bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microphase Separatxon of Charged Diblock Copolymers
Authors: Marko J. F. , Rabin Y. 
Published: March 2011

AbstractThe microphase segregation properties of diblock copolymers composed of a neutral polymer joined to a polyelectrolyte are described. For weakly charged diblocks under melt conditions, we have constructed a theory of weak concentration fluctuations and have used it to study the spinodal instabiity to microphase separation that is driven by incompatibility of the polyion and neutral blocks. As in polyelectrolyte melts, the charging has a strong compatibilizing effect because of the large counterion entropy cost of phase separation. The electrostatic interactions also introduce a new length scale, the Debye screening length, which competes with the free chain radius to determine the microphase wavelength. A scaling theory of the strongly-segregated phase indicates that the salt-free microphases cannot have sharp interfaces beyond a threshold number of charges per chain.
The Polyelectrolyte Brush: Poor Solvent
Authors: Ross Richard S. , Pincus Phil 
Published: March 2011

AbstractWe investigate the end grafted polyelectrolyte brush in the poor solvent regime of the corresponding neutral polymer system. Using Poisson-Boltzmann theory for the electrostatics and Flory-Huggins-mean-field theory for the excluded volume and Van-der-Waals-like monomer interactions, we find the existence of a first order phase transition to a collapsed state for moderate to highly charged polyelectrolytes in the poor solvent regime. Irreversibilities in the disjoining pressure between planar grafted surfaces are predicted. For polyelectrolytes grafted to spherical and cylindrical surfaces with small radii of curvature, the phase transition is predicted to become second order in the infinite molecular weight limit. A phase diagram for the entire poor solvent regime is given.
Selective Formation of Radicals at Polymer-Solvent Interface. A Direct Determination of Solvent Penetration into a Porous Network
Authors: Korb J.-P. , Chachaty C. 
Published: March 2011

AbstractThis work shows that, in studies on porous disordered organic material such as cross-linked resin of poly(4- vinylpyridine, one has to consider a possible interfacial adsorption of solvents. We propose the nuclear relaxation associated with ESR of y-ray induced radicals as an efficient method to estimate the extent of solvent penetration into the interface of the polymer network. This method is however limited to the case where free radicals resulting from solvent-substrate interactions can be selectively generated at interfaces.
Complexing Blends of an Ionomer and a Rigid Rod Polymer
Authors: Shao L. , Weiss R. A. , Lundberg R. D. 
Published: March 2011

AbstractA unique, molecular architecture was developed based on a hydrocarbon soluble backbone with a liquid crystalline side group. Lightly sulfonated polystyrene (SPS) ionomer was complexed with poly(y-benzyl-L-glutamate) (PBLG), an amine terminated synthetic polypeptide, by solution blending in either THF or chloroform. Complexation first occurred by proton transfer from the pendent acid to the amine terminal group. A secondary interaction involved hydrogen-bonding between the sulfonic acid and the carbonyl group on the PBLG chain. This material will have the potential as a molecular composite and unusual solution behavior was observed when the interaction occurred.
The Effect of Molecular Architecture on the Phase Diagram and Mobility of a Polymer Blend Exhibiting a Lower Critical Solution Temperature: Cycles Mixed with Linear Chains.
Authors: Santore Maria M. , McKenna Gregory , Han Charles 
Published: March 2011

AbstractWe examine the role of molecular architecture on the phase diagram of the PS/PVME (poly[styrenel /poly[vinyl methyl ether]) blend, a mixture which in previous studies with linear chains exhibited a lower critical solution temperature, (LCST) i.e. it phase separated on heating. In this investigation, two blends with components exceeding the critical molecular weight for entanglement were compared: one consisting of linear PS and PVME and a second with cyclic PS and linear PVME. Cloud point experiments over a broad composition range reveal that the blend containing cyclic PS undergoes phase separation at temperatures 7-8 °C higher than the analogous linear blend. In other words, the mixture of cycles and linear chains is more thermodynamically stable than the mixture of two linear chains.The LCST nature of the system facilitates examining chain mobility by considering the phase separation kinetics. Time-resolved light scattering studies of blends near their critical compositions tracked the spinodal decomposition following a rapid temperature jump from the one-phase to the two-phase region. An analysis of the scattering intensity growth ultimately led to mutual diffusion coefficients whose temperature dependence confirmed the observed cloud points. An approximation of the second derivative of the free energy function based on SANS studies of the linear PS/PVME blend allowed us to estimate mutual mobilities. The values determined for the cycle-containing blend were considerably lower than those for the blend of linear chains at these molecular weights.
Cellular Automaton Simulation of Polymers
Authors: Smith M. A. , Bar-Yam Y. , Rabin Y. , Margolus N. , Toffoli T. , Bennett C. H. 
Published: March 2011

