bluuebunny/crossref_metadata_2025 huggingface dataset:
High Magnetic Field Phases of the (TMTSF)2X (X = CLO4, PF6) Charge Transfer Complexes
Authors: Brooks J. S. , Fortune N. A. , Chaikin P. M. , Chiang L. Y. , Montambaux G. , Perenboom Jos. A. A. J.
Published: March 2011

The purpose of this talk is to discuss the physical properties of the (TMTSF)2X charge transfer salts in high magnetic fields. This class of materials is of great interest since the effective lower dimensionality and the various ground states are magnetic field dependent at low temperatures. At present, the so-called “standard model” provides a good theoretical description of the low field field induced spin density wave transitions (FISDW). However the reentrance from the last FISDW back to a high field metallic state, and the coexistence of “fast oscillations” in all measured properties, is yet to be accurately described theoretically. The emphasis of this paper is on recent specific heat results which have been obtained on (TMTSF)2ClO4 in magnetic fields as high as 30 T. Here we observe both the reentrant phase transition and the fast oscillations in the specific heat. A main conclusion we draw from our measurements is that the density of states in the reentrant phase is less than it is in the low field metallic state at low temperatures.
Magnetic Evidence for Reentrant Field-Induced Spin Density Waves
Authors: Naughton M. J. , Chamberlin R. V. , Yan X. , Chaikin P. M. , Chiang L. Y.
Published: March 2011

High magnetic field (to 31T) d.c. magnetization measurements on the quasi-one dimensional organic conductor (TMTSF) 2ClO4 yield thermodynamic evidence for the reentrance of a metallic phase from the magnetic field-induced spin density wave state. The H-T phase diagram developed previously from magnetotransport measurements is reproduced from 8 to 26 tesla. The reentrance occurs as a sharp collapse of M(H) to (near) zero magnetization in the high field metal phase. For fields above 27 tesla, deHaas-van Alphen-like oscillations appear, similar to earlier resistance data, as well as other features possibly signifying multiple transitions in the very high field regime.
Sound Velocity Measurements in (Tmttf)2X Salts, X = ReO4, AsF6, SbF6
Authors: Brown S. E. , Javadi H. H. S. , Laversanne R.
Published: March 2011

Young’s modulus E measurements using the vibrating reed technique are reported for salts of the (TMTTF)2X series, where X = ReO4, SbF6, AsF6. All three exhibit softening of the modulus at the structureless transition, with the largest effect in the material with the non–centrosymmetric anion ReO4. The behavior is typical of quadratic coupling to an order parameter plus effects from fluctuations. There is a large stiffening of E below the anion ordering temperature of (TMTTF)2ReO4.
Electron Tunneling in Charge-Density and Spin-Density Waves
Authors: Huang X. Z. , Maki K.
Published: March 2011

First we calculate the tunneling density of states of quasi-two dimensional charge density waves (CDW) or spin density waves (SDW) in the presence of impurity scattering. Second, we consider the tunneling current between two CDWs or two SDWs. We point out the existence of new contribution, which gives rise to the a.c. current when one CDW is sliding relative to the other one.
Fibers of Conducting Polymers: High Electrical Conductivity Combined with Attractive Mechanical Properties
Authors: Andreatta Alejandro , Tokito S. , Smith P. , Heeger A. J.
Published: March 2011

We present a summary of our recent results on the electrical and mechanical properties of fibers made from poly(2,5-dimethoxy-p-phenylene vinylene), PDMPV and poly(2,5-thienylene vinylene), PTV, using the precursor polymer methodology, and from polyaniline, PANI, using the method of processing as polyblends with poly-(p-phenylene terephthalamide), PPTA, from sulfuric acid. The solubility of both PANI and PPTA in H2SO4 presents a unique opportunity for co-dissolving and blending PANI and PPTA to exploit the excellent mechanical properties of PPTA and the electrical conductivity of PANI; we summarize the electrical and mechanical properties of such composite fibers. For PDMPV and PTV fibers, we find a strong correlation between the conductivity and the tensile strength (and/or modulus), and we show from basic theoretical concepts that this relationship is an intrinsic feature of conducting polymers.
Spectroscopic and Molecular Weight Studies of Polytoluidines
Authors: Wei Y. , Hsueh K. F. , Nagy S. , Ray A. , MacDiarmid A. G. , Dykins J. , Epstein A. J. , Wnek G. E.
Published: March 2011

Poly(o-toluidine) and poly(m-toluidine) in base form have been characterized by infrared and lH NMR spectroscopy. Assignments of the proton NMR signals have been facilitated by the use of model compounds. The distinction between benzenoid and quinoid methyl resonances in the NMR permits a semi-quantitative estimation of the oxidation states of the polytoluidines. Infrared studies are consistent with a polyaniline-type backbone having pendant methyl groups. Field desorption mass spectrometry (FD-MS) was employed for estimation of the molecular weight of poly(o-toluidine). Gel-permeation chromatography of the same sample showed a bimodal elution pattern, suggesting that the FD-MS technique detects only the lower molecular weight fraction of the polymer. Despite this inherent limitation, FD-MS yields the interesting information that the polymer contains chains of both odd and even numbers of repeat units, necessitating the coexistence of different oxidation states in the base form of the polymer.
Electrically Conductive Composite of Polyaniline and Poly(p-Phenylene-Terephthalamide)
Authors: Bi Xian-Tong , Wang C. , Bao J. S.
Published: March 2011

The improvement of the processibility and mechanical properties of poly-aniline (PAn) by processing a concentrated sulfuric acid solution of the mixture of chemically prepared conductive PAn powders and poly(p-phenylene-terephthalamide) (PPTA) in different weight ratios are presented.

