bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deformation and structure of doubly oriented polyethylene
Authors: Cowking A. , Munro F. 
Published: April 2003

AbstractDoubly oriented low‐density polyethylene with parallel lamellae was compressed along the initial draw direction (i.e., at right angles to the lamellar surfaces) at 20°C. Wide‐ and low‐angle x‐ray diffraction were used to determine the changes in the molecular orientation and in the texture. During the compression, specimens previously annealed at or near 102°C were found to undergo changes in length, in long spacing, and in molecular orientation which were consistent with an (001) chain slip mechanism. In specimens annealed at higher temperatures x‐ray diffraction indicated that during compression some series component of the long spacing was compressed by a much smaller amount than the remainder of the long spacing, which deformed by chain slip; in these cases it was found that the macroscopic strain along the compression axis (εy) was greater than the strain in the long spacing along that axis (εd). It is suggested that the missing strain which makes εy greater than εd is due to partial melting and the consequent development of amorphous regions between the stacks of lamellae.
Electric field dependence of lower critical phase separation behavior in polymer–polymer mixtures
Authors: Reich S. , Gordon J. M. 
Published: April 2003

AbstractThe electric field dependence of the cloud point temperature of a poly(vinyl methyl ether)–polystyrene mixture has been experimentally measured in a laser light scattering experiment. It is found that the cloud point temperature is depressed linearly with the square of the applied electric field. A thermodynamic derivation of the electric field dependence of the spinodal temperature for polymer–polymer mixtures is also presented. A large disagreement between the experimental and theoretical findings is noted and possible explanations for this discrepancy are discussed.
Molecular motion in poly(L‐histidine) in the solid state
Authors: Oshima Ryuichi , Kumanotani Ju 
Published: April 2003

AbstractMolecular motions in poly(L‐histidine) (PLH) and its hydrochloride in the solid state have been studied by NMR and dielectric measurements. Four relaxation processes, β,γ,δ, and ε, are observed for PLH. The δ relaxation is assigned to rotation of an imidazole ring about the CβCγ bond, since the observed activation energy of 2.7 kcal/mole agrees with the calculated energy barrier for rotation of the central imidazole ring about CβCγ in an imidazole trimer model and the experimentally determined dielectric relaxation strength is consistent with the theoretically estimated value based on the two‐state transition theory. The γ relaxation was attributed to the restricted rotational motion about CαCβ. The β relaxation is related to motion of water molecules bound by PLH. The ε relaxation is assigned to the wagging mode of imidazole groups in the defect region as observed for polymers containing pendent aromatic rings. No relaxation is observed in the hydrochloride of PLH due to the increased interaction between imidazolium cations as side groups. This is confirmed by the comparison of dipole moments of protonated and deprotonated imidazoles estimated by molecular‐orbital calculations.
Diffusion‐controlled formation of porous structures in ternary polymer systems
Authors: Cohen Claude , Tanny G. B. , Prager Stephen 
Published: April 2003

AbstractWe propose a theory for the appearance of two‐phase structures during the formation of polymer membranes from a casting solution immersed in a coagulant bath. Our model is based on diffusion induced phase separation at the spinodal in the ternary nonsolvent‐solvent‐polymer system. A simplified treatment of the interdiffusion process by the diffusion layer method permits the formulation of criteria for the formation of two‐phase structures in the course of the solvent‐coagulant exchange. Our criteria are expressed in terms of the composition dependence of the chemical potentials in the stable and metastable region of the ternary phase diagram. Comparison with experimental results shows qualitative similarities with theoretical predictions.
Phase transitions in cellulose solutions. The kinetics of precipitation of cellulose from diluted cadoxen solutions
Authors: Theil Michael H. , Caviness Elton T. 
Published: April 2003

