PET/PEN blends of industrial interest as barrier materials. Part I. Many-scale molecular modeling of PET/PEN blends

Mesoscale molecular simulations, based on parameters obtained through atomistic molecular dynamics and Monte Carlo calculations, have been used for modeling and predicting the behavior of PET/PEN blends. Different simulations have been performed in order to study and compare pure homopolymer blends with blends characterized by the presence of PET/PEN block copolymers acting as compatibilizer. A many-scale molecular modeling strategy was devised to evaluate PET/PEN blend characteristics, simulate phase segregation in pure PET/PEN blends, and demonstrate the improvement of miscibility due to the presence of the transesterification reaction products. The behavior of distribution densities and order parameters of the compatibilized blends demonstrates that mixing properties improve significantly, in agreement with experimental evidences. Barrier properties such as oxygen diffusivity and permeability have also been evaluated by finite element simulations. Accordingly, many-scale modeling seems to be a successful way to estimate PET/PEN blend properties and behavior upon different concentrations and processing conditions.     

An Overview of the Physiochemical Nature of Metal-Extractant Species in Organic Solvent/Acidic Organophosphorus Extraction Systems

The interfacial behavior of metal-extractant species in the liquid/liquid extraction of metal ions still remain incompletely understood at the molecular level under high loading conditions. Traditionally, metal-extractant complexes in the organic phase under dilute conditions have been characterized by slope analysis. At high loading, the metal-extractant aggregates structure appears to change. The metal-extractant aggregates have been described as either polymers or reversed micelles. This behavior is difficult to confirm by direct experimental measurements. Recently, molecular modeling was used to study the molecular structure of metal-extractant aggregates. The study confirmed that the metal-extractant species are reversed micelles at high loading conditions.     

Molecular geometry effects and the Gibbs–Helmholtz Constrained equation of state

Differences in molecular size and shape have long been known to cause difficulties the modeling and simulation of fluid mixture behavior and generally manifest themselves as poor predictions of densities and phase equilibrium, often resulting in the need to regress model parameters to experimental data. A predictive approach to molecular geometry within the Gibbs–Helmholtz Constrained (GHC) framework is proposed. The novel aspects of this work include (1) the use of NTP Monte Carlo simulations coupled with center of mass concepts to determine effective molecular diameters for non-spherical molecules, and (2) the use of effective molecular diameters in the GHC equation to predict phase behavior of mixtures with components that have distinct differences in molecular size and shape. Numerical results for a CO₂–alkane, alkane–water and CO₂–alkane–water mixtures show that the proposed approach of combining molecular geometry with the GHC equation provides accurate predictions of liquid densities and two- and three-phase equilibrium.     

Molecular mobility in polycyanurate networks investigated by viscoelastic measurements and molecular simulations

The dynamic mechanical behavior of a series of polycyanurate networks has been studied in the glassy state as a function of cyanate conversion. Two relaxations, β and γ, were defined and the Arrhenius dependence and Starkweather treatments were applied. To understand the origin of these sub-T_g relaxations, molecular modeling (both mechanics and dynamics) was used on model molecules representative of the network structure. Two types of molecular motion were examined: rotation of the phenylene ring and crankshaft of the chain segment between crosslinks (i.e., triazine rings).     

Theoretical Models of Thermodynamic Properties of Supercritical Solutions

Abstract

Several separation processes, including supercritical extraction and supercritical fluid chroma-tography, take advantage of the striking solubility behavior of supercritical fluids. A general theoretical framework is presented for modeling thermodynamic properties of supercritical solutions based on the theory of Kirkwood and Buff. The theory is expressed in terms of the Kirkwood fluctuation integral from statistical mechanics and permits introduction of appropriate molecular solution approximations. Thus, the solute-solvent interaction may be expressed using a local composition approximation, for example, with an accurate equation of state for the pure solvent. This approach is illustrated for two molecular solution approximations and is compared with solubility and partial molecular volume data.     

复杂流体-固体界面相互作用热力学机制

具有复杂结构的纳微界面往往是界面复杂作用和宏观实验现象的主导因素。要准确描述界面处复杂流体的行为,需要引入能描述复杂流体-固体界面相互作用的分子热力学模型。本综述围绕分子热力学模型化方法拓展至纳微界面传递问题,提出“分子热力学建模+分子模拟+纳微实验”三者有机配合新思路。并针对复杂流体-固体界面相互作用的定量研究,着重综述了作者在热力学建模,分子模拟以及采用原子力显微镜 (atomic force microscopy,AFM) 实验方面的研究进展,创新性地提出将AFM定量化分析作为桥梁,用于构建分子模拟模型,描述复杂界面作用,揭示分子热力学机制,为构建纳微界面传递模型以及分子热力学模型由体相拓展至界面提供了可能。     

Compatible glassy polyblends based upon poly(2,6-dimethyl-1,4-phenylene oxide): Tensile modulus studies

The mechanical behavior of compatible glassy polyblends based upon poly(2.6-dimethyl- 1,4-phe nylene oxide) (PPO) was investigated. In particular, the influence of composition, molecular weight, and molecular weight distribution upon the tensile modulus of the blend was assessed. Various possible correlations between the experimentally determined moduli and theory are considered. Included are correlations with density, packing density, composite theory, and lattice fluid theory. The modeling of the properties of mixtures via Simplex lattice design is also presented. Finally, attention is given to the development of compatibility criteria based upon tensile modulus and density measurements.     

