bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Superplasticizers on the Workability of Concrete as Evident from Apparent Viscosity, Yield Stress and Zeta-Potential
Authors: Malek R.I.A. , Roy D.M.
Published: March 2011

Modem concrete technology projections indicate a great expansion in low-cost and time efficient construction. Mixture designers will likely be more concerned with the developments in concrete making materials. Among those is the effective use of chemical admixtures and superplasticizers which will lower the water to cement ratio but will still give a dense workable concrete. An investigation of the workability of fresh concrete and the effect of superplasticizers should, therefore, constitute an essential part of modem concrete durability studies.

In this paper we report part of the work on rheological properties of fresh concrete. Various concrete samples covering a range of compositions that are commonly used for highway pavements are prepared. The proportioning parameters are: cement content, aggregate size, gradation and sphericity-roundness, and water and superplasticizer contents. The individual solid ingredients were characterized and the fresh concrete properties were assessed by the slump, two-point workability (Tattersall's) apparatus, air pressure and unit weight methods. The effects of superplasticizer on the apparent viscosity and yield stress of concrete are discussed and the relevance of the findings for field applications (handling of fresh concrete) are discussed. Also discussed are the implications for microstructural development.
The Flow Behaviour of Concentrated Clay Suspensions Under High Pressures
Authors: Briscoe Brian J. , Luckham Paul F. , Ren Shao Ran
Published: March 2011

This paper describes part of recent studies (Briscoe, et al., Proc. 11th Inter. Congs. on Rheology, 588–590, Aug. 1992, Brussels; Briscoe, et al., The properties of drilling fluids at high pressures and high temperatures', submitted to Proc. Roy. Soc.,1992) of the rheology of concentrated clay dispersions (weight fraction from 7%–12%) under the conditions which commonly occur during oil-well drilling operations. The experimental data, which are reported in terms of the Bingham yield stress and the plastic viscosity, show that the application of high pressures modifies the Bingham characteristic parameters in a way which is both temperature and gelation-time (or shear history) dependent. The extent of this shearhistory effect may be described in terms of a “time-dependent gel strength”. The experimental results obtained with controlled shear-history measurements, using a high pressure and high temperature rolling-ball rheometer, support an extended induced volume change model, which presumes an equilibrium state for the system. The data also indicate that long time constants are associated with the gelation process at ambient temperatures of ca 20 °C. The time constants for the gelation process decrease as the temperature is increased indicating that the gelation is a thermally activated process.
NMR Studies of Solvent Dynamics in High Solids Alumina Slurries
Authors: Parker Anthony A. , Wilhelmy Deborah M. , Daunch William
Published: March 2011

Solid state 13C NMR techniques have been used to study the mobility of both toluene and ethanol in slurries containing 70% alumina by weight. A comparison of relative signal intensities from cross polarization experiments, and from single excitation experiments under static conditions (no sample spinning) shows that a portion of the solvent molecules are immobilized with “solid” characteristics, while a majority of the molecules exist in mobile or “liquid” like environments. The immobilized solvent is rigid enough to cross polarize with protons, and hence it is characterized by long correlation times, and by a high viscosity. The remainder of the solvent is too mobile to cross polarize, and hence it is characterized by a lower viscosity. The results suggest that solvent is partitioned with the most viscous components being bound near the particle surfaces. These experiments and calculations will be discussed along with the implied effects of solvent partitioning on bulk rheological behavior.
Coarsening of a Quiescent Electrorheological Fluid I: Experiment
Authors: Martin James E. , Odinek Judy , Halsey Thomas C.
Published: March 2011

We report a real-time, two-dimensional light scattering study of the evolution of structure in a concentrated electrorheological fluid during the ‘liquid-solid’ phase transition. We find that after particle chaining along the electric field lines, strong light scattering lobes appear at a finite scattering wavevector q orthogonal to the field lines, and then brighten as they move to q=0. This indicates the existence of an unstable concentration fluctuation that signifies the segregation of chains into columns. In fact, the observed growth kinetics of the characteristic length, as well as the form of the structure factor, are qualitatively similar to two-dimensional spinodal decomposition in a system with a conserved order parameter.
Shear-Induced Structural Changes Observed in Concentrated Suspensions of Binary Blends of Fluorescent Particles of Differing Size and Color
Authors: Jansma J. B. , Qutubuddin S.
Published: March 2011

Shear-induced structural changes were observed in suspensions of binary blends of fluorescent particles of differing size and color. Median particle size ranged from 8.3 to 13.7 microns for the nearly spherical fluorescent particles. Concentrated aqueous suspensions were studied under shear flow in a Couette fixture modified to accommodate a fused silica cup. The color of the fluorescent particle blends was observed through the cup wall using photometric methods. Suspension color near the cup wall depended upon shear rate. A color shift occurred near the shear thinning to shear thickening transition. With increasing shear rate, the color contribution from the larger particles increased as the thickening transition occurred. Draining films of these suspensions on a flat fused silica plate were also studied using photometric readings from both the free surface and through the silica plate. Color measurements indicated highly non-uniform particle size distributions within the draining films, which varied with drain time.
Shear Thinning Properties of Dense Suspensions: Rheology and Flow Dichroism
Authors: Bender Jonathan W. , Wagner Norman J.
Published: March 2011

