Partial Orientation Research Articles

Analysis of fracturing in short-fiber reinforced polymer composites

Fracturing of polymer composites reinforced by randomly distributed short fibers with a partial orientation is studied. The proposed layered model of the composite makes it possible to derive the differential equation for the description of fracturing in the composites during loading. Numerical analysis makes it possible to distinguish the principal stages of fracturing: the incubation period, the progressing stage, and the avalanche-like stage. For the composites with a constant coefficient of strength variations, the critical degree of damage at the instant of fracture remains constant. In the other case, on condition that all other conditions are the same, the critical stress in the remaining undamaged part of the sample is constant. The results of the oretical calculations are supported by experimental evidence. The revealed principal features are assumed to be characteristic of practically all systems during their transition from one stable state to another in the course of fracturing and during the processes of acquirement of any new property.

Analytical modelling of partial shading and different orientation of photovoltaic modules

Analytical modelling of a photovoltaic (PV) power system for studying the effects of partial shading and different orientation of PV modules is presented. The proposed analytical model, although limited to the case of series PV modules and composed of complicated non-linear implicit functions, allows several important electrical characteristics of a PV system, such as I - V curve, open-circuit voltage, short-circuit current, maximum power and reverse voltage, to be investigated and presented in two- and three-dimensional graphs to provide in-depth physical interpretation of the issue.

Identification of an Aurora-A/PinsLINKER/ Dlg Spindle Orientation Pathway using Induced Cell Polarity in S2 Cells

Asymmetric cell division is intensely studied because it can generate cellular diversity as well as maintain stem cell populations. Asymmetric cell division requires mitotic spindle alignment with intrinsic or extrinsic polarity cues, but mechanistic detail of this process is lacking. Here, we develop a method to construct cortical polarity in a normally unpolarized cell line and use this method to characterize Partner of Inscuteable (Pins; LGN/AGS3 in mammals) -dependent spindle orientation. We identify a previously unrecognized evolutionarily conserved Pins domain (Pins(LINKER)) that requires Aurora-A phosphorylation to recruit Discs large (Dlg; PSD-95/hDlg in mammals) and promote partial spindle orientation. The well-characterized Pins(TPR) domain has no function alone, but placing the Pins(TPR) in cis to the Pins(LINKER) gives dynein-dependent precise spindle orientation. This "induced cortical polarity" assay is suitable for rapid identification of the proteins, domains, and amino acids regulating spindle orientation or cell polarity.

Incoherent light transport in anisotropic media: Form factor influence for oriented prolate ellipsoids

In turbid media, the partial or global orientation of anisotropic particles induces anisotropic light transport. In this study, we discuss the anisotropic incoherent transport of light in media where prolate ellipsoids are oriented in the same direction. In these anisotropic media, incoherent light transport is investigated using Monte Carlo simulations where the influence of particle anisotropy, size and optical properties are explored in a systematic way, from the local scattering event up to the diffusion limit. The database allows inverting the anisotropy of the backscattered image to yield the form factor of the particles. We then illustrate the relevance of such an analysis to assess the deformability of human erythrocytes in blood samples under normal physiological conditions.

Angular distribution of Auger electrons from fixed-in-space and rotating C 1s→2π photoexcited CO: Theory

The one-center approach for molecular Auger decay is applied to predict the angular distribution of Auger electrons from rotating and fixed-in-space molecules. For that purpose, phase shifts between the Auger decay amplitudes have been incorporated in the atomic model. The approach is applied to the resonant Auger decay of the photoexcited C 1s-->2pi resonance in carbon monoxide. It is discussed how the symmetry of the final ionic state is related to features in the angular distributions and a parametrization for the molecular frame Auger electron angular distribution is suggested. The angular distribution of Auger electrons after partial orientation of the molecule by the sigma-->pi-excitation process is also calculated and compared to available experimental and theoretical data. The results of the one-center approach are at least of the same quality as the available theoretical data even though the latter stem from a much more sophisticated method. As the one-center approximation can be applied with low computational demand even to extended systems, the present approach opens a way to describe the angular distribution of Auger electrons in a wide variety of applications.

