bluuebunny/crossref_metadata_2025_split huggingface dataset:
Static small‐angle x‐ray scattering study of polymer deformation
Authors: Young P. , Stein R. S. , Kyu T. , Lin J. S. 
Published: April 2003

AbstractThe small‐angle x‐ray scattering (SAXS) approach has been employed in an effort to understand the deformation mechanism of semicrystalline polymers in terms of submicroscopic structure of lamellae. Isotropic melt‐pressed polyethylenes of low, medium, and high densities (LDPE, MDPE, and HDPE, respectively) having spherulitic texture were investigated by SAXS for various Static elongations between 10% and 40%. The SAXS isointensity contours of the deformed polymers are anisotropic (elliptical) with the long axis perpendicular to the stretching direction. Slice averages at various azimuthal angles between 0° and 90° reveal distinct SAXS peaks with respect to scattering angle. The peak position of SAXS profile characterizes the long period or lamellar spacing, while integrated intensity distribution is relevant to lamellar orientation. At low elongations, there is an increase in intensity at both azimuthal angles of 0° and 90°, suggesting that excess scattering arises during deformation, probably associated with lamellar untwisting process. Lamellar orientation distribution and second‐order orientation are defined to account for the lamellar orientation process. Experimental results are compared with Kratky's floating rod model coupled with Stein's lamellar untwisting model. The lamellar orientation closely follows the affine deformation scheme, while the lamellar spacing deviates appreciably from it, particularly at large elongations.
Stability of spherulite growth rate
Authors: Pawlak A. , Galeski A. 
Published: April 2003

AbstractSpherulite growth rates in thin films of isotactic polypropylene, poly (methylene oxide), and poly (ethylene adipate) have been studied by light microscopy. The growth rate of the parts of spherulites formed from pockets of occluded melt is decreased drastically. The decrease is associated with the negative pressure buildup inside the pockets due to the density change as the melt is converted to spherulites. Material subjected to negative pressure shows a higher melting point of 3–4'C if the pressure is released prior to melting. Slight periodic changes of the growth rate were detected during crystallization of banded spherulites. No changes in growth rate were observed for two spherulites about to impinge or for spherulites growing near a solid obstacle.
X‐ray diffraction of gelatin fibers in the dry and swollen states
Authors: Pezron I. , Djabourov M. , Bosio L. , Leblond J. 
Published: April 2003

AbstractThe aim of this x‐ray diffraction investigation is to establish a comparison between the structure of collagen and that of gelatin gels. The gelatin gels are drawn into fibers, which are dried before use. The xray scattering patterns of the gelatin fibers show a close analogy with collagen, which provides evidence for the presence of bundles of triple helices in the dried, oriented gels. The mechanisms of swelling of the gelatin fibers are identified by investigating the humidity‐sensitive position of the equatorial spots related to the side‐by‐side distance D of the triple helices. The distance D increases continuously as more water is added to the fibers; this is accompanied by a progressive loss of orientation of the triple helices with respect to the fiber axis. The temperature dependence of the x‐ray patterns is also investigated. We discuss the implications of this study for understanding the gelation mechanisms and the structure of gelatin gels. Comparisons are made with other physical gels.
Gel permeation chromatograph interface to collect solvent‐free polymer fractions for composition drift analysis
Authors: Dekmezian A. H. , Morioka T. , Camp C. E. 
Published: April 2003

AbstractAn interface is described that is capable of stripping solvent from polymer solutions emerging from an interfaced high‐temperature gel permeation chromatograph. The chemical composition of each solvent‐free polymer fraction is then determined using Fourier transform infrared (FTIR) or other techniques to obtain the composition drift (CD) pattern of the polymer (i.e., variation of chemical composition as a function of molecular weight). The interface consists of a vacuum oven into which an ultrasonic nebulizer and a stepper motor have been incorporated. The stepper motor drives a fraction collector, equipped with a set of KBr plates, onto which the nebulized polymer solution is sprayed. The temperature and pressure of the interface are maintained so as to strip the solvent from the chromatographic effluent as it impinges on the collector substrates. The technique, which had been applied to the % ethylene CD of ethylene‐propylene rubbers, is employed in the analysis of a block copolymer reaction product. In the example given, the CD pattern of the reaction product generated is simulated along with the observed molecular weight distribution pattern to arrive at the approximate composition of the reaction product. For many applications, this approach eliminates the need to carry out tedious solvent/nonsolvent fractionations commonly employed in the characterization of the compositional heterogeneities in block copolymer reaction products.
The mechanical properties of random copolymers of ethylene: Force‐elongation relations
Authors: Peacock A. J. , Mandelkern L. 
Published: April 2003

