bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical analysis of lamellar thickness distributions
Authors: Voigt‐Martin I. G. , Mandelkern L. 
Published: April 2003

AbstractA comparison of crystallite thickness distributions, as obtained from thin section electron microscopy, small‐angle x‐ray scattering, and low‐frequency Raman acoustical model (LAM), is discussed in detail. It is shown with the aid of a large number of examples that a reliable numerical estimate of crystal thicknesses and long spacings is a complex problem. The values that are obtained by the different experimental techniques depend not only on the crystallite morphology, such as curvature and lateral extension, but very specifically, and crucially, on the nature of the thickness distribution. A series of widely different types of size distributions have been developed by controlling the molecular weight and crystallization temperature. Studies of these distributions, by the aforementioned experimental techniques, have revealed the reasons when and why agreement or disagreement is obtained in the determination of the crystallite thickness distribution.
The equation of state and heat of fusion of poly(ether ether ketone)
Authors: Zoller Paul , Kehl Thomas A. , Starkweather Howard W. , Jones Glover A. 
Published: April 2003

AbstractThe pressure‐volume‐temperature properties of poly(ether ether ketone) (PEEK) were studied experimentally at temperatures of 400°C and pressures to 200 MPa. Specific volume data were fitted successfully to the empirical Tait equation for T < Tg and T > Tm and to the theoretical Simha‐Somcynsky equation of state for the melt. The pressure dependence of the glass‐transition temperature is about 0.57–0.59°C/MPa and that of the melting point 0.483°C/MPa. The pressure dependence of the melting point, the specific volume of the melt at Tm, and the specific volume of the crystal at Tm determined from x‐ray diffraction data at elevated temperatures were combined in the Clapeyron equation to calculate a heat of fusion of 161 ± 20 J/g for the PEEK crystal. This value is somewhat higher than the previously reported value of 130 J/g.
Viscoelastic properties of UHMW‐PE fibers in simple elongation
Authors: Leblans P. J. R. , Bastiaansen C. W. M. , Govaert L. E. 
Published: April 2003

AbstractStress relaxation after a simple elongational step strain, creep under a constant simple elongational stress, and stress build‐up under a constant Hencky strain rate have been measured for ultrahigh‐molecular‐weight polyethylene (UHMW‐PE) fibers. The data from the various experiments are consistent with the Boltzman superposition principle in the experimental region of small strains or short times. This leads to a simple constitutive equation in which temperature can be incorporated via time‐temperature superposition. The measured power‐law relaxation of the UHMW‐PE fiber leads to analytical expressions for the dynamic quantities in simple elongation.The constitutive equation is the one‐dimensional equivalent of the gel equation derived for cross‐linking gels at the gel point. The similarity between the rheological behavior of fibers and cross‐linking gels at the transition point might lead to an enhanced understanding of the molecular processes occurring during deformation.
The initial stages of crystallization of polyethylene from the melt
Authors: Barham P. J. , Keller A. 
Published: April 2003

AbstractSynchrotron x‐radiation has been used to follow the development of low‐angle diffraction in sharp fractions of polyethylene. The polymer is shown to crystallize in very thin lamellae which rapidly thicken in a single step to twice, three times, or four times the original thickness. This dramatic refolding is more pronounced at higher crystallization temperatures. After the sudden integral jumps in fold length, the thick lamellae continue to grow thicker logarithmically with time. The significance of these findings for the most basic issues of polymer crystallization and for the experimental methodology of its study is highlighted.
Light‐scattering study of polyelectrolyte complexes: Heparin with partially aminoacetalized poly(vinyl alcohol) in aqueous solution
Authors: Hara M. , Nakajima A. 
Published: April 2003

