bluuebunny/crossref_metadata_2025_split huggingface dataset:
Prediction and Design of First Super-Strong Mostly-Rigid Polymers from Very Molecular Theories for Smectic and Nematic Polymers
Authors: Dowell F. 
Published: March 2011

ABSTRACTThis paper presents a unique microscopic molecular theory for backbone liquid-crystalline polymers (LCPs), side-chain LCPs, and combined LCPs in the nematic (N) and multiple smectic-A (SA) LC phases and the isotropic (I) liquid phase. There are no ad hoc or arbitrarily adjustable parameters in this theory. The agreement between the theoretical and experimental values for various thermodynamic and molecular ordering properties for existing LCPs is very good (relative deviations between 0% and less than 6.2%). This theory has been used by this author to predict and design (atom by atom, bond by bond) the first super-strong (SS) LCPs. This paper presents the design of SS mostly-rigid (MR) LCPs.
Deformation Micromechanics in Rigid Rod Fibres and Composites
Authors: Young R.J. , Day R.J. , Zakikhani M. 
Published: March 2011

ABSTRACTThe relationship between structure and mechanical properties in as-spun and heat-treated high modulus poly(p-phenylene benzobisoxazole) (PBO) fibres has been examined using a combination of electron microscopy mechanical testing, and Raman microscopy. The structure of the fibres has been determined by obtaining longitudinal sections and electron diffraction from skin and core regions. Well-defined intense Raman siectra werf obtained from individual fibres and three main bands at 1280cm−1, 1540cm−1 and 1615cm−1 have been indentified. It is shown that shifts in Raman bands during straining are a direct reflection of molecular deformation within the fibres.
Compressive Strength of high Performance Fibers
Authors: Kumar Satish , Helminiak T. E. 
Published: March 2011

ABSTRACTSignificant research efforts have been carried out to improve the tensile modulus and tensile strength of high performance carbon and polymeric fibers. Experimental polymeric fibers (ordered polymer fibers) have been prepared with moduli >50 MPSI and tensile strength approaching one MPSI. However, the benefits of the above improvements in tensile properties for aerospace applications are limited because composites of these fibers have low axial compressive strength, which is a direct result of the poor axial fiber compressive strength. The poor axial fiber compressive strength has usually been attributed to the microfibrillar/fibrillar buckling. However, questions concerning the intrinsic limitations at the molecular level and the effects of intermolecular interactions are also considered important. Better understanding of these aspects will help in determining the theoretically achievable compressive strength and may aid in the development of higher compressive strength high performance fibers. These and other issues related to the compressive strength of high performance polymeric and carbon fibers are discussed in this paper.
The Prime Importance of Second-Order Effects in Rigid-Rod Polymers
Authors: Deteresa Steven J. , Farris Richard J. 
Published: March 2011

ABSTRACTThe torsion modulus of high performance rigid-rod polymer fibers is shown to be dependent on axial tensile stress. This behavior is one of at least second-order elasticity. Fiber ultimate tensile strengths are of the same magnitude as torsion moduli, and increases in torsion moduli in excess of 200% were observed for fibers under tension. Consideration of the effect of an axial compressive stress on fiber torsion modulus leads to a prediction of an elastic shear instability that initiates at a compressive stress approximately equal in magnitude to the zero-stress torsion modulus. Hence, it is concluded that the compressive strengths of high performance polymer fibers are limited by the onset of an elastic microstructural instability.
Thermal Stability Of Rigid-rod Polymers
Authors: Denny Lisa R. , Goldfarb Ivan J. , Soloski Edward J. 
Published: March 2011

ABSTRACTOne of the primary factors influencing the research and development of rigid-rod polymers in the Materials Laboratory has been the excellent environmental resistance of this class of aromatic heterocyclic benzobisazole polymers. Thermal stability of these materials has been determined utilizing thermal analytical, Isothermal Aging and combined Thermal Gravimetric-Mass Spectrometry (TG-MS) techniques. Correlations between the thermal stability and chemical structure, varying substituent groups and processing conditions for these polymers have been observed. An overview of the thermal stability of these rigid-rod polymer systems is presented.
Morphology of Rigid-Rod Polymer Fibers: an Overview
Authors: Martin David C. , Thomas Edwin L. 
Published: March 2011