An expression relating dichroism to the non-equilibrium structure was derived through Rayleigh-Gans light scattering theory. Comparison of this expression to a micromechanical expression for the thermodynamic contribution to the total stress demonstrates a stress-optical relationship. Optical dichroism and viscosity measurements on monodisperse, near hard-sphere suspensions as a function of shear rate, volume fraction, and particle size demonstrated the relationship experimentally. This work provides a rheo-optical method for determining the various contributions of the colloidal forces to the overall stress.
Nuclear Magnetiic Resonance Imaging (NMRI) of Flow-Induced Microstructure of Concentratied Suspensions
Authors: Chow A. W. , Sinton S. W. , Iwamiya J. H.
Published: March 2011

The application of nuclear magnetic resonance flow imaging (NMRI) to the study of Couette and falling-ball viscometry of solid/liquid suspensions is described. The suspension consisted of non-Brownian, monodisperse, neutrally-buoyant spheres of 50 vol%. NMRI data demonstrated flow-induced changes in the particle distribution in the suspension that strongly influence the accuracy in viscosity measurements using these flow geometries. In Couette flow, direct correlation between stress measurements and particle concentrations at various locations in the flow cell as a function of shear strain can be made. Our data directly confitrm the shearinduced particle migration theory proposed by Leighton and Acrivos.[1] In the falling-ball experiments, increased particle concentration at the leading edge and decreased concentration at the trailing edge of the ball was observed when the falling ball is big compared to the cylinder containing the suspension. This change in particle distribution can be directly related to the changes in fall velocity of the ball as a function of position in the cylinder.
Laser Fabrication of Micron-Size Structures on CdS
Authors: Daneu V. , Peers J. , Sanchez A.
Published: March 2011

Wet and dry laser-etching experiments have been performed on polished CdS crystals, using a CW Ar laser, with the goal of writing patterns with μm linewidth. A nitric acid solution was found to exhibit no appreciable dark etching and high photoetching rate; surface roughening due to scattered light was its limitation. A dry, low-temperature (< 200°C) laser-etching process was also studied, and used to produce satisfactory line patterns with 1- to 5-μm linewidths and a 3:1 depth ratio.
Photoenhancement of Gas-Solid Reactions by Surface Excitation
Authors: Ashby Carol I. H.
Published: March 2011

Ultraviolet irradiation of the surface of graphite leads to the enhancement of the reaction of graphite with hydrogen to form methane under conditions where photo-induced thermal effects are negligible. Wavelength dependence of the photoenhancement correlates with excitation of the π-valence to π-conduction transition of graphite centered at 260 nm. Subsequent formation of some reactive excited state species leads to enhanced reaction rates. Likely candidates for such reactive species have been identified by comparative kinetic studies of the thermal and the photoenhanced reactions. For example, at low temperatures (< 500 K), the rate-limiting step of the thermal reaction is addition of H to surface CH3 groups, and the observed photoenhancement can be explained by activation of these CH3 groups.
Local Crystal Orientation in Laser Annealed Silicon Using a Raman Microprobe
Authors: Farrow L. A. , Hopkins J.B. , Fisanick G J
Published: March 2011

In this paper, we discuss the application of polarization selective Raman microprobe spectroscopy to the detailed, non-destructive analysis of the local crystal orientation of a polysilicon sample grown over SiO 2 pads and laser annealed. Intensity measurements taken as a function of input polarization angle are fit to an expression derived from the Raman scattering selection rules to calculate the angles by which the crystal structure is twisted within the original substrate plane, as well as the degree of tipping of the crystal plane away from the plane of the Si substrate. The results give some indication as to the direction of seeding during recrystallization.
Gas Phase Spectroscopy of a Ge Film LCVD Reactor
Authors: Osmundsen J. F. , Abele C. C. , Eden J. G.
Published: March 2011

The gas phase photochemistry of an LCVD reactor used to grow polycrystalline Ge films was studied by absorption and emission spectroscopy. Upon photodissociating GeH4 (5% in an Ar or He carrier) at 248 nm (KrF laser), excited states of Ge and GeH are produced. Spatially, spectrally and temporally resolved atomic and molecular emissions are monitored as a function of gas pressure and laser intensity. These data lead to the conclusion that GeH2 is predominantly produced directly from GeH4 by The simultaneous absorption of two 5 eV (λ = 248 nm) photons.
Laser-Induced Fluorescence Detection of Diatomic Products of Reactive Ion Etching: SiN, SiO, and SiF
Authors: Walkup R. , Avouris Ph. , Dreyfus R.W. , Jasinski J.M. , Selwyn G.S.
Published: March 2011

Laser-induced fluorescence is used to detect a variety of silicon-containing diatomic radicals produced by the reactive ion etching and glow discharge sputtering of silicon and its oxide and nitride. The products include SiN, SiO, and SiF. Examination of the concentration of these molecules as a function of plasma conditions provides information about their production mechanisms.
Study of Photo-Induced Thin Film Growth on Cds Substrates.*
Authors: Arnone C. , Call' C. , Riva-Sanseverino S.
Published: March 2011

