的分子模拟研究

构建环四甲撑四硝胺 (HMX) /1,3,5-三氨基-2,4,6三硝基苯 (TATB)不同的共晶结构模型,用分子动力学(MD)模拟得到其平衡结构。基于平衡结构进行X射线粉末衍射（XRD）图谱模拟和能量计算。结果表明,与纯组分相比,HMX/TATB共晶结构的X射线粉末衍射图与主成分HMX相似,并均有新峰出现;TATB在HMX表面自由能最高、生长速率最慢的 (0 1 1) 晶面上发生取代后的能量最低,结构最稳定,据此推测在制备HMX/TATB共晶炸药过程中,TATB分子更容易进入HMX自由能高的晶面,得到结构稳定的共晶而使HMX变得更为钝感。     

TATB/氟聚物PBX力学性能、结合能和爆炸性能的模拟计算

Molecular dynamics （MD） method was used to simulate 1,3,5-triamino-2,4,6-trinitrobenzene （TATB） coated with fluorine containing polymers. The mechanical properties and binding energies of PBXs were obtained. It was found that when the number of chain monomers of fluorine containing polymers was the same, the elasticity of TATB/F2314 was increased more greatly than others and the binding energy of TATB/F2311 was the largest among four PBXs. Detonation heat and velocity of such four PBXs were calculated according to theoretical and empirical formulas. The results show that the order of detonation heat is TATB〉TATB/PVDF〉TATB/F2311〉TATB/ F2314 〉 TATB/PCTFE while the order of detonation velocity is TATB/PVDF 〈 TATB/F2311 〈 TATB/F2314 〈 TATB/PCTFE 〈TATB.     

HMX/TATB复合材料弹性性能的MD模拟

用分子动力学(MD)方法COMPASS力场, 分别在正则系综(NVT)和等温等压系综(NPT)下, 模拟计算了著名常用高能炸药HMX(环四甲撑四硝胺)与著名钝感炸药TATB (1,3,5-三氨基-2,4,6三硝基苯)所构成的混合体系在室温时的弹性性能和结合能. 结果表明, 在NVT和NPT两种系综下模拟所得结果呈平行一致的趋势; 与纯HMX相比, HMX/TATB复合材料的拉伸模量、体模量和剪切模量均有所下降; 在NVT系综下, 还完成了HMX/TATB混合体系的不同温度的MD模拟. 发现当温度在245～345 K范围时, 体系的刚性和弹性变化很小; 但当温度达到395 K时, 材料的刚性减弱, 柔性增强.     

CL-20/HMX共晶及其为基PBX界面作用和力学性能的MD模拟研究

为提高共晶炸药的实际使用价值, 改善其安全性和力学性能, 以CL-20/HMX共晶炸药为基, 分别添加2种高聚物粘结剂Estane 5703(聚氨基甲酸乙酯)和HTPB(端羟基聚丁二烯), 共构建两种共晶基高聚物粘结炸药(PBX)模型, 进行细致的295 K NPT分子动力学(MD)模拟研究. 通过两种PBX模型及其与该共晶炸药的MD模拟结果比较表明, 与基炸药之间的结合能Estane 5703大于HTPB, 预示含少量Estane 5703的PBX稳定性和相容性更佳; 对相关函数g(r)揭示粘结剂与基炸药界面相互作用的方式, 以基炸药中H分别与Estane 5703中羰基O和HTPB中端羟基O之间的氢键较强. 与CL-20/HMX共晶炸药相比, 少量粘结剂Estane 5703或HTPB的加入, 使弹性系数C_ij下降, 拉伸模量(E)、体积模量(K)和剪切模量(G)均显著减小, 而泊松比(ν), 柯西压(C₁₂－C₄₄)和K/G值明显增大, 表明PBXs体系刚性减小, 延展性增强, 力学性能大为改善. 少量粘结剂包覆使PBXs致钝, 主要归因于其隔热、吸热并使体系变“软”的缓冲作用, 而界面作用造成的分子结构引发键键长变化变为次要因素.     

