bluuebunny/crossref_metadata_2025 huggingface dataset:
Durability of High-Performance Cement-Based Materials
Authors: Struble Leslie , Garboczi Edward , Clifton James
Published: March 2011

There is considerable research now underway on high-performance cement-based materials, in particular on issues of processing, microstructure, strength, and related properties. However, very little research has been undertaken regarding the durability, or service performance, of these materials. Therefore the durability of high-performance cement-based materials can only be inferred from the service performance of ordinary materials or from a basic understanding of the factors affecting service performance. In this paper we review what is known about the durability of fiber reinforced concrete, high performance concrete, DSP, and MDF. Durability is discussed from the standpoint of general issues – fluid permeability, ionic diffusivity, and pore fluid composition. Much research is needed in order to predict or improve the durability of high performance cement-based materials.
Advanced Methods of Concrete Characterization
Authors: Lee R. J. , Draper E. A. , Skalny J.
Published: March 2011

The need for the rehabilitation of the infrastructure has lead to the adaptation of modem analytical methods for the characterization of concrete. These techniques are not commonly associated with evaluating concrete but promise to be very useful both as tools of quality assurance and in the determination of existing damage. This paper describes two such techniques, namely, coordinated electron-optical microscopy and gamma-ray tomography. Examples of the use and interpretation of each method are given.
Tensile Strength of Carbon Fiber Reinforced Cement Composites
Authors: Toutanji Houssam A. , Korchi Tahar El- , Leatherman Gary L. , Katz R. Nathan
Published: March 2011

The effect of carbon fibers on the uniaxial tensile strength of cement paste matrix is studied. The tensile strength values are obtained using the novel Cementitious Composites Axial Tensile Technique (CCATT) described previously [1]. The addition of 1.0, 1.5 and 2.0 volume percent of Polyacrylonitrile-based (PAN) carbon fiber results in an increase in tensile strength of 32, 41 and 48 percent respectively, as compared to the unreinforced matrix. A model based on the rule of mixtures is used to predict the tensile strength of the carbon fiber reinforced composites. Results are discussed with respect to fiber, interface bond, and cementitious matrix characteristic.
Characterization of Gas Reburning-Sorbent Injection Technology By-Products
Authors: Mattigod Shas V. , Rai Dhanpat
Published: March 2011

Three samples of fly ashes from pilot-scale tests of gas reburning and sorbent injection (GR-SI) technology were characterized physically, chemically, and mineralogically. Texturally, the samples consist of approximately 97% by weight of silt-size particles. Total chemical analysis showed that Al, Ca, C, Fe, Si, and S were the major elements, making up 56% of the total mass of the sample on average. Approximately 3% of the sample mass consisted of the elements Cl, Mg, P, K, Na, and Ti, and 0.4% consisted of trace elements. Major crystalline compounds found in these samples were lime (CaO), anhydrite (CaSO4), and calcium carbonate (CaCO3). Calculations show that these compounds constituted from 56 to 76% of the mass of the samples. The morphology and chemistry of particles in GR-SI samples were similar to those of particles in conventional coal fly ashes. The particles in the GR-SI samples consisted of fragments and spheres of varying sizes. Most of the particles were calcareous. Silicate and alumino-silicate particles were fewer in number, and iron-rich particles were rare. The EP test indicated that extract concentrations of Ag, As, Ba, Cd, Cr, Pb, and Se were well below the EPA regulatory levels. Predictions of leachate compositions from these types of fly ashes, if disposed of as a landfill at a midwestern U.S. site indicate, that during the first ten years the concentrations of Ca, SO4, Na, B, and OH would remain high. The concentrations of minor constituents (As, Ba, Cd, Cd, Cu, Cr, Fe, Ni, and Se) in the leachate are predicted to be at trace levels.
An Investigation of Fluidized Bed Combustion By-Products from Four Iowa Power Plants
Authors: Kilgour Carol L.
Published: March 2011

Fluidized bed combustion (FBC) residues from four Iowa power plants were characterized to provide background with respect to chemical, physical, mineralogical and microstructural parameters that might affect their utilization potential. Methodologies used include: bulk chemical analysis; grain size analysis; specific gravity determination; mineralogical analysis by x-ray diffraction; scanning electron microscopy; and thermal analysis.

Chemical analysis of the major components showed the separation of the constituents during combustion. The bottom ash is derived from the calcined and partly sulfated limestone, thus the concentration of calcium and sulfur compounds is greater. The fly ash however is derived mostly from the coal and therefore exhibits higher concentrations of coal ash components such as silica (SiO2), alumina (Al2O3), and ferric oxide (Fe2O3). The alkalis appear to be more concentrated in the fly ash.