The concentrated sulfuric acid solution of PAn and PPTA were processed to films and threads, they are liquid crystalline conductive polymer composites, the electrical conductivities of the composites are between 10−4 -10−1 s/cm.

PAn enhanced the tensile strength of PPTA, but does not effect the elongation. The morphology of the PPTA/PAn composite surfaces are fiberlike texture.
Magnetic Properties of Microcrystalline Poly(Phenyl- Diacetylenes) Carrying Radical or Carbene Centers on the Side Chains
Authors: Koga Noboru , Inoue Katsuya , Sasagawa Noriko , Iwamura Hiizu
Published: March 2011

1-Phenyl-l,3-butadiyne derivatives (3 and 4) carrying stable t-butylnitroxide and diazomethyl groups, respectively, have been prepared. Mixed crystals of 3 and the corresponding hydroxylamine 2 (x003c:1:1) polymerized in the solid state at 100°C to give black-violet microcrystals with a metallic luster. A microcrystalline sample of 4 underwent spontaneous polymerization at room temperature when crystallized to give an insoluble polymer which was then photolyzed at cryogenic temperature to generate triplet carbene centers attached to the phenyl rings of the poly(phenyldiacetylene). Some of these microcrystalline polymeric samples were responsive to a magnet at room temperature. Magnetic susceptibility measurements on the two samples revealed only weakly coupled independent spins Hydrogen bonding between the polydiacetylene chains as estimated by X-ray crystal structure of 2 is expected to be effective for increasing the dimension of the spin alignment.
New Second-Order Nonlinear Optical Organic Crystals
Authors: Donald D.S. , Cheng L.-T. , Desiraju G. , Meredith G. R. , Zumsteg F. C.
Published: March 2011

The design of molecular crystals with specific optical properties, which are thought to arise from constituent molecules’ polarizability properties, is a desirable but currently unachievable goal. One can partially achieve this goal by choosing compounds with specific molecular attributes and empirically determining the manner in which these are translated into crystal properties. Besides the fact that there are no certain rules for prediction of crystal packing arrangements, there is also a problem in specifying molecular properties from what are today incomplete polarizability structure-property relationships. We have, realizing these limitations, identified new molecular crystals by a nonlinear optical (powder-SHG) scouting-screening program from lists of compounds chosen because of desirable molecular properties. Examination of successful materials has revealed interesting, new alignment motifs. Some of these materials, a set of halogen and cyano derivatives of aromatic compounds, are described relating properties and structures of molecules and crystals. In particular, the orientation directing influence of intermolecular halogen-cyano interactions and the use of heterocyclic compounds to improve transparency in the near infrared and in the blue and near ultraviolet spectral regions are demonstrated.
Role of Topology in Spin Alignment of Organic Materials
Authors: Itoh Koichi , Takui Takeji , Teki Yoshio , Kinoshita Takamasa
Published: March 2011

It is shown that the spin alignment in organic molecules as determined by single crystal ESR is highly dependent on the topological nature of their molecular pi electron networks. The three topological isomers of a high-spin molecule, biphenyl-n,n′-bis(phenylmethylene), abbreviated as BP-3,3′-BPM, BP-3,4′-BPM and BP-4,4′-BPM are taken as model compounds. BP-3,3′-BPM has a unique spin alignment for which the simple molecular orbital and valence bond methods predict different ground-state spin multiplicities. The above remarkable feature of spin alignment in organic high-spin molecule is interpreted in terms of their spin density distributions which have been determined by a single crystal ENDOR technique and compared with theoretical values calculated on the basis of a generalized Hubbard model as well as the Heisenberg model. This approach is extended to magnetic polymers in order to characterize their structure of the spin sites.
Fused, Three-Ring Donor-Acceptor Molecules as Potential Materials for Efficient Second Harmonic Generation
Authors: McLean Malcolm R. , Badr Mamoun , Dalton Larry R. , Devine Robert L. S. , Steier William H.
Published: March 2011

A series of fused three-ring compounds have been synthesized and characterized for their possible use as organic crystals for second-harmonic generation. Polymer films doped with these compounds were aligned via corona poling and their second order non-linear optical properties compared with layers doped with stilbene like molecules. Values of ¼β0 have been obtained and the effects of different heteroatoms and substituents on λ max and on ¼β0 were examined. An X-ray diffraction crystal structure on one member of the series, 1,2,4-Trichloro-8-nitro-phenoxazin-3-one (Compound 1), revealed a centrosymmetric crystal habit in a P21/n space group, with a = 9.829(3), b = 8.300(2) and c = 15.542(4) Å. Final R(F) = 0.0939 for 754 reflections where I σ; 3σ(I).
Role of High-Spin Molecules as Models for Organic Ferro- and Ferri-Magnets, and Pi-Toporegulated Magnetic Polymers
Authors: Takui Takeji , Endoh Makoto , Okamoto Masayuki , Satoh Kazunobu , Shichiri Toyohiro , Teki Yoshio , Kinoshita Takamasa , Itoh Koichi
Published: March 2011

