bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gelation of Rodlike Polymers
Authors: Russo Paul S. , Chowdhury Aslam H. , Mustafa Mazidah 
Published: March 2011

ABSTRACTSome opportunities for utilizing gelation of rodlike polymers such as poly(p-phenylenebenzobisthiazole) for the production of new materials are described. Morphological studies concerning gels of poly(γ–benzyl–α,L–glutamate) in the solvents toluene, N,N-dimethylformamide and N,N-dimethylformamide/water are reviewed, newly interpreted and extended. A provisional diagram which maps out the gelling behavior in four distinct regions of concentration and temperature concludes the article.
A Model for Nematic Phases in a Reversibly Assembling System of Hard Rods and Plates
Authors: Taylort Mark P. , Berger Alan E. , Herzfeld Judith 
Published: March 2011

ABSTRACT: Liquid crystalline behavior is exhibited by many amphiphilic solutions as a result of the reversible formation of anisotropic aggregates. We model such a system by combining a phenomenological description of aggregation with a lattice statistics calculation of the configurational entropy of a polydisperse collection of hard rods and plates. In this model, nematic liquid crystalline phases of axial, planar and biaxial symmetry are possible. We present a calculated phase diagram, and corresponding particle size distributions, for the case when rod and plate growth are equally favored. Regions of stability are found for axial and planar phases, but not for biaxial phases.
Liquid Crystal-Like Phase Separation in Systems of Macroscopic Rods
Authors: Chick Larry A. , Viney Christopher , Aksay Ilhan A. 
Published: March 2011

ABSTRACTExperiments with monolayers of macroscopic rods indicate separation into isotropic and aligned phases at greater-than-critical concentrations. This behavior is qualitatively similar to that of rodlike liquid crystalline polymers, which in turn has been modelled successfully in threedimensions by Flory and Ronca. We have adapted their approach to predict the ordering of rods in two dimensions. A preliminary phase diagram is presented. The critical rod concentration at which an aligned phase can appear first is a decreasing function of rod axial ratio. Rods of a given axial ratio will phase separate at lower overall concentrations in two dimensions than in three.
Evolved Gas Analysis of Rigid-Rod Polymers
Authors: Jones E. Grant , Pedrick Donald L. 
Published: March 2011

ABSTRACTThe rigid-rod polymer system poly(phenylenebenzobisthiazole), designated as PBZT, has considerable potential in materials engineering. The vacuum thermal behavior of this system and various substituted analogues, including methyl-, phenyl-, and benzothiazolyl-substituted members, has been studied using the combined techniques of thermogravimetry and mass spectroscopy (TG-MS).Primary volatile products identified from the PBZT series include H2S, HCN, CS2, NH3, C6H5CN, C6H4(CN)2, and HSCN. The presence of pendant groups such as methyl, phenyl, or benzothiazolyl results in the evolution of methane, benzene, or benzothiazole in low-temperature degradation processes. The relative abundance and temporal sequence of these gases which are evolved during slow heating in vacuum provide valuable information concerning thermal stability.The implications of the identification and study of evolved gases toward the understanding of the mechanisms of heat treating of rigid-rod polymer systems will be discussed.
Characterization of Polyquinoline Block Copolymer Using Small Angle Scattering
Authors: Wu Wen-Li , Stille John K. , Tsang Joseph W. , Parker Alex J. 
Published: March 2011

ABSTRACTTo determine the compatibility between the rigid rod and the flexible chain polyquinolines, both small angle x-ray and neutron scattering measurements were conducted on a sample containing deuterated flexible components. The scattering intensities from both x-ray and neutron were reduced to absolute scale in order to remove the scattering contribution from microvoids which tended to overshadow the signal of molecular origin. Quantitative information regarding the extent of molecular segregation in a polyquinoline multi-block copolymer was obtained, the result indicated that the material was strongly associated but not segregated into single component phases.
Morphology of Rigid-Rod Molecular Composites: An Overview
Authors: Krause Stephen J. 
Published: March 2011

