Measuring structural inhomogeneity of a helical conjugated polymer at high pressure and temperature

We report on X‐ray scattering measurements of helical poly[9,9‐bis(2‐ethylhexyl)‐fluorene‐2,7‐diyl] by mapping the sample with 10 μm spatial resolution from 0.3 GPa to 36 GPa. We follow the strongest 00l reflection, which moves toward higher scattering angles with pressure indicating planarization of helical polyfluorene. Lateral inhomogeneity is increased for >10 GPa concomitant with the solidification of the pressure transmitting medium (a 4:1 mixture of methanol and ethanol). We also follow the 00l reflection with increasing temperature at the constant pressure of 4.3 GPa in neon. We observe a sharp shift toward higher scattering angles indicative of a phase transition at 167–176 °C. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 392–396     

Theoretical investigation of structural and thermo-mechanical properties of thoria up to 3300 K temperature

We investigated thermo-mechanical properties of thoria up to a very high temperature (3300 K). We demonstrate that, using first-principles molecular dynamics, it is possible to predict thermal expansion of thoria in agreement with experiment. The new generalized gradient approximation functional within the density functional theory predicts, in agreement with experiment, not only the relative thermal expansion but also the absolute values of the lattice constant as a function of temperature. The molecular dynamics approach has an advantage over the previously used quasi-harmonic method, because it can be used even at temperatures (above 2700 K) where the longitudinal optical mode breaks in thoria. The calculated phonon dispersion agrees well with the experimental relation, measured using inelastic neutron scattering. The temperature, at which the negative frequency in the optical mode appears, coincides with the λ-type pre-melting transition reported in thoria.     

Dynamic thickening investigation of the gelation process of PAM/PEI system at high temperature and high pressure

The gelation process of organically polymer gel was investigated by dynamic thickening measurements. Rheological measurements were used to evaluate the viscosity of the gel. During the gelation process, high temperature resulted in higher rate of crosslinking. Rigid and stable gel was formed in neutral and alkaline media, and the higher of the pH value, the faster of the gelation process. However, gel could not be formed in acid condition. Moreover, the rate of crosslinking increased with the increase of concentration of polymer and crosslinker. The addition of NH₄Cl elongated the gelation time significantly, but played a negative role in the gel strength, while a rigid gel was formed in the presence of Sodium acetate or trisodium citrate dehydrate. This paper summarizes the results and discusses how various parameters affect the gelation process of the gel.     

Theoretical studies on the structural,spectroscopic, thermodynamic,and electronic properties of zoledronic acid

The structure, spectroscopic, thermodynamic, and electronic properties of zoledronic acid (ZL, 1-hydroxy- 2-(1H-imidazol-1-yl)ethane-1,1-diyldiphosphonic acid), typical third-generation nitrogen-containing bisphosphonates (N-BPs), have been investigated systematically. Six conformations are taken into account, including three unprotonated and three protonated structures. They are optimized by four different density functional theory (DFT) methods combined with four different basis sets to evaluate their performance in predicting the structural and spectral features of ZL. Thermodynamic properties are calculated based on the harmonic vibrational analysis, including the standard heat capacity (C _p,m ⁰ ), entropy (S _m ⁰ ), and enthalpy (S _m ⁰ ). The ¹H and ¹³C NMR chemical shifts are calculated using the GIAO method and compared with the experimental data. Molecular electrostatic potential (MEP) and frontier molecular orbital (FMO) analyses are also performed to study the electronic characteristics of the title compound.     

Theoretical assessment of structural,mechanical, and thermodynamic properties of Pd2Al

The physical properties, namely structural, mechanical, and thermodynamic properties, of Pd₂Al intermetallic compound were explored through first-principles calculations within the framework of density functional theory. The calculated lattice constants were consistent with the available experimental data. The calculated elastic constants revealed that Pd₂Al was mechanically stable. By the predicted elastic constants, several related properties, namely Cauchy pressures, shear anisotropy factors, directional Young's modulus, bulk, shear and Young's moduli, the ratio of K/G, Vickers hardness, sound velocity, and minimum thermal conductivity for Pd₂Al were evaluated. According to the calculated results, it was found that Pd₂Al possesses a highly anisotropic feature and behaves in a ductile manner with low stiffness. Finally, temperature-dependence of thermodynamic properties, namely Debye temperature and heat capacity, were also evaluated through the quasi-harmonic Debye model.     