A chemical modification exploiting functional groups such as ether and methylene as bridges between high-spin assemblies has been carried out as a usable method to increase dimensionality of spin structure. Exchange interaction via an ether or a methylene bridge between two high-spin assemblies has been studied by single-crystal ESR spectroscopy. Whether it is ferromagnetic or antiferromagnetic depends upon the substituted position of the bridge, demonstrating the important role of the topological nature in spin alignment. It turns out that superexchange interaction or hyperconjugation mechanism can dominate spin alignment between high-spin assemblies. Using the criteria obtained, model compounds for units of organic ferrimagnets have been synthesized. They possess antiferromagnetically-exchange coupled heterospins and the salient features of their spin structures are characterized in terms of the spin density distribution as determined by single-crystal 1H-ENDOR (Electron-Nuclear-DOuble Resonance) spectroscopy.
Photoexcitations in Poly(2,5-Thienylene Vinylene)
Authors: Samuel I. D. W. , Brassett A. J. , Colaneri N. F. , Lawrence R. A. , Bradley D. D. C. , Meyer K. E. , Friend R. H. , Murata H. , Tokito S. , Tsutsui T. , Saito S.
Published: March 2011

Poly(2,5-thienylene vinylene), PTV, can be conveniently prepared via a precursor route to give coherent films suitable for optical measurements. Photoexcitation above the band gap at 1.8 eV gives rise to two transient absorption peaks at 0.44 eV and 1.0 eV that are associated with bipolarons that live for times of order a few ms at 80 K. Photoluminescence, comparable in intensity to the Raman scattering, is found at energies above the band edge, and we assign this to a hot recombination process. Pump and probe measurements of the induced bleaching at 2 eV show a very fast rise and initial fall time, which are within the 100 fsec resolution of the measurement.
Theoretical Calculations of the Nonlinear Dielectric Function of Inhomogeneous thin Films
Authors: Risser Steven M. , Ferris Kim F.
Published: March 2011

The dielectric function of inhomogeneous materials is composed of linear and nonlinear responses which are sensitive to the film microstructure as well as the intrinsic properties of the materials. We have developed a method to self-consistently determine the linear and non-linear contributions to the dielectric function of films with random microstructure. This method is based upon a numerical solution of the general electrostatic equations and is applicable to arbitrary shapes and orientations of model defects. This method provides near exact solutions to the linear response of the dielectric function. We have shown that the nonlinear part of the dielectric function is extremely sensitive to the void shape and void fraction.
Organic Polyradical Models for Organic Magnetic Materials
Authors: Modarelli David A. , Rossitto Frank C. , Minato Masaki , Lahti Paul M
Published: March 2011

A variety of model organic high spin molecules based upon coupled phenoxy and phenylnitrene systems has been examined by semiempirical MO-CI theory. Experimental methodology using photochemical and thermal methods in solution and solid phases to generate and study phenoxy groups for investigation of these models is presented.
An Electron Microscopy Study of the Microstructure and Microarchitecture of theStrombus GigasShell
Authors: Laraia V.J. , Aindow M. , Heuer A.H.
Published: March 2011

A scanning and transmission electron microscopy study is presented of the microstructure of theStrombus gigasshell. The heirarchical nature of this crossed-lamellar structure and the defect content of the mineral component are described. This mineral component consists of small single crystal grains of aragonite, the metastable orthorhombic polymorph of CaCO3. The habit and morphology of the grains discussed here have not been determined previously. The observed habit and defect structure suggest that the organic matrix exerts a high degree of control over the crystal growth of the mineral phase and is responsible for the long range order in the microarchitecture. Electron beam heating of the mineral component leads to certain phase changes and these are discussed.
The Microindentation Behavior of Several Mollusk Shells
Authors: Laraia V. J. , Heuer A. H.
Published: March 2011

An investigation of the relationship between structure and mechanical behavior is reported for mollusk shells employing foliated, nacreous, and crossed-lamellar structures by microindentation in the Knoop and Vickers geometries. Indentation damage zones develop crack systems that reflect the micro-architecture. For the crossed-lamellar structure, the system of cracks about the indentation normally developed in a brittle material is suppressed. Previous reports that shells are harder than the corresponding minerals, calcite and aragonite, are confirmed, but it is found that this effect can be strongly dependent on orientation. This anomalous hardness is not an artifact of the identation test technique, since scratch tests confirm the relative hardness of shell over the mineral. It is suggested that microstructural organization is of central importance in producing this hardness, as opposed to intrinsic properties of the mineral or matrix phases.
Composite Biomolecular/Solid State Nanostructures
Authors: Douglas Kenneth , Clark Noel A. , Rothschild Kenneth J.
Published: March 2011

Parallel nanometer molecular lithography has recently been demonstrated to be a parallel fabrication process for structures with features defined by single molecules [1]. In this process two dimensional (2d) monolayer protein crystals are used as patterning elements in the parallel fabrication of structures on the 10nm length scale (nanostructures). The parallelism of this technique is in contrast to such serial fabrication methods as x-ray and electron-beam lithography.
Quantized Diameters in Self-assembled Cyundrical Aggregates of Chlorophylls
Authors: Worcester D. L. , Michalski T. J. , Bowman M. K. , Katz J. J.
Published: March 2011

