bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of degree of acetylation and solvent on the chiroptical properties of lyotropic (acetyl) (ethyl) cellulose solutions
Authors: Guo J.‐X. , Gray D. G. 
Published: April 2003

Abstract(Acetyl) (ethyl) cellulose (AEC) polymers with an ethyl degree of substitution (DS) of 2.5 and acetyl DS ranging from 0 to 0.5 dissolve readily in a wide range of organic solvents and form chiral nematic liquid crystalline phases in concentrated solution. The chiroptical properties of these liquid crystals are strongly influenced by the acetyl content and solvent. In dichloromethane, dibromomethane, chloroform, bromoform, m‐cresol, acetic acid, and aqueous phenol, the AEC lyotropic mesophases all show a handedness inversion as the acetyl DS of the polymers is increased, changing from left‐ to right‐handed supermolecular helicoidal structures. The temperature dependence of the pitch for these mesophases is also reversed from negative to positive with increasing acetyl DS in all the above solvents except aqueous phenol, in which the corresponding AEC mesophases change from positive to negative. The optical microscopic, optical diffraction, and ORD evidence provide a unique indication that the reversal of the handedness and temperature dependence for the AEC mesophases occurs at a compensated degree of acetylation, DA*. The corresponding compensated mesophases show an infinite pitch and behave optically like nematic mesophases. The value of the DA* is dependent on solvent. In dichloroacetic acid, AEC liquid crystals remain right‐handed, independent of the acetyl DS. At given concentration and temperature, the long pitch samples flow much more readily than short pitch samples. © 1994 John Wiley & Sons, Inc.
Temperature dependence of molecular motions in bulk polystyrene
Authors: Blackburn F. R. , Cicerone Marcus T. , Ediger M. D. 
Published: April 2003

AbstractTime‐resolved optical spectroscopy is used to investigate the reorientation of three rigid probes and one labeled chain in bulk polystyrene. Orientational correlation times for these probes and labels are found to be in the range of 10−8–10−10 s at temperatures of 180–300°C. Consistent with previous studies, the attachment of a chromophore into the chain backbone slows its dynamics by about an order of magnitude. The temperature dependences of the correlation times are similar to the temperature dependence of the viscosity. When combined with probe reorientation times near and below Tg, these results indicate that probe reorientation tracks the temperature dependence of the viscosity quite well over twelve decades in time. In contrast, literature results for the translational diffusion of similarly sized probes indicates a substantially weaker temperature dependence near Tg. Thus it appears that a fundamental change in the mechanism of probe motion occurs near Tg. © 1994 John Wiley & Sons, Inc.
A scattering study on intermicellar interactions and structures of polymeric micelles
Authors: Chu Benjamin , Wu Guangwei , Schneider Dieter K. 
Published: April 2003

AbstractThe micellar structure is usually considered to be composed of a hard sphere (liquid) core and a heavily solvated corona. Therefore, the correction for intermicellar interactions at finite concentrations can be relatively complicated. In this article, small‐angle neutron scattering of a copolymer, known as Pluronic L64 (PEO13PPO30PEO13), in o‐xylene in the presence of D2O is used to demonstrate that, based on the hard sphere approximation, intermicellar interactions can be corrected by representing the micellar size as having an equivalent hard sphere radius. The procedure remains valid even if the micellar shape becomes asymmetric, with axial ratios of 3 ˜ 4. For the present system, the equivalent hard sphere radius corresponds to the micellar core radius plus one‐half of the micellar shell thickness. With the equivalent hard sphere approach, the scattering behavior of the micelle could be described by using a core‐shell structure. © 1994 John Wiley & Sons, Inc.
Investigation of dipolar reorientation dynamics of pure bulk polymers using second harmonic generation
Authors: Guan H. W. , Pauley M. A. , Brett T. , Wang C. H. 
Published: April 2003

AbstractSecond harmonic generation (SHG) in three corona‐poled, pure, bulk polymers is studied as a function of temperature. It is found that this technique readily yields dynamical information that is complementary to that obtained from the technique of dielectric relaxation (DR). The SHG results are compared to those from DR in the same temperature ranges above Tg. It is found that in the temperature ranges examined, the relaxation times obtained from SHG are several orders fo magnitude longer than those measured by dielectric relaxation. This is explained as being due to the strong correlation between oriented dipoles and to trapped charges injected by the poling process. Fitting measured data to the Williams‐Landau‐Ferry (WLF) equation indicates that more free volume is needed in SHG for dipolar reorientation than is needed in DR. An SHG relaxation elongation phenomenon at constant temperature is found to occur in the pure bulk polymers and is similar to that found in chromophore‐doped polymers previously studied. The SHG technique is developed as a new tool to directly study the reorientational dynamics of polar polymer segments. © 1994 John Wiley & Sons, Inc.
Surface studies of tetraalkylammonium bromides and iodides using atomic force microscopy
Authors: Wang Qiguang , Annis Brian , Wunderlich Bernhard 
Published: April 2003