Effect of Partial Orientation in [100] Direction on the Magnetic Properties of Co-Ferrite Prepared from Nano Particles

Effect of Partial Orientation in [100] Direction on the Magnetic Properties of Co-Ferrite Prepared from Nano Particles

Effect of Partial Orientation in [100] Direction on the Magnetic Properties of Co-Ferrite Prepared from Nano Particles

Chemical co-precipitation method was used for the preparation of Co-ferrite nano particles. The particle size was about 18 nm. A magnetic anisotropy of Co-ferrite could be increased by applying an external magnetic field during the pressing of the nano particles before the final sintering. This anisotropy enhanced the squareness and the coercivity of investigated samples.

Aggregation and excitation trapping of 3,3′-diethyl-9-methylthiacarbocyanine iodide in disordered and uniaxially oriented polymer films

Photophysical properties of 3,3′-diethyl-9-methylthiacarbocyanine iodide (MDTCI) in disordered and uniaxially stretched poly(vinyl alcohol) films (PVA) are reported at high dye concentration. Ground-state formation of fluorescent MDTCI aggregates at high concentration was observed in unstretched and stretched PVA films using steady-state and time-resolved spectroscopic methods. It was found that fluorescence of MDTCI aggregates is almost totally depolarized in disordered matrix, but it remains partly polarized in the stretched PVA film despite energy transfer from monomers. The differences between spectral properties of aggregates in both matrices may result from partial orientation of aggregate transition moment and its immobilization in polymer cage.

Linearly polarized IR-spectroscopy of partially oriented solids as a colloid suspension in nematic host: a tool for spectroscopic and structural elucidation of the embedded chemicals

Colloid suspensions in nematic liquid crystal were employed for the first time in 2004 as a tool for the partial orientation of solids, to be examined by linearly polarized IR-(IR-LD) spectroscopy. It has been found is found that a partial orientation (15–20%) of suspended particles, is adequate for the recording of reasonable linearly polarized IR-spectra is achieved when: 5 ± 1% by weight of the given solid compound (organic, inorganic, transition metal complex or glass) with particle size within the limits 0.3–0.9 μm is mixed with a nematic liquid crystal substance (ZLI 1695, ZLI 1538 or MLC 6815) suitable for IR spectroscopy and the slightly viscous suspension obtained is phase pressed between two KBr-plates. These latter are roughened in one direction prior to use with fine sandpaper (C800) (size 5 μm). Then, the KBr-plattes and pressed suspension are moved repeatedly with 3 μm/s for 100 times. The optimal cell thickness is 100 μm. If mathematical procedures are used for polarized IR-spectra interpretation, then it is possible to perform structural elucidation of the embedded compounds, independently of their melting point, crystalline or amorphous state, and the quality of the monocrystals or polycrystalline of the e sample. The method permits the study of organic and inorganic compounds, transition metal complexes and glasses. Here we will discuss the fundamental questions concerning the above state such as the morphology of the suspended particles, the particle size, the influence of the physical chemistry properties of liquid crystal medium on the degree of orientation of suspended particles; the velocity of the shearing of the suspension, the degree of the roughening of the KBr-plates and their effects on the degree of orientation, the influence of the space group on the orientation parameter, the nature and balance of the forces acting on the suspended particles; their degree of orientation, the mathematical model used. Conventional and linearly polarized IR-spectroscopy and electron microscopy are used for elucidation of these points. Statistical approaches have also been applied in order to estimate the impact of the experimental parameters (size, velocity, thickness) on the IR-signal for each of the 13 systems studied. An experimental design of the type involving full factorial design on two levels of variation of the input factors is presented.

Strain hardening of polymer glasses: Entanglements, energetics, and plasticity

Simulations are used to examine the microscopic origins of strain hardening in polymer glasses. While stress-strain curves for a wide range of temperature can be fit to the functional form predicted by entropic network models, many other results are fundamentally inconsistent with the physical picture underlying these models. Stresses are too large to be entropic and have the wrong trend with temperature. The most dramatic hardening at large strains reflects increases in energy as chains are pulled taut between entanglements rather than a change in entropy. A weak entropic stress is only observed in shape recovery of deformed samples when heated above the glass transition. While short chains do not form an entangled network, they exhibit partial shape recovery, orientation, and strain hardening. Stresses for all chain lengths collapse when plotted against a microscopic measure of chain stretching rather than the macroscopic stretch. The thermal contribution to the stress is directly proportional to the rate of plasticity as measured by breaking and reforming of interchain bonds. These observations suggest that the correct microscopic theory of strain hardening should be based on glassy state physics rather than rubber elasticity.