AbstractUtilizing a newly developed apparatus, force‐length measurements were performed on a series of unfractionated random ethylene copolymers having different counit types and a wide composition range. By controling crystallization conditions, crystallinity levels could be varied over wide extremes and a complete repetoire of superstructures was developed. Emphasis was on key mechanical properties such as the initial modulus, yield stress, and the ultimate properties of draw ratio at break and tensile stress. Except for the ethylene‐methacrylic acid copolymers, which behaved in a unique manner, the properties were found to be independent of the chemical nature of the counit and the particular supermolecular structure that was developed. The initial modulus and the yield stress were found to be very dependent on the crystallinity and phase structure. On the other hand, except for the decrease at low counit content, the draw ratio at break was found to be invariant with counit type, crystallinity level, supermolecular structure, and molecular weight. The results are discussed in terms of the molecular constitution of the copolymer and the structure in the crystalline state.
Nonlinear constitutive equation for polyethylene under combined tension and torsion
Authors: Kitagawa Masayoshi , Takagi Hideyuki 
Published: April 2003

AbstractIn order to investigate a viscoelastic‐plastic nonlinear constitutive equation for polymer solids, combined tension and torsion tests were performed using polyethylene (PE) hollow cylinders. The experimental data were compared with the numerical results derived from a multiaxial constitutive equation developed from the uniaxial one proposed by Krempl. It is shown that the proposed theory fairly well describes the stress–strain curves of PE up to relatively high strain ranges not only in simple torsion, but also under combined tension–torsion, provided that the current strain is not below the maximum previous strain.
Small‐angle x‐ray scattering in “bottlebrush” ionomers
Authors: Wollmann D. , Williams C. E. , Eisenberg A. 
Published: April 2003

AbstractBlock copolymers consisting of long styrene midblocks and much shorter 4‐vinyl pyridine end‐blocks were quaternized with n‐iodo alkanes (2 ≤ n ≤ 10) to give block ionomers of a novel architecture. The name “bottlebrush” seems appropriate for these materials. A preliminary investigation of the morphology of these systems, prepared by in situ quaternization, is reported here. The morphology is dependent on both the length of the iodo alkane and the relative sizes of the blocks. Even with identical sample histories, two distinct morphologies are seen. One of these is characterized by a single broad SAXS peak, while the other shows a much narrower peak and higher‐order features. The latter morphology is associated with the higher ionic to nonionic ratios and long side chains.
The dependence of butyl branch density on slow crack growth in polyethylene: Kinetics
Authors: Huang Yan‐Ling , Brown Norman 
Published: April 2003

AbstractWhen the density of n‐butyl branches in an ethylene–hexene copolymer increases from 0 to 4.6 butyls/1000 C, the rate of slow crack growth decreases by a factor of 104 . The activation energy for the process is nearly independent of branch density and is about 120 kJ/mol. It is the number of tie molecules and whether they are pinned that control the rate of crack growth which involves the disentanglement of the fibrils in the craze. Branching increases the number of tie molecules by decreasing the lamella thickness, while the branches pin some of the tie molecules to prevent them from sliding through the crystal or other points of entanglement.
Zone drawing and mechanical relaxation of poly(vinylidene fluoride)
Authors: Grubb David T. , Rich Kearney F. 
Published: April 2003