ABSTRACTRigid-rod molecular composites are a new class of high performance structural polymers which have high specific strength and modulus and also high thermal and environmental resistance. A rigid-rod, extended chain polymer component is used to reinforce a matrix of a ductile polymer with the intent of achieving a “composite” on the molecular level. After synthesis, the key to producing a molecular composite is to control morphology to disperse the reinforcing rod molecules as finely as possible in the matrix polymer. Individual rod molecules or bundles of molecular rods must have dimensions which result in a high ratio of length to width (aspect ratio) for efficient reinforcement. To achieve this, the reinforcing rod component must not phase separate at any stage of processing. Morphological characterization techniques, which can measure the orientation and dispersion (or, conversely, the degree of phase separation) of rod molecules provide the tools for correlating theoretically predicted and experimentally observed mechanical properties. Various morphological techniques which have been applied to molecular composite systems will be reviewed, including wide angle x-ray scattering and scanning and transmission electron microscopy. Structure-property correlations for molecular composite systems will be discussed with regard to models for mechanical properties. Application of new morphological techniques will also be discussed.
Kinetics of Phase Separation in Rigid Rod Polymer and Amorphous Polymer Mixtures
Authors: Nelson Donald S. , Soane David S. 
Published: March 2011

ABSTRACTKinetics of phase separation of PBO in methane sulfonic acid are examined by time-resolved small angle light scattering. Thin films of polymer solutions are spincoated on microscope slides and observed in a controlled environment light scattering cell. These solutions appear to undergo spinodal decomposition, following Cahn- Hilliard type phase separation kinetics upon exposure to water, leading to an exponential increase in the scattered light intensity at short times.
Solid-State Nmr Studies of Molecular Composites and Thermally Cured Copolymers
Authors: Vanderhart D.L. , Tan Loon-Seng 
Published: March 2011

ABSTRACTProton spin diffusion experiments are conducted on two blends of nylon and poly(phenylenebenzobisthiazole) (PBZT). The blends are prepared different ways and utilize either a semicrystalline or fully amorphous nylon. The spin diffusion experiment, which was conducted using three different schemes, yields information about the shortest distances typifying the individual domains. Results suggest that in a 40/60 nylon 6,6/PBZT blend, the nylon and PBZT molecules do not mix on the molecular level, however, each domain is only about 4 nm in its minimum dimension. At the same time, some crystalline nylon regions also exist having somewhat larger dimensions. In contrast, a 50/50 amorphous nylon/PBZT sample, made via a different processing route, showed evidence for similar mixing in only a portion of the material; there was also strong evidence for compositional heterogeneity on a scale larger than 10 nm. The exact stoichiometries describing this compositional heterogeneity could not be uniquely identified on the basis of the spin diffusion studies alone; however the possibilities range from 55% of pure nylon to 35% of pure PBZT being sequestered from the more intimately mixed phase.In a second set of experiments, the 250°C thermal polymerization chemistry of a benzocyclobutene (BCB), a bismaleimide (BMI) and an equimolar mixture of BCB and BMI was studied. These materials are candidates for thermally polymerizable matrix materials in blends with rigid-rod polymers like PBZT. Polymerization of the BCB homopolymer is found to involve multiple pathways and there is reasonably strong evidence that the reactive carbons generated by thermal ring opening of the cyclobutene moiety not only attack one another; they also attack aromatic carbons adjacent to carbonyl carbons at sites far from the ring opening reaction. Spectra of the BCB homopolymer aged at 300°C in vacuum indicate that significant chemical changes occur. This result casts a shadow on the interpretation of the good apparent thermogravimetric stability of the BCB homopolymer in air at this temperature. The equimolar mixture of BCB and BMI ideally can polymerize via the Diels-Alder mechanism to produce a linear chain of alternating BCB and BMI repeat units. The spectrum of this thermally polymerized mixture suggests a maximum of 50% of the reaction following the Diels-Alder addition; the other 50% follows homopolymerization pathways.
Third-Order Optical Susceptibilities of Molecular and Polymeric Materials. Symmetry, Frequency, and Chromophore Structure Dependence as Probed by π-Electron Theory
Authors: Li D. , Marks T. J. , Ratner M. A. 
Published: March 2011

ABSTRACTThird-order optical susceptibilities (γijkl) can be efficiently analyzed for a variety of molecular structures employing perturbation theory and a PPP-SCF-SECI-DECI π-electron model Hamiltonian. The key, frequency tripling second hyperpolarizability γijkl(−3ω;ω,ω,ω) is calculated with full single and double CI. It is found that double excitations play a major role in third-order processes, and that γijkl, like the polarizability αij, is sensitive largely to the overall size (volume) of the π system, although charge transfer excitations may also contribute. The frequency dependence of v and correlations between γijkl and conjugation length are found for a series of trans polyenes.
The Birth of Ordered Polymer Technology for Air Force Applications
Authors: Arnold Fred E. 
Published: March 2011