Prediction of thermodynamic derivative properties of natural condensate gases at high pressure by Monte Carlo simulation

We have employed Monte Carlo simulation in the isobaric–isothermal ensemble to determine thermodynamic derivative properties of naturally occurring hydrocarbon gas mixtures. Thermal expansivity, isothermal compressibility, heat capacity and Joule–Thomson coefficient have been obtained from a fluctuation method detailed in our previous work [Phys. Chem. Chem. Phys. 3 (2001) 4333]. We have investigated two natural gases using an original method to model hydrocarbon distribution in a representative way with a limited number of linear, branched and cyclic hydrocarbon molecules. The composition used in Monte Carlo simulations was represented by 500 molecules of 20 different types with up to 35 carbon atoms. The two condensate gases are composed of rigid and flexible molecules for which intermolecular potentials have been used without fitting any parameters. Predictions are in good agreement with respect to available molar volumes at high pressure. Joule–Thomson coefficients and the other thermodynamic derivative properties have been then predicted at pressures up to 110 MPa at reservoir temperature, showing a consistent behaviour compared with light hydrocarbon gases. Inversion pressure of the Joule–Thomson effect is obtained within 1.2% compared to experimental value from volumetric measurements.     

Theoretical and experimental investigation of the structural and spectroscopic properties of coumarin 343 fluoroionophores

A joint theoretical-experimental investigation has been carried out to unravel the details of the complexation of cations by fluoroionophores based on coumarin 343 and to interpret the modifications in the ligand and also in the coumarin structural, electronic, magnetic, and vibrational properties. It is confirmed that C343-dea (1) complexes the cations by both the lactone and the amide oxygen atoms whereas for C343-crown (2) and C343-dibenzocrown (3), the cations are complexed by the oxygen atoms of the lactone as well as those of the crown ligand. These complexations induce geometric modifications, which are delocalized over the coumarin backbone and are related to electronic reorganizations that modify the spectroscopic signatures. This paper analyzes these signatures and shows how they are related as well as how they can be used to monitor the complexation process. Upon complexation, the UV-visible absorption spectra display a bathochromic shift of the most intense electronic transition; this shift is generally larger for the most flexible compound 1 as well as when complexing divalent cations. NMR spectra bear many signatures of the complexation, of which the most remarkable ones are the large shielding of C(1) and the large deshieldings of C(9) and C(16). Additional makers of complexation are highlighted in the IR vibrational spectra, in particular the bands associated with the lactone and amide CO vibrations, which are downshifted when the corresponding CO is involved in the complexation mode and, otherwise, upshifted. A high degree of consistency characterizes the different geometrical, electronic, magnetic, and vibrational signatures, which substantiates the assignment of the modes of complexation in 1-3. In addition, the agreement between the experimental data and the theoretical values is rather satisfactory, in that it at least enables us to interpret the spectral signatures.     

Melting and dissociation of ammonia at high pressure and high temperature

Raman spectroscopy and synchrotron x-ray diffraction measurements of ammonia (NH(3)) in laser-heated diamond anvil cells, at pressures up to 60 GPa and temperatures up to 2500 K, reveal that the melting line exhibits a maximum near 37 GPa and intermolecular proton fluctuations substantially increase in the fluid with pressure. We find that NH(3) is chemically unstable at high pressures, partially dissociating into N(2) and H(2). Ab initio calculations performed in this work show that this process is thermodynamically driven. The chemical reactivity dramatically increases at high temperature (in the fluid phase at T > 1700 K) almost independent of pressure. Quenched from these high temperature conditions, NH(3) exhibits structural differences from known solid phases. We argue that chemical reactivity of NH(3) competes with the theoretically predicted dynamic dissociation and ionization.     

HgWO4 synthesized at high pressure and temperature

Crystals of mercury(II) tungstate(VI), HgWO₄, were grown in sealed gold tubes under an Ar atmosphere at 300 MPa and 973 K. The monoclinic crystal structure (C2/c) of HgWO₄ consists of zigzag chains of edge‐sharing WO₆ octahedra running along the c axis and layers of very distorted corner‐sharing HgO₆ octahedra in the bc plane. The Hg atom lies on an inversion centre and the W atom is on a twofold axis. No structural effects which can be ascribed to the high pressure used in the synthesis were found.     

Theoretical investigation of the influence of ligands on structural and electronic properties of indium phosphide clusters

Results of a theoretical study of the effects of including ligands on stoichiometric In(n)P(n) clusters are presented. We apply a parametrized density-functional method and consider clusters with n up to above 70. As ligands we consider H atoms and CH3 groups, and the results are compared with our earlier ones for the naked clusters. We find that the ligands lead to only smaller structural changes but that an enhanced In-to-P electron transfer in the outermost parts of the clusters, which we observed for the naked clusters, is largely suppressed, so that there is a more homogeneous In-to-P transfer throughout the whole cluster. Adding the ligands leads, in most cases, to an increase in the HOMO-LUMO gap and, therefore, also to an increase in the stability of the clusters. However, we find also that the HOMO-LUMO gap depends critically on the type, sites, and number of ligands that are added.     

