Static fatigue fracture of polyethylene: A morphological analysis

The fracture properties of a number of high-density polyethylenes were evaluated and related to their morphology. The resistance to initiation of fracture is related to the resistance to voiding of the materials and the rate of coalescence of voids. The propensity of the materials to void has been shown to be related to the size of the amorphous region. The resistance to propagation of the fracture is also related to the above factors as well as the ease of stretching and rupture of fibrils. The ease of fibril formation has been shown to be related to the degree of perfection of the crystallites.     

Precision of Flash Pyrolysis-GC-MS Analysis: Experimental Evaluation of the Sources of Variability

The present study was carried out to evaluate the precision and to identify significant sources of variability in flash pyrolysis-GC-MS experiments. The analysis of variance has been applied to the example of polyethylene pyrolysis to estimate the impact of several controlled factors: sample handling, flash pyrolysis filament ageing and calibration. It was demonstrated that to get the best precision in experimental results, it is recommended to set the operator to reduce the impact of sample handling procedure and the filament to avoid variability due to changes in filament characteristics. In comparison, filament ageing and filament calibration are shown to influence in a limited extent the experimental results.     

What is and what should never be: artifacts,improbable phytochemicals,contaminants and natural products

Abstract

The scope of this review is to sensitize the natural product chemists to the underestimated problem related to artifact, comprising contaminants and improbable natural compounds. This review wants to give an overview about the various facets of this problem and to provide some hints to avoid incurring these situations. It does not pretend to report exhaustively about all the cases available in literature. The issue of artifacts has always existed and is quite impossible to completely eliminate because the results of phytochemical analysis are known only at the end of the work and in many cases there is not the possibility to compare the results. Therefore, it is important to take the necessary precautions during the workout in order to minimize the possibility that an unexpected event may occur. In second instance, anyone involved in these studies should increase the level of self-criticism with respect to the obtained experimental results.     

Curvature Effects in the Analysis of Pendant Bubble Data: Comparison of Numerical Solutions, Asymptotic Arguments, and Data

The pendant bubble method is commonly used to measure the evolution of the surface tension of surfactant solutions. Initially, the bubble interface is free of adsorbed surfactant. As time progresses, surfactant diffuses to the interface, adsorbs, and reduces the surface tension. The surface tension is assumed to be in equilibrium with the instantaneous surface concentration. Therefore, surface tension data are analyzed in terms of interfacial thermodynamics and mass transfer models in order to infer the mechanisms which determine the surfactant transport. Diffusion from the bulk solution to the bubble can be approximated as diffusion to a spherical interface. Approximating this process as diffusion to a plane introduces significant errors into the data analysis. Mass transfer to a sphere differs from that to a plane; the equilibration of the spherical interface is more rapid simply because of geometry. The failure to account for this effect in the interpretation of pendant bubble data can lead to serious errors in the transport coefficients for the surfactants. In the diffusion-controlled limit, surfactant diffuses to the sublayer immediately adjacent to the interface and adsorbs in local equilibrium according to the adsorption isotherm. There is a closed-form solution for Fick's law describing adsorption to a sphere in an infinite solution which reduces to the Ward and Tordai solution when the bubble radius is large. This equation, along with the adsorption isotherm relating the surface concentration and the sublayer concentration, must be solved numerically in order to solve for the time evolution of the surface concentration. At early times, the adsorption isotherm can be expanded about the clean interface state. At long times, small departures from the equilibrium state can be assumed. In these limits, asymptotic expansions can be obtained. The short- and long-time expansions are found in this study for adsorption to a sphere and compared to those obtained previously for adsorption to a planar interface. In particular, the long-time asymptote for adsorption to a sphere is proportional to t(-3/2); this asymptote differs significantly from that for adsorption to a plane, which goes as t(-1/2). The full solution for adsorption to a sphere is compared to the Ward and Tordai solution for adsorption to a planar interface. From a comparison of the full solutions, it is established that curvature cannot be neglected unless the ratio of the adsorption depth to the bubble radius is negligible. This ratio can be calculated a priori from equilibrium isotherm parameters. Using constants which describe the surfactant C(12)E(8), for which curvature plays a strong role in the surfactant adsorption dynamics, the short- and long-time solutions for adsorption to the interface are compared to the full solutions and to dynamic surface tension data to infer the range of validity of the approximations. Copyright 2001 Academic Press.     

