Orthorhombic Lattice Structure Research Articles

Hierarchical Self-Assembled Structures from POSS-Containing Block Copolymers Synthesized by Living Anionic Polymerization

Two kinds of polyhedral oligomeric silsesquioxane (POSS)-containing block copolymers (BCPs), namely PS-b-PMAPOSS and PMMA-b-PMAPOSS, were synthesized by living anionic polymerization. A wide range of molecular weights were obtained with a very narrow polydispersity index of less than 1.09. The bulk samples prepared by slow evaporation from a polymer solution in chloroform exhibit well-defined microphase-separated structures with long-range order. Thermal annealing induced hierarchical structures consisting of a smaller length scale ordered crystalline POSS domains within the larger microphase-separated structures. We report detailed structural characterization of these hierarchical structures in bulk and thin films by transmission electron microscopy and grazing incidence wide-angle X-ray scattering (GIWAXS). On the basis of this structural analysis, we propose a model for the formation of an orthorhombic lattice structure through the aggregation of POSS segments which formed a helix-like structure.

Rotation of the magnetic easy axis in La0.67Sr0.33MnO3 thin film on NdGaO3(112)

The in-plane magnetic anisotropy is studied for pseudocubic {011}pc oriented La0.67Sr0.33MnO3 (LSMO) thin film grown on orthorhombic NdGaO3(NGO)(112)o (the subindices “pc” and “o” indicate the pseudocubic and orthorhombic lattice structure, respectively). The direction of the in-plane remanent magnetization of LSMO thin films with different thicknesses is determined. With increasing film thickness the easy axes rotate and the anisotropy changes from uniaxial to biaxial. This is associated with the increasing symmetry of the LSMO with increasing thickness, starting with a monoclinic LSMO structure at the nonrectangular NGO(112)o surface unit cell of the substrate, developing into an orthorhombic structure at the top part of the thickest films.

Small polaron property of polycrystalline Pr0.7(Sr1-xCax)0.3MnO3 series

We have synthesized polycrystalline bars of Pr0.7（Sr1-xCax）0.3MnO3（x=0，0.1，…，1）with a sol-gel method using citrate as an agent, and grown epitaxial thin films of Pr0.7（Sr1-xCax）0.3MnO3 on （100）-oriented substrates of SrTiO3 （ STO ） by using pulsed laser deposition （ PLD ）. We systemically investigated their lattice structures and electronic transport property. Both polycrystalline and film samples have orthorhombic lattice structure, and their electronic transport behaviors nicely follow a adiabatic small polaron model in high temperature paramagnetic phase when T is larger than the Curie temperature TC. All resistivity data have been fitted by the small polaron model. The fitted results of polycrystalline samples qualitatively agree with that of corresponding film samples. With increasing contents of Ca, polaron hopping energy Ehop increases monotoniccaly, and ρ0 first decreases, then increases. The above results indicate that electronic transport property of high quality polycrystalline samples is less influenced by lattice defects and grain boundaries which are abundant in low quality samples, such that intrinsic small polaron transport behavior can appear in the former.

Influence of dispersed organophilic montmorillonite at nanometer‐scale on crystallization of poly(L‐lactide)

AbstractWe investigated the effects of surface‐treated organophilic clay on the crystallization of poly(L‐lactide) (PLLA) in their hybrids. The natural nano‐clay in PLLA/clay hybrids acts as a heterogeneous nucleating agent to facilitate crystallization. On the contrary, extensive distributions of induction periods for nucleation are observed in the individual spherulites of neat PLLA and PLLA/organophilic clay hybrids. Therefore, it is suggested that nucleation type of neat PLLA and PLLA/organophilic clay hybrids implies nearly growth geometry as a homogeneous one. Further, under the presence of nano‐clay in their composites, PLLA matrix form the orthorhombic lattice structure corresponded to the α‐form crystal. Since this experimental fact implies little effect of the clay particles on polymorphism of PLLA crystal, the nucleating effect of the organophilic clay seems weaker than the natural clay itself. However, an increase in clay content enhances the growth rates of spherulite for hybrids. Consequently, most of hybrids exhibit an increase in overall crystallization rates at any crystallization temperature in spite of relatively lower nucleation rate of PLLA crystallites itself. In addition, the Avrami exponents (n) obtained by relatively low crystallization temperature ranged from 4 to 6, implying that the growth geometry was dominated sheaf‐like structure in early stage of isothermal crystallization. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Effects of current density on preparation of grainy electrolytic manganese dioxide

Grainy electrolytic manganese dioxide was prepared by electrodeposition in a 0.9 mol/L MnSO4 and 2.5 mol/L H2SO4 solution. The structure, particle size and appearance of the grainy electrolytic manganese dioxide were determined by powder X-ray diffraction, laser particle size analysis and scanning electron micrographs measurements. Current density has important effects on cell voltage, anodic current efficiency and particle size of the grainy electrolytic manganese dioxide, and the optimum current density is 30 A/dm2. The grainy electrolytic manganese dioxide electrodeposited under the optimum conditions consists of γ-MnO2 with an orthorhombic lattice structure; the grainy electrolytic manganese dioxide has a spherical or sphere-like appearance and a narrow particle size distribution with an average particle diameter of 7.237 µm.