ABSTRACTSince the late seventies, the Air Force Materials Laboratory and Air Force Office of Scientific Research has had a very energetic program in lyotropic liquid crystalline rigid-rod polymers. The objective of the multifaceted program was the attainment of mechanical properties for a structural material comparable with those currently obtained from fiber reinforced composites. This paper will describe the orgins of this program as derived from the unique aggregation properties of aromatic heterocyclic ladder polymers.
Preparation, Characterization and Conductivity of Li3N, Li3P and Li3As
Authors: Nazri Gholamabbas 
Published: March 2011

AbstractThe superionic conductors lithium nitride and lithium phosphide and the semi-metallic conductor lithium arsenide were synthesized through elemental reactions of lithium melt with nitrogen gas and phosphorus or arsenic powders. A high mobility of the lithium ion was found in this class of compounds. These compounds are hard and brittle and have a dark brown color. The structures of these compounds were studied using x-ray diffraction techniques. All three compounds crystallize in a hexagonal structure with a P6/mm space group. The lattice dimensions expand anisotropically as the size of the anion increases.The ionic and electronic conductivities of the compounds were studied using reversible lithium electrodes and an ion blocking molybdenum electrode. The temperature dependent conductivity measurements (Arrhenius plot) show a high ionic and a negligible electronic conductivity for both lithium nitride and lithium phosphide. However, lithium arsenide shows semi-metallic behavior with a high electronic conductivity. A higher degree of covalency in the ct direction and a more ionic character in x-y plane were observed. The anisotropic nature of the chemical bonds in these compounds provides a shallow potential well in x-y plane and allows the correlated motion of lithium ions.Lithium phosphide and nitride are superionic conductors and useful materials for application in batteries and sensors. Lithium nitride decomposes below 0.5 volts and can be used in low voltage and zero current devices. Lithium phosphide is stable up to 2.2 volts and can be used for higher voltage devices. These compounds decompose in contact with water and are air sensitive.
Ion Conductivity of Nasicon Ceramics: Effects of Texture and Doping With B203 and A12 O3
Authors: Høj Jakob W. , Engell John 
Published: March 2011

AbstractThe Nasiconss, Na1+XZr2SiXP3Xo12 O<X<3, includes some of the best solid state sodium conductors known today. Compositions in the interval 1.6<X<2.6 show conductivities comparable to the best aβ-alumina ceramics. It is well known that the ion conductivity of 8-alumina is strongly dependent on the texture of the ceramic. Here a similar behaviour is reported for Nasicon ceramics. Ceramics of the bulk composition Na2.94 Zr1.49Si2. 20P0.80O10.85 were prepared by a gel method. The final ceramics consist of Nasicon crystals with X=2.14 and a glass phase. The grain size and texture of the ceramics were controlled by varying the thermal history of the gel based raw materials and the sintering conditions. The room temperature resistivity of the resulting ceramics varies from 3.65 103 ohm cm to 1.23 10 ohm cm. Using the temperature comparison method and estimates of the area of grain boundaries in the ceramics, the resistivity of the Nasicon phase is estimated to be 225 ohm cm at 25°C. B203 - or Al2O3 -doping of the glass bearing Nasicon ceramic lower the room temperature resistivity by a factor 2 to 5. The dopants do not substitute into the Nasicon phase in substantial amounts.
Ultrasonic Attenuation Peaks Near the Diffuse Transition Temperature in Solid Electrolytes with Fluorite Structure
Authors: Manasreh M. O. , Pederson D. O. , Aurora T. S. 
Published: March 2011

AbstractMeasurements of the ultrasonic attenuation and velocity have been made in solid electrolytes with fluorite structure, PbF2, BaF2, and CdF2, from room temperature to temperature at or above the diffuse solid electrolyte transition temperature, Tc. The ultrasonic attenuation peaks observed in this class of materials are associated only with the ionic conductivity saturation rather than in combination with crystallographic phase transition found in many other solid electrolytes. The relaxation rates and Arrhenius activation energies for anion motion above the transition temperature were obtained from the temperature dependence of the ultrasonic attenuation and the theory of local site fluctuations. The ultrasonic attenuation peaks observed for the first time in CdF2was used to define the diffuse transition temperature in this material. An Anomalous peak is also observed in the linear thermal expansion coefficient of PbF2.
Peo-Based Polymer Electrolytes Containing Divalent Cations
Authors: Farrington Gregory C. , Yang Hong , Hug Rokeya 
Published: March 2011