NMR spectroscopic study of the Murex trunculus dyeing process

It is widely accepted that indigo dyes derived from Murex trunculus were used to produce the biblical dyes tekhelet and argaman. We describe a method of following the debromination of natural leucoindigos and their binding to wool using NMR spectroscopy. Debromination is observed prior to reaction with the wool and prior to oxidation. Binding to the wool is shown to occur prior to oxidation. NMR allows the dyeing process to be followed. This, in principle, could be used to correct problems during dyeing that would increase the reliability of the process.     

Binding affinity of a small molecule to an amorphous polymer in a solvent. Part 2: preferential binding to local sites on a surface

Crystallization, a separation and purification process, is commonly used to produce a wide range of materials in various industries, and it usually begins with heterogeneous nucleation on a foreign surface in industrial practice and most other circumstances. Recent studies show that amorphous polymeric substrates are useful in controlling crystallization and selectively producing pharmaceutical polymorphs. In our previous publication, we investigated the possible correlation of the binding affinity of one molecule to key binding sites (local binding), and the possibility of using this binding affinity to guide the selection of polymers promoting heterogeneous nucleation. The studied systems were aspirin binding to four nonporous cross-linked polymers in ethanol-water 38 v% mixture. Cross-linked with divinylbenzene (DVB), these polymers were poly(4-acryloylmorpholine) (PAM), poly(2-carboxyethyl acrylate) (PCEA), poly(4-hydroxylbutyl acrylate) (PHBA), and polystyrene (PS). We discovered that the trend of the magnitudes of the average free energies of binding to the best sites is very similar to that of heterogeneous nucleation activities. This Article aims to investigate whether or not local binding to key sites is the important variable to describe heterogeneous nucleation as opposed to the overall/average binding affinity of molecules to a surface, and to investigate the possibility of using the overall binding affinity to guide the selection of polymers. We used the polymer surfaces generated from our previous study to calculate the overall binding affinity of aspirin molecules to the surface as measured by the preferential interaction coefficients of aspirin (1 m) to these polymers. We discovered that the trend of the average preferential interaction coefficients does not correlate as well to that of heterogeneous nucleation activities as the free energies of binding to the best sites. We also computed the average numbers of aspirin molecules associated with the areas of the surfaces' best binding sites and found that they correlate better to heterogeneous nucleation activities than the average preferential interaction coefficients. These results further support that local binding is indicative of heterogeneous nucleation. Moreover, we found a weak trend of the distance order parameters of the aspirin molecules to be similar that of heterogeneous nucleation activities. Our results from the two-part study suggest the importance of local binding to heterogeneous nucleation as well as the possibility of using the binding affinity to the local area (the free energy of binding to the best site and the number of nucleating molecules associated with the area of the best binding site) and the distance order parameters to guide the selection of polymers.     

增强无机化学教学的趣味性策略的案例研究

针对无机化学的理论知识学习的"枯燥",提出无机化学教学趣味性的三大增强策略,一是设定情境,让"枯燥"的知识生动起来;二是善用比喻,让"困难"的知识有趣起来;三是自创"小诗",让"复杂"的知识幽默起来。通过实践,三大增强策略的效果很好,值得广泛推广。     

