bluuebunny/crossref_metadata_2025_split huggingface dataset:
New treatment of the theory for small‐angle x‐ray scattering with applications to polystyrene crazes
Authors: Tang Ming‐Ya , Fellers John F. , Lin J. S. 
Published: April 2003

AbstractThe phenomenon of surface scattering of electromagnetic waves by single or multiple layers of films is reviewed and a special treatment for the total reflection of x rays is developed. This theory is applied to the analysis of the surface scattering observed in small‐angle x‐ray scattering (SAXS) studies of two‐phase matter in polymers having lamella stacks or a flat interfacial boundary structure. Important features of this vector theory are the ability to calculate the surface scattering invariant, the absolute scattering intensity, and the surface roughness, which gives rise to dispersion of specular reflection from perfectly smooth surfaces. By considering the interfacial surface roughness of polystyrene crazes, the surface scattering spectrum is calculated theoretically and compared with some experimental results. Also the theory is presented in such a way as to compare surface scattering with volume scattering; i.e., both two‐ and three‐dimensional scattering events can be simultaneously treated. This provides a new basis for quantitative analysis of crazes in polystyrene.
Synthesis and conductivity of poly acene quinone radical polymers
Authors: Dunn Lee C. , Ford Warren T. , Hilal Nabil , Vijayakumar Pormimilla S. , Pohl H. A. 
Published: April 2003

AbstractPolymers with conductivities from 8.6 × 100 to 7.3 × 10−6 (ω cm)−1 at 2–12 kbar were prepared by zinc‐chloride‐catalyzed condensation of polycyclic aromatic hydrocarbons, heterocycles, and quinones with pyromellitic dianhydride, tetrabromophthalic anhydride, and tetrachlorophthalic anhydride at 450°C. These materials are stable in air and exhibit strong electroactive character without addition of oxidizing or reducing agents (dopants).
Rebuttal to “comments on ‘some evidence against the existence of the liquid–liquid transition. IV. The temperature dependence of shear viscosity’”
Authors: Orbon Stephen J. , Plazek Donald J. 
Published: April 2003

AbstractData on the temperature dependence of viscosity obtained on three different polystyrenes with narrow molecular weight distributions are fitted to the Vogel, Fulcher, Tamman, and Hesse (VTFH) equation as well as to two intersecting Arrhenius lines. Both fits are optimized by means of computer programs. The data were chosen to fit the requirements stated by Boyer. The results of the analyses support the earlier conclusions that temperature‐dependent viscosity data do not indicate the presence of any liquid‐liquid transition TLL above the glass temperature Tg. In addition, evidence is presented which indicates that the viscosity at Tg of high‐molecular‐weight polystyrenes is proportional to the 3.4 power of the molecular weight. Hence Tg is not an isoviscous temperature.
Linear polymers in nonhomogeneous flow fields. II. The cross‐stream migration velocity
Authors: Brunn P. O. 
Published: April 2003

AbstractThe cross‐stream migration velocity v⊥ is that part of the velocity of a particle which has no component in the direction of the undistrubed flow. In order to obtain v⊥ for bead–spring model macromolecules, it is necessary to compute the trace of the matrix product \documentclass{article}\pagestyle{empty}\begin{document}$ \underline \ell \cdot \underline {{\rm \hat C}} $\end{document}, where \documentclass{article}\pagestyle{empty}\begin{document}$ \underline \ell $\end{document} denotes the migration matrix and \documentclass{article}\pagestyle{empty}\begin{document}$ \underline {{\rm \hat C}} $\end{document} is the modified Kramer's matrix. In this paper this is done via an eigenvalue calculation, where the eigenvalues are estimated by using the Rouse eigenfunctions. The results are then checked against the few known exact results and excellent agreement is found. It turns out that v⊥ depends on the third power of the molecular weight for free‐draining polymers. The dependence upon molecular weight becomes weaker with increasing hydrodynamic interaction until, in the nondraining limit, v⊥ ∝ M2.5. A simple yet accurate formula for v⊥ is proposed. In conjunction with the results for D (of Part I), purely rotational flow fields are shown to be characterized by a single parameter, the particle Peclet number Pe. Up to a constant of order one (actually a function of the hydrodynamic interaction parameters h* and h, which can vary only between 0.8 and 2.057), Pe depends only upon D, the mean‐square equilibrium extension R, and q0, the magnitude of the maximum shear rate for the flow.
A simple theoretical study of the dissolution of block copolymer molecules into their own microphases
Authors: Krause Sonja 
Published: April 2003