Neutron small-angle scattering measurements of several different chlorophylls hydrated in deuterated octane-toluene mixtures show that long, hollow cylinders of aggregated chlorophyll are formed. Clear secondary maxima are present in the scattering, and the cylinder diameters are well determined, but depend on the type of chlorophyll. Chlorophyll-a and Bacteriochlorophyll-a were particularly studied, and several samples of each have been measured. Other chlorophylls have also been studied. The results provide strong evidence that chlorophyll cylinders are only certain sizes, with diameters very nearly in the ratio of small integers. Thus, the cylinder diameters appear to be quantized. Neutron scattering results that further test this quantization property are presented here, together with a proposal for the stereochemical features of chlorophyll aggregation which account for the diameter quantization.
Growth-Packed PPT-A Fiber for the Replacement of Native Asbestos
Authors: Yoon Han Sik
Published: March 2011

A now type of crystal that can be defined as a “gel crystal” was first made with oligomeric poly-p-phenyleneterephthalainide (PPT-A), associating a large amount of dimethylacetamide (DMAc) liquid molecules, in which catalytic amount of heterocyclic tertiary amine, coupled with alkali metal cations or phosphoric triamidos are incorporated. Under mechanical orientation of the growing PPT-A, before gelation of the reaction “mixture, a hark agar-like gel crystal is formed. It shows a strong optical birefrin,- gence with four clear extinction positions under crossed polarizers when the gel was sectioned either along the direction of PPT-A orientation or perpendicular to it. When the gel formed without orientation it exhibitil speckled birefringence due to a large number of tiny spherulitic crystallites. The degree of crystalline order was similar to that of lyotropic, nematic liquid crystals when evaluated from X-ray diffractograins. The same type of gel crystals with extinction positions were observed in animal and vegetable tissues. It is assumed that the gel crystal has a threedimensionally ordered molecular network structure in which oligo-PPT-A's are arranged end-to-end in parallel lines. The lines are connected laterally, to form sheets, by DMAc bridges that are linear associations of DMAc molecules, which are connected to the oligo-PPT–A at the CONH groups. PPT-A molecular growth and self-ordering occurs within this gel crystal. A similar process gives rise to wool, cotton and ol.her fibrous biological materials.

The high molecular weight PPT-A fiber thus grown in the gel crystal is constructed with numerous unit fibrils which connect themselves in a three-dimensional network, that resembles native flax or ranie fibers. The molecular growth of PPT-A in the gel crystal reaches ultra high molecular weight that can rarely be attained in ordinary solvent polyinerization. The gel state of PPT-A fibrils are initially formed spontaneously by selfsubdivision of the gel crystal after the molecular growth of PPT-A. Solid fibrils and fibers are finally fortoed by removing DMAc. The PPT-A gel fibrils thus formed resemble closely “the nascent fibril” of cellulose, and the microstructure and morphology of PPT-A fibrils are consequently very similar to those of native cellulose. The thickness of PPT-A fibrils can readily be controlled by the temperature in the gel crystal before fibril formation. The direction of the fibrils depends on the initial orientation of oligo-PPT-A's immediately before the formation of the gel crystal.

This growth-packed PPT-A fibril, that can be produced by a one step chemical reaction, is considered as a good candidate for the replacemerit of native asbestos, because of the lower production cost, microfibrillation property, and inherently high heat-resistance.
Elastomeric Polypeptide Biomaterials: Structure and Free Energy Transduction
Authors: Urry Dan W.
Published: March 2011

The primary, secondary, tertiary and quaternary structures are presented and discussed for elastomeric polypeptides capable of undergoing inverse temperature transitions, that is, these polypeptides fold with the extrusion of water on raising the temperature through a transition. The elastomeric polypeptides, which are comprised of repeating peptide sequences, appear to be dominantly entropic elastomers. As these elastomers exhibit preferred secondary, tertiary and quarternary structure, they are not properly characterized as the random chain networks commonly ascribed to entropic elastomers. Instead, a mechanism of damping of internal chain dynamics on extension is described and referred to as the librational entropy mechanism of elasticity. Indeed, there are emerging a set of structural concepts for elastomeric polypeptides.

Of particular interest is that these elastomers are capable of exhibiting free energy transduction, e.g., thermomechanical and chemomechanical. A principle is stated for thermomechanical transduction and a postulate is given for chemomechanical transduction which is supported by prediction and experimental verification. The underlying mechanism is considered to be an aqueous(hydration) mediated apolar(hydrophobic)-polar interaction free energy which arises out of a competition between apolar and polar groups for limited waters of hydration. In general, there emerges a simple structural perspective of free energy transduction in elastomeric polypeptide biomaterials that involves thermal, mechanical or chemical means of altering the equilibrium between folded and unfolded states, where the folded states are dynamic helices called β-spirals with dominantly hydrophobic intramolecular interturn contacts and the unfolded states have the hydrophobic groups exposed to water.
The Influence of Salivary Proteins on the Growth, Aggregation and Surface Properties of Hydroxyapatite Particles.
Authors: Johnsson M. , Richardson C. F. , Bergey E. J. , Scannapieco F. A. , Levine M. J. , Nancollas G. H.
Published: March 2011