Theoretical study on the thermodynamic properties and self-decomposition of methylbenzenediol isomers

Alkylated hydroxylated aromatics are major constituents of various types of fuels, including biomass and low-rank coal. In this study, thermochemical parameters are obtained for the various isomeric forms of methylbenzenediol isomers in terms of their enthalpies of formation, entropies, and heat capacities. Isodesmic work reactions are used in quantum chemical computations of the reaction enthalpies for O-H and H?C-H bond fissions and the formation of phenoxy- and benzyl-type radicals. A reaction potential energy on the singlet-state surface surface is mapped out for the unimolecular decomposition of the 3-methylbenzene-1,2-diol isomer. According to the calculated high pressure-limit reaction rate constants, concerted hydrogen molecule elimination from the methyl group and the hydroxyl group, in addition to intermolecular H migration from the hydroxyl group, dominates the unimolecular decomposition at low to intermediate temperatures (T ≤ 1200 K). At higher temperatures, O-H bond fission and concerted water elimination are expected to become the sole decomposition pathways.     

Radiation-induced polymerization of hexafluoropropylene at high temperature and pressure

The radiation-induced polymerization of hexafluoropropylene was studied in the pressure and temperature ranges of 4,500–15,000 atm. and 100–230°C., respectively. Retardation was a serious problem; data thought to apply to the unretarded polymerization are summarized below. At 1,500 rad/hr. the polymerization rate was 15%/hr. at 230°C. and 15,000 atm. The activation enthalpy and volume are 9.5 kcal./mole and ?10 cc./mole, respectively. The rate varies as the square root of the radiation intensity. The largest intrinsic viscosity of the polymer is 2.0 dl./g.; values increase with temperature and pressure. At 130°C. and 10,000 atm. the intrinsic viscosity was the same at two radiation intensities.     

The thermodynamic properties of alkali metal compounds at high temperatures

A research program has been in progress to obtain reliable thermodynamic data on various binary and ternary alkali metal compounds in the temperature range of 300 to 1500 K. To date, heat capacity measurements have been made on cesium and rubidium chromates, dichromates, zirconates, molybdates, dimolybdates, and halides in the temperature range of 300 to 800K. In addition, measurements are planned or are currently in progress on cesium and rubidium chalcogenides, aluminates, uranates, silicates, and several other lithium, sodium, and potassium compounds. The status of the research program is discussed.     

Calculating the thermodynamic and structural properties of liquid noble gases

The structural and energy parameters in the liquid branch of the saturation line of noble gases, including ⁴He, are determined.     

First-principles investigations on structural,electronic and elastic properties of BeSe under high pressure

The structural, electronic and elastic properties of BeSe in both B3 and B8 structures have been studied by first-principles calculations within the generalized gradient approximation (GGA). The calculated lattice parameters and bulk modulus of BeSe are in reasonable agreement with previous results. The predicted value of phase transition pressure from B3 to B8 is 50.24 GPa, which is well in line with the experimental data (56 ± 5 GPa). The calculation of the electronic band structure shows that the energy gap is indirect for B3 and B8 phases. Especially, the elastic constants of B8 BeSe under high pressure were studied for the first time. The bulk modulus, shear modulus, compressional and shear wave velocities of B8 BeSe evaluated from elastic constants as a function of pressure were investigated. In addition, Poisson's radio, elastic anisotropy and Debye temperature were analyzed successfully.     

Thermal decomposition of high-energy density materials at high pressure and temperature

High-energy density materials (HEDMs) are being investigated for use as propellants in rocket, air-breathing, and combined-cycle applications. These types of materials may be attractive alternatives to conventional propellants because of their high heat of combustion, density, and high strain energy. Because advanced propulsion systems may operate at very high pressure and temperature (>25 atm and temperatures exceeding 500 °C), the thermal decomposition of individual HEDMs is of interest to future fuel system designers. A laboratory-scale flow reactor was used to subject small amounts (approximately 1 ml) of deoxygenated HEDM to controlled conditions of temperature and residence-time-at-temperature at constant pressure (34 atm) in the liquid or supercritical phase. The reactor was 316 stainless steel HPLC tubing. Using an in-line analytical system, as well as off-line chromatographic analysis of products, the thermal stability of the parent material, as well as the thermal fragmentation products of each HEDM was measured. Some of the candidate materials tested (dimethyl-2-azidoethylamine (DAMEZ), quadricyclane, and bicyclopropylidene (BCP)) showed only marginal thermal stability with major decomposition occurring before 400 °C (3 s residence time). Other candidate materials (JP-10, RP-1, RG-1, RJ-6, and RJ-7) showed excellent thermal stability: little decomposition even at 600 °C. Results show the pyrolytic stability of candidate materials relative to each other, and provided insights to the mechanisms of thermal decomposition for specific fuel candidates.     

多溴代芴热力学性质的理论预测研究

为了预测环境污染物多溴代芴的热力学性质,计算了60种多溴代芴的分子连接性指数、电性距离矢量指数、电性拓扑状态指数以及分子形状指数.采用多元线性回归的方法建立了多溴代芴化合物的标准生成焓(Δ_fH~0)、标准熵(S~0)、标准生成吉布斯自由能(Δ_fG~0)及等容热容等热力学性质的QSPR相关性模型,方程的相关系数值均在0.99以上.与相关文献的相关系数R和标准误差S进行比较,该模型具有良好的预测能力和稳定性.