AbstractIn order to improve our ability to simulate the complex behavior of polymers, we introduce dynamical models in the class of Cellular Automata (CA). Space partitioning methods enable us to overcome fundamental obstacles to large scale simulation of connected chains with excluded volume by parallel processing computers. A highly efficient, two-space algorithm is devised and tested on both Cellular Automata Machines (CAMs) and serial computers. Preliminary results on the static and dynamic properties of polymers in two dimensions are reported.
Threshold Fracture of Networks
Authors: Mazich K. A. , Smith C. A. 
Published: March 2011

AbstractWe discuss the threshold fracture energy, GO, of networks over a wide range of cross-link density. C, for networks with an average number of main chain steps, ςc, that compare favorably with the entanglement spacing, ςc, follow the 1/2 power law, Go - ς1/2. Two views of molecular fracture, one a chain-breaking mechanism and the other a suction process, produce the 1/2 power law. For lightly cross-linked networks (ςc ≫ ςe), Go appears to decrease with increasing ςc. Trapped entanglements limit the extensibility and fracture energy of these networks. Consideration of rupture of trapped entangled chains gives Go -ςc-1/2; this form agrees reasonably well with data at high ςc.
Preparation and Cracterization of Alu1Inur Titanate Plabra Spray Powder
Authors: Shyu L. J. , Brice V. T. , Cambria F. M. , Su B. M. , Tirendi C. , Wandass J. 
Published: March 2011

ABSTRACTAluminum titanate ceramic powder, used in plasma spray coating as a wear resistant material, was prepared from a gel precursor followed by high temperature calcination. The chemically derived gel was made from aluminum sulfate and titanium isopropoxide in an oxalic acid aqueous system. The soluble complex was studied by 13C NMR spectroscopy which showed that the mole ratio of oxalic acid bound to Al and Ti was 2:1. A coprecipitation took place when ammonium hydroxide was added. The gel was examined by solid-state NMR spectroscopy which suggested that aluminum titanium hydroxyl oxalate was present with Al in a distorted octahedral environment. EDX mapping showed that Al and Ti were evenly distributed throughout the gel particles. Thermal analysis indicated that dehydration and combustion of organic groups took place between 100 and 400 ° C. Gel which was heat treated at 1500 °C was identified as a pure AI2TiO5 crystalline phase by XRD.
Synthesis of Rare-Earth-Based Oxides for the Ceramic Industry: From Laboratory to Pilot Plant
Authors: Balachandran U. , Donris S. E. , Lanagan M. T. , Poeppel R. B. , Tourre J. M. , Golowski J. W. 
Published: March 2011

ABSTRACTA wide variety of compounds, e.g., superconductors, chromites, and manganites, can be synthesized by spray drying a mixture of salts or a combination of salts and sols in a flash dryer. The process ensures good control of stoichiometry, morphology, particle size, and surface area. Appropriate particle-growth and synthesis heat treatments of these fine powders have been conducted, and the resultant powders have been evaluated for possible applications in fuel cells and superconductors. The process has been scaled up to a pilot-plant capacity of ≈40 kg per day.
Thermal Reactor Synthesis of Nanoscale Ceramic Powders using Organosilazane Aerosols
Authors: Xiao Tongsan D. , Strutt Peter R. , Gonsalves Kenneth E. , Shankar V. 
Published: March 2011