The adsorption and crystal growth effects of salivary cystatin SA-II and non-glycosylated amylase on hydroxyapatite have been compared to the effects of the salivary cystatins SA-I and SA-III. Amylase was the least active HAP crystal growth inhibitor and adsorbed weakly to HAP. Although the three cystatins were active inhibitors of hydroxyapatite crystal growth in supersaturated solution, their affinities showed marked differences.
Bone Formation: The Rules for Fabricating a Composite Ceramic
Authors: Caplan Arnold I.
Published: March 2011

Bone, teeth and shells are complex composite ceramics which are fabricated at low temperature by living organisms. The detailed understanding of this fabrication process is required if we are to attempt to mimic this low temperature assembly process. The guiding principles and major components are outlined with the intent of establishing non-vital fabrication schemes to form a complex composite ceramic consisting of an organix matrix inorganic crystalline phase.
Air Force Applications of Biotechnology
Authors: Hedberg Frederick L.
Published: March 2011

The Air Force has been supporting a number of research and development programs directed at exploring the possibility of utilizing biological processes for the preparation and modification of materials with aerospace applications. Areas addressed by these programs include biosynthesis of key chemical intermediates, biological removal of materials such as paint or sealants, biodegradation for environmentally safe destruction of wastes, and biological leaching and accumulation of strategic metals, utilization of naturally occurring materials with electrooptical properties, and modeling the design of natural structures with synthetic materials.
Multifunctional Macromolecules – Some Device Options
Authors: Worboys Michael R. , Griffith Michael S. , Davies Nicholas A.
Published: March 2011

Multifunctional macromolecules can, in principal, combine a number of active material functions such as optical nonlinearity and photoconductivity in one material. Multifunctionality may offer new options for device fabrication and implementation. However, in practice the implementation of a device which uses a range of material properties such as piezoelectricity and photoconductivity in a single layer of active material is some distance away. This is in part due to the difficulty of optimising a material simultaneously for two separate properties. Therefore the approach we have taken is to identify device configurations which rely on multilayers, each separate layer providing one of the active device functions. Initial results on the fabrication and characterisation of two such proof of principle devices, a light modulated deformable mirror and a light modulated electro-optic layer, are described.
Protective Coatings for High Temperature, Light Weight, Structural Applications
Authors: Covino J. , Klemm K. , Dykema J.
Published: March 2011

Protective coatings for both titanium-aluminum (Ti-Al) alloys and for carbon-carbon (C-C) composites have been synthesized and characterized for high temperature, light weight, structural applications. Coatings of choice must show protection against oxygen and hydrogen in severe environments. Aluminum-silicate glass ceramics were chosen as coating candidates because they are stable to temperatures of 1500°C, are nonreactive to oxygen, and have minimal reactivity with respect to hot hydrogen.
Nanodesigning of Multifunctional Ceramic Composites
Authors: Liu J. , Sarikaya M. , Shih W. Y. , Shih W.-H. , Aksay I. A.
Published: March 2011

Nanodesigning of multifunctional ceramic composites with colloids is discussed from a fundamental point of view. We start with one-component systems, where packing density is the primary concern. Then we extend the discussion to binary systems and deal with the problem of homogeneity. We show that the structure is controlled by the nature of bonding between the particles and by the particle-particle interaction. Surfactants are used to modiy these properties, by, first, protecting the active particle surfaces to prevent solid bond formation, and, second, altering the interparticle interaction to provide a “lubricating” effect. In weakly attractive multicomponent systems, not only are we able to achieve high-density packing through restructuring, but we can also control the scale of homogeneity.
Periodic Area Minimization Surfaces in Microstructural Science
Authors: Thomas Edwin L. , Gido Samuel P.
Published: March 2011

An A/B block copolymer consists of two macromolecules bonded together. In forming an equilibrium structure, such a material may separate into distinct phases, creating domains of component A and of component B. A dominant factor in the determination of the domain morphology is area-minimization of the intermaterial surface, subject to fixed volume fractions. Surfaces that satisfy this mathematical condition are said to have constant mean curvature. The geometry of such surfaces strongly influences material physical properties. We have discovered domain structures in microphase-separated diblock copolymers that closely approximate periodic surfaces of constant mean curvature. Transmission electron microscopy and computer-simulation are used to deduce the three dimensional microstructure by comparison of tilt series with two-dimensional image projection simulations of three-dimensional mathematical models. Two structures are discussed: First is the double diamond microdomain morphology, associated with a newly discovered family of triply periodic constant mean curvature surfaces. Second, a doubly periodic boundary between lamellar microdomains, corresponding to a classically known minimal surface (Scherk's First Surface), is described.
Modelling Microstructiure in Materials that Contain Anisotropic Particles
Authors: Viney Christopher , Chick Larry A.
Published: March 2011

The spontaneous alignment of molecules in liquid crystalline solutions is characteristic of other materials that contain rodlike particles. We are developing a model to predict the evolution of microstructure in these systems. Its starting point is Flory's thermodynamic analysis of liquid crystalline phase separation. Our preferred method dispenses with the traditional lattice model in favor of a Monte Carlo simulation to calculate entropy. Some advantages and consequences of our approach are explored in this paper
Exploratory Studies of New NLO and Piezoelectric Polymers
Authors: Hall H. K. , Padias Anne B. , Fuso Francesco , NI Zhende , Mitchell Michael A. , Leslie Thomas M.
Published: March 2011

