bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anisotropic effects in thermogravimetry of polymeric composites
Authors: Salin I. M. , Seferis J. C. 
Published: April 2003

AbstractThe weight loss of carbon fiber‐reinforced polymeric composites in air has been found to depend on the sample surface characteristics such as fiber orientation with respect to the exposed surfaces. This phenomenon can be attributed to the diffusion of oxygen through the sample and the dependence of diffusion rate on fiber orientation. Recently, an anisotropic degradation methodolgy was proposed, based on the unreactedcore principle, commonly used in catalysis, as extended to account for the anisotropic effects. In this work, these anisotropic diffusion effects were also identified for small thermogravimetric (TGA) samples. Isothermal TGA experiments were performed in air at 310°C using samples weighing 10–163mg. Weight loss was found to be a strong function of fiber orientation. The anisotropic degradation methodology successfully predicted the weight loss of all samples, although some deviation attributed to the sample edge effects was observed. When samples were examined by optical microscopy, a degraded zone was observed on the sample surfaces. The thickness of this layer depended on the type of exposed surface, validating the anisotropic degradation methodology. © 1993 John Wiley & Sons, Inc.
Diffusion as a probe to assess stretching‐induced morphological changes in polyurethane
Authors: Sreenivasan K. 
Published: April 2003

AbstractAn analysis of the diffusion of toluene through polyurethane based on bis (p‐cyclohexyl diisocyanate), poly(tetramethylene glycol) 1000, and 1,4‐butane diol, subjected to varied degrees of elongation by stretching, is presented. The diffusion coefficient is increased by 60% in polymers drawn to 200% and above. Beyond 400% elongation, the diffusion coefficient attained a constant value. Associated changes are observed in the wide‐angle x‐ray diffraction pattern. These diffusion and x‐ray changes are correlated with restructuring of the polymer induced by stretching. © 1993 John Wiley & Sons, Inc.
Melting behavior of drawn polypropylene
Authors: Yan Rong Jiang , Jiang Bingzheng 
Published: April 2003

AbstractThe melting behavior of drawn, compression‐molded isotactic polypropylene has been ex‐amined in terms of the infuence of drawing conditions on the observed properties. Two endothermic peaks were observed on differential scanning calorimetry (DSC) for samples when high draw ratios and high heating rates were used during DSC tests. The peak at lower temperature is influenced by draw ratio, temperature, and rate, and exhibits a strong superheating effect. The species associated with this peak can partially recrystallize into another species associated with the peak at higher temprature during DSC measurements. The position of the peak at higher temperature depends only on draw ratio. It is proposed that the doubel‐melting peaks at lower and higher temperature result from extremely thin quasi‐amorphous or crystalline layers between microfibrils and the lamellar crystals within microfibrils, repectively. © 1993 John Wiley & Sons, Inc.
Thermal expansion of irradiated polyethylene from 10 to 340 K
Authors: Jayanna H. S. , Subramanyam S. V. 
Published: April 2003

AbstractThe coefficient of thermal expansion of γ‐irradiated polyethylene has been measured from 10 to 340 K by using the three‐terminal capacitance technique. The samples are irradiated to 500 Mrad in steps of 100 Mrad in air at room temperature with γ‐rays from a Co60 source at a dose rate of 0.3 Mrad/h. The crystallinity of the sample is measured by x‐ray diffraction. The crystallinity is found to decrease with radiation dose. The thermal expansion coefficient is found to be constant with radiation doses from 10 to 110 K and decreases with doses from 110 to 340 K. © Wiley & Sons, Inc.
Sorption of carbon dioxide in fluorinated poyimides
Authors: Tanaka Kazuhiro , Kita Hidetoshi , Okamoto Ken‐Ichi 
Published: April 2003

AbstractSorption isotherms of CO2 for ten fluorinated polyimides measured at 35°C and up to about 25 atm are analyzed according to the dual‐mode sorption model. Sorption properties for these polyimides are compared with those for other glassy Polymers including unfluorinated polyimides. The glassy polymers with higher glass transition temperatures Tg tend to show greater CO2 sorption. Introduction of a C (CF3)2 linkage into the repeat unit of the main chain increases the sorption by 20–80%. For glassy polymers, including the fluorinated and unfluorinated polyimides, the Langmuir affinity constant b and Henry's law solubility constant kD are correlated with the content of functional (carbonyl or sulfonyl) groups [FG], and composite parameter reflecting the magnitude of both [FG] and free‐space fraction VF, respectively, with some exceptions. The Langmuir capacity constant C′H is correlated with Tg, but there are two correlation lines; one for unfluorinated polyimides and a different one for other glassy polymers including fluorinated polyimides. The slope of the former group is smaller probably because of smaller differences in thermal probably because of smaller differences in thermal expansion coefficients in rubbery and glassy states. Most fluorinated polyimides show greater solubility of CO2 than unfluorinated polyimides and other glassy polymers, because of their larger C′H and kD. © 1993 John Wiley & Sons, Inc.
Crystal structure of poly(p‐benzamide)
Authors: Takahashi Yasuhiro , Ozaki Yusuke , Takase Minoru , Krigbaum W. R. 
Published: April 2003

