bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relaxation Processes in the Electrorheological Response
Authors: Katsikopoulos P. , Zukoski C. 
Published: March 2011

AbstractThe electrorheological (ER) response is characterized by a reversible increase in suspension viscosity on application of large electric fields. Suspensions displaying this behavior are typically composed of a polar solid phase suspended in a low conductivity oil (1-3). In the past five years considerable work investigating the mechanisms controlling the ER response has established that increases in viscosity are associated with the formation of electrode spanning particulate structures which are degraded by shear (4-8). The structures are the result of polarization interactions produced by the dielectric mismatch between the solid and continuous phases. Extensive modelling studies have shown that much of the rheological behavior of ER suspensions can be understood in terms of a balance of viscous and electrical polarization forces as written in terms of the Mason number, Mn = ηc ṙ/(2ε0εc(βE)2) (9). Here ηc, is the continuous phase viscosity, ṙ is the shear rate, and E is the applied field strength. The relative polarizability of the particulate phase is given in terms of β = (εp−εc)/(εp+2εc) where εp is the particle dielectric constant and γc is the continuous phase dielectric constant. The relative viscosity of many suspensions can be reduced to a single universal function of Mason number and often display a yield stress which scales with E2.
Light Scattering from Magnetic Latex Particles
Authors: Sohn Daewon , DeLong L. M. , Russo Paul S. 
Published: March 2011

AbstractTwo magnetic latex preparations have been measured by polarized and depolarized dynamic light scattering. The adherence of the latexes to a simple physical model, that of a bar magnet embedded in a plastic sphere, is judged adequate in one case, but not the other. Preliminary efforts to use the latex spheres as probes of sodium polystyrene sulfonate solutions are described. A few observations are made concerning the dynamic light scattering behavior of the magnetic latex under the influence of an externally applied, oscillating magnetic field.
Rheological and Optical Properties of Shearing Colloidal Suspensions by Polarized Light Spectroscopy
Authors: Wagner Norman J. 
Published: March 2011

AbstractThe two-particle correlation function serves as an important connection between suspension microstructure, scattering experiments, and macroscopic properties. Formal relationships between the experimentally accessible structure factor for suspensions undergoing simple shear, bulk stresses, and flow dichroism and birefringence are demonstrated. Measurements of flow dichroism using variable wavelength incident radiation provide a method to map out the nonequilibrium microstructure.
Shear Induced Orientational Order of Rigid Rod Suspensions
Authors: Ou-Yang H.D. , Wang C. , Vugmeister B.E. , Wong D. , Dawson A. 
Published: March 2011

AbstractShear induced birefringence was measured for dilute and semidilute rigid PTFE rod suspension. Orientational order of the rods is deduced from the birefringence data and compared with theory by Doi and Edwards′. Although the theory was for dilute solution, the renormalized data agree qualitatively with the theory even far into the nonlinear regime. At high shear the order parameter approaches a saturated value, and at low shear it depends on the shear rate square. The major discrepancy between the theory and experiment comes from the expected slowing down of rod reorientation at higher concentrations. At high concentrations, the slowing down is more than what can be accounted for by the macroscopic viscosity along.
Scaliing in Three-Dimensional Foams
Authors: Durian D.J. , Weitz D.A. , Pine D.J. 
Published: March 2011

AbstractThe coarsening and internal dynamics of a bulk foam are probed noninvasively by exploiting the strong multiple scattering of light that gives foams their familiar white color. By approximating the light propagation as a diffusion process, transmission measurements provide a direct probe of the average bubble size d. A second corroborating measure of d is obtained by analyzing temporal intensity fluctuations of the multiply scattered light within the framework of diffusing-wave spectroscopy. Both sets of measurements show the same behavior: At early times d is approximately a constant (20µm). After about twenty minutes the foam begins to coarsen and scaling behavior is observed such that the growth of d is a power-law in time, tz with z=0.45±0.05. This result is in near accord with the theoretical prediction, z=1/2, for foam in the limiting case of space-filling polyhedral bubbles. In addition, the change in packing conditions during coarsening gives rise to a nonequilibrium dynamical process which also exhibits temporal scaling: Neighboring bubbles undergo sudden structural rearrangements at a rate per unit volume which decays as t−Y with y=2.0±0.2. This value of y cannot be explained by the presence of only a single time-dependent length scale in the foam structure. Since these bubble rearrangement events serve to relax local stress, they must also play a role in the relaxation of externally imposed stress. Therefore, elucidation of their origin and scaling behavior will lead to an increased understanding of the rheology and stability of foams.
Spontaneous Vesicles and other Solution Structures in Catanionic Mixtures
Authors: Kaler Eric W. , Herrington Kathleen L. , Zasadzinski Joseph A. N. 
Published: March 2011

