丙炔基双酚A醚硼聚合物热解过程的ReaxFF分子动力学模拟

聚合物的热解过程涉及的化学反应较为复杂,难以通过测试表征的手段深入探究其机理。本研究在实验表征的基础上,结合ReaxFF分子动力学(ReaxFF-MD)模拟方法,研究了丙炔基双酚A醚硼聚合物(PB)的热解过程。通过观察升温过程中PB的结构变化,可得到其热解过程中的断键顺序。此外,采用ReaxFF-MD模拟,其研究结果不仅验证了实验中热重-红外光谱联用(TG-FTIR)分析所得的PB热解生成小分子的主要组成为CH₄、H₂O、H₂ 和 CO,并且通过追踪上述小分子的生成过程可得到其主要的生成途径。以上研究结果表明,ReaxFF-MD模拟方法不仅有助于理解PB聚合物的热解机理,直观地反映出其热解产物生成途径,而且对聚合物耐热性能的研究有所借鉴。     

Modeling initial stage of phenolic pyrolysis: Graphitic precursor formation and interfacial effects

Reactive molecular dynamics simulations are used to study the initial stage of pyrolysis of phenolic polymers with carbon nanotube and carbon fiber. The products formed are characterized and water is found to be the primary product in all cases. The water formation mechanisms are analyzed and the value of the activation energy for water formation is estimated. A detailed study of graphitic precursor formation reveals the presence of two temperature zones. In the lower temperature zone (<2000 K) polymerization occurs resulting in the formation of large, stable graphitic precursors, while in the high temperature zone (>2000 K) polymer scission results in formation of short polymer chains/molecules. Simulations performed in the high temperature zone of the phenolic resin (with carbon nanotubes and carbon fibers) show that the presence of interfaces does not have a substantial effect on the chain scission rate or the activation energy value for water formation.     

分子模拟在纳米材料改性聚合物中的应用

介绍了近年来国内外分子模拟研究纳米改性聚合物材料的部分工作,主要包括纳米材料的结构模拟,力学性能的模拟,改性剂相互作用的模拟以及聚合物基纳米复合材料界面作用的模拟。     

ReaxFF动力学分析煤热反应机理

为了从微观角度研究煤的热解机理,找出热解过程中反应路径、中间产物等反应信息,用Reax FF动力学的方法分析煤的热反应机理。阐述了模拟过程中煤分子体系的构建、模拟结果的处理方法,介绍了如何通过监测自由基中间体种类,获得反应过程中常见产物的分布和基元反应,进而解释煤热解、氧化和水热处理等反应过程的机理,并对Reax FF动力学在煤热反应体系中复杂化学反应的研究前景进行展望。通过Reax FF方法可模拟煤的热反应过程,可以获得主要产物的生成路径、产物种类、产物的生成顺序等信息,还可以研究煤热解过程中煤分子间或与其他分子间的相互作用,进而分析热解过程中煤的热反应机理。后续可通过时温等效原理建立模拟温度与实际温度的定量关系,解决Reax FF方法模拟温度与实际温度不对应的问题;通过编写相应的后台程序缩短模拟计算结束后数据的处理时间。     

Vacuum pyrolysis of Prince Mine coal, Nova Scotia, Canada

Preliminary results are given on thermal decomposition characteristics of a high volatile A bituminous coal from Eastern Canada using vacuum pyrolysis experiments (pressure 2–200 mm Hg) over the temperature range 322–1000 °C. The objectives of the study were to determine the optimum temperature range for the formation of coal tar and to study the influence of reaction temperature on the nature of the solid residues. Significant decomposition reactions start at 300–400 °C and the optimum temperature range for the production of coal tar was 450–600 °C. The major gaseous products H₂S, CO₂ and CH₄ are formed up to 600 °C. Above 600 °C the coal decomposes mainly into CO and H₂. The solid residues are characterized by volatile matter content, calorific values and elemental analysis. The volatile matter content decreases rapidly from 322 °C and stabilizes at reaction temperatures > 750 °C. The 15% VM level, a minimum requirement in coal combustion processes, was reached at 500 °C. The changes in calorific values do not show any significant trend up to 600 °C, but decrease markedly above 600 °C. From the preliminary results vacuum pyrolysis is regarded as an effective process in which valuable coal tar by-products can be obtained from coal prior to its combustion.     