Photo-induced growth of ZnS on CdS has been studied using amorphous (thin film) and single-crystal substrates. The effect has been found to occur for light of wavelength shorter than the CdS absorption edge; a maximum light-induced thickness enhancement of 700 Å has been obtained for the ZnS film, with a growth rate of 2000 Å/min. The lightinduced growth, with its observed “memory” of several minutes is consistent with photo-desorption of an adlayer.
Electromagnetically-Induced Surface Microstructures and Enhanced Field Effects in Laser Processing
Authors: Brueck S. R. J. , Ehrlich D. J. , Murphy D. V. , Tsao J. Y.
Published: March 2011

The presence of microstructures on surfaces undergoing laser processing modifies the electromagnetic boundary conditions and can lead to dramatic changes in the intensity of the local electromagnetic fields and hence in the reaction rates and final morphologies resulting from the laser reaction. Examples are presented for periodic structures on planar surfaces — the rippling of Ag surfaces during laser oxidation; and for isolated dielectric structures — enhanced scattering (∼ 100x) due to dipolar resonances in Si particles.
Complete Fabrication of Bipolar Devices in Silicon
Authors: Lloyd M. L. , Ibbs K. G.
Published: March 2011

UV laser photochemical doping offers the possibility of direct fabrication of semiconductor devices by high-intensity photolithographic projection. We have recently demonstrated control of parameters such as dopant concentration and junction depth to the extent that npn structures can be readily produced.

Recent work also indicates that contact resistance can be dramatically reduced from the levels found using simple probes, by the low-temperature laser deposition of metals, and that this technique also can be used to connect elements in a circuit.

In this paper the progress made towards the fabrication of complete planar devices is described and the I-V characteristics of some simple diodes are shown.
Resonance Fluorescence and Photon Trapping of Two Atoms on a Metallic Surface
Authors: Huang Xi-Yi , Liu K. C. , George Thomas F.
Published: March 2011

Surface-dressed optical Bloch equations are derived for the purpose of evaluating the resonance fluorescence spectrum of two interacting identical atoms near or adsorbed on a metal surface. The derivation takes into account the influence of reflected photons, dephasing due to atomic collisions, the linewidth of the driving laser field and the resonance excitation of surface plasmons. A unique behavior of the surfacemodified fluorescence, not seen in analogous gas cell experiments, is predicted. Under the appropriate circumstance, a photon emitted from one of the two atoms can be trapped by the two-adatom-surface system, and this is studied by means of a theory which treats the atoms and their surface images on the same footing.
Theoretical Aspects of Laser-Induced Periodic Surface Structure Formation
Authors: Hutchinson Michael , Lee Ki-Tung , Murphy William C. , Beri A. C. , George Thomas F.
Published: March 2011

Laser-induced periodic pattern formation has been observed on a variety of substances. In particular, low-power lasers have been used to deposit a pattern on a metal surface. For a relatively smooth surface grating, this pattern can be explained in terms of a perturbative solution of Maxwell's equations. However, as the surface grating is enhanced by this initial deposition, the perturbative solution breaks down. An alternate non-perturbative solution of Maxwell's equations for such rough surfaces is considered here.
The Influence of Laser Radiation on an Absorbing Aerosol
Authors: Morse T.F. , DiGiovanni D. , Cipolla J.W.
Published: March 2011

When aerosol particles are immersed in a gas in which a temperature gradient is present, a force proportional to this gradient moves these particles toward the lower temperature. This is the thermophoretic force.It is responsible for the deposition of aerosol particles in processes employed in the manufacture of gradient index silicon dioxide, germanium dioxide optical fiber preforms.The deposition efficiency is approximately 50%, and in order to increase this efficiency, we have examined the interaction of an absorbing silicon dioxide aerosol with carbon dioxide laser radiation.The resulting temperature profile mirrors the intensity distribution, since the aerosol temperature is proportional to the local laser intensity.The absorbed radiation thus creates a temperature gradient that results in additional thermophoretic and convective motion. A simple model of laser-induced buoyant convection and thermophoresis is presented, and it is shown how deposition efficiency can be increased with laser radiation.Theoretical and preliminary experimental results are discussed.
Chemical Vapor Deposition of Silicon Films by Pulsed CO2 Laser Irradiaton of Silane
Authors: Pauleau Y. , Stawski R. , Lami Ph. , Auvert G.
Published: March 2011

Silane molecules have been irradiated by a pulsed CO2 laser operating at 10.59 μm. The threshold of silicon formation by homogeneous dissociation of silane has been investigated as a function of laser fluence (0.1–3.5 J/cm2) and silane pressure (1–100 Torr). Silicon films have been deposited on quartz substrates using the laser beam either perpendicular or parallel to the substrate surface. The crystallographic structure and deposition rate of these silicon films are found to be dependent on the incident angle of the laser beam, silane pressure, substrate temperature and laser fluence. The growth mechanism of these films is discussed.
Temperature Distributions in CW Laser Induced Pyrolytic Deposition
Authors: Piglmayer Klaus , Doppelbauer Josef , BÄuerle Dieter
Published: March 2011

Temperature distributions induced by cw laser radiation absorbed on the surface of combined structures, consisting of discs or of stripes on semi - infinite plane substrates, are calculated for different material parameters and different geometries. The relevance of the numerical results is demonstrated by comparison with earlier experimental data obtained in pyrolytic laser-induced chemical vapor deposition.
Laser-Induced Chemical Vapor Deposition of Silicon Nitride Films
Authors: West Gary A. , Gupta Arunava
Published: March 2011

