Home About us Contact
|
Home About us Contact | ||
|
|
||
Shell Layer (shell + layer)
Selected AbstractsA Novel Cathode Material with a Concentration-Gradient for High-Energy and Safe Lithium-Ion BatteriesADVANCED FUNCTIONAL MATERIALS, Issue 3 2010Yang-Kook Sun Abstract A high-energy functional cathode material with an average composition of Li[Ni0.72Co0.18Mn0.10]O2, mainly comprising a core material Li[Ni0.8Co0.2]O2 encapsulated completely within a stable manganese-rich concentration-gradient shell is successfully synthesized by a co-precipitation process. The Li[Ni0.72Co0.18Mn0.10]O2 with a concentration-gradient shell has a shell thickness of about 1,µm and an outer shell composition rich in manganese, Li[Ni0.55Co0.15Mn0.30]O2. The core material can deliver a very high capacity of over 200,mA h g,1, while the manganese-rich concentration-gradient shell improves the cycling and thermal stability of the material. These improvements are caused by a gradual and continuous increase of the stable tetravalent Mn in the concentration-gradient shell layer. The electrochemical and thermal properties of this cathode material are found to be far superior to those of the core Li[Ni0.8Co0.2]O2 material alone. Electron microscopy also reveals that the original crystal structure of this material remains intact after cycling. [source] Cover Picture: Synthesis of Gadolinium-Labeled Shell-Crosslinked Nanoparticles for Magnetic Resonance Imaging Applications (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 8 2005Mater. Abstract Robust, amphiphilic core,shell nanoparticles that are selectively labeled with gadolinium in the hydrophilic and water-swollen shell layer are depicted in the cover picture. These well-defined nanostructured materials exhibit high relaxivity, a large loading capacity, and are based upon a biocompatible platform for ultimate function in magnetic resonance imaging (MRI) applications, as reported by Wooley and co-workers on p.,1248. Shell-crosslinked knedel-like nanoparticles (SCKs; "knedel" is a Polish term for dumplings) were derivatized with gadolinium chelates and studied as robust magnetic-resonance-imaging-active structures with hydrodynamic diameters of 40,±,3,nm. SCKs possessing an amphiphilic core,shell morphology were produced from the aqueous assembly of diblock copolymers of poly-(acrylic acid) (PAA) and poly(methyl acrylate) (PMA), PAA52,b,PMA128, and subsequent covalent crosslinking by amidation upon reaction with 2,2,-(ethylenedioxy)bis(ethylamine) throughout the shell layer. The properties of these materials, including non-toxicity towards mammalian cells, non-immunogenicity within mice, and capability for polyvalent targeting, make them ideal candidates for utilization within biological systems. The synthesis of SCKs derivatized with GdIII and designed for potential use as a unique nanometer-scale contrast agent for MRI applications is described herein. Utilization of an amino-functionalized diethylenetriaminepentaacetic acid,Gd analogue allowed for direct covalent conjugation throughout the hydrophilic shell layer of the SCKs and served to increase the rotational correlation lifetime of the Gd. In addition, the highly hydrated nature of the shell layer in which the Gd was located allowed for rapid water exchange; thus, the resulting material demonstrated large ionic relaxivities (39,s,1,mM,1) in an applied magnetic field of 0.47,T at 40,°C and, as a result of the large loading capacity of the material, also demonstrated high molecular relaxivities (20,000,s,1,mM,1). [source] Synthesis and characterization of carbon nanotube/polypyrrole core,shell nanocomposites via in situ inverse microemulsionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2005Yijun Yu Abstract We demonstrate here a feasible approach to the preparation of multiwalled carbon nanotube (MWNT)/polypyrrole (PPy) core,shell nanowires by in situ inverse microemulsion. Transmission electron microscopy and scanning electron microscopy showed that the carbon nanotubes were uniformly coated with a PPy layer with a thickness of several to several tens of nanometers, depending on the MWNT content. Fourier transform infrared spectra suggested that there was strong interaction between the ,-bonded surface of the carbon nanotubes and the conjugated structure of the PPy shell layer. The thermal stability and electrical conductivity of the MWNT/PPy composites were examined with thermogravimetric analysis and a conventional four-probe method. In comparison with pure PPy, the decomposition temperature of the MWNT/PPy (1 wt % MWNT) composites increased from 305 to 335 °C, and the electrical conductivity of the MWNT/PPy (1 wt % MWNT) composites increased by 1 order of magnitude. The current,voltage curves of the MWNT/PPy nanocomposites followed Ohm's law, reflecting the metallic character of the MWNT/PPy nanocomposites. The cyclic voltammetry measurements revealed that PPy/MWNT composites showed an enhancement in the specific charge capacity with respect to that of pure PPy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6105,6115, 