Thermal degradation of vinylidene chloride/4-vinylpyridine copolymers

Vinylidene chloride polymers are prominent in the barrier plastics packaging industry. They display good barrier to the transport of oxygen (to prevent spoilage of food items) and flavor and aroma constituents (to prevent 'scalping' on the supermarket shelf). However, these polymers undergo thermal dehydrochlorination during processing. This can lead to a variety of problems including the evolution of hydrogen chloride which must be scavenged to prevent its interaction with the metallic walls of process equipment. Such interaction leads to the formation of metal halides which act as Lewis acids to facilitate the degradation. A potentially effective means to capture hydrogen chloride generated might be to incorporate into the polymer a mild organic base. Accordingly, copolymers of vinylidene chloride and 4-vinylpyridine have been prepared and subjected to thermal aging. Results suggest that the pyridine moiety is sufficiently basic to actively promote dehydrochlorination in the vinylidene chloride segments of the polymer.     

Rubber networks containing unattached macromolecules. I. Linear viscoelastic properties of the system butyl rubber–polyisobutylene

Mixtures of butyl rubber with polyisobutylene (molecular weights 0.055 and 2.3 × 10⁶) up to 50% by weight were crosslinked by sulfur, leaving the polyisobutylene molecules free to reptate in the butyl rubber network. Linear viscoelastic properties were measured in shear creep for periods up to 5 × 10⁵ sec at 25°C and oscillating shear deformations from 0.1 to 3 Hz, at temperatures from 2 to 63°C. Comparison with the properties of a butyl rubber crosslinked without polyisobutylene showed contributions to creep and mechanical loss attributable to the reptating species. Comparison with the properties of polyisobutylene (higher molecular weight) showed that the relaxation times associated with the reptating species in the upper part of the terminal zone are the same for different polyisobutylene contents (25% and 50%) and for 100% polyisobutylene in which no permanent network is present; their contributions to modulus appear to be proportional to the volume fraction of polyisobutylene to a power of about 2/3. The time required in stress relaxation for the portion of the modulus attributable to the reptating species to decay to half its plateau value is, based on the two molecular weights employed, proportional to the polyisobutylene molecular weight to the third power. The magnitude of the associated mechanical loss and its location on the frequency scale can thus be controlled independently.     

Robust conductance of dumbbell molecular junctions with fullerene anchoring groups

The conductance of a molecular wire connected to metallic electrodes is known to be sensitive to the atomic structure of the molecule-metal contact. This contact is to a large extent determined by the anchoring group linking the molecular wire to the metal. It has been found experimentally that a dumbbell construction with C(60) molecules acting as anchors yields more well-defined conductances as compared to the widely used thiol anchoring groups. Here, we use density functional theory to investigate the electronic properties of this dumbbell construction. The conductance is found to be stable against variations in the detailed bonding geometry and in good agreement with the experimental value of G=3×10(-4) G(0). Electron tunneling across the molecular bridge occurs via the lowest unoccupied orbitals of C(60) which are pinned close to the Fermi energy due to partial charge transfer. Our findings support the original motivation to achieve conductance values more stable towards changes in the structure of the molecule-metal contact leading to larger reproducibility in experiments.     

Advanced Reprocessing Developments in Europe Status on European Projects ACSEPT and ACTINET-I3

Nuclear energy has more than ever to demonstrate that it can contribute safely and on a sustainable way to answer the international increase in energy needs. Actually, in addition to an increased safety of the reactors themselves, its acceptance is still closely associated to our capability to reduce the lifetime of the nuclear waste, to manage them safely and to propose options for a better use of the natural resources. Spent fuel reprocessing can help to reach these objectives. At the European level, ACSEPT and ACTINET-I3 have worked together to improve our knowledge in actinide chemistry and advanced separation process development.     

Investigation of isothiocyanate addition to alkylidene derivatives of malononitrile and cyanoacetic acid esters

Addition of arylisothiocyanates to active methylene compounds leads to a variety of compounds depending on the structure of the starting material and conditions used to conduct the addition. Addition of arylisothiocyanate to 1c leads to a pyrido[2,3-d]pyrimidine resulting from addition of a second mole of cyanate to the initial adduct. Addition of arylisothiocyanate to 1b led to a mixture of pyridine and thiopyran adducts, while addition to 1a led to open chain structures.     