甲烷水合物声子导热及量子修正

采用平衡分子动力学方法模拟了甲烷水合物的导热,给出了30～150 K甲烷水合物的热导率。采用量子修正对分子模拟结果进行处理,可以得到更接近实验值的结果。当模拟温度低于德拜温度时,量子效应对分子模拟结果的影响较大。通过对热流自相关函数拟合得到了声学声子和光学声子的弛豫时间。结果显示,声子弛豫时间随温度增加逐渐减小,声学声子导热在水合物的导热中比重最大。随着碳氧原子之间相互作用力的增加,碳氧原子之间振动的耦合程度增加,甲烷水合物的热导率增加。     

Molecular Simulation of Oxygen Sorption and Diffusion in the Poly (lactic acid)

Grand canonical Monte Carlo and molecular dynamics simulation methods are used to simulate oxygen sorption and diffusion in amorphous poly(lactic acid) (PLA). The simulated solubility coefficient of oxygen is close to experimental data obtained from the quartz crystal microbalance but much higher than those from the time-lag method. This discrepancy is explained by using the dual-mode sorption model. It is found that oxygen sorption in PLA is predominantly Langmuir type controlled, em.e., through the process of filling holes. The time-lag method only takes into account oxygen molecules that participate the diffusion process whereas a large proportion of oxygen molecules trapped in the void have little chance to execute hopping due to the glassy nature of PLA at room temperature. The simulated diffusion coefficient of oxygen is reasonably close to the data obtained from the time-lag method. The solubility coefficient of oxygen decreases linearly with increasing relative humidity while its diffusion coefficient firstly decreases and then increases as a function of relative humidity.     

客体分子数对甲烷水合物导热性能影响的分子动力学模拟

本文通过采用EMD方法Green-Kubo理论计算263.15 K 晶穴占有率0-100% sI甲烷水合物导热系数,研究客体分子数对甲烷水合物导热性能的影响。模拟结果显示,甲烷水合物的低导热性能由主体分子构建的笼型结构决定。而在相同温压条件下,随着客体分子甲烷进入晶胞数目增多,晶穴占有率增大后,密度增大,同时客体分子对声子的散射也增强,二者均导致导热性能增强。     

Evaluating effects of applying different kinetic models to pyrolysis modeling of fiberglass‐reinforced polymer composites

This research evaluates the effects of applying different kinetic models (KMs), developed based on thermal analysis using thermogravimetric analysis data, when used in typical 1D pyrolysis models of fiberglass‐reinforced polymer (FRP) composites. The effect of different KMs is isolated from the FRP heating by conducting pyrolysis modeling based on measured temperature gradients. Mass loss rate simulations from this pyrolysis modeling with various KMs show changes in the simulations due to applying different KM approaches are minimal in general. Pyrolysis simulations with the most complex KM are conducted at several heat flux levels. Mass loss rate comparison shows there is good overlap between simulations and the experimental data at low incident heat fluxes. Comparison shows there is poor overlap at high incident heat fluxes. These results indicate that increasing complexity of KMs to be used in pyrolysis modeling is unnecessary for these FRP samples and that the basic assumption of considering thermal decomposition of each computational cell in comprehensive pyrolysis modeling as equivalent to that in a thermogravimetric analysis experiment becomes inapplicable at depth and higher heating rates. Copyright © 2014 John Wiley & Sons, Ltd.     