可持续的多功能纳米涂层的设计:一种目标驱动的多尺度系统论方法(英文)

Polymer nanocomposites have a great potential to be a dominant coating material in a wide range of applications in the automotive,aerospace,ship-making,construction,and pharmaceutical industries.However,how to realize design sustainability of this type of nanostructured materials and how to ensure the true optimality of the product quality and process performance in coating manufacturing remain as a mountaintop area.The major challenges arise from the intrinsic multiscale nature of the material-process-product system and the need to manipulate the high levels of complexity and uncertainty in design and manufacturing processes.In this work,the challenging objectives of sustainable design and manufacturing are simultaneously accomplished by resorting to multiscale systems theory and engineering sustainability principles.The principal idea is to achieve exceptional system performance through concurrent characterization and optimization of materials,product and associated manufacturing processes covering a wide range of length and time scales.Multiscale modeling and simulation techniques ranging from microscopic molecular modeling to classical continuum modeling are seamlessly coupled.The integration of different methods and theories at individual scales allows the quantitative prediction of macroscopic system performance from the fundamental molecular behavior.Furthermore,mathematically rigorous and methodologically viable approaches are pursued to achieve sustainability-goal-oriented design of material-process-product systems.The introduced methodology can greatly facilitate experimentalists in novel material invention and new knowledge discovery.At the same time,it can provide scientific guidance and reveal various new opportunities and effective strategies for achieving sustainable manufacturing.The methodological attractiveness will be fully demonstrated by a detailed case study on the design of thermoset nanocomposite coatings.     

Determining the molecular weight distribution of Pocahontas No. 3 low-volatile bituminous coal utilizing HRTEM and laser desorption ionization mass spectra data

Knowledge of the molecular weight distribution is important for rationalizing coal behavior. While many analytical approaches generate average data, inclusion of coal’s inherent structural diversity would improve molecular representations of coal and their usefulness. The molecular weight distribution of Pocahontas No. 3 coal was estimated based on a new approach coupling HRTEM lattice fringe image data and laser desorption ionization mass spectra (LDIMS), constrained by elemental and NMR data. Assuming a shape for the large aromatic coal molecules allows the determination of the aromatic raft size distribution, and prediction of the molecular weight distribution from the HRTEM lattice fringe image analyses. Similar-shaped molecular weight profiles were obtained from these different techniques. Both distributions showed a sharp rise, fall and long tail, with the HRTEM profile being shifted to a lower mass in comparison to the LDIMS data. The mean molecular weight of an aromatic raft, 289 Da, was similar to 299 Da a value reported from NMR data. Cross-linking the fringes generated a diverse network structure of aromatic clusters with a reasonable aromatic H/C ratio and a molecular weight distribution within the appropriate ranges from laser desorption data. A rationale for molecular diversity determination, necessary for large-scale molecular modeling, for a high-rank coal is proposed.     

Modeling nanomaterial physical properties: theory and simulation

ABSTRACT

A brief theory and simulation overview for the purpose of design is presented with examples applies to modeling the physical properties, behavior, and phenomena of nanomaterial. This review paper constructs perspectives that consider coupling traditional domains of simulation by novel pathways to produce accurate representations of nanomaterial properties, behavior and phenomena. It is all about size scaling and how different approaches are able to simulate, integrate or simply pass the baton to the next level of complexity. In macroscopic world, the atomic or molecular information alone may not be directly useful. Nor is the bulk information useful in the microscopic world without intimate knowledge of molecular makeup. Therefore, when designing Nanomaterials, knowledge of properties spanning the complete range of size is the prerequisite of a recommended self-consistent approach. In fact, regarding applications in both industry and academia, the simulation first approach often can lead to great savings in time. This review paper focuses mostly on optical and electronic properties but a section is added that provides a segue into mechanical properties for future consideration.     