AbstractThe surface structures of two series of tetra‐n‐alkylammonium halides, N(CxH2×+1)4I and N(CxH2x+1)4 Br have been investigated with atomic force microscopy (AFM) and compared to hexatriacontane (C36H74). The surfaces could be imaged with atomic resolution. The observed primitive, square surface‐patterns of tetra‐n‐butyl chloride and bromide are in good accord with x‐ray single‐crystal structure. For n > 4, x‐ray powder diffraction showed that increasing the alkyl chain‐length leads mainly to an appropriate increase of the unit cell along the c‐axis, which suggests similar layer structures for all long‐chain salts beyond the butyl homologue. Within the centers of the molecular layers of these crystals reside the halide anions and the quaternary nitrogens. The surfaces accessible for AFM consist of methyl end‐groups. As the number of carbon atoms increases beyond four, the surface symmetry changes to the face‐centered square patterns characteristic of many paraffins. The chains of the tetraalkyl ammonium salts pack, however, less dense than paraffins. © 1994 John Wiley & Sons, Inc.
Hydration in semicrystalline polymers: Small‐angle neutron scattering studies of the effect of drawing in nylon‐6 fibers
Authors: Murthy N. S. , Orts W. J. 
Published: April 2003

AbstractWater absorbed by nylons appears to be partitioned into interlamellar and interfibrillar spaces. The amount of water in the interfibrillar region remains essentially unchanged with increasing draw ratio, whereas that in the interlamellar regions decreases with draw ratio; the latter accounts for the decrease in the water uptake in the drawn fibers. These results suggest that the amount of the amorphous material in the interfibrillar regions remains unchanged during drawing, and the increase in the crystallinity during drawing results from the incorporation of the amorphous chain segments in the interlamellar regions into the crystalline lamellae. Further, the interfibrillar water is more tightly bound than the interlamellar water. The length of the longitudinal channels into which water diffuses is about the same as that of the fibrils, and increases from ca. 1500 to 2000 Å upon drawing. The longitudinal channels are highly oriented even in undrawn fibers, and their misorientation increases from 5° to 15° upon drawing. These channels can be described as surface fractals of dimension 3.4–3.6. © 1994 John Wiley & Sons, Inc.
Crystal structure, morphology, and phase transitions in aromatic polyimide oligomers. 3. Poly(1,4‐phenyleneoxy‐1,3‐phenylene pyromellitimide)
Authors: Liu Jiang , Kim Doyun , Harris Frank W. , Cheng Stephen Z. D. 
Published: April 2003

AbstractAn aromatic polyimide oligomer, poly(1,4‐phenyleneoxy‐1,3‐phenylene pyromellitimide) (PMDA‐3,4'‐ODA), was synthesized from pyromellitic dianhydride (PMDA) and 3,4'‐oxydianiline (3,4'‐ODA) via a melt‐polymerization method. This method permits growth of PMDA‐3,4'‐ODA lamellar crystals and the crystal structure can be studied via electron diffraction (ED) and wide‐angle x‐ray diffraction (WAXD) experiments. Our structure analysis indicates that this polyimide possesses a two‐chain orthorhombic crystal lattice with dimensions of a = 0.848, b = 0.562, and c = 3.365 nm. It has also been found that poly(amic acid) precursors with little imidization possess the same ab lateral lattice packing, but statistical departure from the ordered packing along the c‐direction. Upon increasing the degree of imidization through annealing at elevated temperatures, the order along the c‐axis was progressively enhanced. Increasing the annealing temperature caused the dimensions of the a‐ and the b‐axes to expand while the crystal correlation lengths decreased laterally. Simultaneously the dimension of the c‐axis shrinks with an increase of the crystal correlation length along the chain direction. Crystal morphological study via transmission electron microscopy (TEM) indicates a mainly lamellar crystal texture with different thicknesses depending upon the polymerization conditions. The end lamellar surface is usually smooth. After annealing at elevated temperatures, the lamellar end surfaces become rough, which may be due to chain motion along the c‐axis. The annealed PMDA‐3,4'‐ODA lamellar crystals still show a large amount of defects. © 1994 John Wiley & Sons, Inc.
An analysis of ionic conductivity in polymer electrolytes
Authors: Chung S. H. , Such K. , Wieczorek W. , Stevens J. R. 
Published: April 2003