AbstractSolutions of cellulose (degree of polymerization: 296 ± 16) in tris(ethylenediamine)cadmium(II)hydroxide‐ethylenediamine‐water (cadoxen), 1.015% (weight per volume) were diluted 1:1.5 with water. The ensuing isothermal precipitations were followed dilatometrically at temperatures ranging from 27.50 to 48.45°C. The precipitation data were characterized by a positive temperature coefficient. They generally conformed to a one‐dimensional nucleation rate law; the Avrami exponents were close to unity. Alternatively, they fit a first‐order reaction rate expression with respect to cellulose concentration. The low crystallinity of the precipitated cellulose leads to the interpretation of the kinetics in terms of the dissociation of a cellulose‐cadoxen complex, rather than phase separation, as the rate‐determining step. The nucleation rate law suggests a one‐dimensional nonrandom cooperative chemical process, while the first‐order rate law suggests a random process.
Physical properties and structure of silk. VI. Conformational changes in silk fibroin induced by immersion in water at 2 to 130°c
Authors: Magoshi Jun , Mizuide Michio , Magoshi Yoshiko , Takahashi Kazuo , Kubo Mieko , Nakamura Shigeo 
Published: April 2003

AbstractSilk fibroin films in the random‐coil and β‐form conformations were immersed in water at temperatures from 2 to 130°C, and conformational changes were followed by x‐ray diffraction, infrared spectroscopy and differential scanning calorimetry. On treatment with water below 60°C, the random‐coil conformation is converted to the α form and above 70°C to mixtures of the α and β conformations. The β‐form content increases as the immersion temperature is raised. The β form is not affected by immersion in water in the temperature range studied.
Effect of the solvent upon the diffusion coefficient of polydisperse polystyrene and styrene‐acrylonitrile copolymer in dilute solution
Authors: Raju Krishnam , Blanks Robert F. 
Published: April 2003

AbstractA laser homodyne spectrometer was used to obtain translational diffusion coefficients for dilute polystyrene and styrene‐acrylonitrile copolymer solutions at room temperature. Data were obtained in the concentration range from 0.01 to 2.0 g polymer per 100 cm3 solution for polystyrene in benzene and in decalin; and for copolymer in dimethyl formamide, in methyl ethyl ketone, and in benzene. The samples were polydisperse polystyrenes of weight average molecular weights between 80,000 and 350,000 and polydisperse copolymers of weight average molecular weights between 200,000 and 800,000. The SAN copolymers were random copolymer samples containing 24% by weight acrylonitrile. For each of the systems investigated the concentration dependence of the diffusion coefficient was linear over the concentration range studied, and was expressed as D(c) = D0(1+kDc). Values of D0 could be explained with a modified Kirkwood‐Riseman expression. Values of the parameter kD obtained from the slopes could be interpreted using the two‐parameter theory approach as suggested by Vrentas and Duda. The value of kD is positive for high‐molecular‐weight polymers and negative for low‐molecular‐weight polymers. For a particular polymer, the molecular weight at which kD changes sign is greater for poor solvents than for good solvents. Observed values of D0 were 1 × 10−7 to 7 × 10−7 cm2/sec.
Effect of free volume fluctuations on polymer relaxation in the glassy state. II. Calculated results
Authors: Robertson Richard E. 
Published: April 2003

AbstractThe relaxation following a change in temperature of amorphous polymers near the glass transition has been calculated. The calculation uses a chain model consisting of cis and trans backbone rotational states. The relaxation is assumed to proceed by localized conformational changes whose rates are controlled by the fractional free volume in small enough regions of the polymer that thermal fluctuations need to be considered. The relaxation is treated as a stochastic process, and an approximate solution is obtained for a finite set of relaxation environments. Using what is believed to be the most plausible set of parameters for polystyrene, relaxation curves are computed for the internal energy that are very similar to the curves obtained by Kovacs and others for the volumetric relaxation of poly(vinyl acetate) and polystyrene.
Creep deformation caused by crazing
Authors: Kitagawa M. , Kawagoe M. 
Published: April 2003

AbstractCreep deformation caused by crazing is analyzed using an analog of dislocation dynamics. Results are compared with experiments on polycarbonate and poly(vinyl chloride) subjected to the action of kerosene as a crazing agent. Good agreement between the theory and experiment shows the value of the dislocation analog approach. The theoretical craze creep strain is found to be numerically approximated by the commonly used law similar to the Nutting equation, and may provide a physical foundation for this widely used equation formally derived from rate theory.
Dielectric relaxation in the odd‐numbered polyamides: Nylon 7‐7 and nylon 11
Authors: Yemni Tarik , Boyd Richard H. 
Published: April 2003