Synthetic efforts toward novel NLO and piezoelectric polymers are described. NLO-phores are incorporated in the main chain of a polymer with all the dipoles in the same direction by polycondensation of AB-monomers. The polymers containing p-alkoxy-α-cyanocinnamate units in the backbone show cooperative enhancement of SHG in solution. For comparison, p-thio-α-cyanocinnamate is incorporated in the main chain and in the side chain of polymers. Novel potentially piezoelectric polymers synthesized include polymers containing multicyanocyclobutyl or -cyclopropyl groups and acrylonitrile copolymers.
Design, Characterization, and Optical Properties of Phosphazene-Based Polymers
Authors: Exarhos Gregory J. , Samuels William D.
Published: March 2011

Physical properties intrinsic to linear inorganic polymer systems can be modified through replacement of chemical groups external to the chain backbone. This substitution also perturbs chemical bonding along the chain which can further influence polymer properties. Several phosphazene polymers deposited as thin dielectric films exhibit extended ultraviolet transmission. Second harmonic generation (SHG) has been observed in these polymers as well as in cyclic polymer precursors. The relative magnitude of SHG is found to correlate both with the nature of the substitutional group and molecular conformation. Influence of these parameters on substrate-film adhesion and measured optical properties is discussed in terms of substitutional group electronegativity, and electronic charge localization in the polymer chain which is probed using molecular spectroscopic techniques.
Lognormal Simulation of Pore Evolution During Cement and Mortar Hardening
Authors: Shi Dexiang , Ma Weiping , Brown Paul W.
Published: March 2011

A model to describe the pore sizes in cement paste and mortar, as determined by high pressure mercury intrusion porosimetry, has been developed. The model describes porosity using a compound lognormal distribution. For given material under a given set of curing conditions, the weighing factors and shape parameters of two sub-distributions in the lognormal model may be considered as constants, while the location parameters may be related to curing time and the relationship can be quantified. Therefore, it is possible to predict both the pore size distribution in cement and mortar at any age as well as the evolution in pore size during curing.
Modelling of the Evolution of Porewater Chemistry in a Cementitious Repository
Authors: Haworth A. , Sharland S.M. , Tweed C.J.
Published: March 2011

The current concept for disposal of low- or intermediate-level nuclear waste in the UK includes a largely cementitious backfill. An important factor in determining nuclide release rates from the repository is the pH in the near-field. In this paper, we describe development of a coupled chemistry/transport model of cement degradation and its application in determining the evolution of the chemistry within the repository. In particular, the effect of the cement formulation and interaction with groundwater species on the evolution of the pH is examined. The model is sufficiently flexible to consider a number of different repository scenarios.
Prediction of Radioactive Waste Glass Durability by the Hydration Thermodynamic Model: Application to Saturated Repository Environments
Authors: Jantzen Carol M. , Ramsey W. Gene
Published: March 2011

The effects of groundwater chemistry on glass durability were examined using the hydration thermodynamic model. The relative durabilities of SiO2, obsidian, basalt, nuclear waste glasses, medieval window glasses, and a frit glass were determined in tuffaceous (J–13) groundwater, basaltic (GR–4) groundwater, WIPP–A brine, and Permian Basin brine (PBB–3) using the monolithic MCC–I durability test. In the groundwater–dominated MCC–l experiments, the interaction of the glasses and the initial groundwater (leachant) caused the formation of unique assemblages of secondary phases. The secondary phase formation, in turn, controlled the final groundwater (leachate) pH and ionic strength, I[t].

Correlations of the final leachate pH and I[t] with the Si release from the glass indicated that it is the influence of the secondary phase formation on the leachate pH and I[t] that controls the final dissolution rate of the glass. Since I[t] and the pH of the leachates are functions of the precipitation reactions, inclusion of the experimentally determined solution pH in the free energy of hydration model provides for the functional dependence of the dissolution rate on the secondary precipitation. Therefore, superposition of the linear equation for the groundwater and deionized water experiments occurs and the hydration free energy model can be used to compare glass durability in deionized water and in repository groundwaters.
In-Situ Testing of Nuclear Waste Glasses in a Clay Laboratory - Results After Two Years Corrosion
Authors: Iseghem P. Van , Timmermans W. , Neerdael B.
Published: March 2011

The first retrieval of an in-situ experiment on the interaction waste form - clay host in the underground laboratory under the Mol site has been finished successfully. The test consisted in a two years exposure of various candidate simulated waste glasses at 90°C to Boom clay. The retrieval was done by overcoring. The experimental data showed satisfactorily correspondence between in-situ and laboratory simulation tests both for mass loss and surface analytical data, supporting the validity of the in-situ test as it was performed. The thickness of waste form dissolved within two years varies between 40 and 325 μm (case of the high-level waste glasses), depending on the composition. Matrix dissolution is expected to be the major mechanism of interaction.
The Interaction Between Nuclear Waste Glasses and Clay-II
Authors: Iseghem P. Van , Berghman K. , Timmermans W.
Published: March 2011