AbstractThe structure of soluble polyelectrolyte complexes composed of heparin (Hep) and partially aminoacetalized poly(vinyl alcohol) (PVAA) in aqueous solution was investigated by light scattering. The pH was fixed at 3.2 while the ionic strength and mixing ratio were varied. At high ionic strength (0.5), polyelectrolyte complexes were not formed owing to the screening effect of simple salts on polyion charges. At low ionic strength (0.005), polyelectrolyte complexes formed were stable and dispersed when either the polycation or the polyanion was in great excess, whereas the complexes became unstable and coagulated when the concentrations of polycation and polyanion approached each other. At intermediate ionic strength (0.1), when PVAA was in excess, complex formation was similar to that at low ionic strength (0.005); but with an excess of Hep, polyelectrolyte complexes with similar structure (i.e., roughly spherical with average diameters about 2,700 Å) were formed over a wide range of mixing ratio. This observation is of interest in connection with the physiological activity of Hep in vivo.
FTIR investigation of interactions in blends of PMMA with a styrene/acrylic acid copolymer and their analogs
Authors: Jo W. H. , Cruz C. A. , Paul D. R. 
Published: April 2003

AbstractFourier‐transform infrared (FTIR) spectroscopy was used to examine the interactions in miscible blends of a styrene (92%)/acrylic acid (8%) copolymer (SAA8) with poly(methyl methacrylate) (PMMA). From the residue or interaction spectra and shifts of carbonyl and carboxylic acid stretching bands, it is concluded that there is a significant specific interaction involving hydrogen bonding between the carbonyl groups of the PMMA and the carboxylic groups of the SAA8. Similar FTIR spectra of some low‐molecular‐weight liquid analogs for the various monomer units of these polymers do not indicate a comparable interaction. This explains why direct calorimetry with these compounds fails to model correctly the expected exothermic mixing of the blends. Furthermore, the role of the aromatic moiety in the SAA polymer appears to reduce the degree of self‐association of the carboxylic acid groups based on results for the model compounds. Coupled with molecular rigidity, the above mechanism makes the carboxylic acid units in SAA8 more available for interaction with the PMMA carbonyls.
Crystal structure of polysulfonamides
Authors: Sasaki S. , Takigawa S. 
Published: April 2003

AbstractStructures of poly(alkylene‐1,3‐benzenedisulfonamide)s [HN(CH2)mNHO2SC6H4SO2]n (PMm: 2 ≤ m ≤ 6) were studied by x‐ray diffraction and infrared spectroscopy. The crystal structure of PB6 is monoclinic, space group C2/mC2h3, with a = 7.70 Å, b = 7.76 Å, c (molecular axis) = 14.1 Å, and β = 117°. Two mirror‐image molecules repeating with two monomeric units in an identity period 28.2 Å occupy the same lattice site with equal probability. The alkylene chains assume the planar zigzag conformation, which is the structure isomorphous with PB4. An intermolecular hydrogen bond is formed between each NH group and one of the two O = S groups of the corresponding SO2 unit. The c axis tends to tilt from the fiber axis by an inclination angle of about 3° around the b axis.
Isothermal crystallization of poly(vinylidene fluoride) in the presence of high static electric fields. II. Effect of crystallization temperature and electric field strength on the crystal phase content and morphology
Authors: Marand Hervé , Stein Richard S. 
Published: April 2003

AbstractThe melt crystallization of poly(vinylidene fluoride) in a static electric field was studied for different fields strengths and undercooling conditions. The γ‐phase nucleation process was examined directly by polarized optical microscopy and indirectly by small‐angle light scattering. The crystal phase content was assessed by differential scanning calorimetry. It is shown that the γ‐phase nucleation density and γ‐phase content increase with field strength and that the higher the crystallization temperature, the larger the effect of the field. These experimental results confirm the predictions of the model of nucleation in an electric field that we published previously. It is also noted that the degree of crystallinity and the perfection of crystal orientation along the γ‐phase spherulite radical direction decrease with field strength. The homogeneity of morphology resulting from the crystallization in the field is also examined by polarized optical microscopy on specimens microtomed across their thickness. When the crystallization is carried out under high field (E ≈ 0.1 MV/cm) and high temperature (T > 166°C) a nonuniform morphology results, characterized by a higher nucleation density at the positive electrode than at the negative electrode. Near the negative electrode very large disklike spherulites are seen to grow parallel to the substrate.
Molecular segregation and nucleation of poly(ethylene oxide) crystallized from the melt. IV. Computer modeling
Authors: Cheng Stephen Z. D. , Noid Donald W. , Wunderlich Bernhard 
Published: April 2003

