bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Application of a Coupled Chemical Transport Model in a Trial Assessment of Deep Disposal of Low and Intermediate Level Radioactive Waste
Authors: Liew Steve K. , Economides Vea , Dawes Adrian , Read David 
Published: March 2011

ABSTRACTA series of trial assessments are being undertaken within the United Kingdom to rehearse procedures for post-closure radiological risk analysis of low and intermediate level radioactive waste disposal sites. These trial or “Dry Run” studies draw together workers from a variety of scientific disciplines allowing simultaneous rather than isolated development of assessment procedures. This paper illustrates the use of chemical codes and data within a probabilistic risk assessment framework through a demonstration exercise performed on a hypothetical repository located beneath Harwell, Oxfordshire. The implications for risk assessment practices reliant on the assumption of “conservative” parameters are highlighted by comparison with a more mechanistic approach which takes into account competitive effects.
PGSE-NMR & Sans from TPB Based Microemulsions
Authors: Lindemuth Paul M. , Hammouda Boualem , Duke Joseph R. , Blum Frank D. , Venable Raymond L. 
Published: March 2011

ABSTRACTSelf-diffusion coefficients from pulsed-gradient spin-echo NMR are reported for four components of the tetradecylpyridinium bromide - 85% heptane/15% pentanol - water pseudoternary system. Measurements were taken throughout the inverted microemulsion region and also in a small isotropic region beyond the domain of lamellar liquid crystals. Observations of the self-diffusion coefficients for water relative to those of the surfactant, oil and alchohol show several distinct structural transitions within the water-in-oil region of the phase diagram. The smaller isotropic region exhibits a complete inversion of phase relative to the water-in-oil region. Conductivity measurements were used to further clarify the NMR data. Subsequent small angle neutron scattering (SANS) measurements on the same system show the transition from the single particle (heavy water + Stern layer droplet) scattering regime at low water concentration to the mixed single/interdroplet scattering regime when the intermicellar distance becomes comparable to the size of the micelles.
Curvature Elasticity of Block Copolymers and the Structure of Emulsified Polymer Blends
Authors: Wang Zhen-Gang , Safran S. A. 
Published: March 2011

ABSTRACTWe consider the curvature elastic properties of a layer of block copolymer at the interface between two incompatible homopolymers. We focus on the relation between the relative lengths of the blocks and the elastic properties of the interfacial layer which determines the phase behavior. The curvature elastic moduli K and K, as well as the spontaneous curvature, c0, are obtained. The curvature free energy is used to predict the relative stability of spherical, cylindrical, lamellar, and ordered bicontinuous saddle-shaped structures as functions of concentration and polymer properties.
Nematic-Smectic a Phase-Transition Under Shear Flow
Authors: Bruinsma R. F. , Safinya C. R. 
Published: March 2011

ABSTRACTWe discuss the effect of shear flow on the nematic to smectic A phase transition. The non-Newtonian flow properties (shear thinning and normal stress) ire correlated with the distortions of the structure-factor S(q). As a function of the Deborah number, we find first a deformation of S(q) and, beyond a critical Deborah number, highly distorted, one-dimensional fluctuations. The suppression of fluctuations by shear flow raises the critical temperature.
On Shear Thinning in Dilute Polymer Solutions
Authors: Rabin Yitzhak , Öttinger H. C. , Kawasaki K. 
Published: March 2011

ABSTRACTWhile recent remrmalization group studies predict shear thickening in the limit of large Weissenberg numbers, scaling theories predict shear thinning. The ocntroversy is related to the question whether the Weissenberg number or the shear rate should be kept fixed when taking the limit of infinitely long polymers.
Cooperative Effects in Strained Polymeric Networks
Authors: Deloche B , Sotta P , Herz J 
Published: March 2011

ABSTRACTThe orientational order generated in a polymer network by an uniaxial stress is probed with NMR. The experiments are performed on an end-linked polydimethylsiloxane network. When a uniaxial force is applied a detailed analysis of the spectrum shows that the segmental motions become uniaxial around constraint direction. This experimental fact is explained by shortrange orientational interactions between chain segments.
Colloidal Particles of Noble Metals; A Route to Produce New Materials I
Authors: Hernández R. , Váquez A. , Díaz G. , Avalos M. , José-Yacamán M. 
Published: March 2011

