bluuebunny/crossref_metadata_2025_split huggingface dataset:
Morphological and mechanical properties of nascent polyethylene fibers produced via ethylene extrusion polymerization with a metallocene catalyst supported on MCM‐41 particles
Authors: Ye Zhibin , Zhu Shiping , Wang Wen‐Jun , Alsyouri Hatem , Lin Y. S. 
Published: September 2003

AbstractPolyethylene (PE) fibers were prepared by ethylene extrusion polymerization with an MCM‐41‐supported titanocene catalyst. The morphological and mechanical properties of these nascent PE fibers were investigated. Three levels of fibrous morphologies were identified in the fiber samples through an extensive scanning electron microscopy study. Extended‐chain PE nanofibrils with diameters of about 60 nm were the major morphological units present in the fiber structure. The nanofibrils were parallel‐packed into individual microfibers with diameters of about 1–30 μm. The microfibers were further aggregated irregularly into fiber aggregates and bundles. In comparison with commercial PE fibers and data reported in the literature, the individual microfibers produced in situ via ethylene extrusion polymerization without posttreatment exhibited a high tensile strength (0.3–1.0 GPa), a low tensile modulus (3.0–7.0 GPa), and a high elongation at break (8.5–20%) at 35 °C. The defects in the alignment of the nanofibrils were believed to be the major reason for the low modulus values. It was also found that a slight tensile drawing could increase the microfiber strength and modulus. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2433–2443, 2003
Complete miscibility of ternary aryl polyesters demonstrating a new criterion and horizon for miscibility characterization
Authors: Woo E. M. , Kuo Yu‐Hsiao 
Published: September 2003

AbstractA ternary miscible blend system comprising only crystallizable aryl polyesters [poly(ethylene terephthalate), poly(trimethylene terephthalate), and poly(butylene terephthalate)] was characterized with the criteria of thermal analyses, microscopy, and X‐ray characterizations. The reported ternary miscibility (in the quenched amorphous state of blends of the three aryl polyesters) was truly physical and under the condition of no chemical transesterifications; this justified that transesterification was not a necessary condition for miscibility in polyester blends in this case. This study further proposed and tested a novel concept of a new criterion for miscibility characterization for polymer blends of only crystallizable polymers. A single composition‐dependent cold‐crystallization‐temperature (Tcc) peak in blends of only semicrystalline polymers was taken as an indication of an intimate mixing state of miscibility. The theoretical background for establishing the single composition‐dependent Tcc peak as a valid miscibility criterion for crystallizable polymer blends was examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2394–2404, 2003
Mechanical properties of block copolymer vesicle and micelle modified epoxies
Authors: Dean Jennifer M. , Grubbs Robert B. , Saad Walid , Cook Robert F. , Bates Frank S. 
Published: September 2003

AbstractBlock copolymers with and without reactive functionalities can improve fracture resistance in brittle epoxies even when added in relatively small amounts (<5 wt %). At certain compositions, amphiphilic block copolymers spontaneously self‐assemble into vesicles, spherical micelles, or wormlike micelles in thermoset resins, and these morphologies are retained with the full curing of the resins. The addition of such block copolymers leaves the glass‐transition temperature of these blends relatively unchanged, whereas the fracture resistance increases up to a factor of 3.5 for the vesicle‐modified blends. For epoxies modified with block copolymers self‐assembled into a spherical geometry (vesicles or spherical micelles), the fracture resistance scales with the ratio of the interparticle distance to the average vesicle (or spherical micelle) diameter (Di/Dp) and increases as this quantity is reduced. Greater adhesion between the vesicle and epoxy resin improves the fracture resistance only at higher values of Di/Dp, at which the materials are more brittle. Debonding and subsequent matrix plastic deformation are identified as the toughening mechanisms in these blends. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2444–2456, 2003
Strong diffuse scattering and lamellar morphologies of syndiotactic polystyrene: Polymorphic effects
Authors: Wang Chi , Liao Wei‐Po , Cheng Yong‐Wen 
Published: September 2003