AbstractPoly(vinylidene fluoride), PVF2, has been zone drawn to extensions up to 7 times. Well oriented β phase tapes are produced when the draw neck moved out of the hot zone, at extensions over six times and zone temperatures =<155°C. Other conditions give α phase tapes. The dynamic mechanical spectra of highly drawn PVF2 is exactly the same for both phases, with Tg at −25°C and a sharp rise in tan δ at 50°C. Isotropic α and β phase sheets gave different mechanical spectra, but with similar features at different strengths. As the isotropic sheets were prepared in very different ways, no specific features of the spectra could be assigned to the different phases.
Sorption and transport of pure gases in random styrene/methyl methacrylate copolymers
Authors: Raymond P. C. , Paul D. R. 
Published: April 2003

AbstractPrevious work has shown that permeability coefficients for CO2 can increase with pressure for poly(methyl methacrylate) (PMMA); whereas, those for polystyrene decrease slightly as found for many glassy polymers. This response is attributed to a greater propensity for PMMA to be plasticized by CO2. This issue is considered in detail here by examining the behavior of a series of random styrene/methyl methacrylate copolymers in order to learn how the plasticization response varies with MMA content. At low pressure, the sorption and transport of CO2 and other gases in these copolymers depend on copolymer composition in ways expected from simple theories for multicomponent polymers. The change in CO2 permeability coefficient upon pressurization from 1 to 20 atm ranged from –6% for polystyrene to +57% for poly (methyl methacrylate). Furthermore, upon holding at 20 atm of CO2 driving pressure, there was a significant increase in the CO2 permeability coefficient with time for PMMA; whereas this conditioning effect was much smaller for polystyrene. Conditioning and plasticization effects seem to be related to the same molecular causes. The responses change progressively for the copolymers but not directly in proportion to MMA content. The greater effects of CO2 for PMMA are, to a significant extent, but not entirely, due to its much higher level of CO2 sorption compared with that of polystyrene. The results are discussed in terms of relevant theories.
Sorption and transport of pure C02 and CH4 in miscible bisphenol chloral polycarbonate/poly (methyl methacrylate) blends
Authors: Raymond P. C. , Paul D. R. 
Published: April 2003

AbstractSorption and permeation behavior of CO2 and CH4 was examined in detail for a series of miscible blends based on bischloral polycarbonate (BCPC) and poly (methyl methacrylate) (PMMA). The former pure polymer exhibits decreases in the permeability coefficients for both CO2 and CH4 as the upstream driving pressure increased as predicted by the dual‐mode sorption model. On the other hand, PMMA shows a decrease for CH4 but an increase for CO2. The latter is attributed to plasticization by this more soluble gas. The blends show intermediate behavior. CO2 permeation was examined on pressurization, at constant pressure for two weeks, and then on depressurization. The pattern of behavior progressively deviated between that of BCPC and PMMA as the MMA content of the blends was varied. These trends were contrasted with those previously described for a series of styrene/methyl methacrylate copolymers. Some differences in behavior between the blends and the copolymers were noted when compared at constant MMA content. These results have important ramifications for the design and selection of polymers for membranes to separate the CO2/CH4 gas pair.
Fragmentation of polycarbonate macroinitiators in solution and in the bulk state
Authors: Kuhn K. J. , Hellmann G. P. 
Published: April 2003

AbstractThe diphenylethane initiator 3,4‐diethyl‐3,4‐(p‐methoxyphenyl)‐hexane (T–OCH3) was synthesized. By cocondensation of bisphenol A or C and the bisphenol derivative (“T”) of T–OCH3 with phosgene, polycarbonate macroinitiators PC(TxA1‐x) and PC(TxC1‐x) with different compositions x were made. The thermal fragmentation of T–OCH3 and the copolycarbonates was investigated with and without a radical scavenger both in solution and in the bulk state. The primary dissociation of T–OCH3 is a monomolecular Arrhenius process with a characteristic temperature of T* (τ = 1h) = 140°C (τ: average life time of the intact molecule). When the radicals are not intercepted, the dissociation is excessively reverted by radical recombination, which raises T* to T* = 163°C. The reaction ends then exclusively in radical disproportionation. The chain fragmentation of the copolycarbonates is of the type of a random decondensation. The counits CT dissociate in solution almost exactly like T–OCH3. In the highly viscous bulk state, the reaction proceeds in matrix cages, which have a stabilizing effect, so that T* is increased to T* = 170°C. These copolycarbonates are model polymers for a novel method to study the hitherto unmeasurably slow chain diffusion processes in polymers near the glass transition temperature.
X‐ray modulus and strain distribution in single fibers of polyethylene
Authors: Prasad Keshav , Grubb David T. 
Published: April 2003