Second-harmonic green generation from two-dimensional χ(2) nonlinear photonic crystal with orthorhombic lattice structure

We report the synthesis of nonlinear photonic crystals (NPCs) with a periodical distribution of inverted χ(2) nonlinearity having an orthorhombic lattice structure on Z-cut congruent-grown lithium niobate (LiNbO3) substrate. The quasiphase-matching (QPM) mechanism of nonlinear wave interaction is examined by monitoring the far-field emission pattern of second-harmonic generation (SHG) as the NPC is pumped by a Nd:yttritium–aluminum–garnet laser beam. We observe (i) a series distribution of green SHG in a direction transverse to the fundamental beam, and (ii) an increase of phase-matching temperature in the SHG peak signal with the azimuth rotation angle in the x–y plane. These observations are ascribed to the high-order reciprocal lattice vectors assisted QPM–SHG process in a NPC that has a distribution of χ(2) nonlinearity with an orthorhombic crystal symmetry.

Characterization of Low-Temperature (i.e.,

This study aims to characterize human stratum corneum (SC), focusing on those lipid transitions that occur at or below physiologically relevant temperatures. In the past, a lipid transition near 35 degrees C had been thought to be variable and a consequence of superficial sebaceous lipid contamination. However, analysis here indicates that it is widely present, and cannot be attributed to sebum production. We demonstrate that this transition represents a solid-to-fluid phase change for a discrete subset of SC lipids. The reversibility of this transition upon reheating, and its absence in extracted lipid samples imply that these lipids are not uniformly present throughout the SC, but would appear to be differentially distributed in response to terminal differentiation. Further, such an arrangement could involve a close association with other nonlipid (e.g., protein) components. Evidence for a new transition at approximately 55 degrees C is presented that suggests the loss of crystalline orthorhombic lattice structure. The existence of orthorhombic structure at physiologic temperature is reasoned to involve ceramides and/or free fatty acids. Localization of these lipids at the level of the corneocyte envelope supports a comprehensive picture of water transport across the SC, whereby diffusion occurs primarily via the intercellular lipids. This view, coupled with the hydration-induced changes in lipid disorder observed here provides additional insight into the mechanism by which skin occlusion increases permeability. Summarily, these results i) emphasize the inherent danger of over-interpreting experiments with isolated SC lipids, ii) emphasize the potential advantage(s) of employing several biophysical techniques to study SC structure, and iii) indicate that a full characterization of lipid phase behavior is requisite to our eventual understanding of SC structure and permeability function, particularly those phase transitions that occur near or at normal skin temperature.

Structure and superconductivity of single crystalline C 60

We have succeeded in synthesis of C 60 single crsytals with orthorhombic lattice structure contrary to the known cubic form. The structure of the orthorhombic form was confirmed by a four-circle X-ray diffractometer. The intense microwave absorption signal in low magnetic field was detected on the K-doped C 60 single crystals with the onset of superconductivity at Tc = 17.7 K.

Piezoelectricity and pyroelectricity in polyvinylidene fluoride: Influence of the lattice structure

Piezoelectric and pyroelectric responses of β-phase (Phase I) polyvinylidene fluoride are predicted for a model system of polarizable point dipoles. The model incorporates the influence of the orthorhombic crystal structure by including the dependence of the internal electric field on the lattice parameters. Strong anisotropy in the piezoelectric response under uniaxial stress is predicted as a consequence of the orthorhombic lattice structure. Predictions are found to be in reasonable agreement with room-temperature experimental data.

Vibrational Spectra and Structures of Ionic Liquids. II. The Pure Alkali Metal Nitrates

Attenuated total reflection infrared spectroscopy has been used together with thin-film transmission measurements to obtain detailed spectra for the molten nitrates of lithium, sodium, and potassium in the 250–4000-cm−1 range. The techniques, which yield spectra approaching the ultimate in resolution and precision possible for salt melts, permit the detection of several features which, when combined with Raman data, definitely rule out a melt structure dominated by either ion pairs or simple 1:1 complexes. Rather, systems wherein important factors include both cation distortion of the nitrate symmetry (site effect) and vibrational coupling of neighboring anions (correlation field effect) are definitely suggested. Thus, an assignment based on a perturbed orthorhombic lattice structure is presented which accounts very satisfactorily for all observed features. Order in the melts seems to be slightly greater in LiNO3 than for the other salts.