The interaction between simulated HLW glasses and clay has been investigated, as part of a larger programme to evaluate the performance of vitrified HLW in repository conditions. Experimental conditions were carefully chosen to simulate repository conditions as close as possible. The glass corrosion seems to be controlled by a diffusion process, but there are indications of a (small) final corrosion rate. The leaching of 134Cs, 90Sr, 239Pu and 241Am is characterized by extremely small mobile concentrations leached (for 239pu and 241Am, below detection limit). The presence of a gamma irradiation field does not increase the glass dissolution. The production of radiolythic hydrogen is strongly reduced by the presence of clay.
R7T7 Nuclear Waste Glass Behavior in Moist Clay: Role of the Clay Mass/Glass Surface Area Ratio
Authors: Godon N. , Vernaz E.
Published: March 2011

R7T7 glass alteration was investigated in the presence of various moist clays. In contact with smectite 4a, selected in France as a potential engineered barrier material, the glass was significantly corroded: after 6 months the glass corrosion rate was practically the same as the initial alteration rate in double-distilled water. Substantially lower alteration was observed in contact with bentonite 6 activated by sodium carbonate.

Smectite 4a consumes silicon released by glass corrosion, and thus retards the rise to high silicon concentrations in solution at which the glass corrosion rate diminishes. Glass can therefore in some cases be altered as much in moist clay as in water with high renewal rates. Other experiments with smaller quantities of smectite 4a showed that the phenomenon becomes less important in time: its duration is proportional to the ratio between the clay mass (C) and the glass surface area (SA). Comparing the results of studies at different C/SA ratios indicates that low glass corrosion rates are obtained more slowly at higher C/SA ratios.

Tests with 239Pu-doped R7T7 glass also showed that the radionuclide retention factor in the alteration film at the glass surface is only 6, compared with a factor of nearly 50 in double-distilled water.
Comparison of Surface Layers Formed on Synthetic Basaltic Glass, French R7T7 and HMI Borosilicate Nuclear Waste form Glasses - Materials Interface Interactions Tests, Waste Isolation Pilot Plant
Authors: Jercinovic Michael J. , Kaser Stacy A. , Ewing Rodney C. , Lutze Werner
Published: March 2011

Materials Interface Interaction Test results for up to 2 years indicate that surface layers formed on synthetic basaltic glass in brine are predominantly Mg-chloride or oxychloride. Layers formed on HMI and R7T7 borosilicate glass are Mg-silicates. Layer thickness increases from 1 year to 2 years for basaltic glass and HMI borosilicate glass. Mg-silicate contains Ni and Zr in amounts that are generally related to the composition of associated glass, but layers formed on basaltic glass also contain Ni and Zr, elements not present in the glass. Ni and Zr are, in part externally derived, however, Ti appears to be completely immobile, and is not found in layers formed on Ti-free glass (R7T7). Some chemical components of the surface layers are derived, in part, from alteration of glass but major components of the layers are from the brine.
Grouts and Concretes for the Waste Isolation Pilot Project (WIPP)
Authors: Wakeley Lillian D.
Published: March 2011

The Structures Laboratory of the U.S. Army Engineer Waterways Experiment Station has conducted research on cement-based composites for the Waste Isolation Pilot Project (WIPP) since 1977, in cooperation with Sandia National Laboratories. Field testing requirements guided initial development of grouts. Concurrent and later laboratory studies explored the chemical stability and probable durability of these mixtures. Beginning in 1985, a series of small-scale seal performance tests at the WIPP prompted development of an expansive salt-saturated concrete. Important lessons learned from this ongoing work include: (1) carefully tailored mixtures can tolerate phase changes involving Ca, Al, and S04, without loss of structural integrity; (2) handling and placement properties are probably more crucial to the mixtures than is exact phase composition; and (3) for the environment of a geologic repository, demonstrated chemical durability will be the best indicator of long-term performance.
A Corrosion Localization Assessment of the Mild Steel Used for Nuclear Waste Package
Authors: Akashi Masatsune , Fukuda Takanori , Yoneyama Hiroshi
Published: March 2011

This paper describes a study of corrosion behavior of a mild steel as a candidate of the high-level nuclear waste package in the geological disposal situations, conducted to establish a model for estimating the corrosion allowance requirement to achieve the 1,000 year lifetime for the package. In several series of galvanostatic tests, the maximum penetration depth and the depth distribution were measured for each specimen with a sophisticated ultrasonic inspection technique. The Gumbel distribution model was successfully used in analyzing each set of data for the maximum penetration depth. Relations among the average penetration depth, the maximum penetration depth, and the corrosion allowance requirement were discussed.
Analytic Studies of Colloid Transport in Fractured Porous Media
Authors: Hwang Y. , Chambré P. L. , Lee W. W.-L. , Pigford T. H.
Published: March 2011

Mathematical models of coupled migration of colloids and solute in fractured, porous medium are presented, for two types of colloid-solute interaction. When the colloid-solute interaction is by dissolution, solute that normally has greater retardation than colloids is accelerated by colloid dissolutions. For sorption interaction, the apparent migration speed of pseudocolloids can be greater or less than the solute migration speed without interaction, depending on the choice of parameters.
Migration of Anionic Species of Radioactive Cobalt through Soil
Authors: Ohnuki Toshihiko , Robertson David E.
Published: March 2011