ABSTRACTThe current state of understanding of the morphology of the rigid-rod polymers PBZT and PBZO is reviewed. The morphology is sensitive to both the structure of the rigid polymer molecules and the nature of processing. Structural models of fiber morphology consistent with experiment are presented. An extensive bibliography is included.
Calculations of the Effects of Substituents on the Conformations of Pbzt and Pbo Model Compounds
Authors: Farmer B. L. , Wierschke Scott G. , Adams W. W. 
Published: March 2011

ABSTRACTSemiempirical energy calculations have been used to investigate the conformational properties of poly(p-phenylene benzobisthiazole) (PBZT) and poly(p-phenylene benzobisoxazole) (PBO) having various substituents on the phenyl ring. Substituents considered included methyl, ethyl, t-butyl, hydroxyl, phenyl, and benzthiazole groups. The torsional potential for rotation about the backbone bond joining the phenylene and heterocyclic rings has a significant influence on the conformational energies. X-ray structure data and results of semiempirical molecular orbital calculations were used to determine this critical parameter.The results show that most substituents have surprisingly little influence on the conformations of the molecules. In most cases, the substituent causes a rotation of the backbone rings away from coplanarity, but once the steric interactions are relieved, there is considerable latitude for further rotation. The substituents most effective in locking the molecules into specific conformations were hydroxyl and t-butyl, due, respectively, to the prospect for hydrogen bonding, and non-planarity. In most cases, the conformational freedom is such that packing considerations could significantly influence the conformations of the materials in the solid state.
On the “Lamellar” Morphology of Poly(p-Phenylene Terephthalamide) and Poly(p-Phenylene Benzobisthiazole)
Authors: Roche Eric J. 
Published: March 2011

ABSTRACTRow-nucleated structures in PPTA and PBZT thin films are compared and their dependence upon quench rate and molecular weight illustrated. It is proposed that the lamellar appearance of the morphology is due to a coherent periodic twisting of fibrillar ribbons. The role of crystallosolvate phases is discussed.
A Rigid-Rod Molecular Composile Processed Directly from the Polymerization Medium
Authors: Haghighat R. Ross , Lusignea Richard L. , Vezie Debora L. , Adams W. Wade 
Published: March 2011

ABSTRACTThe goal of this program was to form and demonstrate improved mechanical properties of biaxially oriented films of 30/70 rod-coil polymer blends of PBZT/ABPBT. These polymeric blends were prepared at three different solids contents C<CCR, C≳CCR and C>CCR.Our approach examined PBZT and ABPBT in poly phosphoric acid (PPA) as the common solvent for the first time. Also, we set out to go one step beyond the current state of the art and produce biaxially oriented PBZT reinforced ABPBT molecular composites. Our investigation marked the first time such a study has been attempted. Additionally, fibers of C≳CCR were spun and characterized.
Overview-Rigid Rod Polymers for Nonlinear Optics and Electronics
Authors: Ulrich Donald R. 
Published: March 2011

ABSTRACTIn 1979 the Air Force undertook a program to establish the principles for the design, synthesis, and processing of ultrastructured, electroactive polymers. The promising candidates were determined to be rigid rod polymers. In 1982 this approach was expanded to include the investigation of nonlinear optical properties in rigid rod polymers. The initial results in 1985, demonstrating the concept of multifunctionality, were quite startling. The polymers, PBT and PBO, which were designed as structural polymers with high strength, high modulus, and excellent thermaloxidative stability, were found to possess large nonresonant macroscopic third order optical susceptibilities. Their origin resides in the ultrafast, lossless excitations of highly-charged π- electron states. The state-of-the-art for nonlinear optical rigid rod polymers is reviewed.
Theoretical Studies of the Quadratic Polarizabilities of Rigid-Rod Monomers
Authors: Rondan Nelson G. , Lysenko Zenon , Hwang Wen-Fang 
Published: March 2011

