bluuebunny/crossref_metadata_2025_split huggingface dataset:
Role of Shear in the Isotropic to Lamellar Transition
Authors: Milner S. T. , Cates M. E. 
Published: March 2011

ABSTRACTIn the isotropic to lamellar transition, nonlinear fluctuation terms lower the transition temperature τc and drive the transition first order. Here we show that steady shear, by suppressing the fluctuations, raises τc; in a certain temperature range the lamellar phase can be induced by applying shear. A study of the effective potential indicates that the transition remains first order, though becoming very weak at high shear rate. We argue heuristically that the lamellar ordering first occurs with wavevector normal to both the velocity and the velocity gradient. We estimate the characteristic shear rate for two current experimental systems.
Tracer-Diffusion in Weakly-Ordered Block Copolymers
Authors: Fredrickson Glenn H. , Milner Scott T. 
Published: March 2011

ABSTRACTWe have investigated the self and tracer-diffusion properties of a labeled diblock copolymer in a weakly-ordered lamellar phase. This phase can be a pure copolymer of equal or different molecular weight, or might contain added homopolymer. The spatially-periodic chemical potential field presented by the lamellar phase is capable of strongly influencing the diffusive motion of the tracer. In general, this field serves to slow diffusion, although the manner in which it acts depends on the wavelength of the potential relative to the labeled copolymer radius-of-gyration and on the composition of the copolymer. In the extreme limit of compositional asymmetry of the diblock tracer, we obtain results for the tracer-diffusion coefficient of a homopolymer.
Density Functional Theory of Interactions Between Charged Macroions in Solution
Authors: Stevens Mark J. , Robbins Mark O. 
Published: March 2011

ABSTRACTWe apply density functional theory to the screened interactions between macroions in solution. The approach incorporates the strong correlations between screening ions at high densities, and reduces to the Poisson-Boltzmann equations at low densities. Local density functional theory results for the interactions between parallel planes are within ˜ 1% of Monte Carlo (MC) and inhomogeneous hypernetted chain (IHNC) values when the plane separation L ≥ 50Å. Non-local effects are important for divalent ions at small separations and high surface charge densities. A simple weighted density approximation qualitatively reproduces MC and IHNC results in this regime, and provides a simple explanation for the onset of attractive interactions between like-charged plates.
Structural Properties of Covalently Crosslinked Gels as Probed by Scattering Techniques
Authors: Canda Sauveur J. , Ilnai F. , Schosseler F. , Bastide J. 
Published: March 2011

ABSTRACTThis paper reviews some characteristic results obtained by scattering techniques in two sorts of swollen covalently crosslinked networks : neutral networks swollen by a good solvent and weakly ionized gels. For neutral networks swollen at saturation, the local conformation of the chains was found to be the same as in semi-dilute solutions, whereas some concentration inhomogeneities are observed at larger scale. Ionized gels are characterized by a peak of the structure factor and the absence of long range stationary concentration fluctuations at the concentration of preparation of the gels.
Radial Creeping Flow Between Parallel Disks of Rod-like Nematic Liquid Crystals: Textures and Instabilities
Authors: Rey Alejandro D. 
Published: March 2011

ABSTRACTFour solutions to the Leslie-Ericksen equations for nematic liquid crystals are obtained for pressure-driven radial out-flow between concentric parallel disks and homeotropic director wall anchoring. At low pressure drops the in-plane mode is stable; the centerline director orientation is normal to the flow direction. For each radial distance from the entrance hole there is a critical pressure drop at which the elongational torque twist the director out-ofthe- plane of flow ; left and right rotations are possible. The transition results in the appearance of secondary flows in the azimuthal direction. The radius of the boundary between in-plane and out-of-the-plane modes increases with increasing pressure drops. At higher pressure drops a twist wall develops at the centerline. There is a second critical pressure drop at which the wall collapses with the nucleation and growth of a twist disclination loop. The resulting stable director field is in-plane and flow-aligned throughout the cell.
X-Ray Diffraction Studies of Protein Monolayers Bound to Self-Assembled Monolayers
Authors: Amador S. M. , Pachence J. M. , Fischetti R. , McCauley J. P. , Smith A. B. , Dutton P. L. , Blasie J. K. 
Published: March 2011

