bluuebunny/crossref_metadata_2025_split huggingface dataset:
A rotational rheometer for rheological studies with prescribed strain or stress history
Authors: Berry G. C. , Park J. O. , Meitz D. W. , Birnboim M. H. , Plazek D. J. 
Published: April 2003

AbstractA rheometer utilizing an eddy‐current torque transducer and an air‐bearing suspension is described. The rheometer is coupled with a computer‐based data acquisition system and permits studies of shear deformation for several strain or stress histories. A sinusoidal stress history is used to determine the shear storage and loss compliances J′(ω) and J″(ω), respectively. Step stress histories are used to determine the shear creep compliance J(t) and the recoverable complaince R(t) or more complicated linear and nonlinear rheological responses related to these. Deformation at constant strain rate is used to determine the stress growth function or the steady‐state viscosity. The rheometer may be used over the temperature range – 10–180°C, with torque from 1 to 106 dyn cm, and is adaptabel to use with a variety of sample geometrical shapes (e.g., cone and plate, parallel plate, etc.). Examples of measurements on on viscoelastic fluids and on gels below their yield strain are given.
Measurements of dynamic interactions in thin films of polymer melts: The transition from simple to complex behavior
Authors: Israelachvili Jacob N. , Kott Stephen J. , Fetters Lewis J. 
Published: April 2003

AbstractTwo techniques are described for measuring the shear viscosities of thin liquid films confined between two surfaces. Both techniques employ the surface forces apparatus, which has already been used extensively to measure the static interactions between surfaces in liquids. With either of the new dynamic techniques, shear viscosities of the confined liquids can be measured as a function of film thickness with a precision of about 0.1 nm (1 Å). The techniques complement each other: one is used to best advantage at high shear rates, the other at low shear rates. Results are presented for measurements made on low‐molecular‐weight polymer melts of polybutadienes. At low shear rates, these results provide detailed information on the relation between polymer molecular weight, the conformation of polymer molecules at the surfaces, the intermolecular forces between the surfaces, and the location of the shear plane (plane of no‐slip). At high shear rates, the results suggest the gradual evolution of non‐Newtonian behavior in submicron liquid films.
Structural studies of radiation‐crosslinked poly(ethylene oxide)
Authors: Minkova L. , Stamenova R. , Tsvetanov C. , Nedkov E. 
Published: April 2003

AbstractThe structure and thermal behavior of freeze‐dried gels of radiation‐crosslinked high molecular weight poly(ethylene oxide) (PEO) were investigated by optical and electron microscopy, wide‐angle x‐ray scattering (WAXS), DTA, TGA, and thermomechanical analysis. The gels are highly porous with thin crystalline walls. Small spherulite and hedrite structures are observed on the walls. A model for gel formation in solution is suggested. A statistically homogenous chemical network is formed as a result of intrachain and interchain crosslinking. Simultaneous grafting of macromolecular fragments formed by chain scission also occurs.On increasing the irradiation dose from 1 to 15 Mrad, the degree of crystallinity determined by x‐ray diffraction and the total intensity of diffraction gradually decrease. The temperature and enthalpy of melting diminish steeply up to 5 Mrad, fall only slightly from 5 to 8 Mrad, and do not change from 8 to 15 Mrad. By comparing the x‐ray and DTA crystallinity values, this is shown to be due not only to reduced crystallinity at higher network density but also to Tree energy changes of entropic origin in crystalline and amorphous regions. Radiation chemical yields, G(‐units), for these dose ranges are 100, 38, and 0, respectively.Thermomechanical analysis was used to determine the elastic modulus of compression as a function of the dose absorbed, and the average molecular weight $ \bar M_{\rm c} $
of network chains was estimated. $ \bar M_{\rm c} $
decreases with doses up to 10 Mrad and does not change with further irradiation.
Thermal and dielectric behaviors of poly(vinylidene fluoride‐trifluoroethylene) copolymers at the curie transition
Authors: Moreira R. L. , Saint‐Grégoire P. , Lopez M. , Latour M. 
Published: April 2003