AbstractConductivities for a wide variety of ionically conducting polymer electrolytes with a range of salt compositions have been investigated over the temperature region Tg to 370 K. When the conductivity data are analyzed as a function of temperature using the empirical Vogel‐Tammann‐Fulcher (VTF) equation a common trend is observed in that deviations in the fits to the data invariably occur in the temperature range 1.2 Tg to 1.4 Tg for all of the samples investigated. This deviation is interpreted as a decoupling of the ions from polymer segmental motion. Recent 23Na NMR and 22Na positron annihilation studies of sodium salt‐based polymer electrolytes support this interpretation with evidence of a change in dynamics at about 1.2Tg. © 1994 John Wiley & Sons, Inc.
Strongly stretched polymer brushes
Authors: Milner Scott T. 
Published: April 2003

AbstractPolymer “brushes” are formed when long‐chain molecules are somehow attached by one end at an interface with a relatively small area per chain. Such adsorbed brushes in the presence of solvent may be used to modify surface properties, stabilize colloidal particles, etc. Strongly segregated block copolymer phases, or interfacial layers of such “polymeric surfactants” may also be modeled in terms of “melt brushes,” (i.e., brushes without solvent). In both cases, when chain attachments are crowded on the interface, the chains stretch out to avoid neighboring chains. The resulting physical state has properties markedly different from polymer solutions, gels, or weakly adsorbed polymer layers. When the chains are strongly stretched, their statistical mechanics become simpler, as fluctuations around the set of most probable conformations are suppressed. This makes possible many pencil‐and‐paper calculations of brush properties, including bending and compressional moduli, and detailed knowledge of the chain conformations. As a recent example, I will describe calculations of phase diagrams of strongly segregated block copolymers including bicontinuous double‐diamond phases. © 1994 John Wiley & Sons, Inc.
Experimental and theoretical analysis of the right angle extrusion of polyethylene at room temperature
Authors: Ashok Babel K. , Moosbrugger J. C. , Campbell G. A. 
Published: April 2003

AbstractIn order to obtain high‐performance polymer and products, processing of crystalline polymers below their softening temperature has been employed and studied in recent years. It has gathered attention, for example, in the area of producing high‐strength polymer rods and filaments of higher cross‐sectional area for special applications. Die drawing and extrusion techniques dominate the processes used to achieve these products. Extrusion is primarily achieved by forcing the polymer through converging dies of circular and other cross‐sections. The methods of solid‐state extrusion processing practiced are primarily ram extrusion and hydrostatic extrusion. In this study, we investigate the process of producing cylindrical rods by ram extrusion of plastics at room temperature. Instead of using a converging die, right angle dies of varying extrusion ratios are employed to extrude three commercial grades of polyethylene. A theoretical analysis is also performed to predict the forces required during extrusion. The theoretical analysis closely follows the methodology presented by Coates et al. for the circular extrusion of polymers below their softening temperatures. ©1995 John Wiley & Sons, Inc.
Rheological and dielectric changes during isothermal epoxy‐amine cure
Authors: Simpson Joycelyn O. , Bidstrup Sue Ann 
Published: April 2003

AbstractDynamic viscosity and ionic conductivity were measured simultaneously during the cure of a digylcidyl ether of bisphenol‐A (DGEBA) epoxy resin with diamino‐diphenyl sulfone (DDS) by mounting a microdielectric sensor into the plates of a rheometer. Two different cure temperatures were examined. Periodically, throughout the cure, samples were removed from the plates of the rheometer, quenched, and analyzed for the glass transition temperature and epoxide conversion. The relationship between conductivity and viscosity appeared to be independent of cure temperature. A linear relation with a slope of −1 was observed between the natural logarithms of conductivity and viscosity during the cure up to approximately 85% cure conversion. It was hypothesized that the reaction rate was hindered by diffusion at this stage in the polymerization. A free volume relationship was used to successfully correlate conductivity with viscosity up to the diffusion limited region. ©1995 John Wiley & Sons, Inc.
Rotor‐synchronized two‐dimensional 13C CP/MAS NMR studies of the orientational order of polymers 2. Melt‐extruded poly(ethylene terephthalate) fibers
Authors: Tzou D. L. , Desai P. , Abhiraman A. S. , Huang T.‐H. 
Published: April 2003