ABSTRACTX-ray interferometry was used to study monolayers of the protein yeast cytochrome c and a bimolecular cytochrome c/photosynthetic reaction center complex bound to self-assembled monolayers of 11-trichlorosilylundecyl thiol on inorganic substrates. Optical absorption spectroscopy and dissociation experiments show that the cytochrome c monolayer is covalently attached to the self-assembled monolayer via a disulfide bond and they are consistent with the cytochrome c and its bimolecular reaction center complex forming a close-packed array on the surface of the solid substrate. By sequentially forming these bio-organic monolayers on synthetic inorganic multilayers (“quantum wells”), we were able to determine the electron density profile of the protein layers to ∼13 Å resolution using x-ray interferometry and refinement techniques.
Contact Resistance and Methods for its Determination
Authors: Cohen S. Simon 
Published: March 2011

The problem of low resistance ohmic contacts to silicon has been of considerable technological interest. In recent years this problem has received special attention owing to the effect of scaling in very-large-scale integration (VLSI) technology. The field of ohmic contacts to semiconductors comprises two independent parts. First there exists the material science aspect. The choice of a suitable metallization system, the proper semiconductor parameters and the method of the contact formation is not obvious. Then there is the question of the proper definition of the contact resistance and the way it is measured.Several methods for contact resistance determination have been introduced in the past. All seem to have some drawbacks that either limit their usefulness or raise doubts as to their validity in certain situations. We shall discuss the two-, three- and four-terminal resistor methods of measurement. Relevant theoretical considerations will also be included.For conventional integrated circuits with a moderate junction depth of 1–2 μm, aluminum is uniquely suited as a single-element metallization system. However, for VLSI applications it may become obsolete because of several well-defined metallurgical problems. Thus, other metallization systems have to be investigated. We shall briefly discuss some recent data on several other metallization systems. Finally, the problem of size effects on the contact resistance will be discussed. Recent experimental results suggest important clues regarding the development of alternative metallization systems for VLSI circuits and also point to revisions of estimates of achievable design rules.
Electrodeposition of Nanomodulated Ceramic Thin Films
Authors: Switzer Jay A. , Shane Michael J. , Phillips Richard J. 
Published: March 2011

ABSTRACTElectrochemistry can be used for the atomic-level architecture of ceramic materials. In this report, ceramic superlattices based on the TlaPbbOc/TldPbeOf system were electrodeposited with individual layer thicknesses as thin as 3nm. The superlattices were deposited from a single aqueous solution at room temperature, and the layer thicknesses were galvanostatically controlled. Substitution of Tl2O3 into PbO2 appears to stabilize a face-centered cubic structure with an average lattice parameter of 0.536nm. The lattice parameters for the T1aPbbOc. mixed oxides vary by less than 0.3% when the Pb/Tl ratio is varied from 0.84 to 7.3. Because the modulation wavelengths are of electron mean free path dimensions, this new class of degenerate semiconductor metal-oxide superlattices may show thickness-dependent quantum optical, electronic, or optoelectronic effects.
Magnetic Resonance as a Structural Probe of a Uranium (Vi) Sol-Gel Process
Authors: King Charles M. , Bruce King R. , Ronald Garber A. , Thompson Major C. , Buchanan Bruce R. 
Published: March 2011

ABSTRACTNuclear Magnetic Resonance (NMR) investigations on the Oak Ridge National Laboratory process for sol-gel synthesis of microspherical nuclear fuel (UO2), has been extremely useful in sorting out the chemical mechanism in the sol-gel steps. 13C, 15N, and 1H NMR studies on the HMTA gelation agent (hexamethylenetetramine, C6H12N4) has revealed near quantitative stability of this adamantane-like compound in the sol-gel process, contrary to its historical role as an ammonia source for gelation from the worldwide technical literature. 17O NMR of uranyl (UO2++) hydrolysis fragments produced in colloidal sols has revealed the selective formation of a uranyl trimer, [(UO2)3 (μ3-O)(μ2-OH)3]+, induced by basic hydrolysis with the HMTA gelation agent. Spectroscopic results will be presented to illustrate that trimer condensation occurs during sol-gel processing leading to layered polyanionic hydrous uranium oxides in which HMTAH+ is occluded as an ‘intercalation’ cation. Subsequent sol-gel processing of microspheres by ammonia washing results in in-situ ion exchange and formation of a layered hydrous ammonium uranate with a proposed structural formula of (NH4)2 [(UO2)8 O4 (OH)10]- 8H2)O. This compound is the precursor to sintered UO2 ceramic fuel.
Mechanical Properties of Silica Alcogels and Aerogels.
Authors: Woignier T. , Phalippou J. , Hdach H. , Scherer G.W. 
Published: March 2011