AbstractA simple theoretical treatment of microphase separation in block copolymers [S. Krause, Macromolecules, 3, 84 (1970)] has been extended to the case in which individual molecules of the block copolymer may dissolve in one or the other of the microphases. When the free energy driving force for microphase separation is near zero, the minimum free energy state of the system has a relatively high concentration of block copolymer molecules dissolved in one or in both of the microphases, depending partly on the percent composition of the block copolymer. The theoretical predictions are compared with experimental data in the literature.
Dependence of degree of crystallinity and melting point on time and temperature of annealing for γ‐irradiated polytetrafluroethylene
Authors: Takenaga Mitsuru , Yamagata Kyozo 
Published: April 2003

AbstractThe annealing behavior of polytetrafluoroethylene (PTFE) irradiated with 1 × 105 R of γ rays has been studied in terms of the degree of crystallinity and the melting temperature. At short annealing times the crystallinity changes rapidly to a level characteristic of the annealing temperature. It seems that the crystallization arises from transport of chain segments in noncrystalline regions. The increase in crystallinity at long times of annealing is linear in the logarithm of time. This process is mostly due to elimination of voids formed during γ irradiation, but it also involves slight lamellar thickening and crystallization to form extended‐chain regions.
Defect morphology in oriented systems
Authors: Meakin Paul , Scalapino D. J. 
Published: April 2003

AbstractIn fibrils composed of highly extended chains, a characteristic clustering of defects into laminae perpendicular to the chain axes is often found. One model suggested to explain this morphology assumes that initially the defects are randomly distributed but that under heat treatment the system undergoes a spinodal phase separation in which the defects cluster to form the laminar structure. Here we report results obtained from numerical simulations which support this picture. We then explore the more general question of the response of such a nonequilibrium system to small imposed patterns. We examine under what conditions the patterns are amplified or attenuated.
Polymer decoration: The orientation of polymer folds as revealed by the crystallization of polymer vapors
Authors: Wittmann J. C. , Lotz B. 
Published: April 2003

AbstractA new technique of decoration of the fold surface of polymer crystals is described. It is similar in methodology to gold decoration, but makes use of vapors of crystallizable polymers, principally polyethylene, as decorating material. Upon condensation and crystallization, the highly anisometric decorating molecules become oriented parallel to the fold direction. They build up small crystalline lamellae which, seen edge‐on, appear as elongated rods and can be easily observed by conventional transmission electron microscopy. This decoration technique reveals the sectorization of polymer single crystals grown from solution. It can be used to determine the local fold orientation (with a resolution of ca. 10 nm) of polymers crystallized under a wide range of conditions, including crystallization from the bulk. The technique reveals that under all crystallization conditions so far investigated the outermost part of the polymer fold surface is relatively ordered, and the folds and/or loops are, as a rule, oriented nearly parallel to the macroscopic growth front.
Diffusion study of a polymer–diluent system using the optical mass transport method
Authors: Hakemi H. , Krigbaum W. R. 
Published: April 2003

AbstractThermotropic polymers and low‐molecular‐weight mesogens share many common textural features. This circumstance is exploited to determine diffusion coefficents in a system consisting of a cholesteric polymer and a low‐molecular‐weight nematogen using the recently developed optical mass transport method. The self‐diffusion coefficient and its concentration dependence were determined by using a distance–time approach, whereas the time dependence of the mutual diffusion coefficient was evaluated by a conventional concentration–distance analysis of the diffusion profile. Comparison with literature data indicates satisfactory agreement. The coefficient of the scaling law relating the self‐diffusion coefficient and concentration is in accord with the value predicted by de Gennes for semidilute polymer solutions.
Molecular orientation in stretched poly(vinyl alcohol). I. NMR anisotropy and birefringence
Authors: Spegt P. , Meurer B. , Hornick C. , Weill G. 
Published: April 2003