AbstractA crystal surface is modelled and Monte Carlo simulations are attempted to learn about conformations and motion of a macromolecule that could lead to crystallization. Chains with up to 200 mobile segments have been analyzed. The diffusion distance of a given chain segment increases with positioning closer to the chain end, and completion of crystallization accelerates with decreasing length of remaining amorphous chain ends and increasing temperature.
Rectangular and oblique layer packings of alkane chains and the eutectic solid formed by their interaction
Authors: Dorset Douglas L. 
Published: April 2003

AbstractIn the crystalline state, the paraffin, n‐hexatriacontane, and wax, octadecyl octadecanoate, both pack in either rectangular or oblique layers, have the same methylene subcell in either case and have similar molecular volumes. Despite these similarities, no cosolubility is found in the solid state for binary mixtures of the two compounds, because the favored layer packing for each material is different. Although a morphological description of the eutectic solid based on crystal form for the two compounds grown from the melt would lead to a “faceted‐faceted” nomenclature, implying noncooperative crystal growth, a closer inspection reveals that a one‐dimensional epitaxy is likely to exist across the major (001) faces of the two components. The solid is therefore a special example of a lamellar eutectic for which only two layers can coexist.
Electron spin resonance study of γ‐irradiated poly(acrylic acid)
Authors: Rao B. Sanjeeva , Murthy M. Ramakrishna 
Published: April 2003

AbstractElectron spin resonance (ESR) spectra of poly(acrylic acid) (PAA) γ‐irradiated in air at room temperature and recorded at room temperature and at liquid‐nitrogen temperature have been studied to identify the radiation products. The ESR spectra are composed of eight lines with hyperfine splittings of 23 ± 1 G and 11 ± 1 G. The method of least‐squares total curve fitting, employing the Lorentzian line shape function, to the observed spectra enabled the assignment of the spectra. Computed spectra obtained by the superposition of a singlet and the spectra due to chain radicals are considered to give the best fits to the observed ESR spectra. The singlet is assigned to the radicals COOH, and the component 10‐line spectra are assigned to the chain radicals CH3CHCH2 ∼ and/or ∼ CH2CHCH2 ∼. The observed change in line shape with temperature of the ESR spectra is attributed to the hindered oscillations of the methyl groups about the CαCβ bond axis of the chain radicals. The existence of the methyl groups is confirmed by the measurement of infrared absorption.
Dual‐mode sorption kinetics of gases in glassy polymers
Authors: Subramanian S. , Heydweiller J. C. , Stern S. A. 
Published: April 2003

AbstractThe transport of gases in many glassy polymers can be described satisfactorily by means of a “dual‐mode sorption” model. The transport behavior observed with a given gas/polymer system can be characterized by the model parameters, which are obtained from solubility measurements in conjunction with absorption/desorption or permeability measurements. The present study discusses the inverse problem, namely, the prediction of the absorption/desorption behavior of a gas in a glassy polymer from a specified set of dual‐mode sorption parameters. Satisfactory agreement is obtained between reported absorption rates of sulfur dioxide in glassy polycarbonate and of water vapor in Kapton®††Trademark of E. I. du Pont de Nemours & Co.
and the rates predicted by the dual‐mode sorption model. This study also confirms the consistency of the model.
The effect of morphology on sorption and transport of carbon dioxide in a polyimide from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and 4,4′‐oxydianiline
Authors: Okamoto Ken‐Ichi , Tanaka Kazuhiro , Kita Hidetoshi , Nakamura Asumaru , Kusuki Yoshihiro 
Published: April 2003

AbstractSorption and transport of CO2 have been investigated for polyimide films prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐oxydianilline (ODA) as well as for a chemically identical commercial polyimide film, Upilex‐R. The BPDA‐ODA polyimide films annealed above the glass transition temperature (270°C) are found to have some degree of ordering owing to molecular aggregation of polymer chains, whereas the films as‐cast are amorphous. The solubility, permeability, and diffusion coefficients decrease significantly with increasing density or increasing average degree of molecular aggregation. The influence of morphology on the parameters in the dual‐mode sorption and transport model has also been investigated. With an increase in density, the Langmuir capacity constant and the diffusion coefficients for Henry's law and Langmuir populations decrease by a larger factor than the Henry's law solubility constant. These results can be tentatively interpreted by assuming either a one‐phase or two‐phase structure for these polyimide films.
Permeation of oxygen dissolved in water through substituted polyacetylene membranes
Authors: Tang Ben‐Zhong , Masuda Toshio , Higashimura Toshinobu 
Published: April 2003