Salt concentration dependence of the mechanical properties of LiPF6/poly(propylene glycol) acrylate electrolyte at a graphitic carbon interface: A reactive molecular dynamics study

This reactive molecular dynamics study explores the salt concentration dependence of the viscoelastic and mechanical failure properties of a poly(propylene glycol)/LiPF₆‐based solid polymer electrolyte (SPE) at a graphitic carbon electrode interface. To account for the finite‐size effect of interface‐confined SPE films, the properties of two distinct film thicknesses are compared with the respective bulk properties. Additionally, the effect of uniaxial compression in the interface‐normal direction on free energy profiles of Li‐ion SPE‐desolvation is studied. © 2018 The Authors. Journal of Polymer Science Part B: Polymer Physics Published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 718–730     

Molecular dynamics simulation of surface morphology and thermodynamic properties of polyaniline nanostructured film

To develop predictive models in nanostructured films, there is an ongoing research to validate molecular dynamics (MD) simulation results with experimental data. The morphology and surface topography of polyaniline (PANI) nanostructured film coated on a TiO₂ nanocrystalline surface were investigated by scanning electron microscopy and atomic force microscopy, respectively. The atomistic model of the simulated PANI was generated using energy minimization with a condensed‐phase optimized molecular potential for atomistic studies force field function to reach a thermodynamic equilibrium state. Various parameters of PANI such as density, energy, cavity size, and free volume distributions are calculated. MD simulation has also been used to obtain specific volume (V) as a function of temperature (T). It is demonstrated that this V–T curve can be used to determinate glass transition temperature T_g, reliably. Although experimental data available for the PANI film are very limited, simulation results such as density and T_g are in good agreement with the experimental values reported in the literature. Comparison of the surface topography of PANI demonstrates a reasonable trend between atomic force microscopy image analysis and the MD simulation results at various temperatures. Copyright © 2014 John Wiley & Sons, Ltd.     

RDX基PBX的模型、结构、能量及其与感度关系的分子动力学研究

以RDX（环三亚甲基三硝胺）为基、PS（聚苯乙烯）为粘结剂构成PBX（高聚物粘结炸药）的MD（分子动力学）模拟初始模型.比较分别以1根46链节和2根23链节PS置于RDX（001）晶面上的两种（PBX1和PBX2）模型下的MD模拟结果,发现二者的结构、相互作用能和力学性能均很接近.取PBX2进行5种温度（195,245,295,345和395 K）下的NPT系综、MD模拟系统研究,发现随温度依次升高,各体系中RDX引发键N NO2键的最大键长（Lmax）递增,N–N键连的N与N之间的双原子作用能（EN-N）和内聚能密度（CED）递减,与感度随温度升高而增大的实验事实相一致.综合已有工作,对高能复合材料（如PBX和固体推进剂等）的感度理论研究,建议关注其中易爆燃组分在外界刺激下的结构和能量变化,其引发键Lmax和作为引发键强度度量的双原子作用能（如EN-N）,可作为热和撞击感度相对大小的理论判据.     

Molecular dynamics and mechanical properties correlations of PA6/PPO blends compatibilized with SMA

The effects of the compatibilizer, styrene maleic anhydride (SMA‐8% MA) upon the change of morphology and molecular dynamics of polyamide‐6 (PA6) and poly (2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) blends were investigated by means of solid‐state NMR techniques. With increasing amounts of SMA, the domains correspond to PA6 and PPO are reduced and the polymer segmental mobility increased. The correlation between NMR relaxation time, T, and the bulk mechanical properties provide a molecular level understanding of the modification of molecular dynamics by the compatibilizer (SMA). The correlation shows that the tensile strength is governed mainly by the morphology, but modulated by the PA6 crystallinity, while the tensile elongation and impact strength are closely affected by both the molecular mobility and morphology. The annealing process improved only the tensile strength, but deteriorated tensile elongation and impact strength due to the increase of PA6 crystallinity, which induced phase separation after annealing. This study raised an important point that the polymer mechanical properties are most sensitive to the molecular structure and dynamics take place within the range of 20 Å to few hundred Å. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1155–1163, 1999     

偶联剂对TATB造型粉表面性质及力学性能的影响

采用偶联技术制备TATB造型粉，研究了偶联剂加入前后TATB造型粉的表面行为及其力学性能。结果表明采用偶联技术能够改善TATB造型粉的力学性能和氟橡胶对TATB的粘附。其中，KH550是一种较为理想的改善TATB造型粉性能的偶联剂。     

Molecular dynamics simulation of water near nanostructured hydrophobic surfaces: interfacial energies.