AbstractSyndiotactic polystyrene (sPS) samples melt‐crystallized into neat α″‐ hexagonal and β′‐orthorhombic modifications were prepared at various temperatures thoroughly for extensive morphological studies. The lamellar morphologies of the as‐prepared sPS samples were investigated with small‐angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM). For SAXS measured at 25°C, a barely observed scattering hump was detected for β′‐form sPS, whereas no discernible scattering feature was found for α″‐form sPS because of a small difference in the electron density between the crystalline and amorphous phases. For increased scattering contrast and strength, SAXS was carried out at 150°C so that more reliable morphological parameters would be obtained. In addition to the enhanced scattering peak relevant to the lamellar features, strong diffuse scattering near the beam stop was observed for both α″‐ and β′‐form sPS samples. The contribution of the diffuse scattering at low q regions (where q is the scattering vector) was rather prominent, obscuring the precise position of the scattering peak. On the basis of the Debye–Bueche theory, the strength and inhomogeneity length were derived to render the diffuse scattering. After the subtraction of the diffuse scattering from the observed intensities, scattering intensities exclusively associated with the lamellar features were obtained. Lamellar thicknesses were further derived from the one‐dimensional correlation function of the modified intensities, and a good agreement was reached in comparison with TEM results. From exhaustive TEM observations on the RuO4‐stained samples, long and parallel lamellae were readily observed in β′‐form sPS. However, relatively irregular packing of lamellar stacks with short lateral dimensions was detected in the as‐prepared α″‐form sPS, leading to the absence of spherulitic birefringence under polarized optical microscopy. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2457–2469, 2003
Quantification of preferential orientation in conjugated polymers using X‐ray diffraction
Authors: Breiby Dag W. , Samuelsen Emil J. 
Published: September 2003

AbstractThe varying degree of preferential orientation observed in films of poly(alkylthiophene)s obtained by solution casting from different solvents has been studied quantitatively with X‐ray diffraction. The (uniaxial) orientational distribution function is obtained after some important instrumental corrections that are described in detail. Orientational distribution functions of an exponential type are found to give an adequate description with only a few fitted parameters, unlike Legendre series fits, which require longer series. An attempt has been made to relate the anisotropy to the chemical and physical properties of the solvents used. The anisotropy seems to be higher for samples cast from solvents with low boiling points and, correspondingly, high vapor pressures. Also, the average crystallite size is solvent‐dependent. The characteristic dimension of the crystallites in the a‐axis direction appears to be longest for crystallites with the a axis parallel to the film normal. Along the b axis, that is, the π‐stacking direction, the crystallite dimension is shorter than along the a axis. Also, the amorphous regions of the films exhibit anisotropy. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2375–2393, 2003
Aggregation structure and mechanical properties of functionally graded polyurethane elastomers
Authors: Furukawa Mutsuhisa , Hamada Yukinori , Kojio Ken 
Published: September 2003

AbstractFunctionally graded polyurethane elastomers (FGPUEs) were prepared with two molds fixed at different temperatures (30 and 150 °C). The effects of the molar ratio of the curing agent (60/40, 75/25, or 97/3 1,4‐butane diol/1,1,1‐trimethylol propane) and the molecular weight of the polymer glycol (number‐average molecular weight = 2000 or 3000) on the molecular aggregation state and mechanical properties of the FGPUEs were investigated with differential scanning calorimetry, polarized optical microscopy, dynamic viscoelastic measurements, and tensile tests. The aggregation state of the FGPUEs was changed continuously from the one side (lower temperature side) to the other side (higher temperature side); for example, the glass‐transition temperature gradually increased in this direction. Also, the number of spherulites formed in the FGPUEs increased in the same manner. In the mechanical tests, the tensile strength and elongation at break of the lower temperature side were higher than those of the higher temperature side. This was correlated with the strong phase separation of the lower temperature side. The poly(oxytetramethylene glycol)‐based FGPUE with a chain extender of 75 wt % showed the largest degree of the temperature gradient. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2355–2363, 2003
Finite‐cluster approximation for deep‐level impurities in silicon carbide
Authors: Souza Sarai S. , Matos Maria 
Published: September 2003

