bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrostatic fiber spinning from polymer melts. II. Examination of the flow field in an electrically driven jet
Authors: Larrondo L. , St. John Manley R. 
Published: April 2003

AbstractThe flow field in an electrically driven jet has been examined and quantitatively analyzed. Using a model fluid, the nature of the streamlines and magnitude of the stream velocities were investigated with the aid of tracer particle photography. It was found that the velocity field is not purely extensional, but contains rotational components as well. Furthermore, the only portion of the jet completely free of any rotational component is the region about the symmetry axis. The extensional strain rate along the symmetry axis increases rapidly with the applied electric field intensity and can attain values in excess of 50 sec−1. This suggests that it might be possible to draw continuous oriented fibers from polymer melts by this technique if the jet can be operated at sufficiently high electric field intensity.
Mesogenic polymers. III. Thermal properties and synthesis of three homologous series of thermotropic liquid crystalline “backbone” polyesters
Authors: Griffin Anselm C. , Havens Stephen J. 
Published: April 2003

AbstractDetails of the thermal behavior, including transition temperatures, transition heats and transition entropies, are reported for three series of nematic liquid‐crystalline “backbone” polyesters having the general structure
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All polysters described above were examined by differential scanning calorimetry and were found to have reproducible thermal behavior once the polymer had been annealed by heating to the isotropic phase and then subsequently cooled. Enantiotropic nematic phases were found for all 30 polysters studied. Many polymers showed multiple endotherms on melting to the nematic phase. Plots of solid–nematic and nematic–isotropic transition temperatures versus number of carbon atoms in the diacid segment (x) for each (y) reveal an even–odd alternation reminiscent of trends in homologous series of small‐molecule liquid crystals. Enthalpies for the solid → nematic and nematic → isotropic transitions do not show such a precise alternation.
Polystyrene–polyisoprene block copolymers in dilute solutions: Characterization of the conformation by small‐angle neutron scattering
Authors: Ionescu L. , Picot C. , Duplessix R. , Duval M. , Benoît H. , Lingelser J. P. , Gallot Y. 
Published: April 2003

AbstractThe variable‐contrast method in small‐angle neutron scattering has been applied to a study of the conformation of polystyrene–polyisoprene block copolymers in dilute solution. The experimental results reveal no intramolecular segregation effect in dilute solutions in toluene and cyclohexane.
Nonlinear stress relaxation of a styrene–butadiene random copolymer
Authors: Merriman H. G. , Caruthers J. M. 
Published: April 2003

AbstractThe isothermal uniaxial stress relaxation response in the vicinity of the glass‐to‐rubber transition has been measured for a lightly crosslinked poly(styrene–butadiene) random copolymer, 85% styrene by weight. The volume change during stress relaxation was determined by measuring the time‐dependent lateral contraction of the specimen with a Hall‐effect proximity detector. The specimen exhibited an instantaneous dilation upon application of the strain and a subsequent time‐dependent volume decrease. The stress relaxation behavior and the associated volume relaxation were determined for a variety of strains and temperatures in both the linear and nonlinear viscoelastic regime. As the applied strain was increased the isothermal tensile modulus decreased and the shape of the log(modulus) vs. log(time) curve was altered. At equal levels of strain the tensile modulus exhibited increasing deviations from the linear viscoelastic response as the temperature was decreased. The maximum difference between the nonlinear tensile modulus and the linear viscoelastic response was observed at short times. Subsequently, the nonlinear tensile modulus began to approach the linear viscoelastic modulus with increasing time. Both the instantaneous dilation and the magnitude of the time‐dependent part of the volume change increased as the level of applied strain was increased and/or as the temperature was decreased. The observed nonlinearity in the tensile stress relaxation response has been quantitively related to the experimentally measured volume relaxation with a free‐volume model.
An apparatus for kinetic‐mechanistic studies of polymer burning and regression rates: Poly(methyl methacrylate)
Authors: Kachi H. , Jellinek H. H. G. , Hall M. 
Published: April 2003

