氟化物势能函数和热力学性质的分子模拟研究进展

发展干法铀纯化工艺对我国核能产业发展至关重要,但一直受基础热力学数据缺失的限制。因分子模拟方法具有高效、环保、经济的预测特性,为解决以上挑战提供了机遇。本文归纳总结了分子模拟计算物质热力学性质的多种方法,系统地介绍了模拟计算中不同力场和势能函数的发展情况和优势/缺陷,指明了对氟化物体系的适用性。随后,综述了氟化物热力学性质的分子模拟进展,分析并评价了力场与势能函数选择对计算结果的影响,表明与温度相关的分子间势能函数(TDIP)在第二维里系数、黏度和气液共存性质等的模拟中展现的较高模拟效率和准确性。为进一步提升计算数据的准确性,尚有很多基础科学问题需要解决。因此,本文最后对分子模拟方法在氟化物热力学领域的发展进行了展望,以期为工艺设计提供实践基础。     

分子模拟方法计算相平衡热力学性质的研究进展

化工单元操作与相平衡有着密不可分的联系,相平衡现象一直是化工工程师以及广大科研工作者们研究的热门课题。近年来随着计算机技术和统计力学的快速发展,应用分子模拟方法研究相平衡已成为热点。本文综述了近二十年来该领域的研究进展,归纳总结了分子模拟计算相平衡的多种方法以及4种常用的模拟力场。系统介绍并分析了相平衡分子模拟在宏观热力学数据计算、萃取剂筛选以及热力学机理分析等方面的应用情况,表明分子模拟方法在宏观热力学数据计算方面趋于成熟,能够准确模拟较多物系的相平衡数据,阐明了分子模拟方法在萃取剂筛选方面的优势,同时指出了分子模拟在热力学性质微观机理分析方面的不足和局限性,最后对分子模拟方法在相平衡领域的发展进行了展望。     

基于第一原理力场预测热力学参数的探讨

讨论用第一原理全原子力场计算热力学参数的可行性.新开发的TEAM力场,在用气、液相基本性质验证后,不加任何参数调整,直接用于计算具有代表性的几个分子液体在不同热力学状态下的密度、蒸发焓、混合焓、亨利常数、饱和蒸气压等热力学参数.初步结果表明：液体密度和蒸发焓的预测结果良好,在较大范围内可获得与实验数据相吻合的结果;而混合焓的准确预测需要纯液体内聚能的高精度模拟数据;亨利常数的计算对液体的密度极为敏感.后两种性质的计算均可用全原子力场但需要高质量的力场参数.为了采用全原子力场计算气液相平衡数据,提出了一种半经验的、基于积分Clausius-Clapeyron方程的循环自洽方法计算液体的饱和蒸气压.     

甲烷在石墨化炭黑上吸附平衡的分子模拟

采用GCMC法对不同温度和压力下纯CH4在石墨化炭黑上的吸附平衡进行了分子模拟研究,选用Lennard-Jones 12—6势能函数和联合原子力场参数（TraPPE）对体系进行势能计算,并将吸附平衡预测结果与实验数据进行了比较分析。结果表明,在所研究的温度范围内,除了在低压的一定区间外,GCMC模拟结果在中压和高压条件下与实验数据基本吻合,表明采用GCMC方法模拟甲烷分子在石墨化炭黑上的吸附平衡数据是可以进行准确预测的。在此基础上,利用模拟的吸附平衡数据计算不同温度下CH4的Henry常数进而到得极限吸附热,计算结果与实验数据接近。     

蒙皂石层间结构与性质关系的分子模拟研究进展

综述了计算机模拟中的分子力学、Monte Carlo和分子动力学模拟方法及其在蒙皂石层间结构中的应用进展,涉及粘土-水-离子体系的位能函数、粘土的水化和层间结构、热力学性质、物理机械性质和柱撑蒙脱石等各个方面.指出分子模拟对蒙皂石层间分子行为的基础研究将发挥重要作用.     