裂解气质联用（Py—GC—MS）在涂料及高分子聚合物分析方面的应用进展

采用裂解—气相色谱顺谱（Py-GC-MS）联用仪可对高分子聚合物、涂料等进行定性定量分析。对Py—GC—MS近年来在涂料与高分子聚合物上的分析应用进行了综述。     

Cross‐Scale Modeling and Simulation of Coal Pyrolysis to Acetylene in Hydrogen Plasma Reactors

Coal pyrolysis to acetylene in hydrogen plasma is carried out under ultrahigh temperature and milliseconds residence time. To better understand the complex gas‐particle reaction behavior, a comprehensive computational fluid dynamics with discrete phase model has been established, with special consideration of the particle‐scale physics such as the heat conduction inside particle. The improved chemical percolation devolatilization model that incorporates the tar cracking reactions is adopted. The model predictions are in good agreement with the performances of two pilot‐plant reactors. The simulations reveal the detailed unmeasurable information of gas phase and particle‐scale behaviors, then point out the facts that coal devolatilization almost finishes in the first 100 mm of the reaction chamber and the optimal particle diameter is suggested to be 20–50 μm. The different reactor performances during the scale‐up from 2‐ to 5‐MW unit are analyzed based on the detailed simulation results in combination with the operational experience. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2119–2133, 2013     

Computational study of impact of composition,density, and temperature on thermal conductivity of amorphous silicon boron nitride

We study thermal conductivity (κ) of amorphous silicon boron nitride (a‐SiBN) for different compositions and densities as a function of temperature using density functional theory (DFT) calculations and equilibrium molecular dynamic (MD) simulations. Our library of amorphous structures consists of network models comprising 100‐200 atoms and large‐scale models with up to 57 000 atoms generated using the empirical Marian‐Gastreich two‐body potential. Crystalline structures within the Si₃N₄‐BN system are considered as well. We use 2 distinct approaches to compute thermal conductivity of a‐SiBN. To estimate κ in the high‐temperature limit we feed Clarke's phenomenological model with elasticity data obtained by DFT calculations. We further perform equilibrium MD simulations and apply the Green‐Kubo method. This approach shows decrease of κ with increasing temperature and provides results at high temperatures that agree with results derived within Clarke's model. We find that κ of a‐SiBN depends on composition and increases as the BN content in the structure increases. The effect is pronounced at low temperature but almost vanishes at high temperature. Furthermore, thermal conductivity depends on density and porosity, with a linear relation between κ and density.     

聚酰胺酰亚胺的分子模拟

用COMPASS分子力场对一种具有特殊结构的聚酰胺酰亚胺（PAI）分子体系进行了分子模拟。先运用密度泛函理论（DFT）方法（PW91）研究了PAI单体的几何结构和电子结构,模拟结果表明,单体结构非平面。然后建立了非晶型的PAI周期性结构,运用分子动力学和分子力学法对其热性能、溶解性能和机械性能进行了研究。     

废塑料热解特性研究

采用热重分析法及差示扫描量热法,在氮气气氛下分别以5,10,15,20℃/min的升温速率对四种废弃塑料(PP、PS、PE、PET)热解过程及其动力学进行了研究。实验结果表明:四种塑料聚合物的非等温热解只有1个剧烈失重阶段,热稳定性的排序为:PSPETPPPE。随升温速率的提高,塑料的最大热解速度线性减小,对应的峰值温度线性升高,失重率基本不变。聚合物的热解机理满足一级反应动力学方程,且随着升温速率的提高,其活化能(E)和指前因子(A)线性增大,ln A与E之间存在近似的线性关系。     

醇类有机物热传导的分子动力学模拟及微观机理研究

传热是化工生产的基本问题之一,热导率是化工产品生产工艺设计中一类重要的热力学数据。通过非平衡分子动力学方法模拟了8种液态醇类有机物在不同温度下的导热过程。热导率计算值与实验值的平均相对偏差为3.77%。通过对热流的分解发现,分子动能、分子间库仑相互作用和分子内的二面角对醇类有机物的热传导影响较大。同时随着分子链增长,通过分子内相互作用进行的热传导逐渐占主导作用,表明醇类有机物的热能传输机理与分子结构有显著关系。此外,随着温度的升高,通过分子的动能、分子间库仑作用和分子内键角、键伸缩作用项传输的热流增大,表明温度对液态醇类有机物的热传导也有一定影响。本工作从微观分子间和分子内作用分析了液态醇类有机物结构和温度对热导率的影响,为液态有机物的热传导研究提供了微观依据。