AbstractThe permeation of oxygen dissolved in water through substituted polyacetylene membranes was studied by using an oxygen electrode at 25°C. Many of the membranes (thickness about 200 μm) showed high apparent permeability coefficients P in the range 10−9−10−8 cm3 (STP) cm cm−2s−1 cmHg−1. The resistance r of the boundary layer and the permeability P∞, at infinite membrane thickness were determined from the dependence of P on membrane thickness. The r values of Si‐containing and aliphatic polyacetylenes were usually larger than those of aromatic polyacetylenes. The P∞, values of Si‐containing and aliphatic polyacetylenes agreed closely with the permeability coefficients Pg for gaseous oxygen. In contrast, P∞ values for aromatic polyacetylenes were larger than Pg values.
Direct measurements of the mechanical properties of polymerized and unpolymerized langmuir‐blodgett films
Authors: Halperin K. , Peng J. B. , Sailor M. , Gadwood R. , Ketterson J. B. , Dutta P. 
Published: April 2003

AbstractMechanical measurements can be made on Langmuir‐Blodgett (LB) films that have been peeled from their substrates, and are floating on the surface of water, by compressing them between the moving barrier and the Langmuir balance float in a standard monolayer trough. We have used this technique, which utilizes apparatus commonly available where LB films are made, to study multilayers of lead 10,12‐tricosadiynoate (a diacetylene carboxylic acid) that were first polymerized and then peeled from the substrate. For comparison we have performed the same measurements on pieces of mylar, on unpolymerized films, and on films of calcium octadecanoate (a saturated chain fatty acid). We found Young's modulus for films of the saturated chain material, the unpolymerized diynoate, and the polymerized films, to be 6 GPa (900 kpsi), 0.5 GPa, and 6 GPa, respectively.
An iterative procedure based on the donnan equilibrium for calculating the polymer‐subphase volume of alginic acid
Authors: Jang Larry K. , Harpt Nathan , Uyen Ty , Grasmick Daniel , Geesey Gill G. 
Published: April 2003

AbstractA numerical iterative procedure is presented to predict the polymer‐subphase volume that is formed when anionic polysaccharides such as alginic acid (polyuronic acid from kelp) are suspended in an aqueous solution. (The aqueous region surrounding the polymer chain where a strong electrostatic attractive force for counterions exists is defined as the separate polymer subphase within the colloidal phase enclosed by the polymer coil.) Based on the phase‐partition model of Marinsky et al.5 and Donnan equilibrium theory, this iterative procedure utilizes the base titration data of the acidic polysaccharide at different ionic strengths as well as the osmotic properties of the sodium form of the polysaccharide. No detailed structural information of alginic acid is required. The resulting calculations show that the polymer subphase, which accounts for a small fraction of the total solution volume, should be regarded as the reaction zone for acid dissociation and metal binding reactions. The volume of polymer subphase thus calculated may also serve as an excellent index for the morphology of the polymer molecule at different ionic strengths, degrees of ionization, polymer concentrations, and extent of polymer‐metal binding.
Dielectric relaxation studies of dipolar aromatics in polyethylene. II. Oriented low‐density polyethylene
Authors: Parikh D. , Phillips P. J. , Jang Y. T. 
Published: April 2003

AbstractStretched polyethylene has been used for several years by organic spectroscopists as a means of orienting isolated aromatic molecules. Dielectric relaxation studies are reported which consider dipolar aromatic molecules dissolved in stretched polyethylene in order to learn more about the environment of these oriented molecules. The research builds on earlier studies of the dielectric relaxation behavior of dipolar aromatic molecules dissolved in unoriented low density polyethylene. Studies demonstrate that molecules in the amorphous phase are oriented at temperatures below the glass transition, both the β and γ relaxations being orientation dependent. It is shown through studies of oriented rods that large numbers of the orientable molecules are immobilized by the oriented polyethylene and cannot relax. An essential criterion for immobilization to occur is that molecules exhibit geometrical symmetry.
Long periods in slow‐cooled linear and branched polyethylene: Part II
Authors: Rault J. , Robelin‐Souffaché E. 
Published: April 2003