A Review of Computational Methods in Materials Science: Examples from Shock-Wave and Polymer Physics

This review discusses several computational methods used on different length and time scales for the simulation of material behavior. First, the importance of physical modeling and its relation to computer simulation on multiscales is discussed. Then, computational methods used on different scales are shortly reviewed, before we focus on the molecular dynamics (MD) method. Here we survey in a tutorial-like fashion some key issues including several MD optimization techniques. Thereafter, computational examples for the capabilities of numerical simulations in materials research are discussed. We focus on recent results of shock wave simulations of a solid which are based on two different modeling approaches and we discuss their respective assets and drawbacks with a view to their application on multiscales. Then, the prospects of computer simulations on the molecular length scale using coarse-grained MD methods are covered by means of examples pertaining to complex topological polymer structures including star-polymers, biomacromolecules such as polyelectrolytes and polymers with intrinsic stiffness. This review ends by highlighting new emerging interdisciplinary applications of computational methods in the field of medical engineering where the application of concepts of polymer physics and of shock waves to biological systems holds a lot of promise for improving medical applications such as extracorporeal shock wave lithotripsy or tumor treatment.     

Modeling and closed‐loop control of particle size and initial burst of PLGA biodegradable nanoparticles for targeted drug delivery

An in‐house computer code based on artificial intelligence has been developed and applied in modeling and closed‐loop optimization of release behavior of Poly(lactic‐co‐glycolic acid) (PLGA) biodegradable particles. A series of micro‐ and nanoparticles were prepared via water‐in‐oil‐in‐water double emulsion to be loaded with albumin–fluorescein isothiocyanate conjugate as a typical drug. The interrelationship between input variables (molecular weight of polymer and stabilizer, polymer concentration, and sonication rate) and outputs (PLGA particle size and percentage of initial burst) was uncovered with the aid of artificial neural network modeling. The regression analysis confirmed acceptable correlation coefficients for the aforementioned responses, where the PLGA molecular weight played the most important role among the studied variables. Input variables needed to minimize PLGA size and PLGA initial burst were then obtained via multiobjective optimization performed by a genetic algorithm. PLGA nanoparticles were checked for particle size and particle size distribution using scanning electron micrographs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45145.     

状态方程模拟醇胺系统的密度和汽液相平衡

通过考虑醇胺分子间的缔合作用,结合先前开发的非缔合变阱宽链流体状态方程(SWCF-VREOS)建立了一个缔合方阱链流体状态方程,并利用方程模拟了醇胺系统的密度和汽液相平衡。通过关联不同温度下醇胺的饱和蒸气压和液体体积得到了18种醇胺流体的分子参数,新方程计算的饱和蒸气压和液体密度总的平均误差分别为0.94%和0.88%。结合简单的混合规则,将此方程扩展到混合系统。研究发现,建立的方程可预测二元和三元醇胺混合物的密度。当引入一个与温度无关的可调参数时,方程能满意关联二元系统的汽液相平衡数据,并可进一步预测多元混合系统的汽液相平衡,预示着新方程可模拟醇胺系统的相行为。     

聚合物共混相容性分子模拟进展

从分子模拟角度介绍如何模拟聚合物共混物相容性的方法，引入了溶解度参数和玻璃化温度。概括叙述了用分子模拟方法研究聚合物共混相容性的现状及应用，对分子模拟发展趋势作了展望。     

The application of molecular simulation in ash chemistry of coal

One of the crucial issues in modern ash chemistry is the realization of efficient and clean coal conversion. Industrially, large-scale coal gasification technology is well known as the foundation to improve the atom economy. In practice, the coal ash fusibility is a critical factor to determine steady operation standards of the gasifier, which is also the significant criterion to coal species selection for gasification. Since coal behaviors are resultant from various evolutions in different scales, the multi-scale understanding of the ash chemistry is of significance to guide the fusibility adjustment for coal gasification. Considering important roles of molecular simulation in exploring ash chemistry, this paper reviews the recent studies and developments on modeling of molecular systems for fusibility related ash chemistry for the first time. The discussions are emphasized on those performed by quantum mechanics and molecular mechanics, the two major simulation methods for microscopic systems, which may provide various insights into fusibility mechanism. This review article is expected to present comprehensive information for recent molecular simulations of coal chemistry so that new clues to find strategies controlling the ash fusion behavior can be obtained.     

New Molecular Descriptors to Identify Surfactants and Solubilizers from Electron Density Distributions

In many applications, such as substitution of nonrenewable molecules by renewable ones in formulations or screening of pharmaceutical compounds, knowing whether molecules have associating properties in the liquid phase (i.e., if they are surfactants, hydrotropes, cosolvents, solvosurfactants, or cosurfactants) prior to any experiment may be useful. In this work, two new molecular properties derived from local surface polarity of molecules, denoted as polarity moment and heteropolarity, are proposed. It is shown that when predicted from Density Functional Theory (DFT)-conductor-like screening model (COSMO) polarization charge densities, polarity moment, heteropolarity, and polarity can help determine whether molecules are surfactants or solubilizers (hydrotropes, cosolvents, and solvosurfactants) prior to any experimental measurements. Results also indicate that these molecular properties predict cosurfactant behavior, as fatty esters and long-chain fatty alcohols appear to cluster in a distinct region of the two-dimensional map built by the two molecular properties. In particular, for complex molecular structures, modeling interfacially relevant conformations appeared as an important step to avoid misclassification in the process of calculating the polarity moment.     