AbstractThe second and fourth moments of the proton resonance line in stretched poly(vinyl alcohol) samples have been measured by a pulse technique. Their anisotropy has been analyzed at different elongation ratios λ. The use of the second and fourth moments gives an interesting cross‐check on the reliability of the results. Despite the fact that the lattice sums required for absolute determination of the orientation cannot be calculated, coefficients related to the second and fourth moments of the orientation distribution function can be compared to the prediction of the quasiaffine orientation scheme for the crystalline phase and to the experimental values of the birefringence as a function of λ. It is shown that NMR clearly detects the onset of the orientation of the amorphous chains above λ ≈ 4.
Numerical study of the phase behavior of rods in solution: Warner–Flory model with polydisperse system of rods
Authors: Moscicki J. K. 
Published: April 2003

AbstractPhase equilibria of polydisperse rods in solution are studied in terms of the Warner–Flory model. Numerical calculations are made with a Gaussian‐like asymmetric distribution of rod lengths. The aim of these studies is to investigate (i) the dependence of the phase diagram on the shape of the polydispersity distribution function and (ii) the isotropic–anisotropic phase separation within the coexistence range. It is shown that, as a consequence of polydispersity, even for a narrow distribution, the phase diagram is very simple, with only one type of anisotropic phase present. However, within the biphasic range, the properties of the anisotropic phase vary significantly with temperature. At high temperatures, they are essentially governed by steric effects and at low temperatures by both steric effects and soft anisotropic interactions between the rods.
Crystallization of bisphenol‐A polycarbonate induced by organic salts: Chemical modification of the polymer. II. Model reactions
Authors: Bailly Ch. , Legras R. , Mercier J. P. 
Published: April 2003

AbstractIn the presence of sodium o‐chlorobenzoate, bisphenol‐A diphenylcarbonate (BADPC) undergoes complex chemical modifications from 170°C. Reaction between BADPC and minute amounts of salt produces sodium phenoxide end groups which undergo a fast exchange reaction with the carbonate groups of BADPC. In a closed system, an equilibrium molecular weight distribution is progressively attained which agrees fairly well with the one predicted from a simple model based on Bernoulli statistics. In an open system, the equilibrium is continuously displaced by the evaporation of volatile diphenyl carbonate. This leads to a steady increase of the molecular weight.
Fourier‐transform infrared investigation of conformational changes occurring at the yield point in uniaxially drawn atactic polystyrene
Authors: Theodorou M. , Jasse B. , Monnerie L. 
Published: April 2003

AbstractFourier‐transform infrared measurements on atactic polystyrene have been made during application of strain. On passing through the yield point, spectra indicate an increase of the amount of the higher‐energy gauche conformation corresponding to the conformational distribution observed at 30°C above the glass transition. The trans conformation recovers after yield. The results are in agreement with the theory of Robertson but do not allow the validity of his model to be unambiguously established.
Hydrogen bonding in nylon 66 and model compounds
Authors: Garcia Dana , Starkweather Howard W. 
Published: April 2003

AbstractFourier‐transform infrared spectroscopy was used to study the hydrogen bond‐breaking process in nylon 66 and two model compounds. The resulting enthalpy and entropy values indicated that while there is no interaction between adjacent amide groups in the polymer chain, there is, nevertheless, a substantial cooperative effect in the transverse hydrogen bond direction. We have also established that any analysis of hydrogen bond breaking in semicrystalline polymers (i.e., nylon 66) below the melting point should include a crystallinity correction factor. Extrapolation of our data above the melting point of nylon 66 yielded a 26% retention of hydrogen bonding.
Copolyesters exhibiting a thermotropic cholesteric phase
Authors: Watanabe J. , Krigbaum W. R. 
Published: April 2003