Films of silicon nitride have been deposited using a continuous wave CO2 laser to excite gaseous mixtures of silane and ammonia. A typical deposition rate is 150Å/min. The hydrogen film content and its dependence on the substrate deposition temperature are similar to that observed for plasma CVD silicon nitride. The CO2 laser CVD films are silicon rich with a Si/N ratio = 1.2 at a NH3/SiH4 gas flow ratio of 1000. Conformal step coverage is observed on patterned silicon oxide features.
Beam-Assisted CVD of Microelectronic Films
Authors: Emery K. A. , Thompson L. R. , Bishop D. , Zarnani H. , Boyer P. K. , Moore C. A. , Rocca J. J. , Collins G. J.
Published: March 2011

The properties of SiO2 and Si3 N4 films deposited by an ArF excimer laser, glow discharge electron beam and conventional plasma-enhanced CVD are compared. The deposition apparatus, technique, and conditions in addition to the physical, chemical and electrical properties of the films are discussed.
Silicon CVD by Twin-Beam Processing
Authors: David Binnie T. , Colles M. J. , Wilson J. I. B. , West J.
Published: March 2011

The technique of simultaneous twin-beam processing has been investigated and used to deposit thin films of silicon on a silicon substrate.

An argon ion laser was used to create a large concentration of free carriers in the Si conduction band. These carriers were spatially localized in the beam spot on the surface of the substrate. The effective absorption coefficient of 10.6 radiation (carbon dioxide laser) can thus be increased to greater than 104 cm−1 . Experimental evidence illustrates that this efficient coupling of the high-power CO2 radiation (10–30 W) to the otherwise non-absorbing silicon can be totally controlled by the low-power (1–4 W) argon ion incident beam. The difference between absorption increase due to optically created carriers and thermally created carriers is clearly illustrated.

This synergistic effect has been used to induce pyrolytic deposition of Si from SiH4 non-flowing gas onto a Si substrate. Lines and spots of various widths and thicknesses have been grown by the controlling low-power argon ion beam spot.

Preliminary investigations on the quality of the deposits using i.r. spectroscopy ellipsometry, SEM and Auger analysis have been carried out.
Molecular Simulation of Adsorption of Simple Gases in Aluminophosphates and Pillared Clays
Authors: Cracknell Roger , Koh Carolyn A , Thompson Stephen M , Gubbins Keith E
Published: March 2011

We report Grand Canonical Monte Carlo (GCMC) simulation studies of the adsorption and heat of adsorption of simple inert gases in two model microporous materials: aluminophosphates (AℓPO4-5, AℓPO4-8 and VPI-5) and alumina-pillared clays. The intermolecular potentials are spherical Lennard-Jones for both the fluid-fluid and fluid-solid interactions; both structured and structureless walls are considered. For argon in VPI-5 and AℓPO4-5 we find qualitative agreement with experiment, but the predicted maximum adsorption is about 20% higher than that obtained experimentally; possible reasons for this discrepancy are discussed. For the pillared clays we find a first order phase transition below some critical pillar density. This finding seems to be in qualitative agreement with existing experimental data.
Confinement Between Rough Substrates: Fluctuation-Induced Forces, and Other Manifestations
Authors: Kardar Mehran , Li Hao
Published: March 2011

Most surfaces are rough. In many cases the roughness is self-affine, with a width w that scales with the observation length L as w ∼ LC. We consider the medium confined between two such plates, and discuss how the dependence of various quantities on the separation of plates is modified by their roughness. Specific examples include fluctuation–induced forces, shifts in critical temperatures, and capacitance.
Dielectriic Dispersion Measurements of Salt-Water Saturated Porous Glass Compared with Local Porosity Theory.
Authors: Hansen B. D. , Haslund E. , Hilfer R. , NØst B.
Published: March 2011

A recent study [1] of the dielectric frequency response of a two component composite performed on a single specimen shows that local porosity theory LPT [2] represents a substantial improvement compared with other theories predicting the complex dielectric dispersion [3,4,5]. The purpose of the present work is to extend this investigation to a systematic study on several specimens with different compositions.
Directed Polymers in Restricted Geometries
Authors: Zumofens G. , Klafter J. , Blumen A.
Published: March 2011

We study numerically directed polymers in random potential fields for one-dimensional and fractal substrates. For fractal substrates the time evolution of the mean transverse fluctuations depends besides on the randomness of the potential also on the fractal nature of the substrate. The two effects enter in a subordinated way, i.e. the corresponding characteristic exponents due to the potential and the substrate combine multiplicatively. For a one-dimensional substrate the propagator P(x, t), the probability distribution of the transverse displacement x(t), follows the scaling form P(x, t) ∼ 〈x2(t)〉-1/2f (ξ), where ξ is the scaling variable ξ = x/〈x2(t)〉1/2. The numerical results support the scaling function f (ξ) ∼ exp (-cξδ) with δ > 2 which indicates an “enhanced” Gaussian behavior. These results are compared with those of a related “toy model”.
Spatiially Resolved Spectra of Miicro-Crystals and Nano-Aggiregates in Doped Polymers
Authors: Birnbaum Duane , Kook Seong-Keun , Kopelman Raoul
Published: March 2011

