bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photon correlation spectroscopy of poly(methyl methacrylate) near the glass transition
Authors: Patterson G. D. , Carroll P. J. , Stevens J. R. 
Published: April 2003

AbstractPoly(methyl methacrylate) (PMMA) has been studied by photon correlation spectroscopy in the temperature range 120–150°C. The relaxation functions for longitudinal density fluctuations were determined and analyzed using the empirical function ϕ(t) = exp[−(t/τ)β]. The average relaxation times were calculated for each temperature and compared to mechanical and dielectric relaxation data. The agreement between the various techniques for the primary glass–rubber relaxation was good. The relaxation function observed by light scattering became increasingly broad as the temperature was lowered. This is similar to the results reported previously for poly(ethyl methacrylate) (PEMA). In fact, the light‐scattering relaxation function is dominated by the secondary relaxations in these two polymers. Nevertheless, the average relaxation time 〈τ〉 is dominated by the longest relaxation times associated with the primary glass–rubber relaxation.
Electron‐beam‐induced conduction in fluorinated ethylene propylene copolymer and its acrylonitrile graft copolymer
Authors: Joshi S. G. , Ghatge N. D. , Jog J. P. , Walzade S. J. , Bhoraskar S. V. 
Published: April 2003

AbstractElectron‐beam‐induced conductivity (EBIC) studies were carried out on fluorinated ethylene propylene copolymer (FEP) and its acrylonitrile graft copolymer (FEP‐g‐AN). The current transport parallel to the surface under the influence of an electron beam of medium energy (6–30 keV) is reported. The gain in EBIC is calculated and its characteristic variation as a function of beam energy is studied. Minima in the gain versus energy curves have been obtained around 21 keV for FEP, 12 and 18 keV for FEP‐g‐AN, and 12 keV for polyacrylonitrile (PAN). This behavior is explained by assuming the existence of electron trapping bands close to the surface, at characteristic distances below the surface of the polymeric film corresponding to the range of incident electrons. Gains of the order of 5, 12, and 30 have been obtained respectively for FEP, FEP‐g‐AN, and PAN for the maximum energy of incident electrons used.
The elastic constants of ultradrawn polypropylene
Authors: Leung W. P. , Choy C. L. 
Published: April 2003

AbstractThe five independent elastic constants C11, C12, C13, C33, and C44 for uniaxially drawn polypropylene with draw ratios 1 < λ ≤ 20 have been measured from −40 to 130°C by an ultrasonic method (2.5 MHz). The crystalline and amorphous orientation functions fc and fa were also determined from wide‐angle x‐ray diffraction and birefringence; fc increases sharply at low λ and becomes saturated above λ = 8, but fa increases monotonically up to λ = 20. Below the glass transition temperature (ca. 60°C at 2.5 MHz) only the axial longitudinal and tensile moduli, C33 and E0, show large increase. At 110°C, however, all the moduli increase with λ; E0, E90 (tranverse tensile modulus), C44 (axial shear modulus), and C66 (tranverse shear modulus) increase 30, 3, 5, and 2.5 times, respectively, as λ increases from 1 to 20. The improvement in the mechanical properties can be attributed to the increase in the fraction of taut tie molecules which was monitored by fa. The results were analyzed in terms of the two‐phase models of Takayanagi and Seferis et al. The effects of annealing were also studied.
Longitudinal piezoelectric strain measurements of poly(vinylidene fluoride) films
Authors: Uchino K. , Cross L. E. 
Published: April 2003

AbstractThe longitudinal piezoelectric strain of poly(vinylidene fluoride) (PVF2) films has been measured at room temperature using a high‐sensitivity ac capacitance‐type dilatometer. The dc bias field dependence of the piezoelectric strain coefficient d33 has been determined. The polarization‐related electrostrictive coefficient Q33 obtained is several hundred times larger than the value in normal piezoelectric oxide crystals and is of opposite sign.
One‐dimensional models of polymer dynamics. I. Dashpot‐spring models applied to a single rotor
Authors: Mansfield Marc L. 
Published: April 2003