AbstractThe thermal and dielectric behaviors of poly(vinylidene fluoride‐trifluoroethylene) copolymers near the ferroelectric‐to‐paraelectric phase transition are investigated for samples with 20, 25, 30, and 40 mol% trifluoroethylene (TrFE). The data suggest that the transition becomes continuous for a particular composition near 50 mol% TrFE. Experimental data are sensitive to thermal history (kinetics of crystallization, and kinetics and cycling over the structural transition). It is found that several anomalies are present at the structural change, and in particular the 30 mol% TrFE sample shows the most marked anomalies. These phenomena can be attributed to defects, but another possibility would be the existence of an intemediate supplementary phase. Both hypotheses are discussed.
Chain dimensions in plastically deformed semicrystalline polymers
Authors: Tanzer Joseph D. , Crist Buckley , Graessley William W. 
Published: April 2003

AbstractThe effect of plastic deformation on the chain dimensions of polymers in the semicrystalline state was investigated using linear hydrogenated polybutadiene (HPB), a model ethylene/butene‐1 copolymer having about 40% crystallinity at room temperature. Dilute blends of deuterium‐labeled chains with various molecular weights (20,000 ≤ M ≤ 214,000) in the same unlabeled matrix (M = 95,000) were uniaxially stretched at 25°C to extension ratios of α = 2.4 and 4.4. Radius of gyration normal to the stretch direction R⊥ was measured for the labeled chains by small‐angle neutron scattering. The molecular extension ratio inferred from these data αm = R/R was significantly smaller than α for short chains (M < 50,000) but increased to the affine range αm = α for M > 100,000. This variation in αm/α closely parallels the molecular weight dependence of mechanical strength and ductility in HPB over the same range.
A comparison of the Raman LAM and electron microscopy in determining crystallite thickness distributions: Polyethylenes with narrow size distributions
Authors: Voigt‐Martin I. G. , Stack G. M. , Peacock A. J. , Mandelkern L. 
Published: April 2003

AbstractA detailed quantitative comparison between thin section electron microscopy, utilizing the chlorosulfonation technique, and the Raman low‐frequency acoustical mode (LAM) in determining the crystallite size distribution in polyethylenes having narrow distributions is made. Three different polyethylene systems have been analyzed, one of which was specifically prepared for this work. Very good quantitative agreement is obtained between these two analytical methods when account is taken of the chain tilt and the distribution is restrained to be narrow. Systems having broad crystallite size distributions introduce complexities into this comparison.
Effects of packing density on the gas‐transport properties of poly(phenolphthalein phthalate)s
Authors: Sheu F. R. , Chern R. T. 
Published: April 2003

AbstractThe gas transport and other pertinent properties of three aromatic polyesters, made by reacting phenolphthalein with terephthaloyl chloride (PPha‐tere), 50:50 terephthaloyl and isophthaloyl chlorides (PPha‐50:50), and isophthaloyl chloride (PPha‐iso), are reported. The glass transition temperatures of PPha‐tere, PPha‐50:50, and PPha‐iso are 299, 279, and 249°C, respectively. Unexpectedly, the densities are 1.297, 1.298, and 1.304 g/cm3 in the same order; PPha‐iso, therefore, has a higher packing density than PPha‐tere. The permeability of PPha‐tere to CO2, CH4, N2, and O2 is roughly 25% higher than that of PPha‐50:50, and roughly 100% higher than that of PPha‐iso. PPha‐tere is roughly five times as permeable as polysulfone but has slightly higher permselectivities for the above gases. On the other hand, the solubilities of each gas in these three aromatic polyesters are roughly the same, suggesting that the higher permeability of PPha‐tere is the result of a much larger gas diffusivity in the polymer. It is shown here that the significant difference in gas‐diffusivity is a manifestation of the effects of packing density on the transport properties of glassy polymers.
Effect of temperature and molecular weight on enthalpy relaxation in polystyrene
Authors: Agrawal A. 
Published: April 2003

AbstractIsothermal enthalpy relaxation in polystyrene was measured as a function of temperature and molecular weight on a differential scanning calorimeter. Relaxation spectra were derived from the data and expressed as a distribution of relaxation times. For a given molecular weight the relaxation spectra at different temperatures could not be superimposed by a shift in time. The relaxation curves of samples of different molecular weights could be superimposed only when the difference between the temperature at which the relaxation was monitored (Ta) and their respective Tg was the same. The relaxation spectrum at any temperature for a given molecular weight was also expressed as a distribution of energies. The average energy represented by this distribution was associated with an activation energy required for the motion of a chemical repeat unit. The activation energy extracted from the temperature shift in the relaxation spectra corresponded to the motion of a statistical unit (Kuhn's segment) in polystyrene.
Cation interactions with polyamic acids
Authors: Linde H. G. , Gleason R. T. 
Published: April 2003