AbstractAn apparatus for determination of regression (weight‐loss) rates before, at, and after ignition as a function of oxidant gas flow rates has been constructed and successfully operated with poly(methyl methacrylate). In addition, flame temperatures, gas evolution kinetics and composition can be ascertained. The apparatus allows a proper evaluation of diffusion processes and chemically controlled processes. The regression rate for PMMA is directly proportional to the air flow rate. At low air flow rates the process is diffusion controlled and the energy of activation is identical with the heat of vaporization of the monomer. There is a liquid monomer layer and on top of it a stagnant vapor layer having the equilibrium vapor pressure of the monomer. At higher flow rates the energy of activation increases steeply. The layers become thin and defective and eventually thermal depolymerization becomes rate determining. This depolymerization has an energy of activation between 30 to 40 kcal mol−1. Experiments have also been carried out in closed quartz tubes. Explosion limits, ignition lags and energies of activation have been determined. The latter were evaluated by the method of Semenoff.
Phase separation of polymer blends in thin films
Authors: Reich S. , Cohen Y. 
Published: April 2003

AbstractFilms of polystyrene‐poly(vinylmethyl ether) blends of various compositions are formed by a dip‐coating procedure, the thickness of the film being controlled by the concentration of the solution. The substrates used are glass and gold. The phase separation process is followed by a laser light scattering experiment in which the total forward scattering intensity is monitored as a function of temperature. Morphological examination shows that phase separation occurs by a spinodal decomposition mechanism. A thickness effect on the phase separation temperature is noticeable when film thickness is smaller than 1 μm. This effect is substrate dependent. In all films formed on gold the spinodal temperature increases as film thickness decreases. Films formed on glass exhibit a destabilizing effect on decreasing film thickness. This effect is slight in films of composition poorer in polystyrene than the critical composition, and is enhanced in films richer in polystyrene. The stabilizing effect of decreasing the thickness of films formed on the gold substrate is considered to reflect mainly a purely geometrical effect. The decreasing dimensionality is shown by simple theoretical considerations to increase the phase‐separation temperature. However, the phase separation behavior of thin films on glass appears to be the result of two kinds of substrate‐polymer interactions in addition to the geometrical effect: (a) electrostatic interaction of the charged glass surface (a destabilizing effect at all film compositions) and (b) selective adsorption of polystyrene on glass.
Effect of orientation and mobility of polymer molecules at surfaces on contact angle and its hysteresis
Authors: Yasuda H. , Sharma Ashok K. , Yasuda Takeshi 
Published: April 2003

AbstractThe contact angle of a water droplet on the surface of a solid polymer or hydrogel (water‐swollen three‐dimensional network) depends on whether a hydrophilic moiety of the polymer molecule is oriented towards the air interface or towards the bulk of the solid, but not on the hydrophilicity of the molecule. Therefore, the short‐range rotational mobility of a polymer molecule has a major influence on the apparent hydrophilicity of a polymer surface as measured by the contact angle of water. By the came principle, the abnormally large hysteresis effect observed in advancing and receding contact angles of water on some polymer surfaces can be attributed to the reorientation of hydrophilic moieties of polymer molecules at the surface. These factors are demonstrated by selected polymer surfaces with different degrees of mobility at the polymer‐air interface.
Determination of the persistence length of an aromatic polyamide‐hydrazide by small‐angle x‐ray diffraction
Authors: Krigbaum W. R. , Sasaki S. 
Published: April 2003