AbstractThe proposion of Clark and Zimm that a dashpot and a spring can be used in place of a set of rotational barriers in polymer dynamics is studied. The simplest possible case is examined here, that of a single rotor. Reasons for altering the Clark–Zimm diffusion equation are presented and an alternative diffusion equation is proposed. The results of both diffusion equations for the correlation function 〈exp[−iθ(0)] exp[iθ(t)]〉 (θ is the angular position of the rotor) are compared with the correlation function for a rotor in an n‐fold cosine potential. Although the two diffusion equations differ, both agree well with the n‐fold cosine model for barriers above a few kBT. This agreement is obtained in the absence of adjustable parameters, and motivates the application of these two diffusion equations to polymeric systems.
One‐dimensional models of polymer dynamics. II. A dashpot‐spring model
Authors: Mansfield Marc L. 
Published: April 2003

AbstractThe assumption of Clark and Zimm that coupled dashpots and springs can be used to model the dynamics of polymer molecules is here applied to a model different from that of Clark and Zimm. The precise differences are given in the preceding paper. The dielectric relaxation spectrum of the model is computed in time and frequency domains. The relaxation spectrum can be fitted reasonably well by the empirical Williams–Watts and Havriliak–Negami functions. The best‐fit Williams–Watts and Havriliak–Negami parameters are given as functions of the parameters of the model. The model is compared with several related models found in the literature and possible interpretations are given.
Photon correlation spectroscopy of polymer solutions
Authors: Cha C. Y. , Min K. W. 
Published: April 2003

AbstractA polynomial subdistribution method for analyzing the correlation profile in photon correlation spectroscopy of polymer solutions is described. This method generates a continuous distribution function from the measured photoelectron time‐correlation function, which can be related to particle size or molecular weight distribution of solute. The method is tested using simulated data for unimodal and bimodal distributions and compared with cumulant and histogram methods, respectively. The polynomial subdistribution method has an advantage in that it not only generates a continuous distribution curve but also works well for bimodal distributions whose peaks are close together.
The melt anisotropy of ultrahigh‐molecular‐weight polyethylene
Authors: Zachariades Anagnostis E. , Logan J. A. 
Published: April 2003

AbstractIn the course of melt‐flow crystallization studies with ultrahigh‐molecular‐weight polyethylene (UHMWPE), we observed that the melt of UHMWPE is highly anisotropic above its equilibrium melting point and has a tendency to fibrillate. An examination of the melt anisotropy of UHMWPE by optical, Thermal, and x‐ray analysis indicates that the melt anisotropy persists at 345°C, i.e., the temperature at which the polymer degrades under nitrogen, and appears similar to a smectic liquid‐crystalline phase.
Dynamic small‐angle x‐ray scattering from crystalline polymers
Authors: Young Ping , Kyu Thein , Suehiro Shoji , Lin J. S. , Stein R. S. 
Published: April 2003

AbstractThe variation in small‐angle x‐ray scattering (SAXS) for samples of crystalline polymers subjected to oscillatory strains has been observed employing the 10‐m SAXS apparatus with a two‐dimensional position‐sensitive detector at the National Center for Small‐Angle Scattering Research at Oak Ridge National Laboratory. Signal averaging has been carried out in accordance with the π/2‐sector technique by gating the detection of scattered intensity in synchronism with the sample strain. In‐phase and out‐of‐phase intensity changes have been observed for a high‐density polyethylene at various frequencies (0.05–3.2 Hz) and temperatures (0–70°C). Changes are greatest at small scattering angles. Frequency dependence is greatest at lower temperatures, indicating a time‐dependent response of the structural changes leading to scattering at these temperatures. The behavior is not pronounced at elevated temperatures. The similarity of the scattering at both azimuthal angles of 0° and 90° suggests the existence of an additional mechanism, perhaps microvoid formation. To evaluate void contribution, the dynamic invariant function is determined as a function of frequency and temperature. It appears that the microvoid formation lags behind the applied strain. The static and swelling SAXS studies present further evidence of void generation during elongation.
Small‐angle x‐ray scattering studies of crazed glassy polymers
Authors: Westbrook Paul A. , Fellers John F. , Hendricks Robert W. , Lin J. S. 
Published: April 2003