AbstractPolyamic acid films interact as ion‐exchange substrates for dilute aqueous cation solutions. Three conditions were evaluated: basic solutions which form soluble amic acid salts and dissolve the film, weakly acidic solutions which encourage classical weak acid cation exchange, and strongly acidic solutions which discourage exchange. Thermal treatment of the generated cationamate salts generally causes degradation of the polymer backbone. Furthermore, lead and copper react directly with the polyamic acid to yield surface‐bound salts, but tin and aluminum seem unreactive.
Dielectric studies of the effects of thermal history on secondary relaxation in bisphenol‐a‐polycarbonate
Authors: Pathmanathan K. , Cavaillé Jean‐yves , Johari G. P. 
Published: April 2003

AbstractThe dielectric permittivity and loss of Bisphenol‐A‐polycarbonate (PC) was measured over the frequency range 100 Hz to 200 kHz and temperature range 77–383 K. One sub‐Tg relaxation peak is observed which rapidly broadens with a decrease in temperature. This is attributed to a progressive separation of the γ and β peaks, which at high temperatures are merged to form one peak of high strength. The strength of the sub‐Tg relaxations decreases on physical aging of PC but is increased if the sample is quenched from a temperature above its Tg. Slowly cooled PC has a lower strength of its sub‐Tg relaxation than a quenched specimen. The thermal history of PC affects the magnitude of its sub‐Tg relaxation.
The coagulation of cellulose from anisotropic solutions in the NH3/NH4SCN solvent system
Authors: Cho Jae Jeong , Hudson Samuel H. , Cuculo John A. 
Published: April 2003

AbstractCoagulation of cellulose has been studied in cellulose/ammonia/ammonium thiocyanate anisotropic solutions. The effect of coagulation variables such as coagulant, bath temperature, and cellulose concentration on the coagulation process is reported. The coagulation rate was measured by microscopic observation of the moving boundary associated with coagulation. Results indicate that the coagulation rate increases with increasing cellulose concentration and bath temperature. Methanol has the highest coagulation power among the coagulants employed. Mass transfer rate difference and equilibrium swelling were also measured. The results on the mass transfer rate differences show that the mass transfer rate of NH3/NH4SCN is greater than those of the respective coagulants under all coagulation conditions. The equilibrium swelling decreases with increasing bath temperature and cellulose concentration.
Structure/permeability relationships of polyimide membranes. Applications to the separation of gas mixtures
Authors: Stern S. A. , Mi Y. , Yamamoto H. , Clair Anne K. St. 
Published: April 2003

AbstractThe permeability of nine different polyimide membranes to H2, N2, O2, CH4, and CO2 has been determined at 35°C and at applied pressures of up to 9 atm. The dianhydride monomers used for the synthesis of the polymides were PMDA and 6FDA, whereas the diamine monomers were ODA, BDAF, and p‐PDA. The selectivities of the 6FDA polymides toward CO2 relative to CH4 are higher than those of the PMDA polyimides at comparable CO2 permeabilities. Both types of polyimides exhibit significantly higher CO2/CH4 selectivities than more common glassy polymers, such as cellulose acetate, polysulfone, and polycarbonate. The selectivities of the PMDA and 6FDA polyimides to O2 relative to N2 are of the same magnitude and generally higher than those of common glassy polymers with similar O2 permeabilities. The polymides are more permeable to N2 than to CH4, whereas the opposite is true for many other glassy polymers. Possible factors responsible for the above behavior, such as segmental mobility, mean interchain distance, and formation of charge transfer complexes, are examined. The relevance of the study to the development of more highly gas‐selective and permeable membranes for the separation of gas mixtures is also discussed.
Modulus and yield resistance of glassy blends containing diluents manifesting varying degrees of mobility: Polyphenylene ether/polystyrene/diluent mixtures
Authors: Kambour R. P. , Kelly J. M. , McKinley B. J. 
Published: April 2003