AbstractRedetermination of the crystal structure of poly(p‐benzamide) was made by using newly collected intensity data. The molecular conformation is TCTC, where the internal rotation angles about the NC bond of the amide group and about the virtual bond of N‐phenyl‐C are T (trans) and C (cis) conformations, respectively. Two molecular chains pass through a rectangular unit cell with dimension, a = 7.75 Å, b = 5.30 Å, c (fiber axis) = 12.87 Å, and the space group, P212121‐D. The reflection observed at the spacing of 010 may be attributed to the reflection due to another crystal polymorph or the diffuse scattering due to disorder. © 1993 John Wiley & Sons, Inc.
Cellulose‐based fibers from liquid–crystalline solutions. II. Processing and morphology of acetate/butyrate esters
Authors: Davé Vipul , Glasser Wolfgang G. , Wilkes Garth L. 
Published: April 2003

AbstractFibers were spun from isotropic and anisotropic dimethylacetamide solutions of cellulose esters. Take‐up speeds of the dry jet/wet spinning process varied. Water served as the coagulant. The mechanical properties of the fibers increased as spinning progressed from the isotropic to the anisotropic state of the solution. A trade‐off in solubility and fiber properties was noted as the butyryl acetyl ratio decreased. Whereas high butyryl content enhances both overall solubility and the formation of liquid–crystalline solutions at lower concentration, it results in lower fiber modulus and strength. Morphology of the fibers depended on the coagulation rate which was influenced by the concentration of the sppinning solution. The level of orientation and crystallinity of the fibers increased somewhat when they were spun from liquid‐crystalline solutions. © 1993 John Wiley & Sons, Inc.
Fluorescence study of thermotropic liquid‐crystalline polyesters
Authors: Hashimoto Hideyuki , Hasegawa Masatoshi , Horie Kazuyuki , Yamashita Takashi , Ushiki Hideharu , Mita Itaru 
Published: April 2003

AbstractPhotoluminescence behavior (polarization, lifetime) related to liquid‐crystal (LC) formation was examined for the thermotropic liquid‐crystalline polyesters poly [(ethylene terephthalate)‐co‐(p‐oxybenzoate)] (PET40/OBA60) (OBA content: 60 mol %) and poly [(ethylene 2,6‐naphthalene dicarboxylate)‐co‐(p‐oxybenzoate)] (PEN50/OBA50) (OBA:50 mol %). The Growth of liquid‐crystalline (LC) phases of PET40/OBA60 proceeded during annealing. even at low temperature (e.g., 138°C) and were promoted by an increase in annealing temperatures Ta in the experimental temperature range 138–260°C. The concentration dependence of fluorescence spectra of PET40/OBA60 in solution suggested that the fluorescences at 325 and 395 nm can be attributed to monomer and ground‐state dimer, respectively. The increase in dimer fluorescence intensity and the decrease in the fluorescence anisotropy ratio r from 0.06 to –0.14 were observed with growth of LC phases. These effects are explained by an increase in the ground‐state dimer population and a slight change in the dimer configuration, respectively.PEN50/OBA50 showed monomer fluorescence at 395 nm due to naphthalenedicarboxylate segments and excimer fluorescence at 430 nm. The r value for the excimer fluorescence decreased from zero to about −0.14 with growth of the LC phase. Such an extraordinary phenomena, in comparison with the usual excimer fluorescences which occurs through energy migration, could be interpreted as the result of formation of high‐concentration excimer sites induced by chain orientation in LC domains. © 1993 John Wiley & Sons, Inc.
A small‐angle x‐ray scattering study of starch gelatinization in excess and limiting water
Authors: Cameron Ruth E. , Donald Athene M. 
Published: April 2003