ABSTRACTOne of the requirements in the theoretical determination of optical nonlinearities is the structure of the molecule. Since most of the molecules that we are interested in examining have not been made, we deemed it necessary to determine their molecular geometries. The structures of 2,6-diphenylbenzo[1,2-d:4,5-d']bisoxazole, 2,6-diphenylbenzo[ 1,2-d:5,4-d']bisoxazole, and 2,2'-p-phenylenebisbenzoxazole, and their corresponding donor- and acceptor-substituted derivatives were determined computationally using the AM1 (Austin Model 1) molecular orbital program. The quadratic polarizabilities (β's) of these model compounds were then computed using the CNDO/S (Complete Neglect of Differential Overlap/ Spectroscopy) program and frontier molecular orbital theory. Results from these calculations will be expounded.
Anomalous Dielectric and Non-Linear Optical Response in Main and Side Chain Polymer Nematics and Smectics
Authors: Warner Mark 
Published: March 2011

ABSTRACTI propose that certain, stereo-regular, main and side chain polymer liquid crystals would have a giant, long-time dielectric susceptibility, χ, of unusual temperature dependenceϰ ∼ const.. exp{+h/kBT}with a large ultimate low temperature value χ - χo N where χo is a susceptibility characteristic of a simple dielectric fluid and N the degree of polymerisation. The response would be caused by polarising molecular defects in the nematic ordering; de Gennes hair pins for main chain and torsional defects in side chain polymers. h is the defect energy.Experimentally χ(2) - χo(2) N is known in the non-linear optical response of PBLG, a limiting case of main chain polymers with no hair pins.The timescale for the response of side chain mesogens is predicted to vary as τ ~ N2.
Rigid-Rod Polymer Synthesis: Development of Mesophase Polymerization in Strong Acid Solutions
Authors: Wolfe James F. 
Published: March 2011

ABSTRACTThe development of a method for polycondensation of rigid-rod poly(benzazoles) in poly(phosphoric acid) (PPA) in the lyotropic mesophase has led to an understanding of the synthesis variables that determine the important liquid crystalline product characteristics. These product variables, in turn, control processibility and final fiber or film properties. This paper provides a review of the effects of polymer concentration, solvent composition, polymerization temperature, and monomer purity on two liquid crystalline product characteristics: molecular weight achieved during polymerization, and concentrated solution properties, such as rheological and phase behavior. Central to the understanding of these effects are the factors affecting the polymerization rate. The methods for controlling these synthesis variables are also reviewed. Investigation of alternatives to PPA as the polymerization solvent resulted in a method to obtain high molecular weight poly(2,5-benzoxazole) by adding 40-45 wt % of P2O5 to methanesulfonic acid.
Mesophase-Enhanced Polymerization and Chemo-Rheology of Poly(p-Phenylenebenzobisthiazole)
Authors: Chow Andrea W. , Hamlin Richard D. , Sandell Janet F. , Wolfe James F. 
Published: March 2011

ABSTRACTThe phenomenon of mesophase-enhanced polymerization of the rodlike polymer poly(pphenylenebenzobisthiazole) in polyphosphoric acid was investigated. When the polymer concentration was greater than 5 wt%, the reacting mixture became anisotropic at an early stage of the polymerization. The reaction rate increased significantly at the isotropic-nematic phase transition as the rods were aligned in positions more favorable for the condensation reaction to occur. At 4.5 wt% of polymer, the reacting mixture remained isotropic for up to 1500 min of reaction time. The chemo-rheological properties of the 15 wt% reaction mixture indicate the occurrence of the phase change in either the shear viscosity or the first normal stress difference measurements.
Ionic Properties of Oxide Gels
Authors: Livage J. , Barboux P. , Nabavi M. , Judeinstein P. 
Published: March 2011

AbstractOxide gels are actually hydrous oxides. Water adsorption and dissociation occur at the surface of the oxide network leading to charged particles surrounded by an acid or basic aqueous medium. They can be considered as particle hydrates. Fast proton conduction is observed arising from proton diffusion through the adsorbed water layers. Proton conductivity is actually strongly related to the water adsorption isotherm.Ion exchange readily occurs at the oxide-solution interface when the gel is dipped inside an aqueous solution. Some inorganic gels exhibit a layered structure similar to that of sheet silicates. Ion exchange can then be described as an intercalation process. It can be used as a synthetic route toward new compounds.Electrochemical insertion within the oxide network is highly reversible. This is due to the open structure of the gel and the mixed valence behavior of the transition metal oxide. Reversible cathodes or electrochromic layers have been made from V2 O5, W03or TiO2gels. Thin films or pressed pellets can be easily made from oxide gels. They are therefore good candidates for making "all gel" micro-ionic devices.
Relations Between Structure and Ionic Conductivity of Some Cristobalite-Related Compounds
Authors: Frostiäng Sten , Grîns Jêkabs , Nygren Mats 
Published: March 2011