ABSTRACTThe mechanical properties of silica gels (alcogels and aerogels) are measured by three point bending. The elastic moduli (E,G) and the fracture strength (σ) are investigated as functions of the concentration of silicon precursor, the catalysing conditions, and the aging time.Elastic moduli and strength follow scaling laws as a function of the bulk density of the solid. The scaling exponents are discussed in terms of percolation theory.The evolution of the mechanical properties is also followed during the steps of the gel to glass transformation:- hypercritical drying- oxidation of the organic groups-densification heat treatmentAt each step of the process the increases of the elastic moduli and σ are related to the gel structure. During the hypercritical drying flexible “dead ends” in the network can condense and form new links. The connectivity is also enhanced by the removal of the organic groups creating siloxane bonds. Finally densification leads to a material having mechanical properties identical to those of conventional vitreous silica.
Simple Models for Particle Aggregation, Deposition and Segregation
Authors: Meakin Paul 
Published: March 2011

ABSTRACTMost conventional and experimental methods for the formation of ceramic objects involve the manipulation of small particles and/or structures comprised of these particles. Consequently, a better understanding of the physics and chemistry of small particles could contribute to the development of better ceramics. Here the results of some recent computer simulation studies of processes such as particle aggregation, deposition and segregation are surveyed. More realistic models are needed to represent accurately the behavior of most real systems.
Mechanisms of Silica and Titania Colloidal Particle Formation from Metal Alkoxides
Authors: Bailey Joseph K. , Mecartney Martha L. 
Published: March 2011

ABSTRACTControl of the preparation of monodisperse particles for green body formation can be achieved by understanding the growth mechanism. Growth processes for colloidal silica and titania were followed by cryo-TEM, which allows direct observation of the particles in the liquid state. Structural development was tracked by quenching samples at successive reaction times. The preparation of silica particles involved the formation of ramified species which subsequently collapsed after reaching a certain size. In the titania system, initially small dense nuclei are observed which eventually form uniformly textured homogeneous particles.
Rheological and Related Colloidal Aspects of Aqueous Processing that affect the Development of Microstructure
Authors: Bleier Alan , Gary Westmoreland C. 
Published: March 2011

ABSTRACTShear flow in α-A12O3 suspensions having a volume fraction of solids (φ) in the range between 0.17 and 0.50 was investigated between pH 4 and 12. It is Newtonian if the magnitude of the zeta potential exceeds a critical value which depends on φ;its value is 39 mV if φ= 0.40 and 74 mV if φ= 0.50. If this potential is less than the critical value, shear flow is pseudoplastic; its yield value markedly changes (e.g., 0 to >100 Pa) in a slightly φ-dependent, narrow pH range (<0.5 units). If a second oxide, t-ZrO2 , is present, its pH-dependent colloidal behavior governs the overall rheology, though its concentration may be only 11 % that of α-A12O3. Scanning electron microscopy of composite pieces indicates that a detrimental, rheologically detectable interaction between α-Al2O3 and t-ZrO2 can be avoided and the distribution of t-ZrO2 can be optimized during pressure casting by control of pH. Best conditions correspond to either Newtonian flow or pseudoplastic flow with a very low yield value.
Preparation of Multicomponent Ceramic Powders by Sol-Gel Processing
Authors: Bartlett J.R. , Woolfrey J.L. 
Published: March 2011

ABSTRACTSol-gel methods have been applied to the production of the multicomponent ceramic, Synroc B. These techniques involved the hydrolysis of a mixture of Ti and Zr, alkoxides peptising to form a sol and subsequent sorption of Al3+, Ba2+ and Ca2+ cations under acidic conditions. Powder properties were examined by a variety of techniques, including electron microscopy, x-ray diffraction, N2 sorption, and differential thermal analysis. The effects of processing conditions on the physical properties of the powders are discussed.
Base-Catalyzed Silica Gels: Structure and Chemistry
Authors: Garvey Garry J. , Smith Bruce E. 
Published: March 2011