AbstractA series of 12 silicon carbide finite clusters has been investigated to determine a possible model for transition‐metal deep‐level impurities in several Si sites of the material. All electronic structure calculations were done using the extended Hückel method. By taking account of boundary condition effects upon the electronic structure of the pure and V‐substitutional systems, it was found that the cluster series could be classified into two groups: a large‐gap and a small‐gap group. The small‐gap group arises from spurious border Si‐3p levels that appear inside the forbidden gap. It was consequently suggested that large‐gap clusters are more suitable for describing the impurity. It is also suggested that possibly new V, Si, and C parameters could lead to both a good description of the pure and doped material. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 88–96, 2003
Inversion of simulated positron annihilation lifetime spectra by moving boundary subspaces
Authors: Viterbo V. C. , Neves J. L. , Braga J. P. , Monteiro R. P. G. , De Magalhães W. F. 
Published: September 2003

AbstractThe retrieval of the density function for the positron annihilation lifetime spectrum is obtained from simulated data using the damped singular value decomposition. Two filters factors were discussed, for noise and noiseless data, and under the L curve criterion. The obtained density function is exact in the absence of noise. When noise is considered, the predicted peaks are at positions λ1 = 0.4167 ns−1, λ2 = 2.418 ns−1, whereas the exact results are λ1 = 0.5250 ns−1 and λ2 = 2.538 ns−1. The computed areas for these peaks are also in fair agreement when compared with the theoretical results. In this case, a filter factor that takes into account all the singular values was found appropriate. The current study shows that the damped singular value decomposition approach can be used to invert real laboratory data. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 97–102, 2003
Numerically generated DVR and generator coordinate approximation for calculating rotational energies of H and H2O
Authors: Liu Chao‐Ping , Soares Neto J. J. 
Published: September 2003

AbstractThe numerically generated Discrete Variable Representation (DVR), a recently formulated special type of DVR, is tested for its accuracy and efficiency by applying it to calculate the rotational energies of the triatomic system H for the higher excited states of L = 2, even parity, and L = 3, even parity, where L is the angular momentum of the molecule, and of the triatomic system H2O for the first excited state L = 1, even parity. The description of the rotation of the molecule is done using the generator coordinate approximation (GCA). Comparison of the results with other results show the accuracy and efficiency of the numerically generated DVR. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 103–111, 2003
Determination of main structural compositions of nanoalloy clusters of CuxAuy (x + y ≤ 30) using a genetic algorithm approach
Authors: Lordeiro R. A. , Guimarães F. F. , Belchior J. C. , Johnston R. L. 
Published: September 2003

AbstractThe structures of various compositions of nanoalloy clusters CuxAuy (x + y ≤ 30) were determined using the recently developed molecular genetic algorithm. For compositions up to 18 atoms the algorithm found the global minima in all five runs. For clusters with less than 12 atoms, pure Au clusters are most stable. As the total number of atoms increases, clusters with one, two, three, or four Cu atoms become most stable. It has been observed for larger clusters that there is a tendency for structures based on Cu cores surrounded by Au atoms. The calculated second differences in binding energies are in fair agreement with experimental mass spectra for some nuclearities. Finally, the extrapolated cohesive energies for nanoalloys ((Cu3Au)m, (CuAu3)m, and (CuAu)m) gave an average relative error of 11%, compared with the bulk alloys, whereas for the nanoclusters (AuN and CuN) the error was less than 6%. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 112–125, 2003
An AM1 study on the electron‐donating and electron‐accepting character of biomolecules
Authors: Honório K. M. , Da Silva A. B. F. 
Published: September 2003

AbstractEnergy of the highest occupied molecular orbital (EHOMO) and energy of the lowest unoccupied molecular orbital (ELUMO) are very often related to the electron‐donating (EHOMO) and electron‐accepting (ELUMO) character of a molecule. In this work AM1 calculations for the EHOMO and ELUMO of 15 biomolecules are performed with the aim to obtain a scale for the electron‐donating and electron‐accepting character of biomolecules, as they can interact in the biological environment through a charge‐transfer mechanism. From the EHOMO and ELUMO values obtained with the AM1 semiempirical method, we were able to classify the 15 compounds studied into four groups: A (good electron‐donor molecules), B (good electron‐acceptor molecules), C (moderate electron‐donor molecules), and D (compounds that behave as both electron‐donor and electron‐acceptor molecules). © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 126–132, 2003
Theoretical study on the stereochemistry of intramolecular hetero Diels–Alder cycloaddition reactions of azoalkenes
Authors: Alves C. N. , Romero O. A. S. , Da Silva A. B. F. 
Published: September 2003