ABSTRACTIn the present paper we report the growth of monometallic and multimetallic particles from the reduction of metal sols. In particular the Au and Au–Pd alloys are reported on this work. A number of techniques are applied to the characterization of the particles. It is shown that particles from few nanometers to 100 pm can be prepared with a number of shapes and morphologies. Particularly conspicuous are the shapes with a five–fold symmetry axis.
Two-Component Grafted Polymer Layers
Authors: Witten T. A. , Milner S. T. 
Published: March 2011

ABSTRACTWe report a theoretical study of the equilibrium statistical mechanics of polymer chains end-grafted in the dense liquid state to a surface. We consider the special features which arise when two immiscible polymer species are present. In constrast to ungrafted polymer blends, this system has two distinct scaling regimes of strong immiscibility: endsegregated and fully segregated. We discuss the mixing energy and bistability properties in each regime using approximations valid for large chain elongation.
Surface Hydrodynamic Modes on Concentrated Polymer Solutions and Gels
Authors: Harden J. L. , Pincus P. A. , Pleiner H. 
Published: March 2011

ABSTRACTWe present a coupled two-fluid model for hydrodynamic surface modes on concentrated polymer solutions and swollen polymer gels. This model is used to investigate such surface modes in the limit of strong coupling. We discuss the form of the modes as a function of polymer concentration and the effects of chain diffusion and surface tension on the nature of these modes.
“Aggregation in Block Copolymer Solutions”
Authors: de la Cruz M. Olvera 
Published: March 2011

ABSTRACTThe ability to produce block copolymers has led to new materials with unique properties. The chemical connectivity of incompatible blocks forces segregation to occur at distances of the order of the block sizes. In block copolymer melts, the segregated domains form periodic ordered structures called microphases. Most block copolymers are strongly incompatible. In such cases, in order to ensure equilibrium microphase separated samples, the microphases are prepared from solution. Microphase separation in semidilute solutions of block copolymers in nonselective good solvent is analyzed. The solvent effects on the thermodynamics in the weak segregation limit are discussed. The concentration of block copolymer at the transition in good solvents, scales as φtN−.62and in ϑ solvents as N−.5. The transitions between microphase morphologies as a function of block copolymer concentration are studied.
Fluctuations in Phases of Membranes
Authors: Roux Didier 
Published: March 2011

ABSTRACTSurfactants in solution may associate into two dimensional aggregates (membranes) which self-organize either in liquid crystalline phases or in liquid isotropic phases made of connected bilayers. When specially designed surfactants or mixture of surfactants are used the elastic modulus of these membranes may be of the order kBT. In this case, thermal fluctuations are important and lead to interesting predictions among which the existence of undulation forces and logarithm corrections to thermodynamical properties, characteristic of fluctuations in two dimensional systems, have been observed experimentally.
Behavior and Influence of Oxygen in Chromium Silicide Formation
Authors: Lien C.-D. , WieluŃski L. S. , Nicolet M.-A. , Stika K. M. 
Published: March 2011

We investigated the redistribution of oxygen after a thermally induced reaction of an evaporated chromium film deposited on an Si<100> substrate. To monitor the redistribution, 18O was implanted in the metal film or in the silicon substrate. Depth profiles were determined by the isotope-specific reaction 18O (p,α) 15N before and after thermal annealing. Silicide formation was monitored by 2 MeV 4He+ backscattering spectrometry.It was found that oxygen in the chromium film remains stationary with respect to the chromium during silicide formation, but oxygen in the silicon substrate accumulates at the silicon-silicide interface. The phase formed is CrSi2, as for the unimplanted reference samples. The effect of oxygen on the rate of silicide formation is much more pronounced when the oxygen is in the silicon substrate rather than in the chromium film. This asymmetry is attributed to the fact that silicon is the dominant diffusing species during CrSi2 formation. These results are contrasted with those for nickel and platinum, where the metal moves in the silicide formed by these metals.
Spectroscopic Characterization of a Pre-Ceramic Polymer For Sic/Tic System.
Authors: Babonneau Florence , Barre Patrice , Livage Jacques , Verdaguer Michel 
Published: March 2011