ABSTRACTThe chemical and physical properties of two base-catalyzed silica gels systems were characterized. The sol-gel transition was studied by titration, rheometry, and NMR. Pyrolysis behavior was monitored by TGA and mass spectroscopy. Many characteristics were strikingly similar for the two base-catalyzed systems. However ammonium hydroxide additions resulted in heterogeneities at lower concentrations than ammonium carbonate. Ammonium carbonate enhanced oxidation on pyrolysis.
Catalytic Control of SiO2 Sol-Gel Kinetics - a Mechanistic Study of Bases
Authors: Sanchez Jorge , Reese Mary , Mccormick Alon 
Published: March 2011

ABSTRACTThe aim of this research was to determine the relative effects of three different base catalysts (NaOH, NH4OH, and RbOH) on the rate of gelation of SiO2 from reactive silicon ethoxide solutions in alcohol (the sol/gel method). The time to gelation was determined using a reaction protocol which assured that condensation was the rate controlling step. NMR spectroscopy was used to verify that the nature of the reacting polymers remained similar as the base catalyst was varied. It was determined that under these conditions the condensation reactions avoid diffusional limitations. Furthermore, the base catalyst serves to modulate both the activation energy and also the Arrhenius preexponential factor. This leads to the proposal of a new condensation mechanism.
Organic Catalysts in the Silica Sol-Gel System
Authors: Gallo T.A. , Simms B.L. , Brice V.T. 
Published: March 2011

ABSTRACTEthyl silicate-derived silica gels were synthesized with organic acid and base hydrolysis catalysts. The nature of the organic catalyst was found to strongly affect dry gel structure and carbon content. No consistent relationship between dry gel structure and water content of the calcined gels was identified.
Solvent Selection and the Control of Sol-Gel Reactions
Authors: Jones K , Boulton J M , Emblem H G 
Published: March 2011

ABSTRACTThe hydrolysis and gelation sequence occurring in the formation of a filament or a rigid coherent gel from an organic silicate requires a mutual solvent for the organicsilicate and water if it is to proceed successfully. The solvent is usually a water-miscible alcohol. This alcohol can also be a reaction product, which makes the sequence very solvent dependent. The best control of both hydrolysis and gelation is obtained when the alcohol solvent and the organic silicate each contain the same alkoxy group. The gel resulting is also the best binder for refractory grain. Suitable systems are ethyl silicate and ethanol also isopropyl silicate and isopropanol. The formation of rigid coherent gels, or filaments which on firing convert to ceramic fibres, from hydrolysates of ethyl silicate and aluminium chlorhydrate species is also very solvent dependent. With glycol solvents, aluminium chlorhydrates do not form filaments nor ceramic fibres. With ethanol as solvent, aluminium chlorhydrate-polyol complexes readily form rigid coherent gels and filaments, hence ceramic fibres, because the polyol complex is formed by displacing coordinated water in the aluminium chlorhydrate. This reduces the amount of water available for reaction, which optimises filament and fibre formation.
Preparation of the Porous Supports With SiO2-ZrO2-Na2O Composition.
Authors: Tsurita Y. , Wada K. 
Published: March 2011

ABSTRACTA new method for preparation of porous mixed oxide with SiO2 -ZrO2 -Na2O composition was investigated by heating the sol-gel derived SiO2 microsphere gel in the presence of ZrOCl2 and NaCI. Surface of the -products was composed of sponge-like structure, similar to the porous glasses manufactured by the phase separation method. Their pore volumes ranged from 1.0 to 1.5 cc/g(pore radius 100–lO00Å) and their pore distributions were sharp, with peak tops of about 450–600Å in radius.
Sol-Gel Thin Film Electronic Properties
Authors: Warren W. L. , Lenahan P. M. , Brinker C. J. , Shaffer G. R. , Ashley C. S. , Reed S. T. 
Published: March 2011

ABSTRACTWe have explored the effects of various processing parameters on the dielectric and
electronic integrity of sol-gel derived silicate thin films and have identified several factors that strongly affect the thin film electronic properties. We find that sol-gel dielectrics can exhibit excellent dielectric integrity: viz., low interface trap densities and fairly good insulating properties approaching those of a thermally grown SiO2 film on Si.
Sol-Gel Deposition of Electronic Ceramic Films.
Authors: Bell J.M. , Ben-Nissan B. , Anast M. , West B.O. , Spiccia L. , Cullen J. , Watkins I. , Devilliers D. , Johnston G. 
Published: March 2011