Dynamics of a continuous stirred tank reactor for styrene polymerization initiated by a binary initiator mixture. II: Effect of viscosity dependent heat transfer coefficient

The dynamic behavior of the solution polymerization of styrene in a continuous stirred tank reactor is analyzed with a mixture of tert-butyl perbenzoate and benzoyl peroxide as an initiator system. In the modeling of the reactor, a viscosity dependent reactor wall heat transfer coefficient is used to account for the changing heat transfer efficiency as monomer conversion and polymer molecular weight increase. The steady state and bifurcation behaviors have been investigated with the reactor residence time, initiator feed composition, initiator concentration, feed solvent volume fraction, and coolant temperature as bifurcation parameters. Unlike the reactors with constant heat transfer coefficient, the present system exhibits relatively simple steady state and dynamic bifurcation behaviors. Oscillatory behavior is observed only when the solvent volume fraction in the feed exceeds 0.2. The dynamic simulation of the reactor also indicates that a feedback temperature controller may fail to maintain the reactor temperature when the heat transfer coefficient changes as a result of process disturbances.     

The application of molecular simulation in ash chemistry of coal

One of the crucial issues in modern ash chemistry is the realization of efficient and clean coal conversion. Industrially, large-scale coal gasification technology is well known as the foundation to improve the atom economy. In practice, the coal ash fusibility is a critical factor to determine steady operation standards of the gasifier, which is also the significant criterion to coal species selection for gasification. Since coal behaviors are resultant from various evolutions in different scales, the multi-scale understanding of the ash chemistry is of significance to guide the fusibility adjustment for coal gasification. Considering important roles of molecular simulation in exploring ash chemistry, this paper reviews the recent studies and developments on modeling of molecular systems for fusibility related ash chemistry for the first time. The discussions are emphasized on those performed by quantum mechanics and molecular mechanics, the two major simulation methods for microscopic systems, which may provide various insights into fusibility mechanism. This review article is expected to present comprehensive information for recent molecular simulations of coal chemistry so that new clues to find strategies controlling the ash fusion behavior can be obtained.     

Synthesis and structural characterization of 2'-fluoro-α-L-RNA-modified oligonucleotides

We describe the synthesis and binding properties of oligonucleotides that contain one or more 2'-fluoro-α-L-RNA thymine monomer(s). Incorporation of 2'-fluoro-α-L-RNA thymine into oligodeoxynucleotides decreased thermal binding stability slightly upon hybridization with complementary DNA and RNA with the smallest destabilization towards RNA. Thermodynamic data show that the duplex formation with 2'-fluoro-α-L-RNA nucleotides is enthalpically disfavored but entropically favored. 2'-Fluoro-α-L-RNA nucleotides exhibit very good base pairing specificity following Watson--Crick rules. The 2'-fluoro-α-L-RNA monomer was designed as a monocyclic mimic of the bicyclic α-L-LNA, and molecular modeling showed that this indeed is the case as the 2'-fluoro monomer adopts a C3'-endo/C2'-exo sugar pucker. Molecular modeling of modified duplexes show that the 2'-fluoro-α-L-RNA nucleotides partake in Watson--Crick base pairing and nucleobase stacking when incorporated in duplexes while the unnatural α-L-ribo configured geometry of the sugar is absorbed by changes in the sugar-phosphate backbone torsion angles. The duplex behavior of our new nucleotide follows that of α-L-LNA, by and large.     

Homogenization of mesoscopic theories: Effective properties of model membranes

A new mathematical framework for modeling diffusion in nanoporous materials or on surfaces exhibits heterogeneity in properties over large length scales and retains molecular scale information, typically captured only by molecular simulations (kinetic Monte Carlo). It first uses newly developed mesoscopic equations derived rigorously from underlying master equations by coarse-graining statistical mechanics techniques. Homogenization techniques are then used to derive the leading-order effective mesoscopic models that are subsequently solved by spectral methods. These solutions are also compared to direct numerical simulations for selected 2-D model membranes with defects, when attractive adsorbate-adsorbate interactions affect particle difSsion. Both the density and dispersion of defects significantly alter the macroscopic behavior in terms of fluxes and concentration patterns, especially when phase transitions can occur. In the presence of adsorbate-adsorbate interactions, permeation through a nanoporous film can depend on the face of a membrane exposed to the high-pressure side. Homogenization techniques also could offer a promising alternative to direct numerical simulations, when complex, large-scale heterogeneities are present.