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Abstract: We investigate by first-principles calculations the effect of ferrous iron, Fe2+, on the structure and the equation of state of MgSiO3 post-perovskite. We find that ferrous iron is high-spin over the pressure range of the mantle assuming a ferromagnetic structure. The bulk modulus and the specific volume increase with the addition of ferrous iron to MgSiO3. We find that Fe partitions preferentially to post-perovskite and broadens the two-phase pressure range. [Copyright &y& Elsevier]

Abstract: We report first principles density functional calculations of the Born effective charges and electronic dielectric tensors for the relaxor PMN (PbMg1/3Nb2/3O3). Visualization of the Born charge tensors as “charge ellipsoids” have provided microscopic insights on the factors governing piezoelectric enhancements with polarization rotation. Several 15 and 30-atom ferroelectric and antiferroelectric supercells of PMN involving 1:2 and 1:1 chemical ordering have been studied. A cascading set of ferroelectric phonon instabilities lead to several low symmetry monoclinic structures. We find a ground state with a 15-atom unit cell with 1:2 chemical ordering along [111] with a monoclinic C2 structure. [Copyright &y& Elsevier]

Using a first-principles based, magnetic tight-binding total energy model, the magnetization energy and moments are computed for various ordered spin configurations in the high pressure polymorphs of iron (fcc, or γ-Fe, and hcp, or ε-Fe), as well as ferromagnetic bcc iron (α-Fe). For hcp an antiferromagnetic spin configuration is more stable than non-magnetic ε iron up to about 50 GPa. Accounting for magnetism yields better agreement with the experimental equation of state, in contrast to the non-magnetic equation of state, which is in poor agreement with experiment below 50 GPa. We also studied non-collinear magnetism in γ- and ε-Fe. In ε-Fe the non-collinear effects are quite small energetically; in its stability field the collinear afmII structure is more stable than all non-collinear structures we explored. [Copyright &y& Elsevier]

We have produced, by thermal decomposition of organometallic complexes in a bulk film of poly(styrene-b-2-vinyl pyridine (P(S-b-2VP)), nonagglomerated iron, iron–cobalt, and cobalt–nickel alloy nanoparticles. The particles are patterned on the nanoscale: they reside within the P2VP domains of the block copolymer morphology. These results are made possible by the selective sequestration of organometallic complexes into these domains in amounts sufficient to nucleate and grow substantial quantities of nanoparticles, some of which are large enough to show non-zero coercivity at room temperature. [Copyright &y& Elsevier]

We demonstrate that all solid polymers are intrinsically brittle and will undergo a ductile to brittle fracture transition based on the nature of their bonding alone. The most effective way of avoiding a ductile to brittle transition is to reduce the plastic resistance to delay reaching the brittle strength which in unoriented polymers is governed by intrinsic cavitation. While a number of possibilities for this exist, the most widely used techniques involve incorporation of rubbery particles that can cavitate or rigid particles that can debond prior to plastic flow. In both approaches the continuous homo-polymer is transformed into a quasi-regular cellular solid that is much more capable of undergoing large local plastic flow by ligament stretching between cavitated particles and is less susceptible to the propagation of brittle cracks under the usual conditions of tensile straining. Under impact conditions, however, in a notched sample which concentrates the strain rate at the notch root, the plastic resistance of the stretching ligaments rises sharply due to two separate but related effects. First, by an increase in the shear modulus due to the high frequency nature of the Izod impact test to fracture, viewed as a quarter cycle oscillation, which directly elevates the flow resistance and second, by the further effect of increase due to the much increased plastic strain rate. At the notch root then, the plastically stretching and strain hardening ligaments are left with a much reduced capacity to strain further before the cavitation stress is reached. While rubber particle-modified polymers can still exhibit considerable toughening, rigid-particle-modified polymers suffer severely from clustering of rigid particles into super critical flaws that trigger brittle response, much like what is encountered in structural steels.Based on their known mechanical response in neat form six, semi-crystalline polymers have been analyzed in detail to evaluate their potential for toughening under impact conditions. The results correlate very well with the experimental findings. [Copyright &y& Elsevier]

Presents a technique for solubilizing polyenes that preserves their model nature. Synthesis of triblock copolymers through sequential ring-opening metathesis; Nonlinear optical characteristics of polyenes; Analysis of hyperpolarizability on conjugation length.

Investigates whether the physical properties of iron are consistent with the anisotropy in the earth's inner core. Forward models of the inner core on the basis of predictions on the elasticity of iron; Use of Slater-Koster total energy, tight-binding Hamiltonian in the calculations; Determination of single-crystal, elastic tensor of the phases of seismologic density of inner core.