The measured particle size distributions of the bulk samples varied greatly, from extremely coarse (mean particle size ˜2000 μm) to fine (mean particle size ˜25 μm). The size distributions also varied in breadth. Specific gravities values recorded ranged from about 2.65 to about 3.05.

X-ray diffraction analyses showed that most of the FBC by-products contain, as easily detectable crystalline components, only quartz, anhydrite and lime, and as is to be expected due to the low combustion temperatures, do not show broad peaks characteristic of glass in conventional fly ashes. Scanning electron microscopy revealed the FBC by-products to be extremely intricate mixtures of particles of complex and variable composition and internal structure.

FBC by-products are shown to be extremely complex mixtures of particles of variable composition and internal structure. However, despite their local variation, useful results can be obtained by overall chemical and physico-chemical analyses of their composition. The exploitable properties of FBC residue include the somewhat cementitious nature and the granularity. However, their heterogeneous nature, lack of pozzolanic properties, and elevated sulfate content may limit their uses, especially in construction.
Treatment of Acid Mine Drainage Water Using Fly Ash and Water Softening Sludge
Authors: Atalay Asmare , Chaluvadi Srinivas , Laguros Joakim G. , Black Jerry J.
Published: March 2011

Acid mine drainage (AMD) is being recognized as a major pollution source to surface water. Heavy trace metals emanating from abandoned mines are continuously being released and contaminating surrounding lakes and streams. The potential for utilizing fly ash and water softening sludge (WSS) as buffering and adsorption media for AMD water was assessed. The results indicated that AMD water treated with fly ash either met or exceeded the U.S. Environmental Protection Agency water quality criteria for effluent standards for total iron, manganese, suspended solids, and pH. The optimum dosage of fly ash and sludge needed for treating the acid mine water from Picher field, an abandoned lead and zinc mine in Oklahoma, has been determined. It was observed that each had better than 90 percent efficiency for removal of heavy metals from the AMD water. The combined use of fly ash and WSS was also investigated, but there was no significant improvement compared to using fly ash alone. In general fly ash had a greater buffering capacity to treat acid mine water than did WSS. Consequently, fly ash can be used to treat AMD water and minimize its environmental impact.
Investigation in the System “Portland Clinker-Gypsum Plaster-Condensed Silica”
Authors: Odler I. , Balzer M.
Published: March 2011

Blends of portland clinker and gypsum plaster exhibit fast setting and early strength development if mixed with water. An excessive expansion of such systems may be controlled by the use of a “sulfate resistant” rather than “ordinary” clinker and by adding condensed silica to the system. The water resistance of such hardened pastes is significantly improved as compared to plain gypsum pastes, mainly due to the formation of the C-S-H-and AFt-phases.
Diffuse Yield drop and Snap Action in a Ni-Ti Alloy
Authors: Duerig T.W. , Melton K.N.
Published: March 2011

An unusual yield phenomenon is observed in a heavily worked NiTiFe alloy, which leads to snap action shape memory and superelasticity. The snap action occurs at extremely high velocities and is accompanied by a loud cracking sound. The cause of the instability is attributed to penning, in which martensite growth is halted by having to undergo a reorientation at low angle cell boundaries, which then lowers the resolved shear stress on the martensite plate. Once free of the cell boundary, the plate grows and its strain energy is reduced so that it is able to penetrate subsequent boundaries more easily. This results in a diffuse yield drop, and the said snap action motion.
Microstructural Features and Shape-Memory Characteristics of Melt-Spun Ni-Al-Fe-B Ribbons
Authors: Liu C. T. , Sparks C. J. , Horton J. A. , George E. P. , Carmichael C. A. , Kao Ming-Yuan , Kunsmann Henry
Published: March 2011

This paper summarizes our recent study of NiAI+Fe+B alloy ribbons containing 4 to 20% Fe and doped with 300 wt ppm B. Alloy ribbons were successfully fabricated by rapid solidification via melt spinning. The alloys with 8% Fe and 34% Al-equivalent [=Al%+(Fe%)/2] showed the best bend ductility at room temperature. The ribbons exhibited a reversible martensite (body-centered orthorombic structure) to B2 transformation as evidenced by DSC, X-ray and TEM studies. The shape-memory effect, as characterized by measuring the recovery of bend angles with temperature, is sensitive to alloy composition, with the best recovery observed in SMA-15 (B-doped Ni-27% Al-14% Fe). Annealing at 600°C causes aging embrittlement; in particular, in alloys containing 12% Fe.
Microstructural Characteristics and Shape Memory Effect of Rapidly Quenched Cu-Al-Ni-Cr Alloy
Authors: Koo Horng-Show , Chen Hsing , Chen Fu-Hsing
Published: March 2011