Near-field optics techniques make it possible to by-pass the optical diffraction limit (“uncertainty principle) and attain spatial resolution of λ/50 or better. We present near-field scanning optical spectroscopy (NSOS) data on α and ß mixed micro-crystals of perylene and on various aggregates of tetracene doped into PMMA. The spatial resolution is limited by the size of the scanning photon tip and its distance from the sample. We use nanofabricated optical fiber tips (aluminum coated) that are as small as 100 nm. These can be piezoelectrically scanned close to the sample. Fluorescence spectra easily differentiate between adjoining microcrystallites of α and β perylene, giving spectra identical with those of large (>1 cm) single crystals. The apparently homogeneous molecularly doped polymer samples of tetracene/PMMA have regions that fluoresce anywhere between green and red. Thus the spatially resolved spectra are much sharper and more detailed than the broad and featureless bulk spectra. The different emission spectra are attributed to different aggregates of the tetracene guest embedded in the PMMA host
Experimental Study of An A+B→C Reaction-Diffusion System in a Capillary: Crossovers from Reaction to Diffusion-Limited Regimes
Authors: Koo Yong-Eun , Kopelman Raoul , Yen Andrew , Lin Anna
Published: March 2011

Continuing work on elementary A+B→C reactions in capillaries, we study the reaction front dynamics of xylanol orange with Cr3+ in an effectively one-dimentional system with initially separated reactants. This reaction, in contrast to previously studied systems, is not strictly in the diffusion limited regime. i.e. the probability of reaction between species is not unity. Anamalous behavior not seen in the diffusion-limited case has been observed experimentally for the reaction rate, boundary motion, reaction zone width, and local reaction rate. The observed behavior is consistent with recent theoretical studies.
Mechanisms which can Accelerate the Growth of Phase Separating Domains Near a Wall
Authors: Troian Sandra M.
Published: March 2011

Though the dynamics of bulk phase separation during spinodal decomposition is fairly well understood nowadays, recent experiments have shown that the same process occuring near a wall introduces some surprisingly fast domain growth kinetics. Studies of both polymer mixtures and simple binary fluids at critical composition quenched into the unstable regime reveal the presence of a fast mode associated with domains coarsening at the wall. The scattering data indicates that while the bulk domains grow in time as t1/3, as dictated by usual diffusion driven dynamics, the surface domains coarsen with exponents ranging from about 1.1 to 1.5 depending on the quench depth. We construct a model in which the average size of domains in a binary mixture undergoing spinodal decomposition near a wall can achieve growth exponents much larger than 1/3. The accelerated growth is associated with the domains of the non-wetting phase coarsening anisotropically against a wall coated with the wetting phase.The faster growth evolves from coupling Lifshitz-Slyozov type coarsening for critical volume fractions, modified to include the geometric constraint of growth near a wall, the process of domain coalescence. Included are some predictions for experimental tests of these ideas.
Diffusion Mechanisms of Molecules on Structured Surfaces
Authors: Silverberg Marvin
Published: March 2011

The diffusion of ethane and n-pentane on metallic surfaces is studied by molecular dynamics simulations. On atomically smooth, faced centered cubic (111) crystal surfaces, n-pentane has several conformational states, each of which diffuses at a different rate. Diffusion barriers are distinct from intramolecular conformational isomerization barriers. Weak friction is observed. Hopping diffusion occurs near the diffusion threshold. As the temperature is raised, correlated barrier crossing and recrossing increases. n-Pentane slides, transverse to its axis, without changing its orientation with respect to the surface. Conformational changes occur on a longer time scale than diffusional barrier crossing and are restricted by the surface. Far above the diffusion threshold temperature, partial molecular desorption occurs and conformational isomerization is less restricted. The molecules slide, roll and tumble continuously across the surface. A similar pattern of temperature-dependent change in diffusion mechanisms occurs in ethane but without conformational changes.
Buckling of a Confined Colloidal Crystal
Authors: Chou T. , Nelson D. R.
Published: March 2011

The behavior of colloidal suspensions confined between two plates narrowly spaced is examined. When plate separations are small, only one layer of particles can be confined; however, as plate separation is increased, multiple layers will eventually form. These layers can exist in a variety of structures depending on the energetics of packing. We examine the unstable modes which form as a single layer buckles on its way to forming two layers. Three ordered states are found; which one is selected depends on the form of the interparticle and wall potentials.
Diffusion-Limited Binary Reactions: a Hierarchy of Non-Classical Regimes
Authors: Argyrakis Panos , Kopelman Raoul , Lindenberg Katja
Published: March 2011

We discuss the various regimes of kinetic behavior of the densities of reactants for the A + B → 0 reaction from initial to asymptotic times. Scaling arguments and Monte Carlo simulations demonstrate an unexpectedly rich hierarchy of cross-overs among time exponents ir the decay law ρ ˜ t−α. For instance, in one dimension possible time domains include classical (α = 1), A + A-type (α = 1/2), Zeldovich (α = 1/4), asymptotic correlated (α = 3/4) and finally nonalgebraic (exponential) finite size regimes. Simulation and theory are consistent with respect to both exponefits and cross-over times for one and two dimensions.
Polymer Adsorption.
Authors: Daoud M.
Published: March 2011