AbstractDetermination of the orientational order of morphological components in polyethylene terephthalate (PET) is sought through quantitative application of two‐dimensional rotor synchronized magic angle spinning (ROSMAS) 13C NMR technique. Previous study in our laboratories had established a procedure for resolution of the carbonyl carbon (CA) and glycol ethylene carbon (GE) resonances into those corresponding to four morphological components.1 Due to paucity of sidebands in the GE resonances, the focus has been on the CA resonances in this attempt to obtain orientation distributions. A set of PET fibers possessing a broad range of crystalline and orientational order has been used to infer the meaning of NMR‐based orientation measurements vis‐a‐vis other techniques. A surprising finding of this study is the observation that the orientational orders of the broad component in the 13C CP/MAS spectrum and the narrow component are very similar in these fibers. ©1995 John Wiley & Sons, Inc.
Ferroelectric and piezoelectric properties of nylon 11/poly(vinylidene fluoride) bilaminate films
Authors: Su J. , Ma Z. Y. , Scheinbeim J. I. , Newman B. A. 
Published: April 2003

AbstractThe ferroelectric and piezoelectric properties of a new class of polymer ferroelectric and piezoelectric materials, nylon 11/polyvinylidene fluoride (PVF2) bilaminate films, prepared by a co‐melt‐pressing method, is presented. The bilaminate films exhibit typical ferroelectric D‐E hysteresis behavior with a remanent polarization, Pr, of about 75 mC/m2, which is higher than the value of 52 mC/m2 observed for PVF2 or nylon 11 films measured under the same conditions. The coercive field, Ec, of the bilaminate films is ∼ 78 MV/m, which is higher than that of either PVF2 or nylon 11 films. Measurements of the temperature dependence of the piezoelectric strain coefficient, d31, and the piezoelectric stress coefficient, e31, were also carried out. The bilaminate films exhibit a piezoelectric strain coefficient, d31, of 41 pC/N at room temperature, which is significantly higher than the PVF2 films (25 pC/N) and the nylon 11 films (3.1 pC/N). When the temperature is increased to 110°C, d31 of the bilaminate films reaches a maximum value of 63 pC/N, more than five times that of PVF2 (11 pC/N) and more than four times that of nylon 11 (14 pC/N) at the same temperature. The piezoelectric stress coefficient, e31, of the bilaminate films shows a value of 109 mC/m2 at room temperature, almost twice that of the PVF2 films (59 mC/m2) and about 18 times that of the nylon 11 films (6.2 mC/m2). Measurement of the temperature dependence of the hydrostatic piezoelectric coefficient, dh, of the bilaminate films also shows an enhancement with respect to the individual components, PVF2 and nylon 11. ©1995 John Wiley & Sons, Inc.
The effect of γ‐irradiation on slow crack growth in polyethylene
Authors: Lu X. , Brown N. , Shaker Manal , Kamel I. L. 
Published: April 2003

AbstractHDPE was γ‐irradiated at room temperature. The resistance to slow crack growth (SCG) was measured in single edge notched tensile specimens under constant load as a function of the dose. The resistance to SCG initially decreased to a minimum value at a dose between 0.05 and 0.10 Mrd. The minimum value was 45% less than for the undosed state. For doses greater than 0.10 Mrd, the resistance to SCG increased up to a dose of 50 Mrd, where its value had increased by a factor of 102. The gel point occurred at 1–3 Mrd. MI and the crack opening displacement exhibited maximum values at a dose of 0.1 Mrd. The behaviors of SCG, MI and crack opening displacement were consistent with the explanation that chain scission dominated for doses less than 0.1 Mrd, and cross‐linking dominated at the higher doses. For doses beyond 50 Mrd, the resin became so brittle that it cracked during the loading of the specimen. Beyond the gel point the density increased from 0.9694 to 0.9716 g/cm3 at a dose of 160 Mrd. ©1995 John Wiley & Sons, Inc.
Effect of sample preparation conditions and degree of neutralization on the dynamic mechanical properties of poly(styrene‐co‐sodium methacrylate) ionomers
Authors: Kim Joon‐Seop , Eisenberg Adi 
Published: April 2003