优化温度相关力场预测正构烷烃热力学性质

为了实现不同温度下正构烷烃及其混合物热力学性质的准确预测,以正构烷烃（n-C₄~C₁₀）为训练集,通过对全原子OPLS-AA力场中非键相互作用参数（ε）的模拟优化,得到了ε与对比温度（T_r）以及正构烷烃碳原子个数（N_C）的经验关系式。利用该关系式计算出不同温度不同种类的正构烷烃的ε值,预测了正构烷烃纯物质及其混合物的黏度、密度、扩散系数等物性,并将新力场模拟计算值与理论估算值以及实验值进行比较。结果表明,采用优化温度相关力场预测烷烃及其混合物的物性与实验值最为吻合。密度、黏度和扩散系数的预测值与实验值的相对偏差分别小于2%、5%和10%,显著优于目前的理论方法和原OPLS-AA力场模拟计算的预测值。上述温度相关力场参数的确立,对于利用分子动力学模拟方法准确地预测正构烷烃及其混合物的热力学性质具有重要的实际应用价值。     

机器学习辅助的纳米催化反应动力学研究进展

动力学模拟是催化反应动力学研究的重要手段之一，有助于理解催化反应的内在机理，对于设计高效稳定的纳米催化剂十分重要。基于经验力场的经典分子动力学计算速度快，但计算精度有限。基于第一性原理的分子动力学方法精度高，但计算速度慢，难以大规模实施。近年来，机器学习力场(MLFF)方法被广泛应用于势能面的开发，基于MLFF的分子动力学(MLFF MD)方法兼顾计算速度与准确性，为催化反应动力学研究带来了新契机。本文首先回顾了MLFF势能面构造的主要方法，对基于对称函数的描述符设计原理和以嵌入式网络为基础的描述符构建方法进行了阐述，展示了MLFF MD方法应用于催化剂结构/组分演变和催化反应过程动力学模拟中的最新进展，进一步展望了MLFF在长时动力学模拟中所面临的挑战。     

DMF的力场构建及乙腈-甲醇-DMF三元体系的汽液相平衡模拟

采用量子化学和Gibbs系综Monte Carlo模拟相结合的方法,对TraPPE-UA力场中缺失的N,N-二甲基甲酰胺（DMF）力场参数进行了补充,为含DMF多元体系的汽液相平衡模拟奠定了基础。采用新构建的力场参数,在NVT-Gibbs系综中计算了DMF的汽液相平衡性质,结果表明该力场能准确计算出DMF的饱和液相密度、蒸气压、沸点、临界值和蒸发焓。在NPT-Gibbs系综中,采用TraPPE-UA力场分别计算了乙腈-甲醇、DMF-甲醇、DMF-乙腈二元混合物的汽液相平衡性质,并与实验值进行了比较。模拟结果与实验值较为吻合,验证了力场模型的可靠性。最后在NPT-Gibbs系综中采用TraPPE-UA力场对乙腈-甲醇-DMF三元体系的汽液相平衡数据进行了预测,为设计和优化乙腈和甲醇的萃取分离过程提供了基础数据。     

应用重整化群理论计算超临界水的性质

采用重整化群理论计算了超临界水的性质.计算中考虑了密度涨落影响,水分子之间的势能采用Stockmayer函数.由临界温度回归得到的分子参数用来预测水在超临界和近临界区的热力学性质,并与实验结果进行比较.结果表明所采用的方法适合于预测水的超临界和近临界的热力学性质.     