AbstractThe glass temperatures, moduli, and yield stresses for shear failure have been characterized for homogeneous blends of poly(2,6‐dimethyl‐1,4‐phenylene ether), homopolystyrene (1/1), and a number of diluents of Tgs from −134 to +32°C. In a blend series based of a given diluent, the mechanical properties vary with blend Tg at rates that are characteristics of the particular diluent. These characteristic rates are found to depend strongly on the Tg of the neat diluent. Thus, for blends all with Tg = 90°C, for example, modulus and yield stress differ by as much as 50% over the range of diluents. Low‐temperature relaxation measurements together with a number of previous dynamic spectroscopy studies of polymer/diluent systems at low temperatures suggest that many single‐phase polymer/diluent blends may exhibit two primary relaxations—the depressed alpha relaxation of the resin and a somewhat elevated alpha relaxation of the diluent—at quite different temperatures. Both of these relaxations influence stiffness and strength properties at intermediate temperatures. The often‐studied antiplasticization phenomena are viewed as a aberrations from a much more general influence of plasticizers on properties at temperatures below the alpha relaxation of the resin.
Small‐angle scattering of polarized light. I. comparison of theoretical predictions for isotropic and anisotropic spheres
Authors: Meeten G. H. , Navard P. 
Published: April 2003

AbstractThis paper describes small angle light scattering (SALS) calculations and compares the results for isotropic and anisotropic spheres. For isotropic spheres the exact Mie theory is compared with the Rayleigh‐Gans‐Debye (RGD) and the anomalous diffraction (AD) approximations in order to study the validity of the approximations. For anisotropic spheres the RGD is compared with the AD approximation. A study of SALS in the RGD approximation shows that the first‐order intensity maximum corresponding to a lobe of the four‐leaf clover pattern is not only a function of the sphere diameter but also depends on the isotropic and the anisotropic refractive index of the sphere. The practical implications of this are discussed.
Determination of transition temperatures and crystalline content of linear, high‐molecular‐weight polyethylene by proton NMR spectroscopy
Authors: Kauffman Jon S. , Dybowski Cecil 
Published: April 2003

AbstractDecomposition of the proton NMR spectra of linear, high‐molecular‐weight polyethylene into a Gaussian function and a Lorentzian function is discussed in terms of the Wilson‐Pake two‐component method for an inhomogeneous system. The results of a Goldman‐Shen experiment indicate that spin diffusion does not strongly couple the two regions. The temperature dependence of the Lorentzian (mobile) fraction is fitted to a function derived from the relation of English and Zoller. The critical temperatures give estimates of thermal transitions: Tα = 328 (± 5) K and Tγ = 163 (± 4) K. The fraction of Lorentzian spins excited by the γ relaxation correlates with the amorphous content of the sample as determined by differential scanning calorimetry and x‐ray diffraction.
Unit cell dimensions in model ethylene‐butene‐1 copolymers
Authors: Howard P. R. , Crist B. 
Published: April 2003

AbstractThe lattice parameters of a series of hydrogenated polybutadiene (HPB) model copolymers is measured as a function of branch content between 0 and 73 ethyl branches per 1000 C atoms. Expansion of the a and b axes nearly ceases for branch contents greater than 20 per 1000 C atoms. The c axis is seen to contract by a small amount with increased branching. The major cause of lattice expansion is limitation of crystal thickness by exclusion of branch points from the lamellar crystals coupled with surface stress on thin lamellae. A small fraction of ethyl branches are incorporated in the crystal; these expand the lattice by an additional amount.
Measurement of rotational diffusivity of rodlike molecules in amorphous polymer matrices by the dynamic kerr effect
Authors: Hill Davide A. , Soane David S. 
Published: April 2003

AbstractElectrooptic (Kerr effect) relaxation experiments, designed to measure the rotational diffusivity of collagen (rodlike) molecules in aqueous poly(ethyleneoxide) (amorphous) semidilute solutions under various conditions have been performed. The experimental results have been compared with the predictions of a previously derived model giving the rotational diffusivity of dilute rods in semidilute amorphous polymer solutions as a function of rod length and amorphous polymer concentration. Excellent agreement is found between the predicted scaling Dr ∼ ϕL−7 (Dr = rod rotational diffusivity, pip = polymer weight fraction, and L = rod length) and the experiments.
Gas sorption and transport in substituted polystyrenes
Authors: Puleo A. C. , Muruganandam N. , Paul D. R. 
Published: April 2003