AbstractWe have prepared spontaneous, single-walled, equilibrium vesicles of controlled size and surface charge from aqueous mixtures of simple, commercially available, single-tailed cationic and anionic surfactants. We believe vesicle formation results from the production of anion-cation surfactant pairs which then act as double-tailed zwitterionic surfactants. Although unilamellar vesicles have been created by numerous physical and chemical techniques from multilamellar dispersions, all such vesicle systems revert to the equilibrium, multilamellar phase over time. These catanionic vesicles are stable for periods as long as several years and appear to be the equilibrium form of aggregation. Here we review the phase behavior and structural studies of several such mixtures, with particular focus on the effect of surfactant tail lengths on size and location of the vesicle phase in the appropriate phase diagram. The approach to equilibrium is also discussed.
Cylindrical Micelles in Rigid-Flexible Diblock Copolymers
Authors: Williams D.R.M , Fredrickson G.H. 
Published: March 2011

AbstractWe present a theoretical study of a melt of diblock copolymers consisting of a rigid rod and a flexible tail. It is shown that in addition to the lamellax phases previously discussed, there also exist phases of “hockey puck” micelles, where the rods are packed axially into cylinders. These phases occupy most of the phase diagram previously thought to consist of monolayer lamellae. It is argued that spherical micelles probably do not exist.
The Effect of Short and Long Range Interactions on Break up and Dewetting of Thin Polymer Films
Authors: Reiter Gtonter 
Published: March 2011

AbstractWe report investigations of instabilities of thin polystyrene films (< 100 nm). In the liquid state films break up by creating cylindrical holes. The average distance between holes is approx. proportional to the film thickness squared. This dependence compares well with the prediction of a recent theory on spinodal decomposition of thin liquid films. The subsequent dewetting process (=growth of holes) depends strongly on the composition of the substrate surface whereas the break up does not seem to be influenced by this surface. The importance of long and short range interactions in this context is discussed.
Adsorption of Neutral-Highly Charged Diblock Copolymers in Selective Solvents
Authors: Dan-Brandon N. , Tirrell M. 
Published: March 2011

AbstractWe apply a scaling model to study adsorption of neutral-strongly charged diblock copolymer from concentrated salt solutions, where the range of electrostatic interactions is smaller than that of excluded volume correlations. Adsorbed layer structure is determined by an equilibrium between the solvated block stretching energy, surface-adsorbed block interactions, and the solution chemical potential. We find that adsorption from micellar solutions results in a lower surface density than adsorption from solutions below the CMC. In both cases the surface density increases, and the layer thickness decreases, with salt concentration.
Domain Growth and Wetting in Polymer Mixtures
Authors: Cumming Andrew W. , Wiltzius Pierre 
Published: March 2011

AbstractWe present the results of phase-separation experiments performed on the binary polymer blend polyisoprene-poly(ethylene-propylene). Elastic light scattering and optical microscopy were used to follow the phase-separation after quenches into the coexistence region of the phase diagram. For critical quenches, we observed the well known bicontinuous infinite cluster morphology normally associated with spinodal decomposition, but with two distinct growth modes. In the bulk, we observed L(t) - t1/3 consistent with diffusion driven dynamics, whereas near the sample walls, there obtained a novel fast growth with L(t) -t 3/2, inconsistent with either diffusion or interface driven dynamics. We attribute this large exponent to wetting effects, but still lack any theoretical understanding of the phenomenon.
Internal Associations in Comb Polymers Bearing Multiple Internal Hydrophobes
Authors: Santore Maria M. 
Published: March 2011