AbstractThe architecture of the starch granule, and its subsequent disruption due to the application of heat and water, known as gelatinization, is of wide interest. Small‐angle x‐ray scattering (SAXS) techniques have been used to study gelatinization in limiting and excess water. SAXS allows the absorption of water into the differing regions of the starch granule to be monitored. In excess water, a process of cooperative melting can be seen. In limiting water, the crystalline order melts at a higher temperature. These features have been studied, and observed features of the gelatinization related to those known from other techniques. © 1993 John Wiley & Sons, Inc.
Nuclear spin relaxation dynamics of 13CO2 sorbed in polyisobutene rubber
Authors: Dong Z. P. , Cauley B. J. , Bandis A. , Mou C. W. , Inglefield C. E. , Jones A. A. , Inglefield P. T. , Wen W.‐Y. 
Published: April 2003

AbstractRecently we presented the dynamics of 13CO2 molecules sorbed in silicone rubber (PDMS) ascertained from spin relaxation experiments. Results of a similar investigation for 13CO2 sorbed in polyisobutene (PIB) are presented in this report. The spin‐lattice and spin‐spin relaxation times as well as nuclear Overhauser enhancements (NOE) were determined as a function of temperature and Larmor frequency. The relaxation mechanisms found to be important for 13CO2/PIB system are intermolecular dipole‐dipole relaxation and chemical shift anisotropy with a minor contribution from spin rotation relaxation. We have determined the parameters which characterize correlation times for 13CO2 collisional motion, rotational motion, and translational motions in the PIB. The self‐diffusion coefficient of 5.15 × 10−8 cm2/s obtained from the nuclear magnetic resonance (NMR) data is close to the literature value of the mutual diffusion coefficient of CO2 in PIB at 300 K obtained from permeability measurements. In contrast to the case of CO2/PDMS in which a broad distribution (characterized by a fractional exponential correlation function of the Williams‐Watts type with α = 0.58) is observed, a sharp distribution with a fractional exponent, α, of 0.99 is found for the CO2/PIB system. Instead of assuming an Arrhenius type temperature dependence, we used a Williams‐Landel‐Ferry type temperature dependence and found it to be better suited to describe the behavior of this system. PIB is a densely packed “strong” chain polymer which responds gradually to the temperature variation and gas sorption. In contrast PDMS is a relatively loosely packed “fragile” polymer with a propensity to exhibit rapid dynamic responses to the temperature change and gas sorption. © 1993 John Wiley & Sons, Inc.
Electron and photon emission accompanying deformation and fracture of polycarbonate
Authors: Zimmerman K. A. , Langford S. C. , Dickinson J. T. , Dion R. P. 
Published: April 2003

AbstractElectron and photon emission accompanying tensile loading and failure of polycarbonate show weak emissions during the onset of neck formation and intense emissions during the fracture event itself. These results are interpreted in terms of formation of active species by bond breaking followed by emission driven by energy released by recombination. Fast time scale measurements during fracture show that intense electron and photon emission typically begins about 50 μs prior to the completion of fracture and is most intense at the completion of fracture. The gradual onset reflects the final stages of growth of the failure‐initiating defect. Defect growth was monitored by measuring the intensity of a light beam transmitted through the gauge length of the sample; the transmission is sensitive to scattering by surface and bulk defects. A marked decrease in transmission begins some tens of ms prior to fracture due to scattering from the fracture‐initiating defect. These measurements allow accurate correlations of defect growth with the onset of the electron and photon signals. © 1993 John Wiley & Sons, Inc.
Theoretical prediction of maxima in association constants for complex formation between flavin mononucleotide and indoleacetate in the presence of polyelectrolytes
Authors: Ishiwatari Tsutomu , Itoh Fumiko , Ohbayashi Mie , Mitsuishi Masaru 
Published: April 2003

AbstractThe effects of ionene polymers (6,3‐ionene, 6,6‐ionene, 6,8‐ionene, and 6,12‐ionene) with various charge densities upon association constants K for the complexation between flavin mononucleotide and indoleacetate have been studied. Except for 6,12‐ionene, K increases with increasing polymer concentration then passes through a maximum, and declines at high polymer concentrations. The value of the maximum K increases in the order 6,8‐ionene > 6,3‐ionene > 6,6‐ionene. In contrast, 6,12‐ionene gives only a monotone increasing curve with increasing polymer concentration. These curves are analyzed using the theory of the partition coefficient proposed in the previous paper. The types of the curves that the theory predicts are classified in greater detail than in the previous paper, and examples are given. © 1993 John Wiley & Sons, Inc.
Coionomeric mixtures of polyhydroxyethers and ethylene methacrylic acid copolymers. II. Compatibilizers for blends of polybutylene terephthalate and ethylene butyl acrylate copolymers
Authors: Mascia L. , Moggi A. 
Published: April 2003