ABSTRACTWe describe a dip-coating method of depositing thin electronic ceramic coatings on various substrates from sol-gel solutions. The solutions we use are alkoxide-based, although the specific formulations depend on the system being deposited. We are working with two electronic ceramic systems: barium titanate on glass, and alumina, and yttrium barium copper oxide on alumina. We discuss methods used to reduce and remove processing defects such as crazing, cracking and pin-holing. We are also studying the effects of varying the processing conditions (dipping, hydrolysis and firing) on the electronic properties of the films. Initial results on BaTiO3 indicate that it is better to deposit thin films (∼0.1 – 0.2μm) and build up the coating thickness by repeated dipping.
Glasses and Multi-Component Sol-Gels for Use as High-Temperature Protective Coatings
Authors: Devore Lauri J. , Osborne Nora R. 
Published: March 2011

ABSTRACTTwo multi-component sol-gel compositions were developed and compared to several commercially available high-temperature glasses. All were then used and characterized as protective coatings for intermetallic titanium aluminide.The sol-gels were studied as thin film coatings and the commercial glasses were studied as enameled coatings. Attention was given to (1) the effect of the application temperature on the original microstructure of the metal, and (2) the role of interfacial conditions between the glass and metal in cyclic and isothermal thermal cycles between ambient temperature and 760°C (1400°F).
The Process of Gel Fiber Formation
Authors: Taneda N. , Kawaguchi T. , Arai D. , Matsuzaki K. 
Published: March 2011

ABSTRACTThe gel fiber formation was studied for the spinnable silica sols prepared from a mixture of TEOS, H2O, EtOH and HNO3 ( 1 : 2 : 2 : 0.01, in mole ratio). The effect of polysiloxane molecular size in the spinning sol on spinnability indicated that the tough skeleton of gel, which is preferable for fabrication of high-strength fiber without breakage, was formed by the selective connection of large size polymers (about 106 in M.W.) during the spinning. It was also found that the smaller size polymers in gel fiber continued to react with water in the atmosphere after the spinning, and attached to the skeleton to strengthen the fiber.
Inhomogeneities In Sol-Gel Coatings
Authors: Fabes. B. D. , Klein. D. L. , Raymond L. J. 
Published: March 2011

ABSTRACTThe structure of sol-gel derived silica coatings was investigated using nanoindentation. chemical etching. and cross-sectional TEM. For coatings heated at 100°C. the surfaces were harder, etched slower, and appeared less porous than the interior of the coatings. For samples fired at higher temperatures (400–800°C). the surfaces remained harder and etched slower than the interior. even though the porosity appeared to be evenly distributed throughout the thickness of the coating. It is proposed that this difference is due to inhomogeneities on two scales in the coatings: bulk porosity and skeletal strain.
Grin Rod of Large Diameter and Large Delta-N
Authors: Yamane Masayuki , Yasumori Atsuo , Iwasaki Mitsunobu , Hayashi Kazutaka 
Published: March 2011

ABSTRACTA gradient-index glass rod of about 13 mm in diameter and 20 mm in length with the refractive index difference of about 0.05 between center and perimeter has been prepared by the solgel process from a precursor solution consisted of tetramethoxysilane, tetraethoxysilane, boron ethoxide and aqueous solution of lead acetate. A bubble free wet gel of about 35 mm in diameter and 50 mm in length was obtained by adding acetic acid to the precursor solution as a buffering agent. The liquid in the micropores of the wet gel was totally replaced with acetone. Then the compositional gradient of lead was formed in radial direction of the gel by soaking in an ethanolic solution of potassium acetate. A transparent r-GRIN rod of about 10 mm in diameter was obtained by the sintering of the gel at 580°C.
Studies on the Reproducible Production of Grin (Gradient Index) Glass Rods By A Sol-Gel Process
Authors: Brian Caldwell J. , Che Tessie M. , Cruse Richard W. , Mininni Robert M. , Nikles Randall E. , Warden Victor N. , Banash Mark A. 
Published: March 2011

ABSTRACTOptical quality radial gradient-index (GRIN) glass can be made by first leaching a TiO2-Al2O3-SiO2 gel in aqueous sulfuric acid solution, then drying and firing the gel. In this paper, we present details of a study on the reproducible production of GRIN glasses by this sol-gel process. Physical and optical data on the intermediate gels and resulting gradient-index glass will be discussed.