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Phase Segregation (phase + segregation)

Distribution by Scientific Domains

Polymers and Materials Science	75%

Distribution within Polymers and Materials Science

Polymer Science & Technology General	49%
General & Introductory Materials Science	41%

Selected Abstracts

Phase Segregation in Thin Films of Conjugated Polyrotaxane, Poly(ethylene oxide) Blends: A Scanning Force Microscopy Study,

ADVANCED FUNCTIONAL MATERIALS, Issue 6 2007
L. Sardone
Abstract Scanning force microscopy (SFM) is used to study the surface morphology of spin-coated thin films of the ion-transport polymer poly(ethylene oxide) (PEO) blended with either cyclodextrin (CD)-threaded conjugated polyrotaxanes based on poly(4,4,-diphenylene-vinylene) (PDV), ,-CD,PDV, or their uninsulated PDV analogues. Both the polyrotaxanes and their blends with PEO are of interest as active materials in light-emitting devices. The SFM analysis of the blended films supported on mica and on indium tin oxide (ITO) reveals in both cases a morphology that reflects the substrate topography on the (sub-)micrometer scale and is characterized by an absence of the surface structure that is usually associated with phase segregation. This observation confirms a good miscibility of the two hydrophilic components, when deposited by using spin-coating, as suggested by the luminescence data on devices and thin films. Clear evidence of phase segregation is instead found when blending PEO with a new organic-soluble conjugated polymer such as a silylated poly(fluorene)- alt -poly(para -phenylene) based polyrotaxane (THS,,-CD,PF,PPP). The results obtained are relevant to the understanding of the factors influencing the interfacial and the intermolecular interactions with a view to optimizing the performance of light-emitting diodes, and light-emitting electrochemical cells based on supramolecularly engineered organic polymers. [source]

Crystallization-Induced Phase Segregation Based on Double-Crystalline Blends of Poly(3-hexylthiophene) and Poly(ethylene glycol)s

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 6 2010
Kui Zhao
Abstract Crystallization-induced vertical stratified structures were constructed based on double-crystalline poly(3-hexylthiophene) (P3HT)/poly(ethylene glycol)s (PEG) systems at room temperature, in which the P3HT crystallinity and the mechanism were investigated. Vertical stratified microstructures with highly crystalline P3HT network on the surface were formed when depositing from marginal solvents, while lateral phase-separated structures or low P3HT crystallinity were observed for good solvents. The morphological differences came from the solvent effect. In marginal solvents, p -xylene and dichloromethane, P3HT large-scale microcrystallites were generated in solution, which ensured the priority of P3HT crystalline sequence, and phase separation began in the liquid states. When the PEG matrix began to crystallize, great energy from which the second phase separation was induced drove P3HT crystallites to the surface, resulting in the formation of vertical stratified microstructures with highly crystalline P3HT network on the surface. The method, crystallization-induced phase segregation of crystalline,crystalline blends in marginal solvent, provides a facile way to construct vertically stratified structures, in which P3HT highly crystalline network is favored. [source]

Phase Segregation in Thin Films of Conjugated Polyrotaxane, Poly(ethylene oxide) Blends: A Scanning Force Microscopy Study,

Poly(9,9-dioctylfluorene)-Based Conjugated Polyelectrolyte: Extended ,-Electron Conjugation Induced by Complexation with a Surfactant Zwitterion

ADVANCED MATERIALS, Issue 18 2010
Giuseppina Pace
We report on a conjugated polyelectrolyte (CPE) based on fluorene repeat units, which forms a supramolecular complex with a zwitterion surfactant. The complex self-assembles into multilamellar structures on solid substrates. The luminescence efficiency, low in the uncomplexed polymer, is strongly increased after complexation. This originates from the phase segregation between the aromatic backbone and ionic sides, reducing conformational defects and ionic dipole-induced quenching. [source]

Controlled Growth of High-Quality ZnO-Based Films and Fabrication of Visible-Blind and Solar-Blind Ultra-Violet Detectors

ADVANCED MATERIALS, Issue 45 2009
Xiaolong Du
Abstract ZnO is a wide-bandgap (3.37,eV at room temperature) oxide semiconductor that is attractive for its great potential in short-wavelength optoelectronic devices, in which high quality films and heterostructures are essential for high performance. In this study, controlled growth of ZnO-based thin films and heterostructures by molecular beam epitaxy (MBE) is demonstrated on different substrates with emphasis on interface engineering. It is revealed that ultrathin AlN or MgO interfacial layers play a key role in establishing structural and chemical compatibility between ZnO and substrates. Furthermore, a quasi-homo buffer is introduced prior to growth of a wurtzite MgZnO epilayer to suppress the phase segregation of rock-salt MgO, achieving wide-range bandgap tuning from 3.3 to 4.55,eV. Finally, a visible-blind UV detector exploiting a double heterojunction of n-ZnO/insulator-MgO/p-Si and a solar-blind UV detector using MgZnO as an active layer are fabricated by using the growth techniques discussed here. [source]