AbstractOdd‐numbered polyamides have dipoles with components that point in the same direction in the planar zigzag conformation (rather than alternating as in the even‐numbered polyamides). An investigation of the dielectric properties of two odd nylons was undertaken here to see if dipole correlation resulting from this effect could be detected. It was found that the dielectric constant and relaxation strength associated with the α loss process (amorphous phase glass–rubber relaxation) when normalized for dipole concentration was indeed markedly higher in the odd nylons. The effect of uniaxial orientation induced by solid‐state extrusion on the isotropy of the dielectric properties was also studied. A previous study on nylon 6–10 found a reduction in relaxation strength of the α process in both the parallel and perpendicular directions but with the perpendicular direction being much stronger than the parallel. A similar result was found here for the odd polyamides. Thus the reduction in intensity appears to be due to effective reduction in the amount of amorphous material and not due to any change in dipole correlation induced by orientation. The anisotropy in relaxation strength can be explained by a composite material effect resulting from parallel stacking of crystal lamellas and interlamellar amorphous material and without invoking any anisotropy in the amorphous‐phase dielectric strength. Thus there is no reason to conclude that the amorphous phase undergoes orientation as a result of the crystal‐phase orientation.
A crystal transition in poly(γ‐n‐alkyl L‐glutamate)s
Authors: Sasaki Shintaro , Nakamura Takao , Uematsu Ichitaro 
Published: April 2003

AbstractA thermally reversible crystal transition was found for γ‐helical poly(γ‐n‐alkyl L‐glutamate)s (alkyl = ethyl, propyl, butyl, and amyl). The transition temperature is higher than that of the side‐chain mechanical dispersion, and decreases from 115 to −5°C, as the alkyl groups become longer. The transition in poly(γ‐n‐propyl L‐glutamate) is clearly first order. The structures were analyzed by x‐ray diffraction at various temperatures. It is noteworthy that the pseudohexagonal form observed below the transition temperature is less ordered than the hexagonal form at higher temperatures. The mechanism of this transition is discussed.
Physical and mechanical properties of ultra‐oriented high‐density polyethylene fibers
Authors: Mead W. T. , Desper C. R. , Porter Roger S. 
Published: April 2003

AbstractUltra‐oriented high‐density polyethylene fibers (HDPE) have been prepared by solid‐state extrusion over 60–140°C range using capillary draw ratios up to 52 and extrusion pressures of 0.12 to 0.49 GPa. The properties of the fibers have been assessed by birefringence, thermal expansivity, differential scanning calorimetry, x‐ray analysis, and mechanical testing. A maximum birefringence of 0.0637 ± 0.0015 was obtained, greater than the calculated value of 0.059 for the intrinsic birefringence of the orthorhombic crystal phase. The maximum modulus obtained was 70 GPa. The melting point, density, crystallinity, and negative thermal expansion coefficient parallel to the fiber axis all increase rapidly with draw ratio and at draw ratios of 20–30 attain limiting values comparable with those of a polyethylene single crystal. The properties of the fibers have been analyzed using the simple rule of mixtures, assuming a two‐phase model of crystalline and noncrystalline microstructure. The orientation of the noncrystalline phase with draw ratio was determined by birefringence and x‐ray measurements. Solid‐state extrusion of HDPE near the ambient melting point produced a c‐axis orientation of 0.996 and a noncrystalline orientation function of 0.36. Extrusion 50°C below the ambient melting point produced a decrease in crystallinity, c‐axis orientation, melting point, and birefringence, but the noncrystalline orientation increased at low draw ratios and was responsible for the increased thermal shrinkage of the fibers.
Linear polyethylene in a glassy phase: The value of the glass‐transition temperature
Authors: Cutler D. J. , Glotin M. , Hendra P. J. , Jobic H. , Moritz K. Holland , Cudby M. E. A. , Willis H. A. 
Published: April 2003