AbstractThe molecular mechanism for the intramolecular hetero Diels–Alder cycloaddition reactions of azoalkenes has been studied by using quantum mechanical calculations at the density functional theory (DFT) Becke's three‐parameter exchange functional and the gradient‐corrected functional of Lee, Yang, and Paar (B3LYP) and second‐order Møller–Plesset (MP2) theory levels with the 6‐31G* basis set. The molecular mechanism corresponds to a concerted mechanism with a slightly asynchronous bond‐formation process where the formed internal bond (N4–C5) obtained with DFT is longer than the peripheral bond (C1–C6) formed in the transition state. Otherwise, the (C1–C6) bond obtained with MP2 is longer than the (N4–C5) bond formed in the transition state. Solvent (dichloromethane) effects have been considered with the polarizable continuum model (PCM). The MP2 calculations predicted an endo kinetic preference, whereas the DFT ones rendered endo/exo transition states that are practically isoenergetic. According to our analyses, the dispersion interaction (which stabilizes the endo orientation through π–π secondary contacts) and the solvent effects (which favor the exo addition) are the factors governing the stereoselectivity of the process. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 133–136, 2003
Theoretical modeling of alkynes
Authors: Rosseto Renato , Vargas Maria Domingues , Del Nero Jordan 
Published: September 2003

AbstractIn this work we report a semiempirical investigation of the first excited states and of the spectroscopic properties of a series of substituted alkynes. The analysis of the calculated and experimental absorption spectra and theoretical emission spectra resulting from semiempirical/configuration interaction calculations gives us some insight as to how chemical modifications of these molecules could affect the nonlinear optical properties of alkynes. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 137–143, 2003
Gaussian basis sets for polyatomic molecules containing first‐ and second‐row atoms
Authors: Pires José M. , Jorge F. E. 
Published: September 2003

AbstractContracted Gaussian basis sets plus polarization functions generated from the improved generator coordinate Hartree‐Fock (HF) method are used to calculate some physical and chemical properties of the following molecules: CH4, NH3, H2O, SiH4, PH3, and H2S. Ground‐state HF total energies and, at the HF and second‐order Møller–Plesset levels, geometrical parameters, harmonic vibrational frequencies, and electric dipole moments are evaluated and compared with the corresponding experimental values and with those calculated with the 6‐311G** basis sets. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 144–148, 2003
Quantum and classical study of vibrational states of H and H molecules
Authors: Silva Washington B. , Corrêa Eberth de A. , Acioli Paulo H. , Gargano Ricardo 
Published: September 2003

AbstractIn this work, we present calculations of the vibrational energy levels of the H and H systems using the correlation function quantum Monte Carlo (CFQMC) and normal model analysis. The classical results are a qualitative first approximation of the normal modes. The results of the CFQMC calculations show the importance of the quantum effects as well as anharmonicity in these systems. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 149–152, 2003
Dynamics of polarons and bipolarons with interchain coupling in conjugated polymers
Authors: Da Silva Pinheiro Cleber , E Silva Geraldo Magela 
Published: September 2003

AbstractThe interchain and interactions of two parallel chains are studied numerically through the dynamics of charged polaron and bipolaron in the presence of an electric field by using the Pariser–Parr–Pople model combined with the Su–Schrieffer–Heeger model. The electron–lattice coupling and the Brazovskii–Kirova‐type symmetry‐breaking interaction are introduced in the current model. The electric field is introduced in terms of a time‐dependent vector potential that is included in the Hamiltonian through a Peierls substitution of the phase factor to the transfer integral. The charge‐transfer probability between charged polarons and bipolarons belonging to neighboring chains is determined by the numerical resolution of the equations of motion within the unrestricted Hartree–Fock approximation. The effects of confinement on the polaron and bipolaron motion are determined. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 153–158, 2003
Quasiclassical trajectory calculations of isotopic reactions Na + XF → NaF + X (X = D, T and Mμ) on two different potential energy surfaces
Authors: Vilela Alessandra F. A. , Gargano Ricardo , Mundim Kleber C. , Soares Neto J. J. 
Published: September 2003