Numerical aspects of an algorithm for the Eulerian simulation of two-phase flows

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10-11 2003
Paulo J. Oliveira
Abstract It is often the case that the numerical simulation of two phase flows leads to a number of difficulties associated with the solution algorithms utilized. Those difficulties manifest themselves as an impossibility to converge the iterative solution process, typical of the finite-volume pressure-correction methods, and are particularly persistent in cases with phase segregation (complete, or almost complete, separation of one phase from the other) and with fine meshes. A number of effective measures to overcome such problems are here proposed and tested, encompassing: (1) modification of the momentum equations formulation in a way that avoids singularity as volume fractions (,) tend to zero; (2) bounding of the volume fractions during the iterative algorithm in a way that enforces the physical limits, ,0 and 1; (3) symmetric treatment of some terms in the equations, and consistent formulation of cell-face fluxes in order to prevent numerical-induced oscillations. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Oxidative coupling of methane in dense ceramic membrane reactor with high yields

AICHE JOURNAL, Issue 10 2002
F. T. Akin
Oxidative coupling of methane (OCM) was studied with dense tubular Bi1.5Y0.3Sm0.2O3 (BYS) membranes at various temperatures (870,930°C). BYS powders were synthesized by a citrate method. Tubular-shaped dense membranes of BYS in the fluorite-type FCC phase structure were fabricated by cold isostatic pressing with green machining. The best one-pass C2 (C2H4 + C2H6) yield achieved for OCM in the BYS dead-end membrane reactor was 35% at a C2 selectivity of 54% at 900°C. At the same C2 yield, the membrane reactor mode gives C2 selectivity of over 200% higher than the cofeed mode in the same membrane reactor under similar conditions. The oxygen permeation fluxes through tubular BYS membrane reactors under OCM reaction conditions are approximately 1.5 to 3.5 times higher than those under oxygen permeation conditions with He as the purge. After 6 days of OCM, BYS membrane remained in good integrity with minor phase segregation observed at the reaction side of the membrane. [source]

Hybrid metal,polymer composites from functional block copolymers

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2005
Robert B. Grubbs
Abstract The combination of metals and polymers in hybrid materials is a research area of great current interest. A number of methods for controlling the positioning of metallic species within polymer matrices on the nanometer scale have been developed. This highlight focuses on the use of functional block copolymers for the localization of metal species, especially nanoparticles, on the nanometer scale through block copolymer phase segregation. Research from the author's group on the use of alkyne-functional block copolymers for the preparation of cobalt-containing materials is discussed in this context. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4323,4336, 2005 [source]

Processability and characterization of poly(vinyl chloride)- b -poly(n -butyl acrylate)- b -poly(vinyl chloride) prepared by living radical polymerization of vinyl chloride.

JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 4 2006
Comparison with a flexible commercial resin formulation prepared with PVC, dioctyl phthalate
This work reports the synthesis and processing of a new flexible material based on PVC produced by living radical polymerization. The synthesis was carried out in a two-step process. In the first step the macroinitiator ,, ,-di(iodo)poly(butyl acrylate) [,, ,-di(iodo)PBA] was synthesized in water by single electron transfer/degenerative chain transfer mediated living radical polymerization (SET-DTLRP) catalyzed by Na2S2O4. In the second step this macroinitiator was reinitiated by SET-DTLRP of vinyl chloride (VC), thereby leading to the formation of the block copolymer poly(vinyl chloride)- b -poly(butyl acrylate)- b -poly(vinyl chloride) [PVC- b -PBA- b -PVC]. This new material was processed on a laboratory scale. The DMTA traces showed only a single glass transition temperature, thus indicating that no phase segregation was present. The copolymers were studied with regard to their processing, miscibility, and mechanical properties. The first comparison with commercial formulations made with PVC and dioctyl phthalate (DOP) is presented. J. VINYL ADDIT. TECHNOL., 12:156,165, 2006. © 2006 Society of Plastics Engineers [source]

Bioinspired Mineralization of Inorganics from Aqueous Media Controlled by Synthetic Polymers

MACROMOLECULAR BIOSCIENCE, Issue 2 2007
Katarzyna Gorna
Abstract The formation of inorganic structures in nature is commonly controlled by biogenic macromolecules. The understanding of mineralization phenomena and the nucleation and growth mechanisms involved is still a challenge in science but also of great industrial interest. This article focuses on the formation and mineralization of two archetypical inorganic materials: zinc oxide and amorphous calcium carbonate (ACC). Zinc oxide is selected as a model compound to investigate the role that polymers play in mineralization. Most of the effort has been devoted to the investigation of the effects of double-hydrophilic block and graft copolymers. Recent work has demonstrated that latex particles synthesized by miniemulsion polymerization, properly functionalized by various chemical groups, have similar effects to conventional block copolymers and are excellently suited for morphology control of ZnO crystals. Latex particles might serve as analogues of natural proteins in biomineralization. The second example presented, ACC, addresses the issue of whether this amorphous phase is an intermediate in the biomineralization of calcite, vaterite, or aragonite. Conditions under which amorphous calcium carbonate can be obtained as nanometer-sized spheres as a consequence of a liquid,liquid phase segregation are presented. Addition of specific block copolymers allows control of the particle size from the micrometer to the submicrometer length scale. The physical properties of novel materials synthesized from concentrated solution and their potential applications as a filler of polymers are also discussed. [source]