优化温度相关力场预测正构烷烃热力学性质

为了实现不同温度下正构烷烃及其混合物热力学性质的准确预测,以正构烷烃(n-C4~C10)为训练集,通过对全原子OPLS-AA力场中非键相互作用参数(ε)的模拟优化,得到了ε与对比温度(Tr)以及正构烷烃碳原子个数(NC)的经验关系式。利用该关系式计算出不同温度不同种类的正构烷烃的ε值,预测了正构烷烃纯物质及其混合物的黏度、密度、扩散系数等物性,并将新力场模拟计算值与理论估算值以及实验值进行比较。结果表明,采用优化温度相关力场预测烷烃及其混合物的物性与实验值最为吻合。密度、黏度和扩散系数的预测值与实验值的相对偏差分别小于2%、5%和10%,显著优于目前的理论方法和原OPLS-AA力场模拟计算的预测值。上述温度相关力场参数的确立,对于利用分子动力学模拟方法准确地预测正构烷烃及其混合物的热力学性质具有重要的实际应用价值。     

生物质基铀吸附材料的研究进展

铀资源是国家核工业发展的重要战略资源,安全可持续铀资源供应是核电健康发展的关键。除铀矿资源外,绿色海水提铀技术是最有应用潜力的铀资源供应途径。吸附法是海水提铀和含铀废水处理的常见方法,面对复杂的海洋环境,设计和制备吸附量大、选择性高的吸附材料成为解决问题的关键,以高附加值的生物质基材料为铀吸附剂是一种新型的可持续发展策略。本文详细综述了生物质基铀吸附材料的分类、制备方法及其吸附性能,概括了生物质基吸附材料的研究现状和热点,基于研究现状,展望了未来高效生物质基吸附材料在海水提铀方面的发展方向和研究趋势。     

Recent advances of pharmaceutical crystallization theories

As a technology of separation and purification, crystallization plays a vital role in diverse industries such as inorganic salt, pharmaceutical, and food industries, which has a huge impact on purity, crystal polymorph, crystal morphology, and particle size distribution of final products. In the past few decades, with the rapid advancement of experimental approaches and molecular simulation methods, considerable advances in the interpretation of crystallization mechanisms have been obtained, promoting the investigation and understanding of crystallization theories greatly. In this review, the advances of pharmaceutical crystallization theories in recent years from the perspectives of nucleation and crystal growth are summarized and discussed. Two thermodynamic models that are helpful in the study of the crystallization mechanisms will be introduced. In this section, the perturbed-chain statistical associating fluid theory (PC-SAFT) and a chemical-potential-gradient model will be introduced, which have been successfully applied in pharmaceutical solubility prediction, the research of dissolution mechanism as well as dissolution kinetics analysis. These two models are expected to be applied to the study of pharmaceutical crystallization process and mechanism. Furthermore, molecular simulation based on the interaction between particles can provide structural information, thermodynamics, and dynamics properties of complex systems at the molecular level, like intermolecular interaction and surface adsorption energies. Application and some shortcomings of molecular simulation, especially molecular dynamics simulation, in the field of pharmaceutical crystallization will be expounded.     

Purification of carbon nanotubes

It is predicted theoretically and understood experimentally that carbon nanotubes (CNTs) possess excellent physical and chemical properties and have wide-range potential applications. However, only some of these properties and applications have been verified or realized. To a great extent, this situation can be ascribed to the difficulties in getting high-purity CNTs. Because as-prepared CNTs are usually accompanied by carbonaceous or metallic impurities, purification is an essential issue to be addressed. Considerable progress in the purification of CNTs has been made and a number of purification methods including chemical oxidation, physical separation, and combinations of chemical and physical techniques have been developed for obtaining CNTs with desired purity. Here we present an up-to-date overview on the purification of CNTs with focus on the principles, the advantages and limitations of different processes. The effects of purification on the structure of CNTs are discussed, and finally the main challenges and developing trends on this subject are considered. This review aims to provide guidance and to stimulate innovative thoughts on the purification of CNTs.     