ABSTRACTPolytitanocarbosilane precursor for SiC/TiC ceramics was characterized by various spectroscopic techniques (29Si and 13C CP MAS NMR, Ti K-edge XANES and EXAFS) in order to follow how titanium ions are incorporated into the polycarbosilane-based polymer. This polymer has been fired in argon atmosphere, and the evolution of the local environments of Si and Ti atoms, during the pyrolysis process, have been followed using 29Si MAS-NMR and Ti K-edge X-ray absorption: this study reveals the formation of Si-O bonds above 500°C, while Ti-C bonds clearly appear around 800°C. Above 1000°C, Si-O bonds are consumed by reaction with excess carbon and the system finally crystallizes into SiC/TiC mixture above 1200°C.
Small-Angle Neutron Scattering and 27Al Nmr Studies on the Microstructure and Composition of Alumina Sol-Gels
Authors: Nazar L. F. , Napier D. G. , Lapham D. , Epperson E. 
Published: March 2011

ABSTRACTWe have used small angle neutron scattering, static light scattering and 27Al NMR to examine the structure and composition of alumina sol-gels formed by the hydrolysis of aluminum alkoxides. For LT sols at low acid concentrations, and HT gels over a wide range of acid concentration, 27Al solution NMR suggests, by the dearth of spectral resonances, that high molecular weight species are being formed. Analysis of the small angle neutron scattering data in the Porod regime indicates these sol-gels exhibit a power-law dependence consistent with mass fractal dimensions ranging from 1.45 to 1.8. These fractal dimensions are consistent with models based on diffusion limited cluster aggregation. The fractal dimensions do not differ significantly between LT and HT sols at the same acid concentration. However, for both temperature regimes, the fractal dimension increases with increasing acid concentration, suggesting a progression to a more compact network. Static light scattering measurements indicate the Guiner radii of the cluster aggregates vary from 600 to 2000Å.
Shear Indxuced order of Cncenirated Dispersions
Authors: Ackerson Eruce J. , Morris T .A. 
Published: March 2011

ABSTRACTThe microstructure or interparticle ordering in concentrated dispersions of colloidal pmma (polymethylnethacrylate) particles in a mixture of tetralin and decalin have been monitored using light scattering techniques. These sterically stabilized, uniformly sized, nearly hard, colloidal spheres are observed to exhibit an equilibrium phase transition from a liquid-like ordering to a crystal-like ordering of suspended particles as the volume fraction of solids increases. The crystals have a close packed - random stacked structure. At the largest volume fractions a nonequilibrium glassy phase results.Samples at different volume fractions are subjected to steady and oscillatory shear flow. Four basic structures are observed to exist: liquid or distorted liquid-like, string-like, sliding or randomly stacked layers, and face centered cubic (FCC) structures. Oscillatory shear studies will be reported here and are made as a function of strain amplitude and shear history, in addition to volume fraction. Generally, oscillatory shear is effective in ordering samples. For example, an unstable FCC ordering can be induced in an equilibrium liquid-like sample.
29Si Nmr Study of Silicon Alkoxides: from the Condensation Kinetics in Solution to the Determination of The Fractal Dimension in Aerogels
Authors: Devreux F. , Boilot J.P. , Chaput F. , Lecomte A. 
Published: March 2011

ABSTRACTThe complete condensation kinetics of three silicon alkoxides have been studied by 29 Si NMR in the conditions of rapid hydrolysis (acidic medium, water in excess). The gelation of the tetravalent TEOS takes several weeks, whereas the trivalent MTEOS and VTEOS do not form gels. From a quantitative data analysis, we deduce that the first steps of the condensation proceed by progressive formation of small organized units. This accounts for the occurence of highly condensed agglomerates, the absence of gelation in trivalent systems and the very slow kinetics (logarithmic function of time). For the tetravalent TEOS, this is followed by an aggregation phase, which leads to gelation. After the gel time, the transformation of the sol fraction into gel has been followed by observing the broadening of the static NMR spectra. Moreover, the structures of the aerogels obtained by hypercritical drying and of the densified materials resulting from further sintering are characterized by MAS NMR. In particular, measurements of the nuclear relaxation in samples doped with paramagnetic impurities give directly the fractal dimension D of the silicate lattice. The measured value is in agreement with that obtained by the SAXS technique in aerogels (D≈2.2) and is close to D=3 for the densified materials.
Molecular Orbital Modeling of Water Adsorption on a Tetrasiloxane Ring
Authors: West J. K. , Wallace S. 
Published: March 2011