AbstractDetailed reactive cross‐section calculations (J = 0) of the isotopic reactions Na + XF → NaF + X (X = D, T and Mμ) using classical trajectories at 10 collision energy values are done using two different potential energy surfaces (PES): the generalized simulated annealing (GSA) PES and the bond order 5 (BO5) PES. This study shows that the quality of the GSA PES is comparable to that of the BO5 PES and that the reactivity of the Na + HF → NaF + H reaction is a sensitive function to the mass of isotopic variants of the hydrogen atom, as was expected. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 159–163, 2003
Interaction of MSn (MRu, Rh, Pd) dimers with CH2 and CF2: A density functional study
Authors: Xavier Eder Severino , Duarte Hélio Anderson 
Published: September 2003

AbstractThe importance of Sn to improve the performance of noble metal‐based catalysts has been extensively discussed in the literature. However, a detailed discussion about the effect of Sn on the electronic structure of the metals has not been reported so far. In this work, density functional theory (DFT) calculations have been performed on the M2 and MSn (MRu, Rh, Pd, Sn) dimers and their interaction with CH2 and CF2 carbenes. The electronic structure, geometry, and harmonic frequencies are reported and compared with the available experimental data and to the previous published high level ab initio and DFT calculations. The calculated values of M2 are in good agreement with the experimental and theoretical results. The exception is the binding energy of the Sn dimer, which can be different from the experimental estimates as much as 16 kcal · mol−1. It has been stressed that this difficulty is related to the atomic energy reference used to estimate the binding energy. Transition metal elements are still a difficult task for DFT methods. Calculations on MSnCH2 and MSnCF2 species with different multiplicities and conformations have been performed. Bonding analyses on the MSn metal dimers showed that carbenes prefer to adsorb in bridge sites favoring a donating/backdonating mechanism of interaction that is enhanced with the presence of the Sn atom. The MSnCH2 binding energy is predicted to be 40% smaller than the MSnCF2 binding energy, following the same trends observed for the first‐row transition‐metal MCH2 and MCF2 complexes. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 164–176, 2003
Density functional theory test study on the CO ···· He dimer
Authors: Salazar Mary C. , Paz José L. , Hernández Antonio J. , Manzanares Carlos , Ludeña Eduardo V. 
Published: September 2003

AbstractIn the current paper we have investigated the bonding properties of the weakly bound van der Waals CO ···· He dimer by means of the Perdew–Wang91 exchange and Perdew–Wang correlation (PWPW) and Adamo and Barone's Becke‐style one‐parameter functional using the modified Perdew–Wang91 exchange and Perdew–Wang correlation (mPW1PW) exchange‐correlation functionals in the framework of the supermolecule approach, using density functional theory local‐spin‐optimized atom‐centered basis sets, complemented with bond functions optimized at the mPW1PW level of theory. These calculations show that the use of the mPW1PW functional using bond functions gives a realistic representation of the interaction‐energy potential for this van der Waals molecular complex, as compared with reference Møller–Plesset perturbation theory calculations. In contrast, the PWPW functional is unable to describe the bonding properties of the system, and all values obtained with this functional approximation are considered out‐of‐scale compared with the rest of the calculations presented in this contribution. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 177–183, 2003
Gaussian basis sets for low‐lying excited states of the atoms from He to Kr
Authors: Neto A. Canal , Rodrigues B. L. , Jorge F. E. , De Castro E. V. R. 
Published: September 2003

AbstractThe generator coordinate Hartree–Fock method is used to generate Gaussian basis sets for low‐lying excited states of the neutral atoms from He (Z = 2) to Kr (Z = 36). Our excitation and orbital energies are compared with the corresponding results obtained with numerical Hartree–Fock calculations. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 184–189, 2003