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Homogeneous Phase (homogeneous + phase)

Distribution by Scientific Domains
Chemistry57%
Polymers and Materials Science42%

Selected Abstracts

Recent Advances in the Syntheses and Applications of Molybdenum and Tungsten Alkylidene and Alkylidyne Catalysts for the Metathesis of Alkenes and Alkynes

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2007
Richard
Abstract The last several years have produced some key advances in the area of alkene and alkyne metathesis by high oxidation state alkylidene and alkylidyne complexes along with new applications in organic and polymer chemistry. In this review we cover some of these developments and applications. The first part of this review concerns developments in catalyst synthesis and new catalysts. The second part concerns notable applications in organic and polymer chemistry. We discuss only high oxidation state alkylidene and alkylidyne chemistry of relevance to alkene or alkyne metathesis reactions and favor studies in the homogeneous phase. [source]

Driving force in first-order phase transitions and its application to gas hydrate nucleation from a single phase

AICHE JOURNAL, Issue 9 2009
Bernardo Carreón-Calderón
Abstract Classical nucleation theories of general application are taken as starting point to analyze the driving force for multicomponent gas hydrate nucleation from a single homogeneous phase. It is shown that the ratio between the specific surface energy and the critical radius of nucleation has a single value irrespective of the analyzed driving force expression. From this result, two driving force expressions for multicomponent gas hydrate nucleation are derived in the context of the so-called generalized nucleation theory, and it is demonstrated that the driving force for gas hydrates can be estimated using the same information given for the determination of the incipient formation points of the dispersed phase from a saturated phase. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Synthesis, characterization, and properties of novel ladderlike phosphorus-containing polysilsesquioxanes

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2003
Chin-Lung Chiang
Abstract Novel ladderlike polysilsesquioxanes that contain phosphorus were successfully synthesized by the sol,gel method. The polysilsesquioxanes were characterized by Fourier transform infrared spectroscopy, 29Si NMR, and X-ray diffraction. The characterizations demonstrated that the polymer possesses a typical ladderlike structure. The thermogravimetric and differential scanning calorimetric data revealed that the polysilsesquioxanes possess excellent thermal stability. A kinetic analysis of thermal degradation showed that the activation energy of thermal degradation is 187 kJ/mol, according to Kissinger's method. The activation energy of thermal degradation normally increases with conversion (from 171 to 309 kJ/mol) according to Ozawa's method. The average activation energy, calculated by Ozawa's method, was 209 kJ/mol. The scanning electron microscopic photograph and Si and P mappings of ladderlike polysilsesquioxanes showed that the particles were uniformly dispersed at the molecular level and that the sizes of the polysilsesquioxane particles were less than 100 nm. The ultraviolet,visible spectra of the ladderlike polysilsesquioxanes revealed no absorbance in the range of 400,800 nm. Ladderlike polysilsesquioxanes possess excellent optical transparency and excellent flame retardance. This transmittance may be used as a criterion for identifying the formation of a homogeneous phase. These polymers have great potential in waveguide applications. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1371,1379, 2003 [source]

Microstructure Characterizations in Calcium Magnesium Niobate

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2001
Hwack Joo Lee
Microstructural studies on the domain boundaries in Ca(Mg1/3CNb2/3)O3 (CMN) complex perovskite compound were conducted using X-ray diffractometry and transmission electron microscopy. The 1:2 chemical ordering of B-site cations and the tilting of oxygen octahedra were involved in the CMN microstructure, as inferred from the presence of two types of domain boundaries. One type was the antiphase boundaries (APBs), which did not lie on a specific set of crystallographic planes. These boundaries were caused by the chemical 1:2 ordering of B-site cations, magnesium and niobium. The other type was the ferroelastic domain boundaries, which were parallel to a certain crystallographic plane. Therefore, CMN had the 1:2 ordered monoclinic unit cell distorted by the antiphase or in-phase tilting of oxygen octahedra. CMN had the mixed phases rather than the homogeneous phase. [source]

Modeling of the Phase Separation Behavior of Polydisperse Semi-Flexible Diblock Copolymers

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2004
Andreas John
Abstract Summary: A modified random phase approximation method with a cumulant expansion for the semi-flexible structure factor of diblock copolymers was exercised to describe the phase separation behavior of semi-flexible and polydisperse diblock copolymers. Scattering curves and spinodal diagrams were calculated applying monomer specific input parameters. The influence of polydispersity was included applying basic concepts of mathematical statistics utilizing several probability density distributions in the case of the two single blocks. In contrast to semi-flexibility, the main effect of polydispersity was found to shift the spinodal up, thus to enlarge the range of existence of the homogeneous phase. Twofold Schultz-Zimm distribution of diblock copolymers. [source]

Antibody Labeling of Cholesterol/Ceramide Ordered Domains in Cell Membranes

CHEMBIOCHEM, Issue 18 2007
Luana Scheffer Dr.
Abstract A monoclonal antibody raised against mixed monolayers of 60:40 mol,% cholesterol/C16-ceramide of known structure was used to label cholesterol/ceramide-rich domains in cell membranes. The antibody, Cer,Chol 405F specifically recognizes the mixed crystalline and homogeneous phase in monolayers, but it does not interact with either of the components separately. It interacts differently with mixed monolayers that contain ceramides of different acyl chain length. When used on cells, the antibody labeling is sensitive to changes in cholesterol and ceramide levels, as well as to over-expression of specific ceramides; this is in agreement with the results that were obtained on lipid monolayers. This represents a proof of concept of the applicability of a new approach to the structural characterization of lipid microdomains in cell membranes. The approach consists of raising antibodies that recognize specific structural organizations of lipids in artificial mixtures, characterizing the antibody/ordered domain complexes in vitro, and subsequently using them to detect the presence of the same (or similar) domains in cell membranes. [source]

Chemically selective soft X-ray patterning of polymers

JOURNAL OF SYNCHROTRON RADIATION, Issue 2 2007
Jian Wang
The chemically selective modification of polymer mixtures by monochromated soft X-rays has been explored using the high-brightness fine-focused 50,nm beam of a scanning transmission X-ray microscope. Four different polymer systems were examined: a polymethylmethacrylate (PMMA) polyacrylonitrile (PAN) bilayer film; a PMMA- blend -PAN microphase-separated film; a poly(MMA- co -AN) copolymer film; and a poly(ethyl cyanoacrylate) homopolymer film. A high level of chemically selective modification was achieved for the PMMA/PAN bilayer; in particular, irradiation at 288.45,eV selectively removed the carbonyl group from PMMA while irradiation at 286.80,eV selectively reduced the nitrile group of PAN, even when these irradiations were carried out at the same (x,y) position of the sample. In the last two homogenous polymer systems, similar amounts of damage to the nitrile and carbonyl groups occurred during irradiation at either 286.80 or 288.45,eV. This is attributed to damage transfer between the C[triple-bond]N and C=O groups mediated by primary electrons, secondary electrons or radical/ionic processes, aided by their close spatial proximity. Although the overall thickness of the bilayer sample at 70,nm is smaller than the lateral line spreading of 100,nm, the interface between the layers appears to effectively block the transport of energy, and hence damage, between the two layers. The origins of the line spreading in homogeneous phases and possible origins of the damage blocking effect of the interface are discussed. To demonstrate chemically selective patterning, high-resolution multi-wavelength patterns were created in the PMMA/PAN bilayer system. [source]