AbstractRaman spectroscopy, x‐ray diffraction, and thermal analysis are used to investigate the structure of linear high‐density polyethylene rapidly quenched from the melt to cryogenic temperatures. All the results point to the production of a glassy phase which crystallizes when heated above 170 K.
Properties of cellulose acetate. III. Light scattering from concentrated solutions and films. Tensile creep and desalination studies on films
Authors: Goebel K. D. , Berry G. C. , Tanner D. W. 
Published: April 2003

AbstractLight scattering from concentrated solutions of cellulose acetate in acetone is discussed in terms of exponential correlation functions for refractive‐index fluctuations. These are related to intermolecular aggregation. Light scattering, tensile creep and recovery, and hyperfiltration studies with films of cellulose acetate cast from acetone are discussed in terms of the state of aggregation in the films. It is concluded that intermolecular aggregates are probably small and imperfectly formed regions of microcrystallinity stable up to about 210°C, with the overall state one of near amorphous disorder.
Ultrasonic degradation of polycaproamide in 40% sulfuric acid solution
Authors: Szorek Ryszard 
Published: April 2003

AbstractThe influence of polymer‐polymer interactions and ultrasonic parameters on the ultrasonic degradation of polycaproamide in aqueous 40% H2SO4 was investigated. It was found that the rate data for the concentrations studied could be represented well by Ovenall's rate equation. However values of the rate constant chosen to fit Ovenall's equation tend to decrease with increasing concentration of polycaproamide from 0.5 to 2.0 g/100 cm3. With increasing ultrasonic power, the degradation rate increases, but it decreases as frequency is increased. This suggests that cavitation has a dominant role.
Extensions of the Avrami equation to various polymer crystallization models
Authors: Hay James N. , Przekop Zbigniew J. 
Published: April 2003

AbstractComputer modelling studies of the progress of crystallization in polymer melts have been carried out initially on those systems analyzed by Avrami and then extended to include a number of complications which may be characteristic of real systems, in particular (a) mixed mechanism, (b) volume shrinkage, (c) variable crystalline density, and (d) nonrandom nucleation. It is concluded that the Avrami equation is a reasonable approximation to most of these systems except (c).
Longitudinal growth of polymer crystals from flowing solutions. VI. Melting behavior of continuous fibrillar polyethylene crystals
Authors: Pennings A. J. , Zwijnenburg A. 
Published: April 2003

AbstractThe melting behavior of continuous fibrillar crystals of high‐molecular‐weight polyethylene has been investigated. The macrofibers were grown from dilute solutions in xylene subjected to Couette flow in the temperature range between 103 and 118.5°C. The thermograms, as determined by differential scanning calorimetry, exhibit three melting endotherms with peak temperatures at 141, 150.5, and 159.5°C after extrapolation to zero scan speed. All peaks were found to be strongly superheatable. Reduction of fiber length, in particular by etching with fuming nitric acid, led to the disappearance of the melting peaks at 150.5 and 159.5°C. The remaining peak at 136°C appeared not to be superheatable. The heat of fusion of the fragmented fibers was 69.8 cal/g. Wide‐angle x‐ray diffractograms taken on a macrofiber while gradually heated at a rate of 0.35°C/min at constant length showed that the triclinic phase present in the fiber disappeared at 130°C and that the orthorhombic cell transformed into the hexagonal modification at 150°C. This hexagonal phase was still observable at 180°C. The retractive force developed on heating at constant length displays first a slight decrease followed by a maximum at 150°C. Beyond the latter temperature the stress decays abruptly corresponding to the temperature at which fracture of the fiber could be observed visually. From all these observations it is inferred that the first melting endotherm in the differential scanning calorimeter (DSC) thermograms arises from the melting of unconstrained fibrillar crystal regions which are able to shrink during fusion. Moreover, the melting of lamellar overgrowths on the elementary fibrils on shish‐kebab type may contribute to this endotherm. The second melting endotherm at about 150°C is associated with the transformation of the orthorhombic into the hexagonal lattice in constrained parts of the sample. This latter “rotator” phase allows slippage of the polymer chains past each other, giving rise to stress relaxation. The third endotherm arises from melting of this hexagonal phase and the heat take‐up connected with the formation of higher energy gauche states upon randomization of the chains in the melt. Almost smooth, fully constrained fibrillar crystals grown at high temperature absorb more than 15.5 cal/g during this process, indicating that the polymer chains in such fibers must be highly extended.
Infrared studies of the reversible stress‐induced crystal‐crystal phase transition of poly(tetramethylene terephthalate)
Authors: Stambaugh B. , Lando J. B. , Koenig J. L. 
Published: April 2003