AbstractSynchrotron x‐ray radiation was used to study structural changes during deformation of a single high‐modulus, high‐strength fiber of polyethylene (Spectra 1000, Allied Corp.) 20–40 μm in diameter. The high brightness of the synchrotron beam allowed x‐ray diffraction patterns to be obtained from 0.5 μg fiber samples in ca. 1 min. The (002) chain axis reflection shifted and broadened when the fiber was loaded in tension. When a model of crystals and disordered material in series was used for the fiber, the measured lattice strain at stresses up to 1 GPa gave a crystal modulus of 250 GPa. At stresses above 1 GPa the (002) reflection no longer shifted with increasing load. A noncrystalline part of the material deforms and takes up the load; this effect has been observed by Raman spectroscopy. The (002) peak also broadens under stress. When fiber bundles were used as samples, broadening could be due to uneven loading of fibers, but with a single fiber sample, one can be sure that the loading at the fiber level is uniform. Broadening of the (002) reflection then indicates inhomogeneities within the fiber. Deconvolution with the line profile of the fiber at zero stress should give the distribution of crystal strains. The strain distributions are symmetric and during loading the full width at half maximum (fwhm) is approximately equal to the mean strain. With an assumed constant crystal modulus this describes the stress distribution as extending from zero to twice the mean stress.
Thermal expansion of oriented liquid crystal copolyesters
Authors: Green D. I. , Orchard G. A. J. , Davies G. R. , Ward I. M. 
Published: April 2003

AbstractThe axial thermal expansion coefficients of a series of highly oriented thermotropic liquid crystal copolyesters with random phenylene‐naphthalene main‐chain sequences are reported. In common with many other highly oriented polymers the values are negative. Generally, there are two transitions in the slope of the expansion‐temperature curves. The positions of these transitions are correlated with high activation energy relaxations in the mechanical spectra. Comparison of the thermal expansion properties determined by x‐ray and macroscopic techniques on two of the samples reveals little difference between the bulk material and a unit with a segmental length of ten monomers.
Theoretical foundations of interdiffusion
Authors: Hess Walter , Nägele Gerhard , Akcasu A. Ziya 
Published: April 2003

AbstractExpressions for the interdiffusion and the tracer‐diffusion coefficients in terms of the time‐integrals of force‐correlation functions are obtained using a microscopic description of the inter‐diffusion and tracer‐diffusion processes in a two‐component liquid. The present approach provides a systematic and direct derivation, as well as an extension, of the results of Bearman et al. in their pioneering work in the late 1950s which have been used recently by Cohen and Foley to discuss the two possible relationships between the interdiffusion and tracer diffusion coefficients, referred to as the “fast‐mode expression” of Hartley and Crank and the “slow‐mode expression” based on the random phase approximation. In our analysis we find an additional three‐particle friction term in the exact expression for the interdiffusion coefficient, which is not present in Bearman's work. It is concluded that not much can be said in favor of the fast‐mode or slow‐mode expressions, unless this additional three‐particle friction is neglected. We also show that the center‐of‐volume reference frame, in which the hydrodynamic fluxes are measured, naturally follows from the microscopic description in the isothermal‐isobaric limit.
Diffusion of gases in inhomogeneous polymeric membranes
Authors: Higuchi Akon , Nakagawa Tsutomu 
Published: April 2003