ABSTRACTA water molecule hydrogen bonded to a surface SiOH group produces an IR vibrational transmission peak (ν3) at 2.82 μm. Water was adsorbed into the pores of a metal alkoxide derived silica gel monolith, and the increase in the wavelength of the first vibrational overtone (2ν3) of this peak was measured as a function of the adsorbed water content W (g H2O/g SiO2). The peak shifted from 1.390 to 1.420 μm as W increased by 0.14 g/g. Intermediate Neglect of Differential Overlap (INDO) Molecular Orbital (MO) theory was used to model this process. The effect of a H2O molecule, hydrogen bonded to a hydroxylated tetrasiloxane ring, on the structure of the ring and the water molecule was investigated. The bond length of the O-H group H-bonded to the water molecule increased, as expected from the increase in wavelength of the 2ν3 IR peak.
Formation Of Spinel Iron Oxide In Solution
Authors: Jolivet Jean Pierre , Tronc Elisabeth , Belleville Philippe , Livage Jacques 
Published: March 2011

ABSTRACTThe alkalizing of aqueous mixtures Fe111 + xFe11 has been investigated at pH ≈ 8 for 0≤x≤0.5. Three composition zones have been observed. At x<O.l goethite was the only stable product. At 0.1≤x≤0.25 the early stage, characterized as mixed-valent protoferrihydrite, spontaneously transformed into nonstoichiometric magnetite. At x>0.25 the system, made of spinel particles, was homogeneous during all the evolution.
Characterization Of Ultralow-Density Silica Aerogels Made From A Condensed Silica Precursor
Authors: Hrubesah Lawrence W. , Tillotson Thomas M. , Poco John F. 
Published: March 2011

ABSTRACTSilica aerogels having densities in the range of 0.003 to 0.05 g/cm3, have been prepared from a condensed silica formulation involving a two-step hydrolysis/condensation process with tetramethoxysilane (TMOS). This work describes the preparation of these unique ultralow-density aerogels, and compares several of their properties with those of aerogels made by a single step, base catalysed process.
Microstructural Dependence Of Aerogel Mechanical Properties
Authors: Lemay J.D. , Tillotson T.M. , Hrubesh L.W. , Pekala R.W. 
Published: March 2011

ABSTRACTAerogels are highly porous solids derived from the hypercritical drying of covalently crosslinked gels. SEM, TEM and scattering studies reveal that these materials have an open-cell morphology with a solid matrix composed of interconnected colloidal-like particles (30–200 A) Processing variables and synthetic conditions largely determine the microstructure and morphology. In this study, the structure-mechanical property relationships of silica, resorcinolformaldehyde, and carbon aerogels are examined.
The Effects of Hydrolysis Conditions, and Acid and Base Additions, on the Gel-To-Ceramic Conversion in Sol-gel Derived PbTio3
Authors: Schwartz Robert W. , Lakeman C. D. E. , Payne D. A. 
Published: March 2011

ABSTRACTLead titanate was prepared by the sol-gel processing of metal alkoxide solutions. The effects of hydrolysis level (i.e., moles H2O/mole PbTiO3) and acid and base additions (HNO3 or NH4OH) on the properties of desiccated gels, and the gel-to-ceramic conversion, were studied. Microstructural, structural, and physical properties were characterized at three stages of the processing cycle: (i) the desiccated gel state; (ii) the amorphous state, following organic pyrolysis; and (iii) the crystalline state. Differences in the physical and structural properties for the desiccated gels, which were induced through manipulation of the hydrolysis conditions, persisted in the amorphous state after organic pyrolysis. Minor differences remained after crystallization. Variations in material properties, with low temperature processing (e.g., the gel-to-glass transformation), were considered from the standpoint of hydrolysis and additive effects on the gel network structure and consolidation behavior. Data are reported for the densification and crystallization behavior for the gels. Through proper control of hydrolysis conditions, relatively dense ceramics were obtained at temperatures as low as 700°C.
Properties of Films Prepared from Low Surface Area/Density Alumina-Silica
Authors: Hietala S.L. , Smith D.M. , Hietala V.M. , Frye G.C. , Hurd A.J. , Brinker C.J. 
Published: March 2011