Strain-Induced Crystallization of Crosslinked Natural Rubber As Revealed by X-ray Diffraction Using Synchrotron Radiation

Strain-induced crystallization (SIC) of natural rubber (NR) has been extensively studied even before the advent of macromolecular physics. However, there are still some unsolved basic issues in this field. In this review article, classic studies on SIC of NR are briefly introduced, and then recent results by synchrotron X-ray diffraction studies in separate papers by different authors are categorized and interpreted on the basis of molecular models. Cyclic deformation experiments provided information on partial orientation of the network-chains, on nucleation and morphological changes of crystals and on stress field around the strain-induced crystals. On the other hand, experiments under constant strain provided information on kinetics of SIC, on stress relaxation due to SIC, and so on. The experimental results could be explained under the assumption that the SIC is dominated by strain, and that the crystals are of folded-chain type. However, in order to consistently explain the various experimental results, we have to establish a unified molecular model of the network structure.

Structural and textural characteristics of slate and its response to the point load test

From the geomechanical point of view slate is considered to be one of more trying rock varieties. The results of research have shown close relationship between structural, textural and mineralogical characteristics on the one hand, and its strength and resistance to point loads on the other hand. Its weakened zones are the result of anisotropy. They develop mainly due to dynamo-metamorphosis of the primary mudstone, resulting in the formation of the secondary slaty cleavage, with a pronounced preferred orientation of the phyllosilicates. Low strength is the consequence of the weak Van der Waals chemical bond between individual packets of the internal crystal structure of the sheet minerals, particularly sericite. Bedding and microfolds with a crenulated structure and partial preferred orientation of sheet minerals, as well as directions that are weakened with sigmoidal shear deformations as the predecessors of microfaults, also result in significant but less problematic anisotropy. Thin lepidoblastic lamina, in apparently massive sandy metasiltstone beds in the slate represent discontinuities, which have a decisive influence on the reduction of their strength.

Microgravity crystal growth in a magnet

Polymer crystallization is notoriously difficult to control at a local scale because the growth of polymeric crystals is complicated by the need for cooperativemovements of a large number of connected monomers, resulting in a lack of long-range order and rapid loss of orientational correlation over short distances. Typically, polymeric crystals organize intomicroscale, isotropic, spherical superstructures (spherulites), which are comprised of splaying and branching thin lamellae interleaved with amorphous layers. Here, we report on a fast and easy method to control the orientation of crystals of semicrystalline polymers at the nanometer scale by using nanoimprint lithography [1]. Whenever a hardmold that contains nanoscale features defined on its surface (typical lateral size 50-250 nm; typical height 100 nm), is pressed against a molten film of a crystallizable polymer cast on a substrate under controlled temperature and pressure conditions, themolten polymer is forced to flow into the cavities of the mold. The isolation of polymer in separate nano-cavities, which strongly decreases the importance of nucleation by impurities; the confinement of the polymer in nano-sized cavities, which hinders the transport of polymer chains between cavities and controls the fast crystal growth direction; the partial orientation of polymer chains near the vertical walls on themold due to elongational flow, which eases the formation of nuclei with the crystallographic c axis parallel to the vertical walls on the mold, lead to a fine control over crystallographic orientation, crystal size and shape of polymer crystals. This is shown for a series of geometries, from simple straight lines tomore complex shapes, such as concentric circles and small squares, and for a variety of polymers.