AbstractSmall‐angle x‐ray diffraction measurements were performed upon dimethyl acetamide (DMAc) solutions of four samples of X‐500, an aromatic polyamide‐hydrazide. The solubility improved as the polymer molecular weight increased, the most soluble sample being in the form of a highly oriented, crystalline fiber. Molecular weights determined from the scattering curves indicate that aggregation was present in all solutions. Its extent varied with the solubility of the sample, increased with polymer concentration and, for the lowest concentrations studied, could be reduced by the addition of acetic acid. Radius of gyration values were smaller than those obtained by light scattering, probably because of insufficient resolution of the camera. The mass per unit length along the chain was found to be 18–20 Å, while the radius of gyration of the cross section was 3.5–4.8 Å. Three of the samples gave nearly the same angular intersection for the coil‐and rodlike regions of the scattering curve. Two of these were whole polymers and the other a narrow fraction. The fact that essentially the same intercept was found in all three cases indicates the persistence length as measured for linear chain polymers by small‐angle x‐ray diffraction is independent of the heterogeneity of the sample. The intercepts, after a small correction for excluded volume effects, correspond to persistence lengths in the range 71–88 Å for DMAc solutions, which approximate those determined for dimethyl sulfoxide (DMSO) solutions by light scattering the intrinsic viscosity without correction for excluded volume, but are substantially larger than the DMSO values, corrected for excluded volume of 30–49 Å. We can offer no explanation for this difference.
Piezoelectricity of uniaxially stretched poly(vinylidene fluoride) corona poled at elevated temperature
Authors: Bamji S. S. , Perlman M. M. 
Published: April 2003

AbstractX‐ray diffraction, thermally stimulated depolarization, and piezoelectric current measurements have been carried out on uniaxially stretched poly(vinylidene fluoride) film, corona poled both negatively and positively at room temperature and at 90°C. Corona poling at elevated temperature considerably enhances the piezoelectric constant and is a more efficient way of charging the film than conventional thermal poling. Advantages over the latter are discussed.
The effect of annealing and mechanical constraint on the morphology structure and stiffness of ultrahigh‐modulus polyethylene
Authors: Capaccio G. , Clements J. , Hine P. J. , Ward I. M. 
Published: April 2003

AbstractA study has been made of the effects of annealing at high temperature (130°C) on the dynamic mechanical properties and melting behavior of a series of ultrahigh‐modulus polyethylenes. Although annealing always resulted in a substantial decrease in modulus, there were marked differences between samples of moderate draw ratio, depending on whether they are annealed at constant length or unconstrained. On the other hand, the differences were small for high‐draw‐ratio samples, indicating their greater thermal stability. In all cases the −50°C plateau modulus correlated well with the degree of crystal continuity estimated from wide‐angle x‐ray diffraction measurements of crystal length combined with small‐angle measurements of the long period. The corresponding changes in melting behavior were entirely consistent with the changes observed in the mechanical stiffness. Both types of measurement together with the x‐ray results have been used to gain an understanding of the morphological changes occurring on annealing.
Mesomorphic solutions of cellulose triacetate in halogenated organic acids and mixtures of trifluoroacetic acid and dichloromethane
Authors: Patel D. L. , Gilbert R. D. 
Published: April 2003

AbstractCellulose triacetate (CTA) forms liquid‐crystalline solutions in trifluoroacetic acid, dichloroacetic acid, and mixtures of trifluoroacetic acid and dichloromethane. Brilliant iridescent coloration, high optical rotations, and birefringent regions with swirl‐like fingerprint patterns suggested the formation of cholesteric liquid crystals. Trifluoroacetic acid–dichloromethane is a particularly excellent solvent mixture to form liquid‐crystal solutions of cellulose acetate. Crude bulk viscosity measurements confirm the formation of an anisotropic phase, and the temperature dependence of the critical concentration for formation of the anisotropic phase, obtained by bulk viscosity measurements at various temperatures, provides confirming evidence. Viscosity decreases with aging, suggesting that CTA is slowly degraded in the solvents studied. This is also confirmed by optical rotatory measurements and by polarizing microscope observations. The miscibility gap is observed as a function of molecular weight, and the differences between the experimental data and Flory's prediction are discussed.
Polarization studies by the TSC technique on a blend of cellulose acetate and polyvinyl acetate
Authors: Pillai P. K. C. , Gupta Brijesh K. , Goel Malti 
Published: April 2003