AbstractFick's first law is modified to be applicable for the transport of gases in inhomogeneous polymeric membranes having continuous, concentration‐dependent, gradients of solubility and diffusivity along the flux direction (x axis). The membranes are considered to be in the rubbery state, and all gases in the membranes are assumed to be mobile. The modified Fick's law is derived from the consideration of standard chemical potential difference between the membrane and gas phases, and of fugacity coefficients in the membrane.
\documentclass{article}\pagestyle{empty}\begin{document} $J=-D\left\{dC/dx - C(d\ln {S/dx})\right\}/L$\end{document}
where J is the flux, D is the diffusion coefficient, C is the concentration in the membrane; x is the dimensionless space coordinate (0 ≦ x ≦ 1); S is the solubility; and L is the membrane thickness. The above equation is applicable for the cases where D and S are dependent on concentration. It is also solved analytically or numerically by a simulation method for some model membranes. Flux difference due to the flow direction and concentration profiles in the model membranes are discussed.
Permeability of carbon dioxide at elevated pressures in substituted polycarbonates
Authors: Jordan S. M. , Fleming G. K. , Koros W. J. 
Published: April 2003

AbstractPast work has shown that hysteresis in sorption, volume dilation, and permeation result when standard bisphenol A polycarbonate is conditioned by exposure to 900 psia carbon dioxide at 35°C. This article reports hysteretic permeation results for the same polycarbonate exposed to other carbon dioxide conditioning pressures. Furthermore, permeation results are reported for tetramethyl and hexafluoropolycarbonate following conditioning with carbon dioxide. Permeation measurements with these structurally related polycarbonates show qualitatively similar, but quantitatively smaller long‐lived hysteretic effects compared with standard polycarbonate dilated to similar volume percentages. The percentage increase in permeability following conditioning treatments will be discussed in terms of fractional free volume considerations.
Isothermal refolding in crystals of long alkanes in solution. II. Morphological changes accompanying thickening
Authors: Organ S. J. , Ungar G. , Keller A. 
Published: April 2003

AbstractThe morphological changes accompanying isothermal thickening in C198H398 are studied by electron microscopy. The crystal morphologies confirm previous assertions that thickening occurs in a single step from once‐folded to extended chains and suggest solution‐mediated nucleation of the thickened crystal followed by rapid spreading via solid‐state diffusion.
Effect of bound water on electromechanical properties of modified PMLG films
Authors: Maeda Hideatsu , Ebihara Shigeyoshi 
Published: April 2003

AbstractThe complex piezoelectric, dielectric, and elastic constants of oriented poly(γ‐methyl L‐glu‐tamate) (PMLG) films, treated with ethylene diamine to introduce more hydrophilic groups into the side chains, are changed drastically by hydration. In dynamic mechanical measurements below 0°C, stiffening and plasticizing actions of bound water are observed in hydrated films. This seems to be caused by water bound particularly by the hydrophilic −NH2 groups in the noncrystalline region of the modified PMLG structure. The piezoelectric constant of hydrated modified film exhibits a steep increase beginning at about −50°C and passes through a maximum at about −10°C. The steep increase around −50°C may be caused mainly by increasing electric conduction (and also by the increase of the dielectric constant and the decrease of the elastic constant) in the noncrystalline region of the modified PMLG structure. On the other hand, the decrease above −10°C may be caused by increasing electric conduction, probably surface conduction of the dispersed crystalline (i.e., piezoelectric) regions and electrode polarization. These effects may be enhanced by bound water, particularly around the hydrophilic −NH2, groups.
Gradient energy parameters for polymer–polymer–solvent systems and their application to spinodal decomposition in true ternary systems
Authors: Ariyapadi M. V. , Nauman E. B. 
Published: April 2003

AbstractThe entropic gradient contributions to the free energy of nonuniform polymer–solvent systems and polymer–polymer–solvent systems have been obtained using a mean field approach. The results for a polymer–polymer–solvent system reduce to those of de Gennes for a polymer–polymer system at the appropriate limit. The binary results for a polymer–solvent system predict interfacial tensions that are systematically high but closer to experiment than those predicted by the earlier model of Balsara and Nauman. The ternary results have been applied to spinodal decomposition in polymer–polymer–solvent systems. The linear theory predicts a decrease in the domain size with increasing quench depth. Also, it predicts an increasing domain size with an increase in compatibility between the two polymers for any given quench depth.