We present results from molecular dynamics simulations of water near structured hydrophobic surfaces. The surface structures reported herein are a planar alkane crystal as a reference and crystals with a hole and a protrusion of approximately 2.5 nm diameter and 0.5 nm depth or height. All indicators show that surface structuring increases the hydrophobicity: The water density is reduced near the structure elements, and the number of residual contacts between water and the surface decreases by about 40 % with respect to the planar surface. Thermodynamic integration shows that the interfacial energy of the structured surfaces is about 7 mJ m(-2) higher for structured surfaces than for the planar surface. The hydrophobicity increases by a similar amount for the hole and the protrusion geometries compared to the planar surface.     

Molecular dynamics simulation of brushes formed by star polyelectrolytes under theta solvent conditions

Using molecular dynamics simulations, we have studied polyelectrolyte brushes formed by partially or fully charged star polymers tethered on a planar surface under theta solvent conditions. The diagram of states for salt‐free solutions differs in the location of osmotic regime (OB) compared with the respective diagram reported by Borisov and Zhulina. In contrast, simulation results dictate that the OB regime appears for values of the ratio F /α ^?1/2 l_B ^?1 much larger than unity, which is the threshold of counterion localization, with F denoting the branch functionality, α the charged units fraction and l_B the Bjerrum length. The simulation results support that the brush height scaling laws H ～ α ² l_B F ^1.049S ³s ^?1 and H ～ α^0.302 F ^0.23S for the charged Pincus Brush (PB) and osmotic (OB) regimes, respectively, where S is the spacer length and s is the grafted area per star chain. The respective theoretical scaling laws are H ～ α ² l_B F ^1.88S ³s ^?1 and H ～ α ^1/2 F ^0.44S . © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 1110–1117     

Theoretical investigation of polymer molecular structure influence on dielectric properties and mechanical properties

Triboelectric nanogenerator (TENG) technologies have explosive development in the field of energy harvesting and self-powered sensing. As the key element of triboelectric devices, dielectric polymers have obtained much attention in recent years. The dielectric properties of polymer determine the output performance of TENG. In this paper, we take silicone rubber as an example of dielectric polymers, to study the properties of molecular structure influence on the dielectric properties and mechanical properties by the molecular dynamics simulation method. The free volume fraction, dielectric constant, and mechanical properties of silicone rubbers with different branch chains were calculated. The dielectric constant is highly related to the free volume distribution and the dipole moments of silicone rubbers with different amounts of branch chains. For fewer branch chains silicone rubber, the free volume distribution contributes most to the dielectric constant; for more branch chains silicone rubber, the dipole moment dominates the dielectric constant. Therefore, the silicone rubber ratio has a great influence on the dielectric constant of silicone rubber. With the increase of temperature, the dielectric constant of 2-chain silicone rubber increases at first and then decreases, and the maximum value is obtained near 300 K. Therefore, it is necessary to control the temperature when silicone rubber is used as a dielectric material. This work can be a guide for improving the dielectric properties of silicone rubber, and it provides a new approach to the optimal design of high-performance triboelectric nanogenerators.     

Brillouin light scattering studies of the mechanical properties of polystyrene/polyisoprene multilayered thin films

We have used Brillouin light scattering (BLS) to investigate the mechanical properties of thin polystyrene (PS) and polyisoprene (PI) films incorporated in a multilayer geometry consisting of alternating layers of the two polymers. All samples had a total thickness h ∼ 1600 Å, and consisted of between 2 and 10 individual polymer films; individual layer thicknesses were as small as 160 Å. Ellipsometry was used to determine the thickness of the PS and PI layers. The velocities of several high-frequency film-guided mechanical waves were measured using BLS and the results are compared with values calculated using an effective medium approach. The effective elastic constants of the multilayered films were obtained from those determined for thick films of PS and PI. Remarkable agreement was obtained between the measured and calculated velocities even for samples in which the individual layer thicknesses were much less than the unperturbed size of the polymer molecules. These results suggest that the mechanical properties of polymers change very little even when the molecules are forced into highly confined geometries. © 1996 John Wiley & Sons, Inc.     