AbstractPoly(ethylene oxide) is a non-aqueous solvent which can dissolve high concentrations of a wide variety of monovalent and divalent cation salts. The resulting solutions are generally heterogeneous mixtures of crystalline and amorphous regions. The amorphous components have relatively high ionic conductivities, and PEO ‘quasi-solid’ electrolytes and related polymer materials are arguably a new class of electrolyte, with properties in between those of true solids and true liquids. This paper briefly discusses the preparation and properties of PEO electrolytes containing Mg(II), Zn(II), and Pb(II) salts.
Li ion Conduction in Cross-Linked Peo-LiCF3SO3 Complex
Authors: Tsuchiya Jun 
Published: March 2011

AbstractIonic migration of cross-linked amorphous Poly (Ethylene Oxide)-LiCF3SO3was investigated by measuring ionic conductivity and diffusion coefficient. Pulsed-Field-Gradient NMR (PFG-NMR) was used for the diffusion measurement. The measurements were carried out at a temperature region between room temperature and 120°C. The PFG-NMR mea-surement shows the two modes of migration of both cation(Li) and anion (CF3 SO3-) for specimens containing plasticizer (CH30(CHeiH20)gH3C). The two modes of migration for anion are present for specimens without the plasticizer. Li+ transport number is found to be less than 0.1 for specimens without the plasticizer. Plasticizer is found to increase the Li+ ion transport number.
Fe2+ Electronic Transitions in Raman and Infrared Spectra of FePSe3 and FePS3 Crystals
Authors: Jouanne M. , Sanjuan M.L. , Kanehisa M.A. , Balkanski M. , Cavalli P. , Campagnoli G. , Samoggia G. , Scaglioqti M. 
Published: March 2011

AbstractPolarized Raman scattering and infrared absorption measurements were carried out in FePS3 and FePSe3 as a function of temperature. Features at 700-2000 cm−1 are shown to be essentially due to transitions among the trigonal-field-split 5T2g multiplet of the Fe2+ iron and their phonon sidebands. Though the unpolarized Raman spectra are similar in both compounds, polarized spectra are markedly different. We propose a tentative model to account for this.
Analysis of Transport Phenomena Occurring in Electron-Irradiated Sodium β-Alumina Crystals
Authors: Mariotto Gino , Miotello Antonio 
Published: March 2011

AbstractAuger analysis of sodium β-alumina crystals provides relevant insights concerning Na- transport along the c-axis. In particular, it allows to prove that sodium ion migration is stimulated by electron-irradiation, a result connected to electron-induced relaxation of lattice. Some aspects of the electric fields induced into a dielectric during Auger analysis are discussed.
Hopping Model for the Non-Debye Dielectric Response in Ionic Crystals
Authors: Wang J. C. , Bates J. B. 
Published: March 2011

AbstractA model based on ion hopping in potential double-wells is proposed to explain the non-Debye dielectric response in solids. Relying on some assumptions, an attempt is made to remove the “average” nature of previous diffusion theories. This results in a distribution of activation energies, G(E), which decays exponentially on both sides of some given value E0. It is shown that (a) the existence of a dielectric loss peak is a result of the decay of G(E) for E > E0, (b) the constant-phase-angle behavior above the loss peak is associated with the decay of G(E) for E < E0, and (c) G(E) can produce all the main features of the empirical Havriliak-Negami function. An interesting property of this G(E) is that it broadens with increasing temperature, consistent with many experimental observations.
Hopping Transport in Disordered Systems: Correlation Effects
Authors: Curtin W. A. , Scher H. 
Published: March 2011