Studies the stability of orthorhombic magnesuim-rich silicate perovskite (MgSiO3) in the Earth's lower mantle. Results of electronic-structure calculations of the energetics of displacive phase transitions in MgSiO3 perovskite; Demonstration that the lower-symmetry orthorhombic phase should be highly favored throughout the lower mantle.

Abstract: A complete set of elastic and piezoelectric constants for single-domain rhombohedral Pb(Zn1/3Nb2/3)O3 3 is obtained using Brillouin scattering. The bulk modulus and elastic constants agree with the values obtained from ultrasonic methods, but the piezoelectric constants are smaller. Differences in piezoelectric constants from different techniques are due to frequency dispersion and the contributions of domain boundaries. The pressure dependence of the Brillouin shifts of amorphous BeH2 was measured from ambient pressure to 17GPa. The equation of state is deduced from the pressure dependence of the sound velocity; the bulk modulus is 14.2 (±3.0)GPa and its pressure derivative is 5.3 (±0.5). [Copyright &y& Elsevier]

The effects of interfacial adhesion strength on the mechanical properties of composites of polypropylene and glass particles were investigated. The 3.5 μm average diameter glass particles were surface-treated using two silanes with different functional groups. The functional groups were hydrocarbons, expected to promote adhesion between filler and matrix, and fluorocarbons, expected to reduce the strength of adhesion. Mixtures of the functional groups were also used to treat the surface of the glass to obtain better control of adhesion strength and thus the mechanical properties of the composites. A model study using glass slides and polypropylene films was conducted to confirm the feasibility of treatment. Adhesion strength between glass and polypropylene increased with increasing coverage of the hydrocarbon silanes. The surface-modified particles were incorporated into the polypropylene matrix via melt processing. While surface functionalization of the particles can influence the dispersion of the particles, no significant effect was observed in this study. Tensile tests and toughness tests were performed on injection-molded samples. The tensile strength of the reinforced polypropylene increased with increasing adhesion strength. Impact toughness increased with weaker adhesion but the dependence became less pronounced as deformation rate was increased. [Copyright &y& Elsevier]

The mechanisms of deformation and fracture of isotactic polypropylene filled with CaCO 3 particles were studied. Three types of particles with average diameters of 0.07, 0.7, and 3.5 μm were used at filler volume fraction from 0.05 to 0.30. The experiments included slow tensile tests, notched Izod impact tests with varying notch depths, and fracture resistance tests using double-cantilever-beam sample configurations. In slow tension, addition of fillers increased the modulus and decreased the yield stress independently of filler type. The strain at break increased with initial incorporation of fillers but decreased at higher loadings. The 0.7 μm diameter particles improved Izod impact energy up to four times that of the unfilled matrix. The other particles had either adverse or no effect on the impact toughness. The toughening mechanisms at work were plastic deformation of interparticle ligaments following particle–matrix debonding with additional contribution coming from crack deflection toughening. The failure of the 0.07 and 3.5 μm diameter particles to toughen the matrix was attributed to poor dispersion. [ABSTRACT FROM AUTHOR]

Focuses on the measurement of iron elasticity to reveals that compressional waves traverse the inner core of the earth faster along near-polar paths than in equatorial plane. First-principles calculations of the structure and elasticity; Increase of axial ratio of iron at high temperatures.

Crystalline polar metallocenes are potentially useful active materials as piezoelectrics, ferroelectrics, and multiferroics. Within density functional theory (DFT), we computed structural properties, energy differences for various phases, molecular configurations, and magnetic states, computed polarizations for different polar crystal structures, and computed dipole moments for the constituent molecules with a Wannier function analysis. Of the systems studied, Mn2(C9H9N)2 is the most promising as a multiferroic material, since the ground state is both polar and ferromagnetic. We found that the predicted crystalline polarizations are 30–40% higher than the values that would be obtained from the dipole moments of the isolated constituent molecules, due to the local effects of the self-consistent internal electric field, indicating high polarizabilities. [ABSTRACT FROM AUTHOR]

Abstract Varying the substrate temperature changes structural and magnetic properties of spinel ferrite Ni 0.65 Zn 0.35 Fe 2 O 4 (NZFO) thin films. X-ray diffraction of films grown at different temperature display only (004) reflections, without any secondary peaks, showing growth orientation along the c-axis. We find an increase in crystalline quality of these thin films with the rise of substrate temperature. The surface topography of thin films grown at different growth temperatures reveal that these films are smooth with low roughness; however, the thin films grown at 800 °C exhibit lowest average and root mean square (rms) roughness among all thin films. We find iron and nickel to be more oxidized (greater Fe3+ and Ni3+ content) in films grown and annealed at 700 °C and 800 °C, compared to those films grown at lower temperatures. The magnetic moment is observed to increase with an increase of substrate temperature and all thin films possess high saturation magnetization and low coercive field at room temperature. Films grown at 800 °C exhibit a ferrimagnetic–paramagnetic phase transition well above room temperature. The observed large magnetizations with soft magnetic behavior in NZFO thin films above room temperature suggest potential applications in memory, spintronics, and multifunctional devices. Highlights • Highly c-axis oriented NZFO thin films were grown by PLD technique. • Varying the substrate temperature changes structural and magnetic properties. • All thin films exhibit high Ms, low Mr and low Hc at room temperature. • The M s is found to be increased with increase of substrate temperature. • Thin films grown at 800 °C exhibit a ferrimagnetic Tc ∼716 (±10) K. [ABSTRACT FROM AUTHOR]