AbstractA comparative study of the isotypic Na2BeSiO4, Na1.8[Ga0.2Zn0.8]SiO4 and Na1.8[Ga0.2Zn0.8]Ge04 structures has revealed differences in conduction pathway geometries, and calculations show that the two Na-deficient compounds possess larger “bottlenecks”. A conduction mechanism, with Na ions using interstitial sites during migration is suggested.
In-Situ NMR Studies of Lithium Intercalated Electrode Materials Inside All-Solid-State Electrochemical Cells
Authors: Chabre Y. 
Published: March 2011

AbstractPreliminary results of in-situ NMR studies on lithium intercalated electrode materials in all solid state electro-chemical cells are presented. We discuss the interest for such measurements which, as far as we know, have never been reported before. The design of the cells is briefly presented and our results are compared with previous studies on compounds chemically intercalated with the n-butyllithium technique.
Molecular Dynamics Simulation of Mass and Charge Transport in Superionic Conductors, and Structural Correlations in Chalcogenide Glasses
Authors: Vashishta P. , Rino José P. , Kalia Rajiv K. 
Published: March 2011

AbstractStructural properties, single-particle dynamics, and the charge transport are studied in superionic conductor Ag2Se using the molecular dynamics (MD) technique. The calculations are based on a model of interionic potentials in which ions interact through Coulomb interaction, steric repulsion and charge-dipole interaction due to the large electronic polarizability of the selenium ions. Structural and dynamics correlations are studied at five temperatures in the superionic phase. Among the structural correlations the results are presented for partial pair correlation function, coordination numbers, bond angle distributions and wave-vector dependence of the Bragg intensities. Detailed comparison with neutron and x-ray single crystal diffraction experiments. The calculated temperature dependence of the self-diffusion constant of silver is in good agreement with the tracer diffusion measurements. The spectra of velocity autocorrelation functions and the frequency dependent ionic conductivity are calculated. The Haven's ratio is also in good agreement with experiments.Effective interatomic potentials consisting of two-body (steric effect, charge transfer and charge-dipole interactions) and three-body covalent forces are proposed for GeSe2. Using these interaction potentials in MD simulations, the nature of short-range and medium-range order is investigated in glassy and molten GeSe2. All the features in the static structure factor, S(q), including the first sharp diffraction peak (FSDP), are in good agreement with experiments. The FSDP arises from Ge-Ge and Ge-Se correlations between 4-8Å, and the anomalous decrease in its height on cooling is due to frustration enhanced by the increased density.
Electrical Relaxation Studies in Fluorite Oxides
Authors: Sarkar Partho , Nicholson Patrick S. 
Published: March 2011

AbstractElectric relaxation in CeO2-M203 (M34 sY3+, La3+) solid solutions has been investigated as a function of temperature (373K-673K) using the electric modulus formalism in the frequency range 5 to 107Hz. Two relaxation processes are observed in dilute solid solutions. The low frequency process is identified as a long range migration of free oxygen-vacancies (Process A) and the high frequency process is due to reorientation relaxation of the (MceVo) charged associates (Process B). The relaxation process is analysed using a non-exponential decay function, ø(t)=exp[-(t/τo)B] for O<β≤1, of the electric field. The observed activation enthalpy minimum as a function of dopant concentration for the Process A is explained using the concept of incomplete dissociation of oxygen-vacancies from (MceVo) defect associates and the formation of higher-order defect clusters at higher mole% M203.
Early History of Solid State Ionics
Authors: T. Takahashi 
Published: March 2011

AbstractThough the term “Solid State lonics” was named originally by the present author early in the 1960s, solid ionic conductors which are involved in the field of Solid State lonics have been recognized since the mid-nineteenth century. However, room temperature high coniuctivity solid ionic conductors have been studied only after the 1960s. A field of Solid State lonics covers the stuaies of all phenomena of ions in solids, especially solids exhibiting high ionic and electronic-ionic mixed conductivities at fairly low temperatures below their melting points. The applications of these solids are also included in this fiela. Here, only the early history of high conductivity solid ionic conductors which have the longest history in the field of Solid State Ionics is described briefly.
Lithium Insertion Compounds
Authors: Goodenough J.B. , Manthiram A. , James A.C.W.P. , Strobel P. 
Published: March 2011