AbstractThe thermally stimulated current (TSC) technique has been used to study solvent‐cast blends of a cellulose derivative with a vinyl polymer. TSC peaks are observed at 56, 80, and 120°C. Their origin is investigated because the TSC spectra of the blends differ from the spectra of the individual components. Data on blends with components in the weight ratios 25:75, 50:50, and 75:25 indicate that the 50:50 blend shows the greatest polarization. The enhancement of depolarization currents observed on blending is explained on the basis of a Maxwell–Wagner–Sillars polarization due to increased heterogeneity in the structure. Effects of forming conditions (time, temperature, field) on polarization have been investigated. Activation energies and relaxation times are calculated; there is good agreement between the values obtained from the initial‐rise and the full‐curve methods.
Influence of polymerization initiation rate on permeability of aqueous polyacrylamide gels
Authors: Weiss N. , van Vliet T. , Silberberg A. 
Published: April 2003

AbstractIt was shown by Weiss and Silberberg in 1975 that polyacrylamide gels prepared by copolymerization of acrylamide and N,N′‐methylene bis‐acrylamide in water are heterogeneous. A two‐phase model developed in 1979 satisfactorily accounted for the permeability of the gels. These gels had been prepared under standard conditions of initiator and activator concentrations and involved precooling of the reaction mixture to 0°C with completion of the reaction at room temperature, a thermal history not very suitable for kinetic analysis. A procedure was, therefore, devised where gels are prepared at room temperature throughout. Much better correlations are then obtained, and it can be shown that the initiation is controlled by the initiator (ammonium persulfate) concentration times the activator (N,N,N′,N′‐tetramethylethylene diamine) concentration raised to the 1.5 power. These data, discussed in terms of the two‐phase model, show that the initiator concentration directly determines the number of crosslinks in the more dilute, permeability‐determining, gel phase. The faster the initiation, the less permeable a gel results. An increase of permeability with overall degree of crosslinking at constant monomer concentration is a feature only of gels prepared at sufficiently low polymerization initiation rates.
A model for permeation of mixed gases and vapors in glassy polymers
Authors: Koros W. J. , Chern R. T. , Stannett V. , Hopfenberg H. B. 
Published: April 2003

AbstractA model is discussed which explains reported complex effects of feed composition and pressure on component permeabilities in high‐pressure gas separators based on glassy polymer membranes. A special form of Fick's law which accounts for the fact that penetrants in glassy polymers sorb into and diffuse through two different molecular environments provides the basis for the analysis of gas mixture permeation. Potential deviations from the theory are discussed in terms of separable solubility‐and mobility‐related effects.
A light‐scattering study of deformation of liquid‐crystalline spherulites of poly(γ‐benzyl‐L‐glutamate) in an electric field
Authors: Matsuo Masaru , Ozaki Fumihiko , Konno Yasuyuki , Ogita Tetsuya 
Published: April 2003

AbstractThe deformation of liquid‐crystalline spherulites of poly(γ‐benzyl‐L‐glutamate) (PBLG) in an electric field was investigated by light scattering, polarized‐light microscopy, and birefringence measurements. Under the polarizing microscope, the deformation was found to be dependent upon the field strength. The spherulites deformed perpendicular to the field. Above 75 V/cm in N,N‐dimethylformamide or 120 V/cm in 1,1,2‐trichloroethane, the deformed spherulites were transformed to rodlike textures. With increasing voltage, the rods gradually oriented parallel to the electric field. On the basis of the experimental results, models for affine deformation are proposed. With these models, light‐scattering patterns are calculated. The calculated and experimental patterns agree semiquantitatively.
Small‐angle x‐ray scattering studies of isothermally crystallized bulk polyethylene
Authors: Varnell W. D. , Harrison I. R. , Wang J. I. 
Published: April 2003

AbstractA set of isothermally melt‐crystallized polyethylene samples was examined using small‐angle x‐ray scattering (SAXS). Time and temperature of crystallization were the variable parameters used to create the set of samples. Following background subtraction, desmearing, and application of the Lorentz factor to the raw SAXS data it is possible to see many orders of reflection. This suggests that much higher degrees of order are present in isothermally melt‐crystallized samples than had previously been thought possible. A combination of SAXS and DSC data indicates that there is no evidence for isothermal thickening in these samples. This study, coupled with data obtained from PE single crystals, produced information concerning the extrapolation of single‐crystal data to fit bulk systems. In addition, the equilibrium melting point T determined is somewhat lower than previously claimed. This study also suggests that the surface energy of the mature crystals is always lower than that of the nucleated state and/or the nucleation factor Kσen increases with decreasing supercooling.
Viscoelastic properties of sulfonated styrene ionomers
Authors: Rigdahl M. , Eisenberg A. 
Published: April 2003