AbstractBlends of polybutylene terephthalate and ethylene butyl acrylate copolymers were studied at two extreme concentration levels so that each polymer would form, in turn, a particulate dispersed phase. The blends contained 5% by weight of a coionomeric compatibilizer, which was produced from 1 : 1 mixtures of a polyhydroxy ether of bisphenol A and the sodium ionomer of an ethylene methacrylic acid copolymer, using sodium ethoxide to enhance the formation of ionomeric clusters together with an A‐B‐A block oligomer to assist the solubilization of the two ionomeric polymers. In all cases the addition of the coionomeric compatibilizer mixture to the blend was found to decrease the size of the dispersed particles with a concomitant reduction in the interphase gap. It was also observed that the dispersed polymer exhibited a lower level of crystallinity and a slightly lower melting point than when it was present as a matrix, particularly for the case of the ethylene butylacrylate copolymer. The inability of the compatibilizer to completely prevent the formation of an interfacial gap which did not allow the blends to achieve more substantial improvements in mechanical properties, was attributed to the vast difference in crystallization temperature between the two polymers. © 1993 John Wiley & Sons, Inc.
Partial molar volume of small molecules in glassy polymers
Authors: Kirchheim R. 
Published: April 2003

AbstractThe sorption of atoms or molecules in glassy polymers is assumed to occur within a variety of sites belonging to the intermolecular volume and providing different space for the dissolved molecules. If the size of the small molecule is larger than the size of the site, the glassy polymer is elastically distorted during sorption of the solute molecules. Minimizing the total free energy yields the result that large sites are occupied first, giving rise to small volume changes only. By increasing the solute concentration, smaller sites have to be occupied as well and the corresponding volume changes are larger. Thus the molecules can be considered to act as probes for the intermolecular space. A quantitative analysis and comparison with experimental results provides information on the intermolecular space in a glassy polymer. Compared to the dual‐sorption model, the model of this study is able to explain the nonlinear relationship between volume change of the polymer and the partial pressure of the solute. At large solute concentrations, swelling of the glassy polymer or its transformation into the rubbery state occurs, which gives rise to structural changes after desorption. © 1993 John Wiley & Sons, Inc.
Self‐nucleation and enhanced nucleation of polymers. Definition of a convenient calorimetric “efficiency scale” and evaluation of nucleating additives in isotactic polypropylene (α phase)
Authors: Fillon B. , Lotz B. , Thierry A. , Wittmann J. C. 
Published: April 2003

AbstractA simple, convenient and reliable calorimetric efficiency scale is proposed for the evaluation of nucleating additives for polymers. The scale is based on conventional differential scanning calorimetry cooling runs and makes use of a crystallization range determined in self‐nucleation experiments. It can be correlated with spherulite sizes, and indicates the potential range of improvement of nucleating additives. Typical nucleating agents for isotactic polypropylene are evaluated; at best they rate at 60 to ca. 70% on this efficiency scale. © 1993 John Wiley & Sons, Inc.
Self‐nucleation and recrystallization of polymers. Isotactic polypropylene, β phase: β‐α conversion and β‐α growth transitions
Authors: Fillon B. , Thierry A. , Wittmann J. C. , Lotz B. 
Published: April 2003

AbstractThe mechanisms which, in isotactic polypropylene, create α phase nuclei on partial melting of β phase spherulites are investigated by thermal analysis and optical and electron microscopy. Nuclei concentrations are determined from recrystallization characteristics. α phase nuclei are formed within β spherulites via two different mechanisms: (1) a low temperature formation of latent α phase nuclei (αβ* nuclei) linked with a hitherto unsuspected β to α growth transition at T = T* ∼ 105°C, and (2) a high temperature α phase nucleation process (αβ nuclei), also linked with a similar β to α growth transition at 140°C first reported by Varga et al. The low temperature nucleation mechanism is the more efficient one: it significantly affects the melting of β phase, and results in samples with over 1013 α nuclei · cm−3. © 1993 John Wiley & Sons, Inc.
Electronic transport properties of polyaniline/PVC blends
Authors: Subramaniam C. K. , Kaiser A. B. , Gilberd P. W. , Wessling B. 
Published: April 2003