冲击载荷下TATB晶体滑移和各向异性的分子动力学研究

采用ReaxFF反应力场和分子动力学方法,研究了1,3,5-三氨基-2,4,6-三硝基苯(TATB)炸药晶体在沿不同方向冲击载荷下的滑移和各向异性。冲击方向分别垂直于(101)、(111)、(011)、(110)、(010)、(100)和(001)晶面,冲击强度为10 GPa。研究结果表明,各冲击方向下可能被激发的滑移系均在{001}面,而其它滑移系均因很大的剪切阻力不容易被激发,这与TATB晶体沿c轴的层状结构和平面分子结构相符。预测了七个冲击方向下最容易被激发的滑移系,分别为(101)/{001}100、(111)/{001}010、(011)/{001}010、(110)/{001}010、(010)/{001}110、(100)/{001}120和(001)/{001}010。TATB晶体的冲击响应具有各向异性,动力学过程中体系的应力、能量、温度和化学反应都依赖于冲击方向。对垂直于(100)和(001)晶面的冲击,体系在滑移过程中遭遇的剪切阻力较高、持续时间较长,使得能量和温度较快升高,化学反应较容易发生;对垂直于(101)和(111)晶面的冲击,体系在滑移过程中遭遇的阻力较小且出现次数少,使得能量和温度缓慢升高,化学反应不易发生;对其余冲击方向,体系的响应居中。据此评价了7个冲击方向的相对敏感程度:(101)、(111)(011)、(110)、(010)(100)、(001)。本研究有助于在微观层次深入认识动载荷下TATB的响应机制、结构与性能的关系,为高能低感炸药的设计和研制提供理论参考。     

Molecular dynamics simulation on the interaction between polymer inhibitors and anhydrite surface

Investigation on the microscopic interaction between polymer inhibitors and calcium sulfate will be helpful for understanding its scale inhibition mechanism and can provide a theoretical guidance to developing new scale inhibitors. In this work, molecular dynamics simulations with COMPASS force field have been performed to simulate the interaction between hydrolyzed polymaleic anhydride (HPMA), polyaspartic acid (PASP), polyepoxysuccinic acid (PESA), polyacrylic acid (PAA) and the (001) and (020) surfaces of anhydrite (AD) crystal with and without water. The results show that the sequence of binding energies between four polymer inhibitors and AD (001) and (020) with water is PESA > PASP > HPMA > PAA. The binding energy of the same polymer inhibitor on AD (001) is smaller than that on AD (020). Water molecules weaken the deformations of HPMA and PAA but aggravate those of PASP and PESA. Natural bond orbital (NBO) charges of the repeat units of polymer inhibitors were calculated by B3LYP/6‐31G* method. The Coulomb interaction is formed between the O atoms of polymer inhibitors and the Ca atoms of AD crystal. The system of polymer–AD is mainly contributed from the non‐bonding interaction. Polymer inhibitors do not interact directly with AD crystal, but indirectly through the interactions between inhibitor–H₂O and H₂O–AD, i.e. water molecules participate in scale inhibition of polymer inhibitors to AD crystal. Water molecules cannot be ignored when the interaction models are constructed, i.e. solvent effect cannot be ignored. Copyright © 2015 John Wiley & Sons, Ltd.     

Selection of solvent for the mechanical activation process: A molecular dynamics simulation and experiment study

Herein, molecular dynamics simulations and experiments were carried to select solvent for the mechanical activation process. The interaction between solvent and each component of the Al‐PTFE mechanical activated energy composites has been studied by means of molecular dynamics. Then, the status of Al and PTFE in solvent was analyzed, and the microstructure of the composite was also studied combined with experiment. At last, the mechanical activated energy composites were prepared with n‐hexane as the solvent. The results show that the adsorption of PTFE, toluene, and hexane on the (0 0 1), (0 1 0), and (100) surface of Al₂O₃ is stable. Al₂O₃ (0 0 1) surface and Al₂O₃ (0 1 0) surface interact with 3 substances mainly via the electrostatic force. Al₂O₃ (1 0 0) surface interacts with 3 substances mainly via the van der Waals force. The binding energies of toluene‐Al₂O₃ and hexane‐Al₂O₃ are larger than PTFE‐Al₂O₃. PTFE cannot adsorb on the surface of aluminum in the existence of n‐hexane and toluene. n‐Hexane can make PTFE disperse uniformly, and a considerable part of these PTFE will be coated on the surface of Al after n‐hexane is removed. The uniformity of Al/PTFE mechanical activated energetic composites prepared in n‐hexane is good, and it increases with the milling time.