ABSTRACTThis investigation involves the thermal conversion of an organosilazane precursors into ultrafine ceramic particles. In this process, aerosols of a reactive organosilazane precursor, [CH3SiHNH]nn = 3 or 4, are injected into a hot furnace to obtain Si3N4/SiC ceramic powders. One critical feature examined in this process was the rapidity of the powder synthesis, in a reaction which involves (i) elimination of ligand groups, (ii) formation of ceramic species, and (iii) condensation of ceramic species into ultrafine ceramic particles. Accompanying studies a model has been formulated to determine the gas cooling rate and particle size.
Dip Coating of Boron Nitride Thin Films on Nicalon Fibers
Authors: Shen Lu , Tan Beng Jit , Suib Steven L. 
Published: March 2011

ABSTRACTA process involving dip coating of ceramic fibers in H3BO3 solution followed by reaction with NH3 has resulted in the formation of a BN coating on Nicalon and a carbon coated Nicalon fiber. BN coated C-Nicalon fiber maintained its strength during the coating process, while the BN coated Nicalon did not.
Interpartical Attractions and the Mechanical Properties of Colloidal Gels
Authors: Rueb C. J. , Zukoski C. F. 
Published: March 2011

ABSTRACTThe influence of the strength of interparticle attractions on the mechanical properties of colloidal gels is explored. As attractions increase, suspensions gel. At the gel point the zero shear rate viscosity diverges while the low frequency modulus becomes measurable. In addition at the gel point, storage and loss moduli were of the same order and displayed power law sealing on oscillation frequency. With much stronger attractions, the critical strain required to rupture the gel scales in a power law manner or elastic modulus. These observations are discussed in terns of recently developed models of gel fonnation and dynamics.
Three Dimensional Printing: Surface Finish and Microstructure of Rapid Prototyped Components
Authors: Lauder A. , Cima M.J. , Sachs E. , Fan T. 
Published: March 2011

ABSTRACTThree Dimensional Printing is a process for rapid prototyping of functional components. Thin layers of powder are bound in selected areas by ink-jet printing of a liquid binder. Layers are added sequentially until a three dimensional part is completed. The unbound powder is then removed. The raster scan pattern and layering used in forming has an observable effect on the surface finish and microstructure of the part, as does the chemistry of the particular materials system used. Important phenomena include ballistic interaction of the jet with the powder bed and wicking of the binder. Process parameters such as layer height, flow rate, and powder density were studied. Microstructural examination of the printed components is also reported.
Characterization of the Products of the Pyrolysis of Inorganic Polymers Used as Dispersants
Authors: Samuels William D. , Exarhos Gregory J. , Burton Sarah D. , Tarasevich Barbara J. , Stasko Daniel J. 
Published: March 2011

ABSTRACTA series of alumina particles coated with inorganic polymers, that have utility as preceramic dispersants, have been pyrolyzed and the products of the pyrolysis studied to help determine the possible decomposition routes. The inorganic polymers, bis(amino)polyphosphazenes and siloxanes, appear to undergo loss of the organic sidechains via a nucleophilic process which would incorporate inorganic backbone into the alumina matrix. The bis(alkoxy)polyphosphazenes decompose by nucleophilic attachment but also exhibit polymer loss by formation of cyclic oligomers.
Effect of Silicon Exposure on Pyrolysis of Preceramic Polysilazane
Authors: Han Helen N. , Lindquist David A. , Haggerty John S. , Seyferth Dietmar 
Published: March 2011

ABSTRACTPreceramic polysilazane was added to high purity Si powders as a reactive binder during synthesis of reaction bonded Si3N4parts to improve the defect structures in both the unfired and nitrided parts. This study examined how the presence of Si powder affected the polymer-to-ceramic transformation of the polysilazane. Pyrolysis of both polysilazane and polysilazane+Si samples were characterized by TGA. Also, the gaseous volatiles evolved during pyrolysis were characterized by infrared and mass spectrometry. Results show that between 100- 550°C, silicon powder inhibits the loss of silazane oligomers from the polysilazane. However, for temperatures above 550°C, the weight loss differences between the pure polysilazane and the polysilazane+Si samples were less pronounced. Specific solvents used in the preparation of the polysilazane+Si mixtures affected the quantity and type of species in the volatiles during pyrolysis.
Microscopy Studies of Sol-Gel Derived Lithium Niobate
Authors: Joshi Vikram , Goo Grace K. , Mecartney Martha L. 
Published: March 2011