AbstractThe electrical conductivity and thermoelectric power of polyaniline/PVC blends was measured. Surprisingly, the conductivity of the blends is greater at low temperatures than that of the pure polyaniline sample. The conductivity follows approximately an exp (−T−1/2) law over a considerable range of temperature, with deviations from this law observed at high temperature increases (with positive sign) except at very low temperatures, where negative peaks are observed. Possible models to interpret these observations are mentioned. © 1993 John Wiley & Sons, Inc.
Interaction of slightly cross‐linked gels of poly(diallyldimethylammonium bromide) with sodium dodecyl sulfate. Diffusion of surfactant ions in gel
Authors: Philippova O. E. , Starodoubtzev S. G. 
Published: April 2003

AbstractThe dynamics of the changing microenvironment of the fluorescent probe pyrene in slightly cross‐linked networks of poly(diallyldimethylmmonium bromide) during diffusion of sodium dodecyl sulfate (SDS) in the gel phase has been investigated by fluorescence spectroscopy. Values of the spectral ratio I3/I1 for pyrene monomer included in SDS micelles in the swollen networks fall between the corresponding values for pyrene in water and for pyrene dissolved in SDS micelles in aqueous solution. In the narrow interval of the surfactant concentrations in the gel phase, the formation of pyrene excimers is observed. The values of the critical micelle concentration in the gel phase (ca. 5 × 10−4 to 8 × 10−4 mol/L) are tenfold lower than in aqueous solutions of the surfactant. The effective micellar diffusion coeffecient D in the gel phase increases with increasing swelling of the network. © 1993 John Wiley & Sons, Inc.
Study of free volume and crystallinity in polybithiophene and poly(3‐methylthiophene)
Authors: Nicolau Y. F. , Moser P. 
Published: April 2003

AbstractCompressed pellets of partly crystalline, chemically synthesized, doped (Cl−and FeCl) polybithiophene (PBTd), poly(3‐methylthiophene) (P3MTd), and their neutral (dedoped) forms (PBTn and P3MTn) were studied by wide‐angle x‐ray diffraction and positron annihilation lifetime spectroscopy. As synthesized, PBTd and P3MTd polymers have a helicalsynconformation they crystallize in the hexagonal system. On dedoping, PBT macromolecules change their helicalsynconformation in a rodlikeanticonformation and crystallize in the orthorhombic or monoclinic system, whereas P3MT macromolecules retain their helicalsynconformation. Chemical doping–dedoping cycles lead to amorphous PBT and P3MT in either doped or dedoped states. The P3MT helical macromolecule behaves like a spiral spring; by doping, it becomes axially compressed. The unit‐cell volume of P3MTd is smaller than that of P3MTn. The positron lifetime spectra for all polymers were resolved, without constraint, into three components. The τ1lifetime is attributed to free‐positron annihilation events, the τ2lifetime to positrons annihilating trapped in voids, and the τ3lifetime to positrons annihilating as o‐Ps trapped in cavities located inside the polymer grains for P3MTn and at the surface of the grains for PBTd, PBTn, and P3MTd. Most positrons annihilate when trapped in voids, both in doped and dedoped PBT and P3MT. The doping apparently increases the concentration of the voids and their mean diameter in P3MT, and probably also in PBT. Cavities anchored in the bulk are produced by dedoping. © 1993 John Wiley & Sons, Inc.
Gas transport properties of polyphenylene ethers
Authors: Aguilar‐Vega M. , Paul D. R. 
Published: April 2003

AbstractGas transport properties of the polyphenylene ethers poly(2,6‐dimethyl‐1,4‐phenylene oxide)PDMPO, and poly(2,6‐diphenyl‐1,4‐phenylene oxide), PDPPO, and the thioether poly(1,4‐phenylene sulfide), PPS, have been measured as a function of pressure and temperature. The PPS material and free volume correlations were used to estimate the behavior of the unavailable poly(1,4‐phenylene oxide), PPO. The results show that symmetrical substitution of phenyl groups on the backbone of polyphenylene ether, PDPPO, increases the gas transport properties by one order of magnitude relative to the unsubstituted material, PPO. Symmetrical methyl substitution, PDMPO, however, increase the permeability, apparent diffusion and sorption coefficients even further. The gas transport coefficients correlate with the fractional free volume of the polymers. PDMPO has the largest fractional free volume and gas transport coefficients followed by PDPPO and the PPS. The results show that substitution of phenyl groups, which leads to polymers that have better thermal and oxidative stability than methyl substituted ones, can be a useful means for increasing free volume and gas permeability coefficients. While methyl groups appear to be more effective for the latter, the enhanced chemical stability of phenyl rings may be useful when gas separation membranes are to be used in harsh environments. © 1993 John Wiley & Sons, Inc.