The role of errors related to DFT methods in calculations involving ion pairs of ionic liquids

Ionic liquids (ILs) play a key role in many chemical applications. As regards the theoretical approach, ILs show added difficulties in calculations due to the composition of the ion pair and to the fact that they are liquids. Although density functional theory (DFT) can treat this kind of systems to predict physico–chemical properties, common versions of these methods fail to perform accurate predictions of geometries, interaction energies, dipole moments, and other properties related to the molecular structure. In these cases, dispersion and self‐interaction error (SIE) corrections need to be introduced to improve DFT calculations involving ILs. We show that the inclusion of dispersion is needed to obtain good geometries and accurate interaction energies. SIE needs to be corrected to describe the charges and dipoles in the ion pair correctly. The use of range–separated functionals allows us to obtain interaction energies close to the CCSD(T) level. © 2017 Wiley Periodicals, Inc.     

Manganese Kβ X-ray emission spectroscopy as a probe of metal-ligand interactions

A systematic series of high-spin mononuclear Mn(II), Mn(III), and Mn(IV) complexes has been investigated by manganese Kβ X-ray emission spectroscopy (XES). The factors contributing to the Kβ main line and the valence to core region are discussed. The Kβ main lines are dominated by 3p-3d exchange correlation (spin state) effects, shifting to lower energy upon oxidation of Mn(II) to Mn(III) due to the decrease in spin state from S = 5/2 to S = 2, whereas the valence to core region shows greater sensitivity to the chemical environment surrounding the Mn center. A density functional theory (DFT) approach has been used to calculate the valence to core spectra and assess the contributions to the energies and intensities. The valence spectra are dominated by manganese np to 1s electric dipole-allowed transitions and are particularly sensitive to spin state and ligand identity (reflected primarily in the transition energies) as well as oxidation state and metal-ligand bond lengths (reflected primarily in the transition intensities). The ability to use these methods to distinguish different ligand contributions within a heteroleptic coordination sphere is highlighted. The similarities and differences between the current Mn XES study and previous studies of Fe XES investigations are discussed. These findings serve as an important calibration for future applications to manganese active sites in biological and chemical catalysis.     

Progress toward a rationally designed, chemically powered rotary molecular motor

Building on prototype 1, which achieves 120 degrees of phosgene-powered unidirectional rotation to rotamer 6 (see Figure 5 in the full article), 7 was designed to accomplish repeated unidirectional rotation (see Scheme 7). Compound 7 contains an amino group on each blade of the triptycene and a 4-(dimethylamino)pyridine (DMAP) unit to selectively deliver phosgene (or its equivalent) to the amine in the "firing position". The synthesis of 7 is described: the key constructive steps are a benzyne addition to an anthracene to generate the triptycene, a stilbene photocyclization to construct the helicene, and a Stille coupling to incorporate the DMAP unit. The DMAP unit was shown to regioselectively relay 1,1'-carbonyldiimidazole (but not phosgene) to the proximal amino group, as designed, but rotation of the triptycene does not occur. Extensive attempts to troubleshoot the problem led to the conclusion that the requisite intramolecular urethane formation, as demonstrated in the prototype (1 --> 4), does not occur with 7 (to give 85) or 97 (to give 100). We speculate that either (i) hydrogen bonding between the hydroxypropyl group and functionality present in 7 but absent from 1 or (ii) a Bürgi-Dunitz (or similar) interaction involving the DMAP (see 106) prevents achievement of a conformation conducive to intramolecular urethane formation.     