ABSTRACTLithium niobate prepared by sol-gel techniques can crystallize at temperatures as low as 200°C, and achieve a high homogeneity. In this sutdy, nucleation, crystallization, and morphological development are examined by TEM for alkoxide derived LiNbO3. Preliminary studies show that the as-dried gel is completely amorphous and homogeneous. Between 150-200°C, crystallization begins with crystallites on the order of 10-20 nm appearing in the amorphous matrix. By 450°C, single crystal spheroidal particles (0.05 - 0.2 gm) form. By 600°C, facetted large crystallites on the order of 1 gtm develop. Grain size and porosity are strongly dependent on the amount of water of hydrolysis in thin films.
Sintering of Glass Powder Packings with Metal Inclusions
Authors: Jagota A. , Boyes E.D. , Bordia R.K. 
Published: March 2011

ABSTRACTThe sintering of glass powder packings with metal inclusions has been studied using (a) a loading dilatometer, and (b) an in-situ SEM hot-stage. The addition of a small volume fraction of metal particles unexpectedly increases the sintering rate of the composite. With a further increase in the volume fraction of inclusions the sintering rate decreases rapidly to zero at a well-defined threshold. The in-situ sintering experiments have been used to observe the sintering mechanisms and to determine the parameters that contribute to this phenomenon: to assess the distribution of inclusions, and the nature of inclusion-inclusion and matrix-inclusion interaction. Predictions of the effective sintering rate are computed using a truss model with randomly distributed inclusions. The computations capture accurately the decrease in sintering rate (beyond the initial increase) with increasing volume fraction of inclusions. The initial increase is attributed to a reduction in viscosity of the glass due to chemical interaction with the metal.
Effect of Whisker Distribution on the Densification and Microstructures of AI2O3-Si3N4 Composites
Authors: Tseng W.J. , Funkenbusch P.D. 
Published: March 2011

ABSTRACTThis study focuses on (1) the co-dispersion behaviors of dissimilar phases exhibiting different surface chemistry in ceramic suspensions and (2) the effect of local whisker distribution on matrix densification. Si3N4 whiskers and Al2O3 powders are mixed and slipcast in aqueous solution. Local whisker clusters are observed and remain stable even after prolonged sintering. High shear-rate agitation of the composite suspension does not eliminate the whisker agglomeration. Surface pre-treatment of whiskers, such as acid/base-washing, effectively reduces the clustering and sintered flaw size. From SEM observation it is found that the matrix powder densifies highly inhomogeneously because of the constraint imposed by the reinforcement. Matrix powder is inhibited from diffusing into “inter-whisker” voids.
Aluminothermic Synthesis of Al2O3/ZrO2/SiC Composite Powders
Authors: Erauw J.P. 
Published: March 2011

ABSTRACTThe synthesis of Al2O3/ZrO2/ SiC composite powders by aluminothermic reduction of zircon in the presence of carbon is reported. The effect of the temperature on the progress of the reaction, as assessed by XRD analysis, is outlined. The morphological characteristics of the reaction products are described. Based on the experimental results, a reaction scheme is proposed. The possible propagation of the reaction is discussed in terms of the adiabatic temperature.
Synthesis of Inorganic Polymer-Ceramic Molecular Composites
Authors: Samuels William D. , Exarhos Gregory J. , Burton Sarah D. 
Published: March 2011

ABSTRACTThe logical development of thermally stable polymers is based upon forming true molecular composites comprised of both polymer and ceramic components. This paper describes our initial studies on the synthesis of composite materials that are expected to produce films with thermal stability to 500°C.
Effect of Cu on Al-Transition Metal Reaction Kinetics
Authors: Huang H.-C. W. , Wittmer M. 
Published: March 2011