2005 [source] The structure of the outer shell layer in radiolitid rudists, a morphoconstructional approachLETHAIA, Issue 3 2008JOSE MARIA PONS Radiolitids (Bivalvia, Radiolitidae) built the calcite outer layer of their shell with compact structure as many other bivalves, or with repetitively layered non-compact structure following different patterns: continuous radial ridges, discontinuous radial ridges, normal cellular, cellular with radially elongate cells, discontinuous cellular, and discontinuous cellular with elongate cells. Some special structures may develop in localized parts: radial structures and inner-marginal or radial grooves. All these structures are currently used in the diagnosis of the family and for the characterization of subfamilies. Constructional morphology analyses and re-evaluation of all these structures reveal that they were misunderstood in some important aspects in the bivalve Treatise and that, consequently, the diagnosis of the family has to be emended and their subfamilies reconsidered. All outer shell layer structure related characters are described, illustrated, and interpreted under a constructional approach, some characters are proposed to emend the diagnosis of the family, and two possible clades are preliminarily distinguished. [source] Fabrication and characteristics of SiOx -core nanowires: Comparison study between uncoated and ZnO-coated SiOx nanowiresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2008Hyoun Woo Kim Abstract We have demonstrated an approach to the synthesis of SiOx -core nanowires, on which ZnO shell layer would be subsequently deposited. We have discussed the possible growth mechanism of SiOx nanowires, in regard to the role of Au catalyst. For a comparison study between uncoated and coated nanowires, samples were characterized by X-ray dif- fraction (XRD), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). This method can be applied to a wide range of materials and results in various heterostructures, which may serve as potential building blocks in various nanodevices. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Crystal mismatched layers in pentagonal nanorods and nanoparticlesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2010L. M. Dorogin Abstract Pentagonal nanorods (PNRs) and nanoparticles (PNPs) covered by mismatched shell layers are theoretically investigated. Mechanical stresses and elastic energies of such objects are calculated analytically and analyzed in the framework of linear isotropic elasticity. Difference between elastic modules of core and shell is taken into account. The threshold radiuses as the minimal radiuses of PNR and PNP for which the formation of the shell layer is energetically favorable are found. The threshold radius is approximately 10,nm for PNPs and 100,nm for PNRs of typical face-centered cubic (FCC) metals. The optimal magnitudes of mismatch parameter giving the maximal energy release for shelled PNRs and PNPs are determined. [source] Synthesis and characterization of dual-responsive micrometer-sized core-shell composite polymer particlesPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3 2008M. Ashraful Alam Abstract Dual-responsive micrometer-sized core-shell composite polymer particles were prepared by dispersion polymerization followed by seeded copolymerization. Polystyrene (PS) particles prepared by dispersion polymerization were used as core particles. N-isopropyl acrylamide (NIPAM) and methacrylic acid (MAA) were used to induce dual-responsive that is thermo- and pH-responsive properties in the shell layer of composite polymer particles, prepared by seeded copolymerization with PS core particles. Temperature- and pH-dependent adsorption behaviors of some macromolecules on composite polymer particles indicate that produced composite polymer particles exhibit dual-responsive surface properties. Copyright © 2007 John Wiley & Sons, Ltd. [source] Surface Properties and Photocatalytic Activity of Ptcore/Agshell Nanoparticle-Loaded TiO2CHEMPHYSCHEM, Issue 8 2006Hiroaki Tada Prof. Bimetallic nanoparticles are successfully formed on the surface of TiO2 (see figure) with Ag shell layer (nL) control. Pt@Ag/TiO2 exhibits unique photocatalytic performances for reduction of nitorobenzene at nL,1, however when nL exceeds ,1 they are similar to those of Ag/TiO2. Furthermore at the critical value of nL,1, the surface properties of Pt@Ag nanoparticles change from Pt to Ag. [source] Magnesium and sulphur in the calcite shells of two brachiopods, Terebratulina retusa and Novocrania anomalaLETHAIA, Issue 1 2007JENNIFER ENGLAND This study determines the distribution of magnesium and sulphur in the shells of two species of brachiopod from the same environment to highlight environmental and biological influences on shell composition. In Terebratulina retusa there are differences in magnesium concentration between the primary layer and the outer and inner regions of the secondary layer. In contrast, Novocrania anomala has a shell composed of high magnesium calcite and there is no significant difference