Because of both their practical importance and their fundamental properties [1], polymers at interfaces have been under constant study. In this paper, we will consider the adsorbtion of linear chains on flat surfaces. Theoretical interest in this question was renewed recently by the introduction of scaling methods by de Gennes [2], Pincus [3], Binder, Kremer and Eisenriegler [4]. This allowed a new approach to the problem. New experimental methods such as neutron reflectivity [5] and small angle neutron scattering [6] also provided a much more detailed information than was previously available. This combined progress in theory and technique improved tremendously our understanding of the adsorption of linear chains on a flat impenetrable surface when the surface attraction is not too large. Many important questions however remain open. These are related both to the quality of the surface and to the nature of the solvent. Actual surfaces are never completely flat or homogeneous. Work is in progress to take into account surface roughness [7,8] and chemical imperfections [9,10]. Similarly, the quality of the solvent was considered in many directions. These include surface driven phase separation [11], or the effect of a mixed solvent on a copolymer. A somewhat different solvent effect will be considered here and is related to the length of the solvent molecules. Previous studies were concerned with solutions in a simple solvent [12]. It is possible both theoretically and experimentally to consider long polymers, made of N monomers, dissolved in shorter chains, with P units, of similar nature and slightly different interaction with the surface. The interest in this question is twofold. First by changing P, it is possible to have either adsorbed or desorbed probe chains as we shall see. Second, a generalization of this problem is to consider a mixture of both long and short chains in a simple solvent. The question then is the displacement of an adsorbed polymer by another one. In the following, we will only consider the equilibrium properties for the first case, in the absence of any simple solvent. As we shall see, this question is already very rich.
Nanoengineering with DNA
Authors: Seeman Nadrian C.
Published: March 2011

DNA is a tractable medium for controlling the structure of matter on the nanometer scale. We have explored ligating together stable branched DNA molecules to form geometrical objects. By this means, we have assembled a 3-connected molecule whose helix axes have the connectivity of a cube. The construct is a hexacatenane, each of whose cyclic strands corresponds to a face of the object. Each of its twelve edges contains a unique recognition site for cleavage by a restriction enzyme; these sites are used to demonstrate the assembly of the object. The plectonemic structure of DNA also permits the directed synthesis of molecular knots. Recently, we have constructed trefoil knots from B-DNA and an amphichiral figure-8 knot whose helical domains contain both B-DNA and Z-DNA.

We have developed a solid-support methodology for the synthesis of geometrical objects. This approach provides greater control over products and topological purity, and lends itself better to automation. Branched molecules containing 3–6 double helical arms can be formed from equimolar mixtures of their component strands, thereby enabling the construction of 3–6 connected networks. The goals of this work include the construction of periodic multiply-connected networks of DNA. The aims of these DNA constructions include using them as scaffolding to build periodic macromolecular arrays for diffraction purposes, as well as directing the assembly of molecular electronic devices. There are wellcharacterized molecular transformations of DNA that make nano-scale machines feasible to build in this molecular context. These materials are likely to be useful for understanding crystallization processes and structure-function relationships.
α-Helical Polypeptide Materials
Authors: Enriquez E. P. , Jin M. Y. , Jarnagin R. C. , Samulski E. T.
Published: March 2011

Poly(γ-benzyl-L-glutamate) (PBLG) may be derivatized on its periphery by covalently attaching χ-active NLO chromophores at the termini of its sidechains and thereby give a new class of SHG materials. The inherent liquid crystalline properties of concentrated solutions of α-helical PBLG may be exploited to establish unique supramolecular structures prior to E-field poling. When PBLG is derivatized at its N-terminus with lipoic acid, it will self-assemble on gold to give a thin film. Angle-dependent XPS, ellipsometry, contact angle measurements, and grazing angle IR reflection-absorption spectroscopy give quantitative information about the orientation of the polypeptide α-helices relative to the substrate surface. Consequently, polypeptides, in particular, Merrifield-synthesized or recombinant DNA-expressed synthetic polypeptides, present a novel fabrication route to thin films wherein molecular-engineered functionalities (chemical, electrical, or optically active species) may be encoded into the macromolecule's primary structure and subsequently expressed spatially via the spontaneous self-organization of these rod-like polymers.
Mechanical Properties of Biopolymer Chains
Authors: Pachter Ruth , Haaland Peter D. , Crane Robert L. , Adams W. Wade
Published: March 2011

Molecular simulations that predict the molecular mechanical response of alpha-helical biopolymers with a reinforcing intra-molecular hydrogen bonding network, viz,, a ‘spring-like’ behavior, are presented in this study. Mechanical properties of extended biopolymer strands based on naturally occurring amino acids, namely poly(L-A1a) and for comparison poly(LGlu), versus synthetic PPTA containing an amide bond, are compared to those assuming alpha-helical structures. Thus, the pivotal role of such motifs in biological systems utilizing superior compressive mechanical properties can be inferred.
Crystalline Structure and Moisture Effects on Deformation Mechanisms of Gelatin Films Under Mode I Stress Field
Authors: Ni Beta Yuhong , Faou Anne Le
Published: March 2011

Crazing and shear-deformation phenomena are found in thin gelatin films. The gelatin crystallinity and relative humidity affect these deformation mechanisms significantly. A deformation map of gelatin films at low strain rate is established.
Hydroxyapatite/Al2 O3 Composite Biomaterial Implant
Authors: Shaoxian Zeng , Zhixiong Yang , Ping Ling , Guanghong Xu , Wanpeng Cao
Published: March 2011