Indication of Local Phase Separation in Polyimide/Silica Hybrid Polymers,

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2010
Antonino Bartolotta
Abstract PI/SiO2 hybrid polymers involving the in situ generation of SiO2 particles through the sol/gel route have emerged as promising materials in many fields of modern technology thanks to their unique structural characteristics. In this paper their structural and dynamic properties were investigated by FT-IR and DMTA as a function of SiO2 content. All data consistently highlight a loosening of polymeric structure due to the presence of SiO2 nanoparticles and suggest a silica-induced structural change most probably due to a sub-micrometer scale SiO2 phase separation. Our results demonstrate how the analysis of sub-glass ,-relaxation dynamics can be exploited to investigate sub-micro phase segregation in such materials. [source]

Crystallization-Induced Phase Segregation Based on Double-Crystalline Blends of Poly(3-hexylthiophene) and Poly(ethylene glycol)s

From pre-cells to Eukarya , a tale of two lipids

MOLECULAR MICROBIOLOGY, Issue 1 2003
G. Wächtershäuser
Summary A mechanistic hypothesis for the origin of the three domains of life is proposed. A population of evolving pre-cells is suggested to have had a membrane of a racemate of chiral lipids that continuously underwent spontaneous symmetry breaking by spatial phase segregation into two enantiomerically enriched membrane domains. By frequent pre-cell fusions and fissions these membrane domains became partitioned between two pre-cell subpopulations having predominantly one lipid enantiomer or the other. The origin of the Bacteria and Archaea is explained by divergence of first a population of proto-bacteria and later a population of proto-archaea from the evolving pre-cells, each by the emergence of an enantio-selective lipid biosynthesis within the corresponding pre-cell subtype. The origin of the Eukarya is explained by symbiosis between a population of Bacteria and a subpopulation of pre-cells with a predominance of the bacteria-type lipid enantiomers. [source]

On the strength of the double exchange and superexchange interactions in La0.67Ca0.33Mn1,yFeyO3 , an NMR and Mössbauer study

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2006
J. Przewo
Abstract A combined study of La0.67Ca0.33Mn0.9757Fe0.03O3 compound by means of zero field 55Mn and 57Fe NMR as well as 57Fe Mössbauer spectroscopy (MS) is reported. The 55Mn NMR spectra exhibit a single double exchange (DE) line up to the magnetic ordering temperature (TC), 200 K, determined from magnetization measurements. The hyperfine field (HFF) remains finite at the TC, which reveals discontinuous character of the transition and the occurrence of a ferromagnetic-paramagnetic phase segregation. The 57Fe MS HFF decreases much faster with increasing temperature than the 55Mn NMR HFF. Application of a molecular field model to the temperature dependence of the 55Mn and 57Fe HFF allows to estimate values of the Mn,Mn and the Fe,Mn exchange integrals, which amount to 1.24 meV and ,0.6 meV, respectively. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Oxygen Effects in Plasma Nitriding of Ferrous Alloys

PLASMA PROCESSES AND POLYMERS, Issue S1 2007
Carlos A. Figueroa
Abstract In this paper, we study the oxygen effect in low energy nitrogen implanted stainless steel AISI 316 at different oxygen partial pressures and temperatures. The samples were studied by photoemission electron spectroscopy (XPS) and sputtered neutral mass spectrometry (SNMS). Increasing the oxygen partial pressure during nitriding decreases the nitrogen content in the material depth. Surface oxidation induces phase segregation. The presence of oxygen forms CrO, on the top most layer of the sample and, subsequently, a nickel layer appears at approximately 9,10 nm beneath the surface. Moreover, the surface oxidation reaction of metal elements depends more strongly on the oxygen atoms landing on the surface rather than on the temperature process. At higher temperatures, on the other hand, the NO, species are degraded. [source]

Organic,inorganic hybrid materials derived from epoxy resin and polysiloxanes: Synthesis and characterization

POLYMER ENGINEERING & SCIENCE, Issue 1 2008
C.F. Canto
In this study, hybrid materials based on epoxy resin were prepared as transparent self-supported films by a sol,gel process. 4,4,-Diaminodiphenylmethane or oligomeric epoxy resin were used as precursors, which were conveniently functionalized with trialkoxysilanes as end-groups. The effect of the introduction of poly (dimethylsiloxane) was also investigated. The hybrid films showed good thermal stability, a nondefined glass transition temperature, and a dense morphology without phase segregation. The tendency to a flat surface could be observed by atomic force microscopy. The hybrid films also showed good performance as coatings for glass plates, with an improved hydrophobic character in comparison to neat epoxy resin. POLYM. ENG. SCI., 48:141,148, 2008. © 2007 Society of Plastics Engineers [source]