AbstractIt is shown that the long periods L in slow‐cooled polyethylene materials obey the general law L = L0 + αrw, where rw is the weight average dimension of the coil before crystallization, and L0 is a parameter of the order of lc, the crystalline core thickness, which increases as the cooling rate V decreases. α is a parameter independent of M and V but decreasing with the number of long‐chain branches per molecule. The two terms in the above relation are, respectively, the contributions of crystalline and amorphous layers. For cooling rates from 800°C/min to 0.2°C/min, it is shown that the temperature Tc of crystallization is constant; hence the change of morphology (long period, crystalline core thickness, crystallinity) cannot be explained by supercooling. The increase in long period and crystallite thickness in slow‐cooled materials with decreasing cooling rate is interpreted in terms of annealing of the crystallized materials between the crystallization temperature Tc and the secondary transition temperature Tαc. Crystallization proceeds by a two‐step process of solidification and annealing. During the annealing stage, the mobility of the chains in the crystalline phase is due to defects; the kinetics of thickening is then governed by the mobility (or nucleation) of the defects appearing above Tαc. In the proposed model of crystallization, the assumption that the energy of activation is proportional to Tαc explains the observed laws L ≡ lc ≡ log ta, where the annealing time ta is equal to (Tc − Tαc)/V. The model applies also to polymers crystallized from the melt and subsequently annealed.
A study of the mechanical anisotropy in shear of high‐draw, low‐draw, and voided poly(vinylidene fluoride)
Authors: Lewis E. L. V. , Ward I. M. 
Published: April 2003

AbstractThe mechanical anisotropy in shear of oriented from I poly(vinylidene fluoride) sheet has been studied, completing the measurement of all nine independent compliances for this material. The morphology is parallel‐crystallite; however, the crystalline regions are not lamellar in shape, but take the form of blocks with a bricklike shape oriented along the draw direction. The results have been analyzed in terms of a three‐dimensional generalization of the Takayanagi model. First, modelling of the three principal extensional compliances based on previous measurements indicates that the gaps between the crystalline units are smaller in the transverse directions than in the draw direction. A voided sample shows a marked increase in the transverse compliances of the amorphous regions and considerable anisotropy owing to the voids. Secondly, a novel development of the Takayanagi model has been made to analyze the shear behavior. This has enabled the calculation of the shear compliances of the amorphous regions and indicates that the larger magnitude of the shear compliance in the plane normal to the draw direction is due to the large magnitude of the corresponding amorphous shear compliance, and that this is not affected by increased draw ratio or by the voids.
Solid‐state carbon‐13 NMR Studies of vulcanized elastomers. V. Observation of new structures in sulfur‐vulcanized natural rubber
Authors: Andreis Mladen , Liu Juwhan , Koenig Jack L. 
Published: April 2003

AbstractThe complementary application of the NMR inversion recovery measurements and the computer fitting of the overlapping spectral region is found to be a useful method for structural analysis of vulcanized natural rubber in the solid state. Since the linewidths in 13C‐NMR spectra of solids are relatively broad compared with the differences between chemical shifts, some weak signals are completely obscured in the resulting spectra. If the resonances have sufficiently different relaxation times, such as methyl and methylene carbons, it is possible to detect neighboring heavily overlapped signals by using the inversion recovery delay τ value at which the interfering strong resonance has null intensity. The 20 resonances observed in the spectra of crosslinked rubbers are tentatively assigned to the structural units formed during the vulcanization process. It is found that vulcanizates containing smaller amounts of sulfur (1 and 3%) show insignificant changes in the NMR spectra for curing times of 30 and 90 min. Structural modifications in rubbers cured with 10% sulfur continuously increase with the increasing curing time up to 120 min, indicating a significant loss in double bonds in the later stages of the reaction.