ABSTRACTThe effect of Cu on the kinetics of compound formation between Al and transition metals such as Hf and Ti has been studied by resistivity measurement and Rutherford backscattering (RBS) in the temperature range of 325°C to 450°C. Thin film couples consisting of 150nm-thick transition metal film and 600nm-thick Al-Cu film were used, in which the Cu content was varied from 0 to 9 wt%. The intermetallic phases were found to grow as (time)1/2. Most interestingly, the reaction rate constants were found to decrease significantly with increasing Cu content, but to level off for Cu contents greater than about 2 wt%. The corresponding activation energy for a given Altransition metal reaction was found to increase with increasing Cu for Cu contents up to 2wt%. For example, when 4 wt% Cu is added to Al, the rate constant at 400°C for HfA13 is reduced by about a factor of 5, while the activation energy increases from 1.5 eV to 2.0 eV. RBS results indicate that the Cu addition seems to inhibit the diffusion of Hf into Al. Diffusive intermixing in the Al/Ti system is much smaller and, consequently, the effect of Cu additions in preventing Ti diffusion into the Al is also much smaller.
Electron and Ion Beam-Enhanced Adhesion
Authors: Mitchell I.V. , Williams J.S. , Sood D.K. , Short K.T. , Johnson S. , Elliman R.G. 
Published: March 2011

ABSTRACTHelium ions of 2 MeV energy and electrons of 5 to 30 keV energy have been used to irradiate a variety of thin (10–330 nm) metal films after deposition on semiconductor and insulator substrates. Dose thresholds for increased adhesion were found following irradiation with either type of particle. It is argued that the stronger bonding arises from an electronic, rather than a collisional, process. Representative results are presented and discussed within the framework of a recent model for heavy ion-induced effects.
The Radiation Enhanced Adhesion of Gold on PTFE
Authors: Sofield C.J. , Woods C.J. , Wild C. , Riviere J.C. , Welch L.S. 
Published: March 2011

ABSTRACTThe effect of γ-ray and electron irradiation on the adhesion of gold films to PTFE has been ascertained. The film adhesion has been found to undergo a sharp increase at a γ-ray dose of 5 × 106 to 1 × 107 rads. Qualitative ‘Scotch tape’ tests also show an increase in adhesion when the films are irradiated with electrons (250 eV - 3 keV).Examination of the interface region of very thin (∼ 20 Å) gold films on PTFE by X-ray photo-electron spectroscopy indicates the increase in adhesion results from radiolytic processes and consequent chemical interaction with the gold.
Effects on Metal/Metal-Oxide Interface Adhesion Due to Electron and Ion Irradiation
Authors: Bøttiger J. , Baglin J. E. E. , Brusic V. , Clark G. J. , Anfiteatro D. 
Published: March 2011

ABSTRACTThe influence of electron and ion irradiation on the adhesion at chromium-copper thin film interfaces has been studied. The measurements were carried out with different types and thicknesses of well-characterized oxides at the interfaces. The electron energies were varied between 5 and 10 keV, with doses up to 1018cm−2. lons of He+Ne+and P+were used in the range of energies between 150 keVand 1.0 MeV, with fluences ranging from 1015cm−2to 6× 1016cm−2. Substantial improvement of the adhesion is observed in cases where the beam has a significant nuclear stopping power component. Electronic processes may also play a role in improving adhesion, although they are not dominant in the case of the present films.
Modification and Study of Polymer Films Using High Energy Ion Beams
Authors: Venkatesan T. 
Published: March 2011

ABSTRACTRecent results on the effects of high energy ion beam irradiation in polymer films are reviewed in this paper. High energy ions (>10 keV/amu) deposit a large amount of energy (∼several cV/atom) in ionizing the electrons of the target atoms. This results in significant destruction of bonds in the films as a result of which polymers undergo rapid dissociation. Using a quadrupole mass spectrometer the study of transient emission of molecular species produced by an ion pulse has been shown to yield information about the diffusion and reaction kinetics of various molecules in the polymer. The fact that polymers undergo dissociation and those atoms which form volatile species are selectively depleted from the film could be utilized in producing useful inorganic composites by ion bombardment of polymers. For example, hard SiC composite films have been produced by ion beam irradiation of organo-silicon polymers. Eventually, polymer dissociation leads to a predominately carbon containing film which exhibits interesting electronic transport properties. Experiments on ion irradiated, pure carbon films indicate that a metallic form of carbon is produced from the polymer films at high irradiation
doses.