AbstractMesomorphic copolymers were synthesized by incorporating varying ratios of azelaic acid and (+)‐3‐methyl adipic acid into copolyesters based upon 4,4′‐dihydroxybiphenyl. Introduction of the phenylene (+)‐3‐methyl adipate unit broadens the temperature range of the nematic phase of the azelate homopolymer and, at the same time, produces a chiral nematic (cholesteric) mesophase which exhibits various iridescent colors. Circular dichroism measurements were used to determine the pitch of the cholesteric liquid crystals. The pitch decreased gradually with increasing temperature, and the inverse pitch increased in direct proportion to the molar content of the units containing (+)‐3‐methyl adipate. The twisted cholesteric structure could be conserved by quenching to produce films with various colors at room temperature. Annealing these films at a temperature immediately below that of the crystal–mesophase transition improved the regularity of the cholesteric structure.
Rheo‐optical studies of concentrated polystyrene solutions subjected to transient simple shear flow
Authors: Zebrowski Beth E. , Fuller Gerald G. 
Published: April 2003

AbstractConcentrated polystyrene solutions were investigated on the inception and cessation of simple shear flow by means of the technique of two‐color flow birefringence. Both monodisperse solutions of various molecular weights and bimodal mixtures were studied. The molecular weight affected both the amount of overshoot in the birefringence and the response time on the inception of shear flow. Large overshoots in birefringence, up to 250%, and undershoot in the orientation angle were observed. The shear stress and the first normal stress difference were calculated by using the stress–optical rule. The amount of strain at the peaks in the stress growth curves are presented along with the steady‐state viscosity and primary normal stress coefficient. The experimental results are compared qualitatively with theoretical predictions of various molecular models.
Bead–spring model for adsorbed polymer chains in shear flow: Hydrodynamic interaction
Authors: Goh C. J. , Phan‐Thien N. , Atkinson J. D. 
Published: April 2003

AbstractWe consider the hydrodynamic interaction between two absorbed polymer chains in a simple shear flow, each modeled by a bead connected to the wall by a linear spring. It is concluded that hydrodynamic interaction between the beads or between the beads and the wall cannot be responsible for the experimentally observed increase in hydrodynamic thickness.
Monte Carlo simulation of the crystal structure of the low‐temperature phase of polytetrafluoroethylene
Authors: Yamamoto Takashi 
Published: April 2003

AbstractAn energy analysis based on molecular field theory and Monte Carlo simulation is carried out for the crystal structure of the low‐temperature phase of polytetrafluoroethylene (PTFE). PTFE molecules in right‐handed and left‐handed 13/6 helical conformation are assumed to be packed in a hexagonal array, with each molecule having 13 possible orientations around the chain axis. Interactions between nearest‐neighbor chains are calculated from van der Waals interactions between nonbonded C‐C, C‐F, and F‐F atom pairs. First, an approximate molecular field calculation is made of the critical fluctuation of the chain orientation at the order–disorder transition point. This suggests that the low‐temperature phase has two chain stems in the unit cell. The Monte Carlo calculation, similar to that used for spin systems, is then applied to the equilibrium packing mode in the low‐temperature phase. A crystal structure containing two chain stems in the unit cell is again obtained. A large amount of disorder in the chain orientation is indicated and is believed to be essential in the PTFE crystal.
Comparative study of dielectric, mechanical, and nuclear magnetic relaxations in linear polyethylene. II. Relaxation spectroscopy of the α, β, and γ loss bands with special emphasis on fine structure
Authors: Kakizaki Maeko , Kakudate Takuo , Hideshima Teruo 
Published: April 2003

AbstractDielectric, mechanical, and NMR retardation (correlation) spectra for relaxations in linear polyethylene were calculated in normalized form and intercompared. For each of the two local‐mode relaxations in the γ region, called γ1 and γ2, these spectra are found to be in excellent agreement. For the α region, the spectra for two mechanical processes, called α1 and α2, two NMR processes, called α′ and α, and one dielectric process α were calculated. Excellent agreement is found between the spectra for the dielectric α and NMR α′ processes and also spectra for the mechanical α2 and NMR α processes, due to molecular motion in the interior of crystals. However, the spectrum for the mechanical α1 process is different from that for the dielectric α and NMR α′ processes, though the activation energy for the first process is almost the same as for the other two. This behavior is interpreted on the assumption that the dielectric α and NMR α′ processes are caused by molecular motion in lamellar surface layers while the mechanical α1 process is due to grain‐boundary slip with viscous resistance of the surface layers in the boundaries. The shapes of the spectra, including the spectrum for the β process, are not affected by diluent.
Coherent elastic scattering of a reptating chain in a melt during transient relaxation
Authors: Boue F. , Osaki K. , Ball R. C. 
Published: April 2003