AbstractThe reversible stress‐induced crystal‐crystal phase transition of poly(tetramethylene terephthalate) (PTMT) has been studied using infrared spectroscopy. Two spectral regions were used to study this transition: the 900–1000 cm−1 methylene rocking region and the 1300–1550 cm−1 methylene bending region. The bands at 917 and 1456 cm−1 are assigned to the ∝ phase. The bands at 935 and 1388 cm−1 have components from the α phase and the β phase. Dynamic stretching experiments performed above and below the glass‐transition temperature indicated different mechanisms of the phase transition.
Effects of polymer solutions on colloid stability
Authors: Joanny J. F. , Leibler L. , De Gennes P. G. 
Published: April 2003

AbstractSome theoretical properties of a semidilute polymer solution (in a good solvent) near a repulsive wall (no adsorption) are discussed. (i) Near a single wall, the existence of a depletion layer (where the concentration is strongly reduced) with thickness equal to the correlation length ξ(c) is predicted. Scaling laws are obtained for the concentration cs at the first layer as a function of the bulk concentration c, and for the concentration profile c(z) at distance z from the wall. (ii) When two parallel walls are separated by a slab of polymer solution (thickness d), there is an attractive interaction between the plates. The range of the attraction is ca. 3ξ(c) and can be varied by suitable choice of concentration. It may lead to destabilization of certain colloidal systems.
Isobaric volume and enthalpy recovery of glasses. II. A transparent multiparameter theory
Authors: Kovacs A. J. , Aklonis J. J. , Hutchinson J. M. , Ramos A. R. 
Published: April 2003

AbstractA multiordering parameter model for glass‐transition phenomena has been developed on the basis of nonequilibrium thermodynamics. In this treatment the state of the glass is determined by the values of N ordering parameters in addition to T and P; the departure from equilibrium is partitioned among the various ordering parameters, each of which is associated with a unique retardation time. These times are assumed to depend on T, P, and on the instantaneous state of the system characterized by its overall departure from equilibrium, giving rise to the well‐known nonlinear effects observed in volume and enthalpy recovery. The contribution of each ordering parameter to the departure and the associated retardation times define the fundamental distribution function (the structural retardation spectrum) of the system or, equivalently, its fundamental material response function. These, together with a few experimentally measurable material constants, completely define the recovery behavior of the system when subjected to any thermal treatment. The behavior of the model is explored for various classes of thermal histories of increasing complexity, in order to simulate real experimental situations. The relevant calculations are based on a discrete retardation spectrum, extending over four time decades, and on reasonable values of the relevant material constants in order to imitate the behavior of polymer glasses. The model clearly separates the contribution of the retardation spectrum from the temperature‐structure dependence of the retardation times which controls its shifts along the experimental time scale. This is achieved by using the natural time scale of the system which eliminates all the nonlinear effects, thus reducing the response function to the Boltzmann superposition equation, similar to that encountered in the linear viscoelasticity. As a consequence, the system obeys a rate (time) ‐temperature reduction rule which provides for generalization within each class of thermal treatment. Thus the model establishes a rational basis for comparing theory with experiment, and also various kinds of experiments between themselves. The analysis further predicts interesting features, some of which have often been overlooked. Among these are the impossibility of extraction of the spectrum (or response function) from experiments involving cooling from high temperatures at finite rate; and the appearance of two peaks in the expansion coefficient, or heat capacity, during the heating stage of three‐step thermal cycles starting at high temperatures. Finally, the theory also provides a rationale for interpreting the time dependence of mechanical or other structure‐sensitive properties of glasses as well as for predicting their long‐range behavior.