Subduction of oceanic lithosphere transports surface H 2 O into the mantle. Recent studies show that dense SiO 2 in the form of stishovite, an abundant mineral in subducted oceanic crust at depths greater than ∼270 km, has the potential to host and transport a considerable amount of H 2 O into the lower mantle, but the H 2 O storage capacity of SiO 2 phases at high pressure and temperature remains uncertain. We investigate the hydration of stishovite and its higher-pressure polymorphs, β -stishovite and seifertite, with in situ X-ray diffraction experiments at high pressures and temperatures. The H 2 O contents in SiO 2 phases are quantified based on observed increases in unit cell volume relative to the anhydrous SiO 2 system. Density functional theory (DFT) computations permit calibration of water content as a function of volume change based on interstitial substitution of H 2 O. Regression of our experimental data indicates an H 2 O storage capacity in stishovite of ∼3.5 wt% in the transition zone and shallow lower mantle, decreasing to about 0.8 wt% at the base of the mantle. We find that SiO 2 -bearing subducted oceanic crust can accommodate all the H 2 O in slab lithosphere that survives sub-arc dehydration. Hydration of silica phases in subducted oceanic crust and their unparalleled capacity to host significant amounts of H 2 O even at high mantle temperatures provides a unique mechanism for transport and storage of water in the deepest mantle. • Quantification of the H 2 O storage capacity in hydrous silica in the deep mantle. • Parameterization of the H 2 O storage capacity in hydrous silica as a function of P-T. • Interstitial substitution of H 2 O dominates incorporation water of hydrous silica. • Hydrous silica plays an important role in transporting water to the deep Earth. [ABSTRACT FROM AUTHOR]

Abstract: The mechanical hysteresis and recovery behaviors of an elastomeric ethylene methacrylic acid butyl acrylate (EMAABA) copolymer, its sodium-neutralized (EMAABANa) and zinc-neutralized (EMAABAZn) counterparts are evaluated and compared under large strain loading conditions. Experiments at different rates, under cyclic loading conditions and in relaxation indicate two major hysteresis mechanisms: a characteristic viscoelastic mechanism operative at all strains and a microstructural evolution/breakdown mechanism incurred during large strains. Loading-unloading cycles show large rate-dependent hysteresis loops with significant recovery of strain upon unloading, revealing a highly dissipative yet resilient behavior. The microstructure breakdown mechanism occurs during the initial strain excursion as revealed by subsequent loading cycles showing a significantly more compliant behavior and dramatically reduced hysteresis loops. The neutralized materials are found to be significantly stiffer, stronger and more dissipative compared to the neat material while still retaining the same level of recovery. Therefore the neutralization of this material provides an excellent means to tune stiffness and dissipation while retaining resilience, providing mechanical performance properties attractive for abrasion, impact and puncture resistant applications. [Copyright &y& Elsevier]

Abstract: The large strain deformation behaviors of an ethylene methacrylic acid (EMAA) copolymer and an ethylene methacrylic acid butyl acrylate (EMAABA) copolymer are evaluated and compared in compression over nearly eight orders of magnitude in strain rate, from 10−4 to almost 104/s. Transition regimes are quantified using dynamic mechanical analysis. The stress–strain behavior of these copolymers exhibits a relatively stiff initial behavior followed by a rollover to a more compliant response. The low strain modulus, the rollover stress and the large deformation stress–strain behavior are strongly dependent on strain rate. The proximity of the material glass transition to the room temperature test conditions results in a substantial change in the nature of the rate sensitivity of the stress–strain behavior as one moves over the range of strain rates. The mechanical behavior of the EMAA is contrasted to that of a corresponding EMAABA terpolymer and to its sodium-neutralized counterpart (EMAABANa). The nature of the rate sensitivity of the room temperature stress–strain behavior of EMAA transitions from a behavior near the glassy end of the leathery regime at low rates to a near glassy behavior at high rates. The butyl acrylate content in the EMAABA lowers the glass transition temperature and leads to a more compliant mechanical behavior (reduced initial stiffness, reduced rollover stress, reduced post-rollover stress level) at room temperature. The EMAABA behavior transitions from a rubbery-like behavior at the lowest rates to a leathery-like behavior at the highest rates. Upon sodium neutralization, the overall stiffness and flow stress levels are enhanced likely due to the presence of the ionic aggregates; the glass transition of EMAABANa is broadened in comparison to the EMAABA, giving a rate dependent room temperature behavior that transitions through the leathery regime with increasing strain rate. A constitutive model that separately accounts for the distinct deformation resistances of the crystalline domains and the amorphous domains is able to capture the changes in rate dependent deformation behavior of the EMAA copolymers studied herein. The crystalline domains provide resistance to flow across a wide window in rate and temperature whereas the amorphous domains provide increasing resistance as the strain rate is increased and the material effectively transitions through the glass transition regime, providing a mechanism for changing rate sensitivity. [Copyright &y& Elsevier]