Locally controlling the orientation of polymer crystals by nanoimprint lithography

Polymer crystallization is notoriously difficult to control at a local scale because the growth of polymeric crystals is complicated by the need for cooperativemovements of a large number of connected monomers, resulting in a lack of long-range order and rapid loss of orientational correlation over short distances. Typically, polymeric crystals organize intomicroscale, isotropic, spherical superstructures (spherulites), which are comprised of splaying and branching thin lamellae interleaved with amorphous layers. Here, we report on a fast and easy method to control the orientation of crystals of semicrystalline polymers at the nanometer scale by using nanoimprint lithography [1]. Whenever a hardmold that contains nanoscale features defined on its surface (typical lateral size 50-250 nm; typical height 100 nm), is pressed against a molten film of a crystallizable polymer cast on a substrate under controlled temperature and pressure conditions, themolten polymer is forced to flow into the cavities of the mold. The isolation of polymer in separate nano-cavities, which strongly decreases the importance of nucleation by impurities; the confinement of the polymer in nano-sized cavities, which hinders the transport of polymer chains between cavities and controls the fast crystal growth direction; the partial orientation of polymer chains near the vertical walls on themold due to elongational flow, which eases the formation of nuclei with the crystallographic c axis parallel to the vertical walls on the mold, lead to a fine control over crystallographic orientation, crystal size and shape of polymer crystals. This is shown for a series of geometries, from simple straight lines tomore complex shapes, such as concentric circles and small squares, and for a variety of polymers.

Optical transmission of polymer dispersed liquid crystals doped with carbon nanotubes

The optical transmission of polymer-dispersed liquid crystals (PDLCs) doped with multiwall carbon nanotubes (MWNTs) has been studied in comparison to the analogous system without MWNTs. The transmission of MWNT-doped PDLC cells in crossed polarizers exhibits an anomalous dependence on the control voltage. The anomalous behavior is attributed to a preliminary partial orientation of molecules in the presence of carbon nanotubes in the dispersed liquid crystal droplets.

Effect of self-assembled monolayer film order on nanofriction

Self-assembled monolayers have increasingly been explored as potential protective films in devices against friction and adhesion. However, detailed characterization of the monolayer film structure is difficult. This article utilizes a combination of near edge x-ray absorption fine structure (NEXAFS) spectroscopy and Fourier transform infrared (FTIR) spectroscopy to determine the film structure in order to explain the observed nanofriction measurement results. A series of n-alkyltrichlorosilane self-assembled monolayer films with various chain lengths (C5–C30) was prepared on silicon (100) surfaces. Nanofriction measurements were conducted using an atomic force microscope. Results showed that the lowest friction was obtained with a C12 film with higher friction values observed for C5 and C30 films. To explain these observations, the x-ray absorption technique NEXAFS was used to quantitatively measure the surface molecular orientation (order) of these films. It was observed that C12, C16, and C18 films were highly ordered with a molecular orientation of the carbon backbone nearly perpendicular to the surface. C5 and C30 films were less oriented and C10 film showed partial orientation. FTIR spectra suggested that these films possessed different degrees of order. This combination of molecular orientation and order supports and confirms that nanofriction results were heavily influenced by the order and structure of these films.

Increased Fatigue Endurance in Pb(Zr,Ti)O3 Thin Films through Use of PbZrO3 Buffer Layers

Thin PbZrO3 (PZ) films were investigated as a buffer layer to improve fatigue endurance of Pb(Zr0.45Ti0.55)O3 (PZT) thin films. The PZ thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by RF magnetron sputtering from a loose powder target containing a mixture of PbZrO3 and ZrO2 powders. The PZT thin films on the PZ buffer layer were obtained by sol–gel spin coating. The PZ buffered PZT films had well crystallized, uniform and dense microstructure with partial (111) orientation. The P–E hysteresis measurements indicated comparable or slightly lower remnant polarization values (2Pr=50–70 µC/cm2) and higher coercive field levels compared to unbuffered film (2Pr=66 µC/cm2). The PZ buffered films displayed an asymmetric leakage current. The fatigue endurance of PZT thin films with PZ buffer layers was superior compared to the unbuffered counterpart with fatigue-free behavior observed up to 109 switching cycles.