AbstractA small‐angle x‐ray scattering (SAXS) study of the relaxed craze structure in polystyrene was performed using the Oak Ridge National Laboratory 10‐m SAXS facility. Coupled with known results from transmission electron microscopy studies, the SAXS patterns can be interpreted as scattering from an open‐cell foam with void spaces interspersed among the fibrils. Results have shown the scattering centers in crazed polystyrene can be modeled as cylinders the axes of symmetry of which are parallel to the tensile axes. Scattering centers are bimodal in their size distribution, with aspect ratios of 1.0 and 2.6. Crazes in lower‐molecular‐weight polystyrene have more and larger scattering centers than crazes in higher‐molecular‐weight polystyrene, while variations in strain rate and test temperature during craze formation have no effect on the relaxed craze morphology. A comparison of SAXS patterns from polystyrene and polycarbonate indicates that the morphologies of their respective crazes are significantly different.
Friction coefficients in self‐diffusion, velocity sedimentation, and mutual diffusion for poly(ethylene oxide) in aqueous solution
Authors: Brown Wyn , Stilbs Peter , Johnsen Robert M. 
Published: April 2003

AbstractThe concentration dependences of the friction coefficient(s) for poly(ethylene oxide) have been determined on well‐defined fractions in dilute aqueous solution. Three independent techniques have been used: FT‐pulsed field gradient NMR (self‐diffusion), photon correlation spectrosccpy (mutual diffusion), and velocity sedimentation, in the concentration range 1‐25 kg m−3. The results establish that, at a given concentration, the friction coefficient in self‐diffusion is appreciably smaller than that operating in mutual diffusion and sedimentation; the friction coefficient in the latter processes are identical within experimental error.
Solid‐state 13C NMR evidence for gas–polymer interactions in the carbon dioxide–poly(vinyl chloride) system
Authors: Sefcik M. D. , Schaefer Jacob 
Published: April 2003

AbstractThe presence of small amounts of CO2 in poly(vinyl chloride) (PVC) results in increased main‐chain molecular motions of the polymer as measured by the carbon rotating‐frame relaxation rate. This effect increases with increasing gas concentration. Since molecular motions of the polymer and the diffusion coefficient of the gas are related, the latter must be concentration dependent. Main‐chain motions of PVC also increase upon exposure to CO2 followed by degassing. This result is interpreted in terms of the effect of the penetrant gas on the interchain packing in amorphous PVC. These results cannot be reconciled with the dual‐sorption‐mobility model, which claims that gas molecules preferentially occupy preexisting sorption sites in a conditioned polymer with no perturbation of the polymer matrix.
Relationship between piezoelectricity and superstructure in highly oriented poly(vinylidene fluoride) film prepared by zone drawing
Authors: Yamada K. , Oie M. , Takayanagi M. 
Published: April 2003

AbstractThe oriented superstructure of poly(vinylidene fluoride) is controlled by using a forced‐quenching type of zone drawing apparatus. Systematic variation of the weight fraction χ(I) of form‐I crystals and the orientation function fa of amorphous chains shows that the piezoelectricity increases with increasing χ(I) and fa. A change in the state of molecular aggregation during poling is also effective in increasing the piezoelectricity and the orientation of the crystal b axis along the poling direction. Equations relating piezoelectricity to the form‐I crystallinity, the orientation of amorphous chains, and the orientation of the crystal b axis along the poling direction are derived. These are based on a mechanical model having regions of taut tie molecules in parallel with composite regions consisting of crystalline and amorphous blocks in series.
Effects of pressure on the compressibility and crystallization of fiber‐forming polymers
Authors: Wei Kei‐Yi , Cuculo John A. , Ihm Dae Woo 
Published: April 2003

AbstractThe effects of pressure on the compressibility and crystallization of three fiber‐forming polymers, poly(tetramethylene terephthalate), nylon 66, and Qiana® nylon, have been studied. The Instron capillary rheometer was adapted as a high‐pressure dilatometer for all the high‐pressure experiments. The compressibility results reaffirmed that polymers are highly compressible, and their compressibilities are nonlinear at temperatures above the glass transition temperatures. Polymer melts show higher compressibility than do polymers in the solid state. The kinetics of crystallization of these polymer melts under high pressures were studied. Analysis of the data revealed low Avrami exponents at high pressures. It seems that the kinetics of crystallization of these polymers from the melt under high pressure are different from those at normal pressure. Crystallization temperatures of these polymers were also measured. The crystallization temperatures are considerably higher at higher pressures.
Thermotropic homopolyesters. I. The preparation and properties of polymers based on 4,4′‐dihydroxybiphenyl
Authors: Asrar J. , Toriumi H. , Watanabe J. , Krigbaum W. R. , Ciferri A. , Preston J. 
Published: April 2003