Using viscoelastic modeling and molecular dynamics based simulations to characterize polymer natural fiber composites

The potential for polymer natural fiber composites for manufacturing storage units for products with high ethanol content is explored. The influence of ethanol diffusion into the microstructure of the storage unit on its long-term mechanical (specifically creep compliance) and viscoelastic properties are measured. Burger's model for polymer viscoelasticity is used to predict durability and other fundamental properties of the composite based on the creep compliance trends. Properties such as the Maxwell moduli and Maxwell viscosities are then modeled as a function of net ethanol uptake and the concentration of natural fiber dispersed phase. Later, a combination of classical molecular dynamics (MD) and semi empirical modeling is used to predict the trends in ethanol diffusion coefficient as a function of temperature and natural fiber concentration. The most efficacious models for this purpose and the ways and means of further improving the simulation accuracy are discussed.     

Tribological properties of hydrogenated amorphous carbon under dry and lubricated conditions

Diamond-like carbon (DLC) coatings are considered as potential surface coatings for many engineering applications including gears and engine parts. It is important to know whether conventional extreme pressure (EP) additive-containing oil can work with DLCs and provide tribological performance as effective as they provide on steel surfaces. This study examines the friction and wear properties of hydrogenated amorphous carbon (a-C:H) under dry, base oil (BO)- and fully formulated gear oil (FF)-lubricated conditions. Pronounced graphitisation occurs due to rubbing under dry condition and provides low friction but promotes wear. However, BO and FF greatly suppress graphitisation and wear. Tribofilms formed from FF in a-C:H/steel contact appear to exhibit superior antiwear properties than those formed in steel/steel contact.     

碳纳米管的纯化

介绍了碳纳米管的结构特征和种类,并详尽论述了近年来碳纳米管的提纯方法和条件,并对各种方法进行比较和总结。     

Separation of light hydrocarbons with ionic liquids: A review

Light hydrocarbons(C_1–C_4) are fundamental raw materials in the petroleum and chemical industry. Separation and purification of structurally similar paraffin/olefin/alkyne mixtures are important for the production of highpurity or even polymer-grade light hydrocarbons. However, traditional methods such as cryogenic distillation and solvent absorption are energy-intensive and environmentally unfriendly processes. Ionic liquids(ILs) as a new alternative to organic solvents have been proposed as promising green media for light hydrocarbon separation due to their unique tunable structures and physicochemical properties resulting from the variations of the cations and anions such as low volatility, high thermal stability, large liquidus range, good miscibility with light hydrocarbons, excellent molecular recognition ability and adjustable hydrophylicity/hydrophobicity. In this review, the recent progresses on the light hydrocarbon separation using ILs are summarized, and some parameters of ILs that influence the separation performance are discussed.     

碳纳米管的纯化、性能及应用

碳纳米管因具有独特的结构、性能及广泛的应用前景而受到科学界的关注,然而,所制备的碳纳米管均含有碳杂质和金属杂质,影响其性能并限制其应用。分析了碳纳米管的物理纯化法及化学纯化法的特点,在此基础上综述了物理与化学法相结合的综合纯化法,并介绍了碳纳米管的力学性能、场发射性能和电磁性能及其在相关领域中的应用进展。     

Research progress of graphene oxide membrane for water purification

Graphene oxide membranes have ultra-high water flux, controllable interlayer spacing and excellent separation properties. These outstanding characteristics make graphene oxide membranes promising to be a new generation of membrane materials and used for the precise separation of substances in the water environment. At present, researchers have performed numerous studies on graphene oxide membranes and achieved breakthrough results, including the transfer behavior of water in the membrane, the separation mechanism of the membrane and the preparation methods of the membrane, etc. However, there is still a lack of comprehensive understanding of graphene oxide membranes. This review systematically described the structural properties and structure-effect relationships of graphene oxide membrane, and summarized the typical preparation methods. In terms of the challenges faced by graphene oxide membrane in practical application, we focused on the existing modification methods of graphene oxide membrane. The applications of graphene oxide membrane in various water environments were also discussed. Finally, the future development of graphene oxide membrane was summarized and prospected. The aim of this paper is to provide novel ideas for the design and synthesis of high-performance graphene oxide membranes for water purification.