AbstractThe internal associations of comb-shaped associative thickeners are modeled by Gaussian statistics to predict the probability of chain collapse and that for various types of internal associations. In addition to the idealization of the polymer backbone to a random walk, the hydrophobic groups at the ends of each tooth of the comb are treated as point“stickers.” The model considers all the ways by which stickers can form clusters of two or more teeth. The number of teeth per chain is not limited by the model, but rather by computation facilities. It is predicted that even with weak pairwise sticker interactions (2kT) adding short teeth to a long backbone drastically increases the probability of some internal associations, though the probability of complete chain collapse decreases significantly as teeth are added, due to the effect of backbone entropy.
Fracture at Finite Temperature: a Statistical-Thermodynamic Approach
Authors: Selinger Robin L. Blumberg , Wang Zhen-Gang , Gelbart William M. 
Published: March 2011

AbstractWe discuss both theory and simulation of fracture of ideal and almost ideal crystals at finite temperature. We propose that a solid under stress is in a metastable state, and that the onset of fracture may be characterized as the nucleation of the (stable) broken phase from the (metastable) intact phase. The role of atomic-scale defects is also discussed.
Dielectric Friction in Restricted Geometries
Authors: Urbakh M. , Klafter J. 
Published: March 2011

AbstractThe influence of a solid-liquid interface on the relaxation of a point dipole embedded in the liquid side is discussed. The dielectric friction of a dipole as a function of its distance from a boundary is calculated. The calculations are carried out assuming a nonlocal dielectric function of the liquid, characterized by a typical correlation length which may depend on temperature. The corrections to the relaxation of a dipole due to the presence of a boundary are shown to be small. Larger corrections can be introduced by postulating structural changes in the nature of the liquid near the boundary.
Entropic Elasticity of Lamellar Tethered Membrane Phases
Authors: Golubovic Leonardo , Lubensky T.C. 
Published: March 2011

AbstractEntropic elastic constants of lamellar tethered membrane phases are considered both in the vicinity of and at temperatures well below the membrane crumpling transition critical point. We calculate entropic forces acting on boundaries of these systems. Various predictions of the statistical physics of tethered membranes, such as the breakdown of the classical membrane elasticity theory at low temperatures or the existence of the crumpling transition, can be tested experimentally by using our results.
Molecular Order in Silk Secretions
Authors: Viney Christopher , Kerkam Keven , Gilliland Lisa , Kaplan David , Fossey Stephen 
Published: March 2011

AbstractTransmitted polarized light microscopy of various natural silk secretions reveals their ability to form nematic liquid crystalline phases. Observations of microstructure, together with a simple secondary structure analysis of known amino acid sequences in silk proteins, suggest that the rodlike structures forming the nematic phase are supramolecular aggregates, rather than individual rigid molecular segments. The optical birefringence of dragline fiber produced by controlled silking depends on the linear haul-off velocity, and can exceed the birefringence of naturally spun fibers; this suggests the possibility of in-vitro spinning of silk to obtain values of strength and stiffness even greater than those achieved in vivo.
The Synthesis of Ultrafine Ba/Sr Titanate Powders
Authors: Lin C.H. , Yan T.S. , Chin T.S. 
Published: March 2011

ABSTRACTBa/Sr titanate powders were obtained by reacting TiO2.xH2O gel in Ba(OH)2 and/or Sr(OH)2 aqueous solution. Different reaction temperatures between 68°C and 98°C and different mole ratios of Ba(OH)2 and Sr(OH)2 were used.X-ray diffraction analysis showed that the titanate powders are cubic, and they are solid solutions of barium and strontium. The lattace spaces of the titanates are affected by the Ba(OH)g/ Sr(OH)g, mole ratio. TEM analysis showed that the titanate powders were spherical, ultrafine, and almost monodispersed. The particle size of the powders is about from 41 to 50 nm depending on the reaction temperature.The titanate powders were compacted and sintered at various temperatures. The best sintering temperature of the powders is about 150°C lower than that of powders made by solid state sintering method.
Aerosol Synthesis of Aluminum Nitride Powders
Authors: Adjaottor Albert A. , Griffin Gregory L. 
Published: March 2011