Polyelectrolyte multilayers (PEMs), formed by the sequential adsorption of poly(acrylic acid) and poly (allylamine hydrochloride) possess architectures that can be tuned as a function of polyelectrolyte solution pH. PEMs are easy to fabricate, requiring little or no substrate pretreatment, and provide conformal nanocoatings that are resistant to scotch-tape peel tests on metallic, plastic, and glass substrates. Their tribological behavior has received little or no attention.We have studied the friction and wear behavior of PEM-coated materials primarily using a meso/micro-scale flexure-based apparatus; a 1 or 2 mm diameter flat pin was made to articulate against a larger sliding surface. The friction coefficient of film-coated steel substrates against glass was higher than that exhibited by the bare substrates at all stresses; the average value decreased with an increase in the applied normal load, a trend predicted for polymeric materials. PEM constructs prevented wear of steel substrates in the dry state, and also in the presence of water and bovine calf serum, used to simulate synovial fluid in human joints. At these higher stresses, the delaminated film fragments prevent contact between the mating surfaces, thus eliminating substrate wear. The adhesion, deformation, and dragging of the fragments causes the friction force to be higher than the bare substrates (prior to the onset of their wear). Wear can be prevented without a substantial increase in friction force by using thinner films on the larger slider surface or coating the smaller pin counterface. The capacity for PEM-induced wear reduction was confirmed at larger scales of testing in the dry state using a pin-on-disk tester. [Copyright &y& Elsevier]

Polymer/clay nanocomposites have been observed to exhibit enhanced mechanical properties at low weight fractions (Wc) of clay. Continuum-based composite modeling reveals that the enhanced properties are strongly dependent on particular features of the second-phase ‘particles’; in particular, the particle volume fraction (fp), the particle aspect ratio (L/t), and the ratio of particle mechanical properties to those of the matrix. These important aspects of as-processed nanoclay composites require consistent and accurate definition. A multiscale modeling strategy is employed to account for the hierarchical morphology of the nanocomposite: at a lengthscale of thousands of microns, the structure is one of high aspect ratio particles within a matrix; at the lengthscale of microns, the clay particle structure is either (a) exfoliated clay sheets of nanometer level thickness or (b) stacks of parallel clay sheets separated from one another by interlayer galleries of nanometer level height, and the matrix, if semi-crystalline, consists of fine lamella, oriented with respect to the polymer/nanoclay interfaces. Here, quantitative structural parameters extracted from XRD patterns and TEM micrographs (the number of silicate sheets in a clay stack, N, and the silicate sheet layer spacing, d(001)) are used to determine geometric features of the as-processed clay ‘particles’, including L/t and the ratio of fp to Wc. These geometric features, together with estimates of silica lamina stiffness obtained from molecular dynamics simulations, provide a basis for modeling effective mechanical properties of the clay particle. In the case of the semi-crystalline matrices (e.g. nylon 6), the transcrystallization behavior induced by the nanoclay is taken into account by modeling a layer of matrix surrounding the particle to be highly textured and therefore mechanically anisotropic. Micromechanical models (numerical as well as analytical) based on the ‘effective clay particle’ were employed to calculate the overall elastic modulus of the amorphous and semi-crystalline polymer–clay nanocomposites and to compute their dependence on the matrix and clay properties as well as internal clay structural parameters. The proposed modeling technique captures the strong modulus enhancements observed in elastomer/clay nanocomposites as compared with the moderate enhancements observed in glassy and semi-crystalline polymer/clay nanocomposites. For the case where the matrix is semi-crystalline, the proposed approach captures the effect of transcrystallized matrix layers in terms of composite modulus enhancement, however, this effect is found to be surprisingly minor in comparison with the ‘composite’-level effects of stiff particles in a matrix. The elastic moduli for MXD6-clay and nylon 6-clay nanocomposites predicted by the micromechanical models are in excellent agreement with experimental data. When the nanocomposite experiences a morphological transition from intercalated to completely exfoliated, only a moderate increase in the overall composite modulus, as opposed to the expected abrupt jump, was predicted. [Copyright &y& Elsevier]