AbstractThe solid‐state viscoelastic properties of polystyrene containing randomly distributed groups of styrene‐p‐sodium sulfonate are studied and compared with the corresponding properties of copolymers of styrene and sodium methacrylate (S‐NaMA). The viscoelastic behavior in the primary transition region of these two ionomers is very similar. As for the S‐NaMA copolymers, it is proposed that sulfonated polystyrene is composed of ion‐rich regions (clusters) immersed in a matrix of low ion concentration. Two peaks are observed in the plot of mechanical loss tangent versus temperature for the sulfonated material. The lower peak is assigned to the glass transition of the ion‐poor matrix and the upper to the glass transition of the clustered regions. As for some other ionomers, the presence of ions is found to slow down the stress relaxation rate, giving a broad distribution of relaxation times. Above a certain ion concentration, the sulfonated polystyrenes are thermorheologically complex owing to the onset of a secondary relaxation mechanism associated with the ion‐rich regions.
The morphology in nafion perfluorinated membrane products, as determined by wide‐ and small‐angle x‐ray studies
Authors: Gierke T. D. , Munn G. E. , Wilson F. C. 
Published: April 2003

AbstractThe morphology of the ionomer resin from which Nafion perfluorinated membrane products are made was studied with wide‐angle and small‐angle x‐ray diffraction. A reflection observed in the small‐angle x‐ray scan from hydrolyzed polymer is attributed to ionic clustering. The effects of equiv wt, cation form, temperature, water content, and tensile drawing on this reflection were studied and are discussed.
Finite‐element analysis of craze deformation
Authors: Bevan I. 
Published: April 2003

AbstractThe finite‐element method is applied to a craze model in order to estimate surface displacements and stresses of an isolated craze in a thin rectangular plate. The limitation of assuming linear‐elastic behavior of the craze fibrils is demonstrated by comparing computed profiles with published experimental ones. Accurate finite‐element estimates of craze surface stresses are obtained from the experimental displacement profile. The analysis is extended to the three‐dimensional case but the difference between the craze displacements at the surface of the plate and those at midthickness is too small to justify the considerable increase in computer time in comparison with that required for two‐dimensional analysis.
A quantitative electron‐microscopic study of a linear polyethylene fraction crystallized at different temperatures
Authors: Voigt‐Martin I. G. , Mandelkern L. 
Published: April 2003

AbstractReplica and thin‐section electron microscopy was performed on a linear polyethylene fraction (Mw = 1.89 × 105, Mn = 1.79 × 10 5) which was either isothermally crystallized or quenched at difference temperatures. The results are numerically analyzed in such a manner so as to give the distribution of the total long spacing and of the crystallite and amorphous thicknesses. The quantitative information about the maximum and minimum values for these parameters at each crystallization temperature yields important clues as to possible molecular processes involved. Qualitative information regarding general morphology, molecular tilt with respect to the lamellar surface, and possible crystallographic faults are also discussed.
Epitaxial crystallization of polyethylene on organic substrates: A reappraisal of the mode of action of selected nucleating agents
Authors: Wittmann J. C. , Lotz B. 
Published: April 2003

AbstractElectron microscopy and electron diffraction studies show that polyethylene crystallizes epitaxially onto crystals of homologous series of (i) condensed aromatic hydrocarbons and (ii) linear polyphenyls. The contact planes of the PE chain‐folded lamellae with the (001) faces of the substrate crystals are found to differ for the two series, being (100) and (110), respectively. The underlying epitaxial relationships are best explained by a two‐dimensional lattice matching of polymer and substrate networks. In view of the structural similarities of the present substrates and some well‐known nucleating agents for polyethylene, epitaxy is suggested as a possible mechanism which could explain the nucleating ability of the latter. This is experimentally demonstrated with the potassium salt of phthalic acid.