CuAlNiCr shape memory alloy ribbons with thickness ranging from 65 to 60 pm and about 15–20 mm width have been produced by melt-spinnig technique. Finer grain and homogenous columnar structure could be examined. Transformation temperatures and grain size of CuAlNiCr alloy increase with increasing heat treatment time. The reversible color change phenomena( red copper color=bronze color ) associated with phase transformation in alloy ribbons was also observed. Microstructural and transformation characteristics of rapidly quenched CuAlNiCr alloys were observed by x-ray diffraction, optical microscope, four-probe electrical resistivity method, scanning and transmission microscope.
Shape Memory Effect Due to Phaselike Transition in High Tc Superconductors
Authors: Wang Y.N. , Shen H.M. , Zhu M. , Huang Y.N. , Zhang Z.F. , Liu Z.M. , Fung P.C.W.
Published: March 2011

Tensil tests for YBaCuO, Bi(Pb)SrCaCuO and TiBaCaCuO show that there always appear ferroelastic loops and shape memory effect due to the phaselike transition at tens degrees above Tc (<150K), which disappear for nonsuperconducting YBaCuO, Y(Pr)BaCuO and CuO. The property of the phaselike transition and the discrepancy on the internal friction peaks near Tc for YBaCuO have been studied and discussed.
Production and Characterization of FE-NI-CO-TI Shape Memory Springs with One- and Two-Way Effect
Authors: Jost Norbert
Published: March 2011

It has been shown that ausaged Fe-Ni-Co-Ti alloys exhibit a reversible martensitic transformation with a small temperature hysteresis between the forward and the reverse transformation. This is due to the precipitation of small coherent (Ni,Co,Fe)3Ti particles. On the one hand they lead to a very effective precipitation hardening of the austenite and on the other hand to high elastic back stresses after shearing together with the martensite into a metastable structure. The martensitic morphology in such states is typically lathlike (thin plate martensite).

While yield stress and tensile strength increase during ausaging, the toughness, especially the elongation at fracture changes for the worse. The results of this work show that this can be prevented by a combined thermo-mechanical treatment. At the same time a remarkable twoway shape memory effect can be observed.

For practical applications the use of springs seems the best way for this type of Fe-based alloys because the recovery strain is low in comparison to Ni-Ti alloys. On the other side, due to the special transformation mechanism in Fe-Ni-Co-Ti alloys it can be assumed that the possible power in the two-way-effect should nearly reach the value of that obtained in binary Ni-Ti alloys.

Mechanical and thermal properties of different springs made from Fe-Ni-Co-Ti shape memory alloys were studied by means of special deformation tests. Thereby, the maximum obtainable power in the reversible shape-memory effect of the investigated springs was of special interest. The martensite morphologies were investigated by optical-microscopy.
Hrem Studies of Rapidly Solidified Ni-Fe-Al-B Shape Memory Alloys.
Authors: Pērez R. , Juārez-Islas J. A. , Johansson P. , Wallin M. , Savage S. J.
Published: March 2011

A series of (NixFeyAlz)0.9983B0.0017 (where x=58-60, y=13-15 and z=26-28, in at%) alloys have been rapidly solidified by - melt spinning. The ribbons have been characterized by HREM, DSC, X-ray diffraction and recoverable strain measurements. The as-cast alloys exhibit excellent bend ductility (in contrast to B2 type alloys conventionally cast) and a wide range of transformation temperatures: Ms=244-466 K, Mf=200-395K, As=236-427K and Af=262-526K. X-ray diffraction shows the presence of β (NiAl), β′ (NiAl), γ (Ni3Al), γ′ (Ni3A1), Ni and other phases such as Fe3Al, FeAl, FeNi and Al5Fe2. It is the β- β′ diffusionless transformation which is responsible for the shape memory effect. The results obtained by transmission electron microscopy (TEM) show two different types of crystalline grains. In one case, the grains have a high density of twins which are the fingerprints of the martensite transformation. However, other areas in the specimen show crystalline grains with very poor image contrast due to the transformation from β′ -β. There are also sections in the specimens with domains of both crystalline sgrains in coexistance. Both crystalline grains have large amounts of precipitates. In the β′ (NiAl) phase the size of the precipitates range fron lnm to lOnm. In the γ (Ni3Al) phase large precipitates (20nm) can be found. Some of them display pentagonal shapes which resemble the image contrast obtained in the TEM for small icosahedral metallic particles. Experimental evidence is also obtained on different habit or twin planes. HREM images from the twinned areas suggest diferent kinds of atomic structures for the parent and martensite crystalline sections. These results give some insights into the nature of the martensite transformation.
Mass Production of Thermomarkers
Authors: Raymond M. , Pothet J.B. , Weynant E.
Published: March 2011

The Thermomarker is the first industrial application of copper based shape memory alloys which knows a very large spreading. It's a tester that gives a signal very easy to read. However it is a precision instrument and its testing remains an essential care.