AbstractWe calculate the elastic scattering of a long chain in a polymer melt during the process of relaxation after a sudden deformation, i.e., the return to equilibrium with time, while the deformed shape is maintained. The scattering thus depends on the duration t of the relaxation, as well as on the scattering vector, and is a physical quantity characteristic of the dynamics of long chains. The reptation model of de Gennes is used as developed for deformed melts by Doi and Edwards: the chain is confined by other chains in a tube, from which disengagement by the ends is the only way of renewing its configuration. The tube diameter is taken as a parameter. We give both an analytic form and numerical evaluations. On comparison with calculations based on the Rouse model, in which the chain is assumed to be free in a viscous medium, it is seen that the experimental data (given elsewhere) should enable one to distinguish between the two models.
Quantitative aspects of internal reflection spectroscopy: Polymer surface composition measurement
Authors: Mirabella Francis M. 
Published: April 2003

AbstractThe use of band‐ratioing techniques in internal reflection spectroscopy (IRS) for a wide variety of polymer surface composition and orientation measurements is discussed. It is shown that quantitative data can be obtained under a wide range of experimental conditions. The effects of variations in sample contact, internal reflection element, and angle of incidence are considered in detail. The applicability and limitations of calibration procedures for the determination of surface composition under various experimental conditions are considered. The requirements for obtaining quantitative results by IRS are shown to be far more lenient than is typically assumed.
Fracto‐emission from filled and unfilled polybutadiene
Authors: Dickinson J. T. , Jensen L. C. 
Published: April 2003

AbstractWe further examine the mechanisms involved in the emission of electrons and positive ions from polybutadiene accompanying fracture. Experimental evidence is given in support of a previously presented model involving a microdischarge accompanying fracture which excites the fracture surfaces by particle bombardment. Calculations of the time dependence for the emission from such excitations for both isothermal and thermal stimulation from a simple trap model are presented. We conclude that both filled and unfilled polybutadiene are experiencing the same excitations except at a considerably reduced intensity for the unfilled material.
Influence of tacticity on Tβ, Tg, and TLL in poly(methyl methacrylate)s by the method of thermally stimulated current (TSC)
Authors: Gourari A. , Bendaoud Mohamed , Lacabanne Colette , Boyer Raymond F. 
Published: April 2003

AbstractThe thermally stimulated‐current method (TSC) has been employed to determine the temperatures and intensities of Tβ, Tg, and T > Tg for pure isotactic, pure syndiotactic, and five atactic specimens with syndiotactic triad content from 49.5 to 75%; Tg was found to increase linearly with syndiotactic triad content as Tg (°C) = 48.0 + 0.856 (% syn), with R2 = 0.970 standard error 5.6°C; Tg for the syndiotactic specimen is 136.6°C measured, 133.6°C calculated. Several atactic specimens exhibit a second glass temperature 15 to 35 K above the regression line ascribed to some pure syndio content, and/or some isotactic–syndiotactic stereocomplexes. All specimens exhibited the liquid–liquid or TLL transition (relaxation) which increases linearly with 100‐% isotactic triad content. Isotactic PMMA shows a T′LL relaxation 50 K above TLL. The Tg and TLL values obtained correlate extremely well with values from differential scanning calorimetry (DSC) determined in a separate study, as well as with most literature data. Intensities of Tg and TLL by TSC are greatest for isotactic, next for syndiotactic, with a broad, low minimum for atactic materials. The intensity of a β relaxation increases slowly from isotactic to syndiotactic. The TLL found by TSC compares well with literature values for isotactic PMMA obtained by several methods, and TLL in the atactic region compares well with literature values for atactic material. The ratio TLL/Tg ranges from 1.09 to 1.20 with no dependence on tacticity. Tg follows simple Arrhenius behavior with enthalpies of activation about one‐half of the values normally calculated from dielectric and mechanical loss. The frequency dependences of TLL and T′LL follow a Vogel–WLF relationship with temperature. The origin of TLL is discussed in terms of the Frenkel hypothesis of segment–segment interaction. Evidence for TLL and TLL from a variety of methods indicates that these two temperatures are not artifacts of the TSC method.