AbstractStarting from a Master Equation description of particle hopping between localized sites in a disordered system, we systematically analyze the influence of spatially-correlated hopping (memory) on the excitation transport. Correlations are introduced by accounting exactly for the hopping among a finite cluster of sites which are coupled in an uncorrelated manner to the remaining sites outside the cluster (background). Our results for quantities such as Ps(t). the probability of being at site s at time t for given initial conditions, compare well with simulation results on systems with both e−r and r−6 hopping rates, the agreement improving systematically with increasing cluster size. A simple interpretation of the time development of the cluster-background coupling is seen to be analogous to the overlapping-sphere construction of the percolation path.
The Effect of Substituting Rdf on the Physical and Environmental Properties of Coal Fly Ash
Authors: Mohamad Ashaari B. , Gress David L. 
Published: March 2011

ABSTRACTRefuse-derived-fuel (RDF) consisting mainly of waste paper and plastics is a viable fuel source for the production of power. An experimental test burn partially substituting coal with RDF was undertaken by the Public Service of New Hampshire at the Merrimack Power Station.Five percent and ten percent RDF were substituted, on a BTU basis, for coal in the test bums. The chemical and physical properties of the resulting fly ash were determined. Twelve test burn days were run with 4 days of 5% RDF and 8 days of 10% RDF. Emphasis was placed on investigating the effect of the RDF fly ash on Portland cement concrete.Most of the chemical and physical properties of the coal-RDF fly ash were found to be comparable with ordinary coal fly ash except for the amount of cadmium and lead, the pozzolanic activity index and the compressive strength of fly ash concrete. Cadmium and lead were at average levels of 5.1 ppm and 102.6 ppm for the 5% RDF, and 7.8 ppm and 198.3 ppm for the 10% RDF, respectively. Although the pozzolanic activity index of coal-RDF fly ash increases over normal coal fly ash, preliminary results show that the 28-day compressive strength of concrete with direct replacement of cement and sand decreases by up to 30%. Leaching tests on crushed concrete were conducted to evaluate the environmental effect of acid rain.
Quantification of Fly Ash in Concrete by Image Analysis Techniques: a Preliminary Investigation
Authors: Ferrell Ray E. , Drew Allison W. 
Published: March 2011

ABSTRACTThe fly ash present in concrete mixtures is readily identified with qualitative electron microscope techniques. Quantification of the fly ash present in samples is more difficult. Visual analysis of a representative sample volume can be accomplished in a reasonable amount of time through use of image analysis techniques.Our research efforts have focused on the development of an image analysis technique which uses particle shape and composition to quantify the fly ash present in samples. The resultant binary image is filtered to eliminate the smallest particles and pieces of particles. Shape factor analysis distinguishes spherical fly ash particles from irregularly shaped grains of unhydrated cement clinker. The volume percent of nearly spherical particles is calculated and adjusted to compare the percentage of spherical particles in the matrix of fly ash-containing specimens to the percentage in a control specimen with no fly ash.There is a 2.2-fold increase in the number of spherical particles associated with the substitution of Portland cement by 60 wt% fly ash. Proportional changes in this ratio should be observable in samples with varying amounts of fly ash. The most obvious limitation of the method is related to the requirement that one knows the percentage of high atomic number particles in the fly ash beforehand.
Small Angle Neutron Scattering Studies Of Pore And Gel Structures, Diffusivity, Permeability And Damage Effects
Authors: Allen A. J. , Baston A. H. , Wilding C. R. 
Published: March 2011

AbstractThe pore-gel microstructures of hydrating cement and effects of their interaction with the environment have been studied using the non-destructive technique of small angle neutron scattering (SANS). The results presented for the cement microstructures are statistically representative of such structures over macroscopic sampling volumes.
The Use Of Backscattered Electron Microscopy And Image Analysis To Study The Porosity Of Cement Paste
Authors: Scrivener Karen L. 
Published: March 2011

AbstractIn backscattered electron images of polished sections of cement paste pores can be identified down to a size of about 0.05 microns. Moreover, the contrast between pores and the solid phases is sufficient to allow the pores to be distinguished and quantified by an image analyser. There is a good correlation between measures of porosity obtained by this technique and those obtained by methanol absorbtion methods despite the lower limit to resolution.The bse method can also be used to study the distribution of the porosity in space. However, as only two dimensional sections can be examined, there are difficulties in determining the connectivity by this method. The possibility of using serial section reconstruction is examined and discussed.Despite the difficulty in relating two dimensional characterisation to three dimensional properties, several techniques have been used with some success for sandstones. Results from these techniques for cement paste are presented and discussed.