The migration of an anionic species of 60Co through soil has been examined utilizing data on the migration of radionuclides leached from an aqueous waste disposal site. Correlation coefficients between concentrations of the anionic species of 60Co and those of the particulate, cationic and non-ionic species of 60Co reveal that the anionic species of 60Co was not interconverted from the other species during migration. The cross correlations of changes in the concentrations of the anionic species of 60Co with time between three different down gradient positions give a calculated retardation factor of the anionic species of 60Co of approximately 19, being 1200 times lower than the results of laboratory measurements. The average concentration distribution of the anionic species of 60Co suggests that the migration of the anionic species of 60Co consists of two migration fractions which were driven by different migration mechanisms.
Effective Diffusivity of Carbon Dioxide and Iodine through “G” Tunnel Tuff
Authors: Bardakci Tevfik , King Franklin G. , Sein Maung K.
Published: March 2011

The effective diffusivity of carbon dioxide and iodine through “G” tunnel tuff were determined using a steady-state method and an unsteady-state method respectively. Results show that the effective diffusivity of carbon dioxide and iodine through dry tuff increased with temperature. The effective diffusivity of carbon dioxide decreased as the moisture content of the “G” tunnel tuff increased. An emprical correlation was obtained to estimate the effective diffusivity of carbon dioxide as a function temperature and the percent saturation. Specific surface area and pore volume of tuff was determined using a mercury porosimeter. A scanning electron microscope was utilized to further characterize the porous structure of the tuff samples.
Transport of Gaseous 14C in a Partially Saturated, Fractured, Porous Medium
Authors: Light W. B. , Chambré P. L. , Lee W. W.-L. , Pigford T. H.
Published: March 2011

We predict the transport of 14C from the proposed nuclear waste repository at Yucca Mountain using a porous medium model. Use of this model is justified if the Peclet number, which indicates equilibrium between gas in fractures and liquid in rock pores, is much less than unity. For the assumed release rates, maximum predicted concentrations of 14CO2 in rock near the ground surface are comparable to the USNRC limit for unrestricted areas. Furthermore, dilution near the ground surface as the 14CO2 enters the atmosphere will lower the concentrations by several orders of magnitude. Travel times from the repository to the surface are predicted to be hundreds to thousands of years. For a wide range of the parameters, the release rate from the source has negligible effect on the maximum concentrations at the ground surface.
Analysis of Mass Transport in an Engineered Barriers System for the Disposal of Used Nuclear Fuel
Authors: Garisto Nava C. , Leneveu Dennis M.
Published: March 2011

The Vault Model has been developed to assess the performance of engineered barriers in a conceptual geological disposal vault for used nuclear fuel. It represents container failure, release of radionuclides from used fuel and mass transport of released radionuclides through the clay-based sealing materials surrounding the waste containers. This paper focusses on mass-transport processes represented by the Vault Model, including diffusion, convection and retardation.

In particular, we present results of several scoping calculations carried out with the Vault Model. We consider cases where the clay-based barriers are represented by either a one- or a two-layer system adjacent to an intact rock and a case where the two clay-based barriers are adjacent to a highly fractured rock. These calculations provide insight into the model and produce test cases for comparison with both relatively simple analytical estimates and similar computer codes, as they become available. The analytical estimates generally support the Vault Model results and thus enhance our confidence in the accuracy of the Vault Model calculations.
The Effect of Pressure on the Critical Temperature of Four-Component Microemulsioms
Authors: Goyette Jacques , Bose T. K. , Thoen J. , Lalanne J. R.
Published: March 2011

We present results for the pressure dependence of the critical temperature (dTc/dP) for several microemulsions of n-dodecane, water, n-pentanol and sodium dodecylsulfate with critical points along a criticial line ending at a critical end point (CEP). The variation of dTc/dP as a function of the water to surfactant ratio X shows a nonlinear behavior, with large changes near the CEP, and similar to the X dependence previously observed for the correlation length amplitude ξo. From the negative sign of dTc/dP we also conclude that a possible anomaly in the density must be opposite to the anomaly recently reported for the refractive index.
Molecular-Thermodynamic Approach to Predict Micellar Solution Properties
Authors: Blankschtein Daniel , Puvvada Sudhakar
Published: March 2011

Introduction

In this paper we present a conceptual overview of our recently developed molecular-thermodynamic approach to predict micellization, thermodynamic properties, and phase separation of micellar solutions. A detailed exposition may be found in Ref..
Phase Diagram for Reversibly-Assembled Rod-Like Aggregates: Nematic, Columnar and Crystalline Ordering
Authors: Taylor Mark P. , Herzfeld Judith
Published: March 2011

Aqueous solutions of amphiphilic molecules which reversibly assemble into well defined polydisperse rod-like aggregates display a characteristic sequence of lyotropic mesophases including translational as well as orientational ordering. We have developed a model for such systems which incorporates a phenomenological description of aggregate assembly with a scaled particle calculation of the configurational entropy in the fluid dimensions and a cell theory description of the configurational entropy in the translationally ordered dimensions. The model reproduces many of the features seen in the experimental phase diagrams, including regions of isotropic, nematic, columnar and crystalline stability. In addition to the calculated phase diagram, related aggregate size distributions are reported.