AbstractA study was undertaken of the effect of sample preparation conditions, especially moisture content, annealing conditions, and degree of neutralization, on the dynamic mechanical properties of poly(styrene‐co‐sodium methacrylate) ionomers. Water plasticizes the ionic cores; however, very small amounts of water do not affect the cluster glass transition mechanism. The study of the annealing effect showed that the morphology of ionomers is fixed during sample molding. No clustering was observed in samples below a degree of neutralization of 50%, possibly due to a decrease in the lifetime of the multiplets. The 50 and 75% neutralized samples showed weak clustering, with the cluster tan δ peaks shifting to higher temperatures with increasing degree of neutralization. The addition of neutralizing agents causes an increase in the size of multiplets; as a result, the strength of the electrostatic interaction between ion pairs increases. The 100–150% neutralized samples showed identical tan δ peaks and also very similar SAXS peaks. Therefore, it is speculated that excess NaOH resides in or near the multiplets and does not affect the electrostatic interaction between ion pairs. The 200–300% neutralized samples showed increased flow above the cluster Tg, as well as a strong small‐angle upturn in the SAXS profile. In agreement with previous results, it appears that in these materials, the excess NaOH resides in the hydrocarbon phase in the form of NaOH crystals, which can act as sites on which the carboxylate ion pairs can reside temporarily; the binding, however, is believed to weaken at high temperatures, which allows flow to occur. The 200% overneutralized Ba2+ sample showed the cluster Tg at much higher temperatures than the 100% neutralized sample, which implies that, for this sample, the stability of the multiplets is higher. © 1995 John Wiley & Sons, Inc.
Transmission electron microscopy of saturated hydrocarbon block copolymers
Authors: Khandpur Ashish K. , Macosko Christopher W. , Bates Frank S. 
Published: April 2003

AbstractContrast for transmission electron microscopy (TEM) of microphase‐separated saturated hydrocarbon diblock copolymers has been obtained using ruthenium tetroxide (RuO4). This technique exploits differences in the rate of transport of the oxidizing stain in rubbery amorphous versus semicrystalline, or glassy, microdomains. Rapid quenching from above the melting (Tm), or glass transition (Tg) temperature is shown to preserve the equilibrium melt morphology in poly(ethylene)‐poly(ethyl‐ethylene) (PE‐PEE), poly(ethylene)‐poly(ethylene‐propylene) (PE‐PEP), and poly(vinylcyclohexane)‐poly(ethyl‐ethylene) (PVCH‐PEE) diblock copolymers; PE melts at 108°C, PVCH is glassy up to about 140°C, while PEE and PEP remain rubbery down to approximately‐20°C and −56°C, respectively. Treatment of ultrathin sections of the quenched specimens with RuO4 vapor led to welldefined TEM images, that revealed microdomain type and order. These results are consistent with SANS data taken under equilibrium conditions. © 1995 John Wiley & Sons, Inc.
Fundamentals of polymer coagulation
Authors: Termonia Yves 
Published: April 2003

AbstractPolymer coagulation is studied by a Monte Carlo diffusion model in which coagulant, solvent, and polymer particles move on nearest neighbor lattice sites according to the change in local interaction energy. Our approach has allowed, for the first time, to describe the coagulation process beyond the initial quench state and to reproduce the wide variety of different polymer structures that can be obtained, ranging from dust‐ to finger‐ to spongelike morphologies. We show that these morphologies are fully controlled by the coagulation rate which is itself strongly dependent on the degree of miscibility between solvent and coagulant. © 1995 John Wiley & Sons, Inc.
Preferential sorption and permeation of binary liquid mixtures in poly (vinyl chloride) membrane by pervaporation
Authors: Okuno H. , Nishida T. , Uragami T. 
Published: April 2003

AbstractPreferential sorptions and pervaporation selectivities in poly (vinyl chloride) (PVC) membrane for various binary liquid mixtures were investigated. Methanol/n‐propanol, benzene/n‐hexane, and ethanol/water mixtures were selected as the binary liquid mixture. In the methanol/n‐propanol mixture, methanol was preferentially sorbed in the PVC membrane and predominantly permeated. In the benzene/n‐hexane mixture, benzene was incorporated and permeated preferentially. In the ethanol/water mixture, ethanol was preferentially sorbed in the PVC membrane and water was preferentially permeated. The preferential sorptions were analyzed according to Mulder's model derived from Flory‐Huggins thermodynamics. The pervaporation selectivity in these systems were discussed using a sorption selectivity and diffusion selectivity. © 1995 John Wiley & Sons, Inc.