The paper will explain the special feature of the Thermomarker which falls in with two tests of working: one during the martensite → austenite transformation, one during the austenite → martensite transformation. We shall expose what kind of working test (in fact a screening inspection) we have set up to get a good accuracy and a whole reliability even on a mass production.

Then we shall expose our system of production tracing that is able to trace back the whole historical account of any Thermomarker.
An Apparatus for Extinguishing a Lighted Cigarette.
Authors: Koo Horng-Show , Chang Li , Chen Hsing , Shieh Kai-Liang
Published: March 2011

An apparatus for extinguishing a lighted cigarette comprises a hollow housing and a cigarette ash storage chamber. A cutter for cutting and extinguishing the burning portion of a lighted cigarette is provided within the housing comprising a bias spring and two pieces of shape memory alloys having different temperature reaction gradients, wherein one of the shape memory alloys is used in the cutter and the other is used in a L-shaped gate. When the burning portion of a cigarette is placed into the inside of the housing and comes into contact with the cutter, the cutter will restore to its memory shape by the temperature response to cut the burning portion of the lighted cigarette and to extinguish the burning portion by pressing it on the gate. Then, the gate will stretch straight to let the cigarette ash drop into the storage container by the temperature response. When the temperature of the gate is decreased, the gate will recover to its original position to cover the storage container, thus, the cigarette ash is restricted within the storage chamber to prevent it from dispersing and cause pollution. If a lighter is attached with the apparatus, it facilitates carrying and provides a safe and clean environment.
Stability and Phase Behavior of Mixed-Surfactant Vesicles
Authors: Mackintosh F. C. , Safran S. A.
Published: March 2011

While ideal fluid membranes are characterized solely by curvature elasticity, many structural (“external”) properties of real membranes are strongly influenced by “internal degrees of freedom”. In particular, recent experimental reports of stable vesicles in surfactant mixtures seem to illustrate the important interplay between composition and curvature in bilayer membranes. Such stable vesicles are unexpected in single-surfactant bilayers. We show theoretically how the energetic stabilization of mixed vesicles can occur in mixed-surfactant systems. This is illustrated by a microscopic model of mixed-surfactant bilayers, which is treated within both the random mixing and strongly interacting limits. The predictions of the ranges of stability of the various phases as a function of the three concentrations (solvent - e.g., water - and the two amphiphiles) is in qualitative agreement with recent experiments.

In addition, we consider the effect of phase separation in a mixed-surfactant system. In contrast with a bulk system, we find that for a binary mixture in a two dimensional fluid bilayer membrane, phase separation determines a length scale for the formation of stable vesicles. This results in a stable, one phase vesicle region near the critical composition, with a simple dependence of the vesicle size on composition. We also find regions of coexistence of vesicles with lamellae.
Melt Diffusion in Model Liquid Crystalline Polyiers
Authors: Hall E. , Ober C.K. , Kramer E.J. , Colby R.H. , Gillmor J.R. , Galli G.
Published: March 2011

Diffusion of model main-chain and side-chain liquid crystalline polymers was studied in the nematic phase. The concentration of deuterium labeled polymer vs. depth in a thick matrix layer was profiled with Forward Recoil Spectrometry to determine diffusion coefficients. In each system, the tracer diffusion coefficient was measured as a function of temperature, and correlated both with phase transitions determined by thermal analysis and with melt viscosity data.
Rheo-Optiics for Multicomponent Liquids
Authors: Fuller G. , van Egmond J. , Zawada J. , Archer L.
Published: March 2011