A new type of composite biomaterial was developed and is described in this paper. The composite is based on a high strength Al2O3 ceramic substrate, sintered with a layer of hydroxyapatite. The layer was examined by x-ray diffraction and infrared spectroscopy. Animal experiment showed that the composite has good biocompatibility, and can form tight osteointegration with bone in 12 weeks. It is a bioactive material with a high strength.
Large Scale Thermally Synthesized Polyaspartate as a Biodegradable Substitute in Polymer Applications
Authors: Wheeler A.P. , Koskan L.P.
Published: March 2011

Polyanionic proteins isolated from biominerals serve as models for the development of biodegradable surface-reactive commercial polymers. A simple model for the natural polyanions is polyaspartic acid. This polymer may be made on a large scale using thermal polymerization of dry aspartic acid. The immediate result of the reaction is polysuccinimide which is hydrolyzed with base to form the polypeptide. The overall process yields up to 99% conversion of aspartic acid to polyaspartate. The thermal polyaspartate (TPA) is a copolymer having 70% of the amide bonds formed from β-carboxyl groups and 30% from α-carboxyl groups. TPA is as effective as the commercial polyanion polyacrylate in mineral dispersion and growth inhibition assays. Biodegradation of the TPA has been established using standard BOD and CO2 evolution assays. In contrast, polyacrylates appear to be non-degradable. Modifications of the TPA have been made by reacting the succinimide with nucleophiles. Crosslinking of the polymer has been achieved, a process which results in absorbent gels. Because TPA can be produced in large scale, has similar activity to polyacrylate and is biodegradable, it seems a likely candidate for use in numerous applications in which non-degradable polyanions are employed. These applications include use as detergent additives, water treatment chemicals, dispersants for the paint and paper industry and as superabsorbents in health and sanitary products.
Engineered Proteins for Biomaterials
Authors: Stayton Patrick S. , Chilkoti Ashutosh , Long Cynthia J. , Pettit Dean K. , Tan Philip H. S. , Chen Guohua , Hoffman Allan S.
Published: March 2011

A molecular adaptor for interfacing environmentally sensitive, soluble polymers and antibody molecules has been developed. The gene coding for the minimally sized, 55 amino acid IgG binding domain from protein G has been constructed by total gene synthesis. This domain is thermally stable, exhibits a highly reversible folding and unfolding equilibrium, and recognizes IgG and Fab molecules with high affinity. These properties make the protein G domain a potentially useful adaptor for non-covalent immobilization of antibodies to soluble polymers and hydrogels. Engineered single-chain Fv antibody fragments have also been constructed and a method for expanding the usefulness of the protein G adaptor to these molecules is proposed. The engineered antibodies also provide a model system for developing general immobilization strategies aimed at maximizing binding affinities and therapeutic responses. The overall goal is to develop optimized engineering designs for functionally optimized antibody-material hybrids.
In Situ Characterization of Interfacial and Bulk Properties of Lithium Polymer Batteries Using 4-Probe DC Techniques
Authors: Liu Meilin , Visco Steven J. , De Jonghe Lutgard C.
Published: March 2011

The use of transient and steady-state 4-probe techniques for the evaluation of the limitations to performance in solid-state electrochemical devices is described. The application of sequential, bipolar square-wave current pulses to a solid polymer cell with two internal reference electrodes allows separation of the polarization behavior of the various components of the cell, and indicates the rate limiting processes in the cell. Careful design of the experimental cell and appropriate selection of current pulse width allows evaluation of fundamental kinetic and transport properties, as well as activation parameters. Steady state constant-current measurements using 4-probe cells allows in situ observation of interface stability and/or polarization as a function of time as the cell is cycling.
Theory of Ionic Diffusion Across Material Interfaces
Authors: Balkanski M. , Nachev I. , Deppe J. , Wallis R. F.
Published: March 2011

Ion diffusion across material interfaces is considered in a sequence of approximations with increasing complexity. First, the one-dimensional lattice gas model of particle diffusion is generalized to include a finite width interface region, and the possible existence of an energy barrier at the interface. Overvoltage measurements on InSe, and dielectric loss measurements on B2O3 - 0.5Li20 - 0.15Li2SO4 are used to determine the field-free hopping rates in the two materials. It is shown that the energy barrier is a dominant parameter. This model is then modified by considering the disorder of the glass structure and the blocking effect resulting from the ion interaction. Next, a more rigorous treatment is presented by solving the Poisson equation with appropriate boundatry conditions, and a self-consistent theory of the ionic diffusion is proposed. To clarify this problem, an intermediate step and two additional models with increasing sophistication are considered: first, the potential φ(x) of the moving charge density n(x) is calculated and it is shown that φ(x) is not negligible. Then, a feed-back is provided by including this potential in the diffusion equation. This treatment is already self-consistent and more realistic but leads to long computations even for the simple one dimensional lattice-gas model. A remedy of this difficulty is proposed whereby the theory is reformulated in order to guarantee from the beginning the self-consistency of the solution of the non-linear diffusion problem. Straightforward extensions to the two-dimensional case are then possible. The results of the computations are illustrated with numerical examples for different values of the physical parameters.
A Cluster Modelling Study of Conductivity of Yttria-Stabilized Zirconia
Authors: Depero Laura E. , Zocchi Marcello , Parmigiani Fulvio
Published: March 2011