AbstractThe topotactic insertion/extraction of lithium in layered oxides and sulfides is compared with that in the oxo- and thiospinel frameworks [M2]X4 for both the technical interest of tailoring secondary-battery cathode materials and the scientific interest of exploring narrow-band phenomena and magnetic interactions in compounds and/or phases not accessible by conventional high-temperature techniques. It is pointed out that in layered LiyCoO 2 the higher voltages accessible in oxides is compatible with the higher Li+ -ion mobilities needed in power cells, but that fast three-dimensional Li+ -ion conduction in oxides requires a framework structure such as the monoclinic/orthorhombic Fe2(MO4)3 structure stabilized by M = Mo, W, and S. The influence of the counter cation on the working redox potential is illustrated by a 0.6 eV shift in the Fe3+/2+ redox couple on going from M = Mo or W to M = S.
Sodium and Lithium Intercalation Within The Layered Oxides Na(Li)xMo2O4
Authors: Tarascon J. M. , Colson S. 
Published: March 2011

AbstractThe structural, chemical and electrochemical behavior of the layered molybdate oxides Na(Li)xMo2O4 have been investigated. We found a reversible sodium intercalation process over the range of composition 0.5 < x < 1.9 for the NaxMo2O4 system with 5 single phase domains at x = 0.55, 0.9, 1-1.4, 1.6, and 1.9. We took advantage of the high mobility of sodium diffusion in this compound to exchange sodium for lithium at relatively low temperature (300°C) and to prepare crystallographically pure LixMo2O4. Electrochemical data for the Li system shows that this material, which reversibly intercalates up to 1.7 Li atoms at an average potential of 3.1 volts, is a new promising cathode material for secondary lithium batteries. The ease with which these new molybdate phases can be intercalated is not limited to the alkali metals, since we also were able to intercalate H2O molecules.
Lithium Intercalation in Perovskite and Hexagonal Tungsten Bronze Derivatives
Authors: Delmas C. , Nadiri A. , Flem G. Le , Chang S.H. , Chaminade J.P. , Menetrier M. 
Published: March 2011

AbstractLithium has been intercalated chemically and electrochemically in LnNb3O9 (Ln = La, Nd) perovskite-type phases and LiW3O9F which can be considered as a hexagonal tungsten bronze derivative.The crystallographic formula of the LnNb3O9 starting material is □3/2 (Ln□1/2 )Nb3O9. In both systems, solid solutions are observed in the fir part of the intercalation reaction. While almost all perovskite cavities are filled in the neodymium phases, the higher ionic character of the La-O bonds prevents practically the Li intercalation in the □' sites.In the LiW3O9F phase two lithium atoms can be electrochemically intercalated via a single phase mechanism. The reaction is completely reversible. For higher amounts of intercalation (x > 3), irreversible structural modifications occur.In both systems the unit cell parameter variation is negligible during intercalation. This behavior results from the blocking up of the framework by Ln3+ ions in LnNb3O9 phases or by the stacking of the three octahedra triangular arrangement in the hexagonal tungsten bronze structure.
High Temperature Humidity Sensing Materials
Authors: Tsai Ping Ping , Tanase Shigeo , Greenblatt Martha 
Published: March 2011

AbstractNew proton conducting materials were prepared and characterized for potential applications in humidity sensing at temperatures higher than 100°C by complex impedance or galvanic cell type techniques. Calcium metaphosphate, β-Ca(PO3)2as a galvanic cell type sensor material yields reproducible signals in the range from 5 to 200 nmm Hg water vapor pressure at 578°C, with short response time(-30 sec). Polycrystalline samples of α-Zr(HPO4)2and KMO3P5.8Si2O25, and the gel converted ceramic, 0.10Li2O-0.25P2O5-0.65SiO2as impedance sensor materials show decreases in impedance with increasing humidity in the range from 9 nmn Hg to 1 atm water vapor pressure at 179*C.