AbstractA homologous series of polyesters was prepared from 4,4′‐dihydroxybiphenyl and dibasic acids having 5‐12 methylene units. The mesophases formed at elevated temperatures were studied by differential scanning calorimetry and polarized light microscopy. This family exhibits an unusual odd‐even effect when the transition temperatures are plotted as a function of the number of methylene units in the dibasic acid. Not only do the points for odd and even members fall on different curves, but the odd members exhibit a nematic phase over a very short temperature interval, while the even members form a highly ordered smectic phase. For both the odd and even series, the transition temperatures are significantly depressed when the inherent viscosity falls below 0.2 dL/g. The largest depression occurs for the crystal melting transition, so that polymers of low ηinh show anisotropic and biphasic regions over wider temperature ranges. A copolymer formed from an equimolar mixture of sebacic and chiral (+)‐3‐methyl adipic acid forms a cholesteric phase. Evidently copolymerization destabilizes the smectic phase which would have been expected. The results are discussed in terms of existing theory.
Stress‐optical behavior of polydimethylsilmethylene [Si(CH3)2CH2], a hydrocarbon analog of polydimethylsiloxane, and a silicon analog of polyisobutylene
Authors: Llorente M. A. , Mark J. E. , Saiz E. 
Published: April 2003

AbstractElastomeric networks were prepared from polydimethylsilmethylene (PDMSM) [Si(CH3)2CH2], a polymer closely related to polydimethylsiloxane (PDMSO) [Si(CH3)2O] and polyisobutylene (PIB) [C(CH3)2CH2]. The birefringence of PDMSM in elongation was found to be qualitatively similar to that of PDMSO, in that there was no evidence for strain‐induced crystallization. However, the values of the optical‐configuration parameter Δa were considerably larger, and both Δa and its temperature coefficient are essentially the same as those of PIB. Swelling the PDMSM networks generally decreased Δa; the largest decreases, obtained as expected with the most nearly symmetrical diluent, were also approximately the same as those observed for PIB. Use of cyclic PDMSO pentamer as diluent in a PDMSM network was found to increase the birefringence, presumably because of orientational effects. Various network‐diluent combinations involving the significantly anisotropic PDMSM and the more nearly isotropic PDMSO should be extremely useful for elucidating the nature of these intermolecular correlations. Results obtained from rotational isomeric state theory considerably underestimate both Δa and its temperature coefficient for PDMSM, as they do for PIB. Although the origin of the discrepancy is not necessarily the same for both polymers, the results on PDMSM suggest that the discrepancy for PIB is not due to the severe steric congestion known to be present in this polymer.
Tests of a free‐volume model for the permeation of gas mixtures through polymer membranes. CO2‐C2H4, CO2‐C3H8, and C2H4‐C3H8 mixtures in polyethylene
Authors: Stern S. A. , Mauze G. R. , Frisch H. L. 
Published: April 2003

AbstractSteady‐state permeability coefficients have been measured for equimolar mixtures of CO2‐C2H4, CO2‐C3H8, and C2H4‐C3H8, as well as for a mixture of 74.9 mol % CO2 and 25.1 mol % C2H4 in polyethylene membranes. The measurements were made at 20, 35, and 50°C and at pressures of up to 28 atm. Each component of the permeating mixtures studied had the effect of increasing the permeability coefficient for the other component. Furthermore, at equal partial pressures and at the same temperature, the component exhibiting the highest solubility in the polymer had the largest effect in increasing the permeability coefficient of the other component. This behavior is in agreement with the predictions of a free‐volume model for the permeation of gas mixtures proposed by Fang, Stern, and Frisch. From a quantitative viewpoint, the permeability coefficients for the components of the mixtures agreed, on the average, to better than 25% with the predicted values. The theoretical permeability coefficients can be estimated from the model by using parameters determined with the pure components only.
Localized volume deficiencies as an effect of spherulite growth. I. The two‐dimensional case
Authors: Gałeski A. , Piórkowska E. 
Published: April 2003