On the basis of a previously described structural model for the Yttria-Stabilized Zirconia, the conductivity for this material can be calculated. A fixed number of clusters is generated in a structure of 70×28 polyhedra to simulate different Y contents in the structure. The results are compared with the experimental results obtained by others and discussed.
Ionic Properties of Hydrous Oxide Gels
Authors: Livage J.
Published: March 2011

The sol-gel process offers new opportunities for the synthesis of ionic materials, specially in the shape of thin films. Hydrous oxides are obtained which exhibit specific properties arising from strong interactions betwwen adsorbed water molecules and the oxide network. Sol-gel derived coatings are good candidates as electrode materials for lithium batteries or electrochromic devices. Their open structure allows easier diffusion of Li+ions in the liquid phase while electrons are delocalized through the oxide network. Moreover, water molecules favor the formation of ordered phases leading to the deposition of layers with preferred orientation. Electrochemical insertion can then be described as an intercalation process between solid particles.
Structure, Diffraction and Energetic Stability of the Spinel form of LiCoO2
Authors: Reimers J. N. , Li W. , Rossen E. , Dahn J. R.
Published: March 2011

A recently reported new phase of LiCoO2, called LT-LiCoO2 (LT stands for Low Temperature) by the discoverers, was synthesized at 400°C and studied using X-ray diffraction and electrochemical de-intercalation of lithium. The first reports of LT-LiCoO2 give convincing evidence that the compound is layered with the same structure type as LiCoO2 prepared at 850°C (HT-LiCoO2). However, the electrochemical properties of LT and HT LiCoO2 are markedly different, which is hard to understand if the crystal structures are almost the same. A better understanding of the diffraction and electrochemical data is attained if the LT structure is assumed to be spinel related analogous to Li2Ti2O4. We show that the layered structure (with suitable lattice constants and layer spacings) and spinel structure give identical powder diffraction patterns. We also show that the formation energies of the layered and spinel structures are also identical using a lattice gas model with pair-wise atom-atom interactions.
Influence of the Metal/Ceramic Interface Characteristics on Conductivity Measurements of Na-β" Alumina by Impedance Spectroscopy
Authors: Schreiber M. , Butchereit E. , Lutz C.
Published: March 2011

The quality of the metal/ceramic interface of solid ionically conducting materials is an important when undertaking impedance spectroscopy measurements. One major concern is the contact area between the metal and the ceramic. This work focussed on the treatment of the ceramic to the metal application by utilizing a standard quality Na-β" alumina. Next, a number of different metals were applied to the ceramic surface by different techniques, i.e. sputtering and evaporation, to serve as blocking electrodes in impedance spectroscopy measurements. The impedance spectroscopy measurements were carried out at temperatures from 30 - 300°C over a frequency range from 1 to 5 ×105 Hertz. The results are discussed in terms of the various parameters of impedance plots. Surface analysis techniques were applied to investigate the metal/ceramic interface before and after impedance spectroscopy measurements.
Surface Oxygen Exchange Kinetics in Oxide-Ion Conducting Solids
Authors: Boukamp Bernard A. , Bouwmeester H.J.M. , Verweij H. , Burggraaf A.J.
Published: March 2011

The surface oxygen exchange on oxides with high oxygen ion mobility is modelled with a two step reaction with adsorbed mono-atomic oxygen species as intermediate. Interpretation of the Po2 dependence of the exchange rates, following from this model, indicates that these adsorbed oxygen atoms are singly charged.

For the stabilized δ-Bi2O3 solid electrolyte a good agreement has been found between the isotope exchange model and the electrochemical study of the oxygen exchange using gold electrodes. For the mixed La-Sr cobaltite perovskite a change in the surface exchange reaction is observed going from room temperature to 600°C. Indications are that above 450°C the bulk exchange is rate limiting with a (Po2)−1 dependence while below this temperature it is assumed that the dissociative adsorption is rate limiting with a (Po2)1/2 dependence.
The Structure and Ionic Conduction in Fluorite-Type Solid Solutions
Authors: Ito Yoshiaki
Published: March 2011

The crystal structure of β-Pb0.9Bi0.1F2.1 has been investigated in the temperature range 294 to 710K by single crystal X-ray diffraction method. Phase transition is observed at about 700K and the mean square displacements (MSD) of metal and fluorine ions show a rapid increase near the transition temperature. The fluorine ions do not show anharmonic thermal vibrations in the regular site in the temperature range.
Crystal Phase Effects in Electrochromic WO3
Authors: Klein J. D. , Yen A.
Published: March 2011

The electrochromic behavior of crystalline WO3 thin films of two different crystal structures was investigated. The films were deposited on ITO-coated Coming 7059 glass and transparent single crystal sapphire substrates by electron beam evaporation. The usual monoclinic crystal structure was obtained by post-annealing films deposited at low substrate temperatures. An alternative phase was generated by in-situ growth of crystalline films at high substrate temperatures. The reversible electrochemical insertion of Li was demonstrated by cyclic voltammetry. Optical switching was observed by comparing visible transmittance, visible reflectance, and infrared reflectance spectra of films before and after Li intercalation. The two film types assumed similar crystal structures upon lithiation. High infrared reflectance in the monoclinic phase was described well by an elementary freeelectron plasma edge model. However, the high-Ts. film exhibited significantly poorer reflectance in the infrared when lithiated.