ABSTRACTWe describe a new laboratory-scale aerosol process for producing AIN powder. A two-stage reactor design is used. In the first stage, triethyl aluminum (TEA = AI(CC2H5 )3) and NH3 react to form an aerosol adduct in a laminar flow diffusive mixing zone. The aerosol then enters the furnace stage, where it is converted to AIN. We have examined the influence of the major operating variables (e.g., inlet TEA concentration, reactor residence time, and furnace temperature) on the particle size and distribution, yield, and efficiency. For example, increasing the TEA concentration from 0.12 to 1.30 µmol/cm3 causes an increase in the mean particle diameter (from 0.07 to 0.13 Pim), a slight increase in polydispersity (from 0.31 to 0.43), and a decrease in yield efficiency (from 90% to 73%). In contrast, decreasing the reactor residence time (by increasing the flow rate) has little effect on mean particle diameter, but causes a significant increase in yield efficiency (approaching 100%). The overall behavior of the reactor suggests a model in which the particle size distribution of the final product is determined primarily by the aerosol formation steps in the mixing stage (i.e., nucleation, growth, and coalescence), while the composition and crystallinity of the product are determined by furnace conditions.
Synthesis of Titania Powder by Titanium Tetrachloride Oxidation in an Aerosol Flow Reactor
Authors: Akhtar M. Kamal , Xiong Yun , Pratsinis Sotiris E. 
Published: March 2011

ABSTRACTVapor phase synthesis of titania particles by oxidation of titanium tetrachloride (TiCI4) was studied in an aerosol reactor between 1200 K and 1723 K. The effect of process variables (reactor residence time, temperature, reactant concentration) on powder size and phase characteristics was investigated using the differential mobility particle sizer, scanning electron microscopy and X-ray diffraction. The morphology of the particles remained unchanged under the process conditions investigated; titania particles were primarily anatase though the rutile weight fraction increased with increase in reactor temperature. The geometric number average diameter of the particles was between 0.13 µm and 0.35 [m and the geometric standard deviation of the particle size distribution was about 1.4. The average particle size increased with increasing temperature, TiCI4 concentration and residence time. The observed changes in the particle size distribution were compared with those predicted by solving the aerosol dynamic equation by a sectional method and accounting for coagulation and first order chemical reaction.
Boron Carbide-Based Ceramics Via Polymer Route Synthesis
Authors: Zheng Haixing , Thorne Kevin , Mackenzie J.D. , Yang Xiaoguang , Hawthome M.F. 
Published: March 2011

ABSTRACTBoron carbide is a ceramic material with excellent high temperature physical properties. As compared to conventional techniques, the preparation of boron carbide from polymeric precursors is attractive as this technique offers a number of unique advantages. In this paper, the screening of polymeric precursors to boron carbide will be discussed. Two promising boron carbide, carborane containing polymeric precursors have resulted in 60-70 wt.% ceramic yields. The chemistry of polymer synthesis and the transformations from the polymer to amorphous and crystalline boron carbide were investigated with infrared spectroscopy, NMR spectroscopy, thermal analysis, and x ray diffraction.
Sol-Gel AL2O3 Coatings on SiC Fiber
Authors: Xiao Youming , Tan Beng Jit , Suib Steven L. , Galasso Francis S. 
Published: March 2011

ABSTRACTCoating of SiC (BP-SIGMA) fibers with alumina by a sol-gel process did not cause degradation even after heating to 1000°C in air for 24 h. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Auger electron spectroscopy (AES) and scanning electron microscopy (SEM ) methods were used to study the coating fiber interface.
Effects of Surface Charge on the Processing of Nonaqueous Silicon Slurries
Authors: Bleier Alan 
Published: March 2011