AbstractThe effects of pendant groups on gas transport were investigated using a series of substituted polystyrenes. Permeability coefficients were measured at 35°C and 1 atm for He, N2, O2, CH4, and CO2, and diffusion coefficients were calculated from time lag data. The absolute permeabilities for the polystyrenes are correlated reasonably well using a free volume model. All pendant group substitutions resulted in a reduction of the mobility selectivity for CO2/CH4 separation relative to polystyrene, although there was very little effect on the O2/N2 selectivity. The effects of the various substituents were individually analyzed in terms of their size, rigidity, and polarity. The addition of a methyl group to the backbone significantly decreases transport, while attachment to the para ring position increases permeation. Bulky rigid groups, such as t‐butyl, enhance permeation even more. Methoxy and acetoxy substitutions provided an excellent means of examining plasticization of polymers by CO2, such as cellulose acetate, which contain these same moieties. The response of these polymers indicates that the degree of plasticization is related to the polarity and flexibility of the pendant group.
Studies of ESR Nitroxide probe mobility in polymer blends
Authors: Jamil T. , Jamieson A. M. 
Published: April 2003

AbstractWe report studies of the temperature‐dependence of the ESR spectrum of the nitroxide spin radical 4‐(2‐bromoacetamide)‐2,2,6,6 tetramethyl‐1‐oxyl piperidine (BRAMO) dispersed in poly(vinylidene fluoride) (PVDF), poly(methyl methacrylate) (PMMA), poly(vinyl acetate) (PVAc), and PVDF/PMMA and PVAC/PMMA blends of varying composition. In PVDF/PMMA blends which show a single composition‐dependent Tg, the mobility of BRAMO is identical to that in pure PMMA. On the other hand, in PVAC/PMMA blends, the mobility of BRAMO corresponds to that in pure PVAC. The results suggest that (1) BRAMO selectively binds to polymers based on hydrogen bonding affinity, (2) the spin probe is sensitive to segmental motions on a length scale shorter than those which give rise to the glass transition, and (3) compatible polymer blends are heterogeneous on the length scale of the BRAMO probe (ca. 8.3 Å).
On the possibility of using organic phosphors in thermoluminescence dosimetry
Authors: Moharil S. V. , Deshmukh B. T. , Muthal P. L. 
Published: April 2003

AbstractOrganic materials in general and polymers in particular have traditionally been considered as to be phosphors and have been ruled out as materials which could be useful in dosimetry of ionizing radiations by thermoluminescence. Some results reported during the past decade suggested possibilities of organic phosphors with good thermoluminescence characteristics. Experiments were undertaken to exploit the various possibilities. The results show that “crystalline polymers” can have adequate thermoluminescence properties to be useful in dosimetry. It is suggested that further studies on thermoluminesence in crystalline polymers and highly drawn fibers of high polymers will prove fruitful.
Free energy of an inhomogeneous polymer‐polymer‐solvent system
Authors: Ariyapadi M. V. , Nauman E. B. 
Published: April 2003

AbstractThe free energy of an inhomogeneous polymer‐polymer‐solvent system has been obtained by extending Debye's approach for a polymer‐solvent system. Our ternary result reduces to Debye's result for a binary polymer‐solvent system and to McMaster's result for a binary polymer‐polymer system at the appropriate limits. Like Debye's work, we neglect the entropic gradient contribution to free energy. Based on the ternary result we suggest a generalized expression for the free energy of multiple polymers dissolved in a common solvent. This expression is used to find the free energy of an inhomogeneous polydispersed polymer‐solvent system.
Effect of a block copolymer on the adhesion between incompatible polymers. I. Symmetric tests
Authors: Cho K. , Brown H. R. , Miller D. C. 
Published: April 2003

AbstractWe have studied the adhesion (welding) of polystyrene (PS) and poly (methyl methacrylate) (PMMA) and the effect of incorporating a thin layer of PS/PMMA block copolymer in the joint. The minimum thickness of copolymer layer necessary to increase the joint failure energy G to that of the bulk was about half the interlamellar spacing (long period) of the block copolymer. This tends to suggest a simple model of the block copolymer organizing on the interface with the two halves of the copolymer dissolved in the relevant homopolymers, however, we have no direct evidence for this. X‐ray photoelectron spectroscopy and optical microscopy were used to study the failure path. Without copolymer the crack propagated partly in the polystyrene and partly on the interface. Crazes grew from the interface into the polystyrene and the crack tended to follow such a craze for a short distance then jump back to the interface. With the copolymer, the failure mode was very similar, but there was evidence now of crazing on the interface. In no case was there evidence of a significant amount of PMMA on the PS side of the failure.