A Structural and Dynamic Characterization of the EF-Hand Protein CLSP

The structure and dynamics of human calmodulin-like skin protein (CLSP) have been characterized by NMR spectroscopy. The mobility of CLSP has been found to be different for the N-terminal and C-terminal domains. The isolated domains were also expressed and analyzed. The structure of the isolated C-terminal domain is presented. The N-terminal domain is characterized by four stable helices, which experience large fluctuations. This is shown to be due to mutations in the hydrophobic core. The overall N-terminal domain behavior is similar both in the full-length protein and in the isolated domain. By exploiting the capability of Tb3+ bound to CLSP to induce partial orientation of the molecule in a magnetic field, restricted motion of one domain with respect to the other was proved. By using NMR, ITC, and ESI-MS, the calcium and magnesium binding properties were investigated. Finally, CLSP is framed into the evolutionary scheme of the calmodulin-like family.

Structure–activity correlations in thin film model catalysts: CO hydrogenation on Rh/VO x: Part I. The morphology, composition and structure of vanadia-supported and -promoted Rh particles upon oxidation and reduction

The combination of (high-resolution) electron microscopy and electron diffraction was applied to study the structural and morphological alterations of a number of Rh/VO x -model systems upon oxidation and reduction, and to discriminate between different phenomena of metal–support interaction. Well-defined Rh particles (mean size 10–15 nm) were grown epitaxially on NaCl(0 0 1) surfaces and subsequently covered by layers of VO x of varying thickness (0.07–25 nm), prepared by reactive deposition of V metal in 10 −2 Pa O 2. Most films were covered with a stabilizing layer of amorphous alumina. The resulting model catalysts were subjected to an oxidative treatment at 673 K in O 2 for 1 h and to subsequent reduction in the temperature range 373–873 K. While higher VO x exposures (mean VO x coverage ≥ 3 nm) favour the formation of crystalline V 2O 3 phases in partial epitaxial orientation to the Rh particles in the as-deposited state, lower exposures result in less ordered layers of cubic VO. Similarly, after a treatment in 1 bar O 2 at 673 K the oxidation states of vanadium vary between V 5+ and V 2+, depending on the film thickness. Decoration of Rh by reduced VO x species was found to be the dominant feature of metal–support interaction upon reduction at low temperatures ( T < 573 K), whereas at increasing reduction temperature the formation of distinct Rh–V alloys (V 3Rh 5, Rh 3V, V 3Rh and VRh, respectively) was observed. On a “VO x /Rh/Al 2O 3” catalyst, prepared by depositing 1ML VO x prior to Rh deposition alloy formation was not detected, and decoration of the metal particles was the dominant effect of reduction at 673 K. A counterpart to Rh/V “subsurface” or “surface” alloys, known to be formed on bulk Rh surfaces under similar conditions, could not be observed.

Dispersion of Layered Organosilicates in Isobutylene-Based Elastomers

Abstract Dispersion morphologies of polymer-layered silicate nanocomposites based on either brominated poly(isobutylene-co-para-methylstyrene), BIMSM, or brominated poly(isobutylene-co-isoprene), BIIR, and an organosilicate, dimethylditallow ammonium-exchanged montmorillonite, Cloisite™ 6A, with and without N660 carbon black fillers were examined using SAXS, WAXS, AFM, and TEM. These compounds were prepared using an internal mixer and cured for property measurements. Due to the observed partial orientation of organosilicates and their possible heterogeneous intercalation, degrees of exfoliation and dispersion of organosilicates in BIMSM and BIIR were unable to be characterized and quantified simply by TEM, AFM, or SAXS alone. Instead, using the projected aspect ratio of organosilicates in BIMSM or BIIR, extracted from Gusev-Lusti equation based on measured permeability ratios, was found to provide a relative measure of their dispersion state. Since better dispersion, higher planar orientation, and/or increasing extent of exfoliation lead to higher aspect ratio, this calculated aspect ratio was used as a measure of organosilicate dispersion in BIMSM and BIIR compounds. According to experimentally extracted projected aspect ratios, it was found that BIMSM disperses organosilicates better than BIIR and that carbon black filler does not affect the organosilicate dispersion in BIMSM. Addition of tertiary amines in BIMSM enhances the dispersion of organosilicates, possibly through favorable interactions between organosilicates and quaternary ammonium functionalized BIMSM, resulting in further reduction in permeability.