in magnesium concentration between the primary and the secondary shell layers. Sulphur provides an indication of the distribution of sulphated organic matrix within the shells of T. retusa and N. anomala. In T. retusa the distribution of magnesium and sulphur correlates across the shell; however, there is no evidence for a relationship between magnesium and sulphur distribution in N. anomala. The relationship between magnesium and sulphur in T. retusa indicates that a proportion of the magnesium content of the shell is associated with the sulphated fraction of the organic matrix. In these two species of brachiopod, from the same environment, magnesium and organic concentration and distribution are very different, emphasizing the importance of fully understanding the factors that control biomineral composition before the application of these biominerals to environmental studies. [source] Shell structure, ontogeny and affinities of the Lower Cambrian bivalved problematic fossil Mickwitzia muralensis Walcott, 1913LETHAIA, Issue 4 2004UWE BALTHASAR Exceptionally preserved carbonate- and shale-hosted Mickwitzia muralensis from the Lower Cambrian Mural Formation, southern Canadian Rocky Mountains, complement one another to yield an unusually complete account of its ontogeny, ecology and phylogenetic relationships. The shell of M. muralensis is composed of dense phosphatic layers interspersed with porous organic-rich layers. At the insertion of shell-penetrating tubes, shell layers deflect inwards to produce inwardly pointing cones. The tubes are interpreted as having hosted setae that were secreted by outer-epithelial follicles. Follicular setae also occurred at the mantle margin, where they were oriented within the plane of the shell as in modern brachiopods. During ontogeny, the initial setae oriented in the plane of the shell occurred before the first shell-penetrative setae. In the juvenile and early-mature stages of shell secretion, a posterior opening was present between both valves and was used for the protrusion of an attachment structure. In the late-mature shell, this opening became fixed in the ventral valve. Based on the posterior margin and the shell microstructure, a close relationship between Mickwitzia and the paterinids is proposed with differences interpreted as heterochronic. The shell-penetrative setal apparatus of M. muralensis is distinct from that previously described of Micrina, though both types are conceivably homologous to adult and juvenile setae of modern brachiopods. [source] N -Isopropylacrylamide/2-Hydroxyethyl Methacrylate Star Diblock Copolymers: Synthesis and Thermoresponsive BehaviorMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 24 2006Zhiqiang Cao Abstract Summary: Tri-arm star diblock copolymers, poly(2-hydroxyethyl methacrylate)- block -poly(N -isopropylacrylamide) [P(HEMA- b -NIPAAm)] with PHEMA and PNIPAAm as separate inner and outer blocks were synthesized via a two-step ATRP at room temperature. The formation, molecular weight and distribution of polymers were examined, and the kinetics of the reaction was monitored. The PDI of PHEMA was shown to be lower, indicating well-controlled polymerization of trifunctional macro-initiator and resultant star copolymers. The thermoresponsive behavior of diblock copolymer aqueous solution were studied by DSC, phase diagrams, temperature-variable 1H NMR, TEM and DLS. The results revealed that introducing a higher ratio of HEMA into copolymers could facilitate the formation of micelles and the occurrence of phase transition at lower temperatures. TEM images showed that I-(HEMA40 -NIPAAm320)3 solutions developed into core-shell micelles with diameters of approximately 100 nm. I-(HEMA40 -NIPAAm320)3 was used as a representative example to elucidate the mechanism underlying temperature-induced phase transition of copolymer solution. In this study we proposed a three-stage transition process: (1) separately dispersed micelles state at ,17,22,°C; (2) aggregation and fusion of micelles at ,22,29,°C; (3) sol-gel transition of PNIPAAm segments at ,29,35,°C, and serious syneresis of shell layers. Molecular architecture of Poly(HEMA- b -NIPAAm). [source] Crystal mismatched layers in pentagonal nanorods and nanoparticlesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2010L. M. Dorogin Abstract Pentagonal nanorods (PNRs) and nanoparticles (PNPs) covered by mismatched shell layers are theoretically investigated. Mechanical stresses and elastic energies of such objects are calculated analytically and analyzed in the framework of linear isotropic elasticity. Difference between elastic modules of core and shell is taken into account. The threshold radiuses as the minimal radiuses of PNR and PNP for which the formation of the shell layer is energetically favorable are found. The threshold radius is approximately 10,nm for PNPs and 100,nm for PNRs of typical face-centered cubic (FCC) metals. The optimal magnitudes of mismatch parameter giving the maximal energy release for shelled PNRs and PNPs are determined. [source] | |||||||||||||