ABSTRACTThe influence of surface charge on the dispersion aspects of the nonaqueous processing of silicon powder is explained by the relationship between the liquid medium's dielectric constant and the maximum particle size that is stabilized by colloidal forces. The effects of surface charge, derived from the chemistry of the solid-liquid pair or the adsorption of ionic processing aids, are either great, significantly increasing the maximum particle size that is stable against agglomeration from the nanometer range to the micrometer range, or virtually undetectable, contributing nothing to enhanced stability. Guidelines for the processing of silicon powder when surface charge exists are discussed.
Phosphate Substituted Phosphazenes as Dispersants in Colloidal Ceramic Processing
Authors: Burton Sarah D. , Samuels William D. , Exarhos Gregory J. 
Published: March 2011

ABSTRACTA new phosphate substituted phosphazene trimer [N3P3Cl5(OP(O)Ph2)] has been synthesized and characterized by 31p NMR and Raman spectroscopy. The course of each solution-state substitution was followed with 31P NMR, and this technique was used to determine the best reaction conditions for the experiment. Information such as phosphorus to phosphorus connectivity and purity were analyzed. This paper will discuss the synthesis and characterization of phosphazene moieties which are substituted by phosphorus(V) centered substituents.
Tape Casting Using Fine Ceramic Powders
Authors: Wilkinson David S. , Plucknett Evin P. , Caceres Carlos H. 
Published: March 2011

ABSTRACTTape casting technology has been developed for the production of ceramic composites using fine powders of alumina and zirconia with an average particle size in the range 0.25-0.3 μm. These powders require careful control of the dispersant/solids ratio in order to minimize the slip viscosity, and to prevent the rejection of excess dispersant during solvent evaporation. In this regard phosphate ester has been found to be an effective dispersant. The choice of solvent is also important, with a non-polar solvent exhibiting more forgiving behaviour. The use of such fine powders lowers the solids loading permitted in the tape casting slip to about 22 vol.%, with a resulting green density of less than 54% of theoretical. However, high sintered densities can be achieved in both single tapes and laminates. Constraints imposed on the tape during solvent evaporation lead to a difference in green density within the tapes, and strategies need to be developed to counteract this.
Consolidation of Si3N4/SiC Whisker Composites by Colloidal Filtration
Authors: Erauw J.P. , Luyten J. , Sleurs J. 
Published: March 2011

ABSTRACTStable Si3N4/SiCw co-dispersions containing up to 20 wt.% of whiskers have been prepared. Homogeneous green bodies with relative green density above 55% and pore size in the range 40-50 nm have been obtained by pressure assisted colloidal filtration. By optimizing the temperature and/or the amount of sintering additives, densities above 90-95 % have been achieved by pressureless sintering of these consolidated compacts.
Solid Solution Additives and the Sintering of Ceramics
Authors: Rahaman Mohamed N. , Hu Ching-Li 
Published: March 2011

ABSTRACTThe use of solid solution additives has been shown to be very effective for the formation, by conventional sintering, of ceramic materials with high density and with controlled grain size. However, the number of systems for which such additives have been successfully found remains quite small, and the role of the additives is fairly well understood in only two or three of these. This paper describes the initial part of a systematic study into the effects of solid solution additives on the sintering of ceramics. Cerium oxide was chosen as a model host powder for this work because it has appreciable solubility for many additives. A combination of kinetic data and microstructural observations indicate that the sintering and grain growth are influenced significantly by the additive size but less significantly by the additive charge. The density versus grain size relationship is almost independent of the additive below relative densities of = 0.90 but depends strongly on the additive above this density. The data are interpreted in terms of the effect of the additives on the densification to coarsening ratio.
Miicrostructural Evolutiion Duriing Sinteriing
Authors: Page R. A. , Pan Y. M. 
Published: March 2011

ABSTRACTSmall-angle scattering techniques have been used in a number of studies to characterize pore evolution in ceramic compacts. Parameters characterizing the pore distribution, such as total pore surface area, pore size, and pore density, have been measured through both intermediate and final stage sintering. A review of these results indicates that pore sizes were generally found to remain constant during intermediate-stage sintering; supporting a topological decay model of sintering. Pore sizes generally increased and the size distribution broadened during final-stage sintering. The scattering results also suggest the presence of a unique pore surface area versus density curve.