The application of techniques in optical rheometry for the study of multicomponent systems is reviewed. Small angle light scattering (SALS) patterns are related to the structure of concentration fluctuations with length scales of the order of the wavelength of light. Scattering techniques such as SALS and scattering dichroism have been applied to monitor the transient evolution of anisotropic concentration fluctuation enhancement during simple shear induced phase separation in a semi-dilute solution of polystyrene (PS) in dioctyl phthalate(DOP). Furthermore, the Onuki- Doi theory relating scattering dichroism and structure factor has been used to verify the consistency between scattering dichroism and anisotropy in structure factor. Infrared polarimetry is a useful technique in probing the transient microstructural orientation of individual chemical species in multicomponent systems. The simultaneous measurement of intrinsic infrared dichroism and birefringence is particularly effective and has been employed to monitor component relaxation dynamics in miscible blends of poly(ethylene oxide) and poly(methyl methacrylate). Polarization Modulated Laser Raman Scattering (PMLRS) has been successfully employed to study the orientation dynamics of a polymer melt subjected to transient uniaxial extension. PMLRS provides quantitative information about the time evolution of both the second and fourth moments of the orientation distribution function of molecular segments.
Does Shear-Flow Enhance or Suppress Fluctuations in Shectics?
Authors: Bruinska R. , Rabin Y.
Published: March 2011

We investigate the effects of shear-flow on the smectic phase of thermotropic and lyotropic liquid crystals. We show that shear-flow transforms a Smectic-A thermotropic into an orthorombic solid by the suppression of undulation fluctuations. In contrast, the lyotropic Lαphase exhibits, in addition, a very striking enhancement of shortwavelength concentration fluctuations - a phenomenon which is closely analogous to a well-known effect in polymer solutions. We demonstrate this result using both hydrodynamic theory as well as a microscopic model based on the Helfrich theory of membranes. The dispersion relation of the concentration fluctuations is in qualitative agreement with recent experiments on the Lαphase in shear flow.
Nucleation and Growth of Liquid Droplets Under a Shear Flow
Authors: Perrot F. , Baumberger T.
Published: March 2011

Phase separation in an off-critical binary mixture is studied under an uniform and steady shear flow. The nucleation and subsequent growth of droplets in aweakly supersaturated mixture (volume fraction of the new phase smaller than 10%) is studied by small angle scattering and turbidity measurements. The completion of the nucleation process is shown to be accelerated by the shear flow. At very low supersaturation, a strong effect of shear is detected which can be related to shear-triggered nucleation. In situ measurements ’of the surface tension between the two phase-separating phases obtained by studying the deformation and tilt of the growing droplets is discussed.
Relaxation Processes in the Electrorheological Response
Authors: Katsikopoulos P. , Zukoski C.
Published: March 2011

The 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

Two 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

The 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

Shear 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

The 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

We 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

We 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

We 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

We 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.
Adsorption of Copolymer Chains at Liquid-Liquid Interfaces: The Effect of Sequence Distribution
Authors: Yeung C. , Balazs Anna C. , Jasnow David
Published: March 2011

The presence of copolymers at an interface between two immiscible fluids is crucial to such processes as emulsion stabilization and microemulsion formation [1]. Recently Marques and Joanny [2] and Garel et al. [3] have studied the behavior of a random copolymer at a liquid-liquid interface. However, the arrangement or sequence distribution of the monomers in a copolymer can vary widely from random to blocky or purely alternating. In this paper, we use both analytic arguments and molecular dynamics simulations to determine how the sequence distribution affects the adsorption and conformation of a single macromolecule at the boundary between two immiscible fluids [4]. In particular, we derive an expression for the free energy of a copolymer at the interface and compare the resulting predictions with the outcome of the simulations. Our findings yield design criteria for fabricating polymers that display the desired interfacial properties.
Kinetics of Polymer Adsorption on Colloidal Surfaces
Authors: Gao Z. , Ou-Yang H. D.
Published: March 2011

Interfacial behavior has been one of the current focuses of polymer research. 1,2 The practical importance of the problem is directly related to coating, colloidal stability, etc. Several of the important issues on the kinetics of the polymers at the interface such as reversibility, equilibrium and polymer rearrangement at the surface have drawn particular interests recently.3,4
Domain Growth and Wetting in Polymer Mixtures
Authors: Cumming Andrew W. , Wiltzius Pierre
Published: March 2011

We 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

The 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

We 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

The 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.
On the Origin of the Bump in the Profile of Surface-Tension-Gradient-Driven Spreading Films
Authors: Carles P. , Cazabat A.M.
Published: March 2011

We show that the presence of a bump, in the profile of spreading films driven by forces such as surface tension gradients, can be explained by a simple analysis of the steady-state velocity, without taking into account contact line effects.
Entropic Elasticity of Lamellar Tethered Membrane Phases
Authors: Golubovic Leonardo , Lubensky T.C.
Published: March 2011

Entropic 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

Transmitted 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

Ba/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

We 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

Vapor 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

Boron 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

Coating 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

The 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

A 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

Tape 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

Stable 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

The 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

Small-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.