AbstractTwo‐dimensional spherulite growth leads to the encirclement of regions of molten polymer in a polymer film. On further crystallization localized volume defects arise, resulting in thin spots in the film. Since this effect lowers the mechanical strength of films, we call these volume defects “weak spots.” A computer program is developed to evaluate the number, size, and shape of such volume defects for athermal, thermal, and mixed modes of primary nucleation of spherulites. It is shown that the total area of weak spots exceeds 10% of the sample area for all types of nucleation studied. The largest weak spots arise in samples crystallized via athermal and mixed nucleation; their size is of the same order as that of an average spherulite. Formation of weak spots is observed in thin films of poly(ethylene oxide) and poly(methylene oxide). The disadvantageous role of weak spots is confirmed by observation of electric breakdown occurring preferentially in weak spots in polypropylene films.
Formation, structure, and elasticity of loosely crosslinked epoxy‐amine networks. I. Statistics of formation
Authors: Dušek K. , Ilavský M. 
Published: April 2003

AbstractUsing the theory of branching processes based on cascade substitution, relations are derived for structural parameters characterizing network formation from diepoxide, monoepoxide, and diamine for various initial compositions. The different reactivities of the hydrogen atoms of the primary and secondary amino groups (the latter being formed in the reaction) and possibly different reactivities of epoxy groups in diepoxide and monoepoxide are taken into account. Relations are derived for the critical conversion at the gel point and for changes as a function of conversion in the average molecular weight in the pregel stage, changes in the sol and gel contents, effective functionality of the crosslinks, and concentration of elastically active network chains. The derivation includes the trapping factor that appears in the theory of permanent interchain interactions (trapped entanglements) of the Langley type. An analysis of the approximation usually employed in the statistical theory based on network formation from dyads of structural units shows that this approach is quite satisfactory for small differences in the reactivities of epoxy groups in diepoxide and monoepoxide.
Ab initio calculation of polyethylene deformation including electron correlation effects
Authors: Suhai S. 
Published: April 2003

AbstractThe longitudinal acoustic elastic modulus of polyethylene has been calculated with the aid of the ab initio crystal orbital method applying corrections also for electronic correlation effects. The basis set and correlation dependence of the elastic modulus have been investigated. The best theoretical value of 305 GPa of this modulus is in reasonable agreement with the published experimental values. At an elongation of ca. 0.1 the deviation from Hooke's law is found to be substantial.
EXAFS studies of nickel nafion ionomers
Authors: Pan H. K. , Yarusso D. J. , Knapp G. S. , Cooper S. L. 
Published: April 2003

AbstractNafion membranes neutralized with Ni2+have been examined by extended x‐ray absorption fine‐structure (EXAFS) and x‐ray absorption near‐edge‐structure (XANES) spectroscopy. The results indicate that in both the dry and water‐soaked membranes, the nickel is in an octahedral site with six oxygen atoms as nearest neighbors. The degree of disorder in the NiO distance is comparable to that in ionic crystals in both the dry and hydrated materials. A contribution from a second shell of neighbors is very weak in the dry samples but, surprisingly, this contribution is strongly accentuated in the hydrated membranes. The data indicate that this contribution is due to neighboring Ni2+cations. Thus the water absorption seems to enhance the local ordering of the cation environment. The local structure does not depend strongly on the concentration of ionic groups in the materials.
Thermal expansivity of oriented poly(ethylene terephthalate)
Authors: Choy C. L. , Ito Masayoshi , Porter Roger S. 
Published: April 2003

AbstractThe linear thermal expansivity of poly(ethylene terephthalate) extruded at 50 and 90°C to extrusion ratios λ of 1–4.8 has been measured between 120 and 300 K. With increasing λ, the expansivity along the extrusion direction (α∥) decreases sharply, while that in the transverse direction (α⊥) shows a slight increase. For λ < 3, the large drop in α∥ and the accompanying increase in the axial Young's modulus E∥ can be ascribed to chain alignment in the crystalline regions and to an increase in number and tautness of intercrystalline tie chains. At higher λ, however, the crystalline orientation apparently becomes saturated, so that taut tie molecules are solely responsible for further changes in both α∥ and E∥. On the other hand, α⊥ is mainly determined by crystalline orientation for all λ, thus showing very little increase at large λ. For the highly oriented samples (λ ≥ 3), the Takayanagi model provides a reasonable description of the behavior of α∥ and α⊥.