卡尔费休滴定法测定液体推进剂混胺燃料中水分

液体推进剂混胺燃料中作为主要组分存在的三乙胺使其显示较高的碱性,对用卡尔费休滴定法测定其水分含量时产生干扰。提出了在试样的甲醇滴定介质中加入一定量的乙酸,保持液体混胺试样和乙酸的体积比小于或等于3比5,达到使滴定介质的酸度控制在最佳pH范围5～6之间。经此操作,由三乙胺的高碱度引起的干扰可消除。对已知水分含量的混胺试样按方法进行分析,算得其水分测定值的相对标准偏差(n=12)为2.1%。取不同批号的混胺试样7件,按方法进行分析并用标准气量法对结果进行校核。两种方法测定结果的相对偏差在-0.023%～0.033%之间。又根据t-检验法的结果认定,两方法所得测定值之间不存在显著差异。     

Defects,flexoelectricity and RF communications: the ZBD story

ABSTRACT

The zenithal bistable display (ZBD) was the first liquid crystal device mode to be commercialised that uses nematic disclinations in a constructive fashion, to use the flexoelectric effect inherent to all liquid crystals but at the time was considered too weak an effect to be useful, and to transfer nano-replication methods to the LCD manufacturing environment. The genesis of the invention and spin-out company ZBD Displays Limited will be described, and the evolution of that company from licensing model, through fabless manufacturer to display provider and finally to a system provider for the retail sector. The story may be useful not just to those interested in the science behind a rather unusual LCD, but also those involved in taking technology from laboratory to manufacturing, from idea to commercial success.     

Automated thermal conductivity apparatus

The importance of reducing the time required for taking thermal conductivity measurements has increased due to the need to conserve energy. A method is described that reduces man-hours to a minimum while getting the maximum information from the measurements.The equipment uses a microprocessor to automatically scan the temperature, a data logger to make the required temperature measurements, and a computer to plot the results of the thermal conductivity values obtained. Early experiments produced values accurate to within 5%. With further refinements this can be improved to 1%.Already, the effect of curing thermosetting materials has been seen in measurements. Future applications can include tailoring materials to provide specific thermal conductivity properties and make it possible for some of the differences between a priori calculations and experiments to be better understood.     

Classical molecular dynamics study of [60]fullerene interactions with silica and polyester surfaces

This study examines the interaction of neutral and charged fullerenes with model silica and polyester surfaces. Molecular dynamics simulations at 298 K indicate that van der Waals forces are sufficiently strong in most cases to cause physisorption of the neutral fullerene particle onto the surfaces. The fullerenes are unable to penetrate the rigid silica surface but are generally able to at least partially infiltrate the flexible polymer surface by opening surface cavities. The introduction of charge to the fullerene generally leads to an increase in both the separation distance and Work of Separation with silica. However, the charged fullerenes generally exhibit significantly closer and stronger interactions with polyester films, with a distinct tendency to absorb into the "bulk" of the polymer. The separation distance and Work of Separation of C60 with each of the surfaces also depend greatly on the sign, magnitude, and localization of the charge on the particle. Cross-linking of the polyester can improve resistance to the neutral fullerene. Functionalization of the polyester surface (F and OH substituents) has been shown to prevent the C60 from approaching as close to the polyester surface. Fluorination leads to improved resistance to positively charged fullerenes, compared to the unmodified polyester. However, hydroxylation generally enables greater adhesion of charged fullerenes to the surface due to H-bonding and electrostatic attraction.     

Synthesis and Rearrangement Reactions of C-Alkylidene Carbohydrates

Direct: olefinations on one hand in comparison to eliminations of aldols cf various uloses on the other each proved to be specific as to the sice of unsaturation in the branched-chain products, found to be interconvertible with one exception under a variety of conditions. Although shown to be generally equivalent to its Witcig-counterpart:, the Peterson reagent employed is liable to cause eliminations in the initial olefin. One of the branched-chain products appears to be of unusual molecular rigidity as evidenced by a large 5J coupling.