ABSTRACTA sol-gel method was used to prepare bulk, closed pore, amorphous alumina-silica. Films
prepared from this 47wt% A12O3-SiO2 composition were examined by SAW, ellipsometry and electrical measurements. The films were found to have a surface area of 1.1 cm2/cm2, a refractive index of 1.44 at 633 nm, and a relative permittivity of 6.2 at 200 KHz. These properties indicate potential applications as hermetic seals, barrier coatings, dielectric layers for capacitors and passivation coatings for electronic circuits.
Molecular Structure Of Metal Alkoxide Precursors
Authors: Sanchez C. , Toledano P. , Ribot F. 
Published: March 2011

ABSTRACTOxo-alkoxides and allied derivatives are the organic counter part of polyanions and polycations. Most of them do not lead to further polymerization and are therefore dead endswhich are grnerally not directly involved in the formation of macromolecular oxide networks. However their well defined structure make them good models for the basic understanding of the first steps of hydrolysis- condensation reactions. The structural characterization of a new metal oxo species Ce6(μ3-O)4(μ3-OH)4(acac)12 obtained via the hydrolysis of acetylacetone modified cerium isopropoxide is presented. Possible mechanisms of formation of this compound as well as for some other titanium Ti6(μ2-O)2(μ3-O)2(μ2-OAc)4(μ2-OPri)6(OPri)6 and niobium Nb8O10(OEt)20 based oxo-alkoxides will be discussed.
Molecularly Modified Alkoxide Precursors for Synthesis of Dielectric Ceramics.
Authors: Phule Pradeep P. , Khairulla Farida 
Published: March 2011

ABSTRACT:Chemical synthesis of titanate and zirconate based multicomponent electronic ceramics using molecularly modified alkoxide precursors is discussed. Controlled chemical polymerization of the modified alkoxides was conducted to prepare multicomponent gels which on calcination at moderate temperatures (700 – 1000°C) formed high purity, ultrafine powders (e.g. BaTiO3, ZrTiO4, LiTaO3). In the sol-precipitation technique modified precursors were used to prepare ultrafine (< 100 nm) and crystalline powders of such ceramics as BaTiO3 and BaZrO3 at low temperatures (< 100°C), under highly alkaline (pH > 13) conditions.
Crystallization of In-Situ SiC-Mullite Composites from Multicomponent Alumina-Silica Gels
Authors: Jagota S. , Parvizi-Majidi A. 
Published: March 2011

ABSTRACTSilica and alumina gels were mixed to make a hybrid of a mullite precursor gel and a silicon carbide precursor gel. The crystallization of these above 1400 °C, to form in-situ composites of silicon carbide whiskers in a matrix of mullite, cristobalite and a glassy phase, was studied for different processing conditions.
Sol-Gel Coatings on Acoustic Wave Devices: Thin Film Characterization and Chemical Sensor Development
Authors: Frye Gregory C. , Jeffrey Brinker C. , Ricco Antonio J. , Martin Stephen J. , Hilliard Janice , Doughty Daniel H. 
Published: March 2011

ABSTRACTWe have investigated the use of porous oxide coatings, formed using sol-gel chemistry routes, as the discriminating elements of acoustic wave (AW) chemical sensors. These coatings provide several unique advantages: durability, high adsorption capacity based on large surface areas, and chemical selectivity based on both controlled pore size and acid/base, ion exchange or chelation chemistry. The porosity of these coatings is determined by performing nitrogen adsorption isotherms using the AW device response to mass changes to monitor the uptake of nitrogen at 77 K. These studies demonstrate how sol-gel chemistry and film deposition can be combined to tailor the microstructure of thin oxide coatings. The chemical sensitivity and selectivity obtained with this class of coatings will be demonstrated using several examples: hydrous titanate ion exchange coatings, zeolite/silicate microcomposite coatings, and surface-modified silicate films.
Crystallization Kinetics Of Metallo-Organics Derived Pzt Thin Film
Authors: Chen K.C. , Mackenzie J. D. 
Published: March 2011

ABSTRACTPZT films on fused silica substrates were prepared by a multiple dipping-firing process from a stable solution of titanium isopropoxide, zirconium n-propoxide and lead 2- ethylhexanoate. The crystallization kinetics of the amorphous PZT films was studied by quantitative X-ray analysis. The crystallization of the amorphous film to perovskite phase
involved a transitional pyrochlore structure phase. The entire crystallization was described by a consecutive phase transformation process in which nucleation dominated.