INTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 9 2007
H. Lottmann
Summary Aims:, Desmopressin is a useful treatment for primary nocturnal enuresis (PNE), a common childhood condition that can persist into adolescence. This open-label, randomised, cross-over study evaluated the preference of children and adolescents with PNE for sublingual desmopressin oral lyophilisate (MELT) vs. tablet treatment, and the efficacy, safety, compliance and ease of use associated with each formulation. In total, 221 patients aged 5,15 years who were already receiving desmopressin tablets were randomised 1 : 1 to receive desmopressin treatment in the order MELT/tablet (n = 110) or tablet/MELT (n = 111) for 3 weeks each. Each formulation was administered in bioequivalent doses (0.2/0.4 mg tablets , 120/240 ,g MELT). Following treatment, patients were questioned regarding treatment preference. Diary card data and 100 mm Visual Analogue Scale scores were also recorded. Results:, Overall, patients preferred the MELT formulation to the tablet (56% vs. 44%; p = 0.112). This preference was age dependent (p = 0.006); patients aged < 12 years had a statistically significant preference for desmopressin MELT (p = 0.0089). Efficacy was similar for both formulations (MELT: 1.88 ± 1.94 bedwetting episodes/week; tablet: 1.90 ± 1.85 episodes/week). Ease of use of both formulations was high. Compliance (, 80%) was 94.5% for MELT patients vs. 88.9% for the tablet (p = 0.059). No serious/severe adverse events were reported. Conclusions:, There was an overall preference for the MELT, and a statistically significant preference for desmopressin MELT in children aged 5,11 years. Desmopressin MELT had similar levels of efficacy and safety at lower dosing levels than the tablet, and therefore facilitates early initiation of PNE treatment in children aged 5,6 years. [source]

Application of MELTS to kinetic evaporation models of FeO-bearing silicate melts

METEORITICS & PLANETARY SCIENCE, Issue 1 2004
Article first published online: 26 JAN 2010
No abstract is available for this article. [source]

Melt,wall rock interaction in the mantle shown by silicate melt inclusions in peridotite xenoliths from the central Pannonian Basin (western Hungary)

ISLAND ARC, Issue 2 2009
Csaba Szabó
Abstract In this paper we present a detailed textural and geochemical study of two equigranular textured amphibole-bearing spinel lherzolite xenoliths from Szigliget, Bakony,Balaton Highland Volcanic Field (BBHVF, western Hungary) containing abundant primary silicate melt inclusions (SMIs) in clinopyroxene rims and secondary SMIs in orthopyroxene (and rarely spinel) along healed fractures. The SMIs are dominantly composed of silicate glass and CO2 -rich bubbles. Clinopyroxene and orthopyroxene are zoned in both studied xenoliths, especially with respect to Fe, Mg, Na, and Al contents. Cores of clinopyroxenes in both xenoliths show trace element distribution close to primitive mantle. Rims of clinopyroxenes are enriched in Th, U, light rare earth elements (LREEs) and medium REEs (MREEs). Amphiboles in the Szg08 xenolith exhibit elevated Rb, Ba, Nb, Ta, LREE, and MREE contents. The composition of silicate glass in the SMIs covers a wide range from the basaltic trachyandesite and andesite to phonolitic compositions. The glasses are particularly rich in P2O5. Both primary and secondary SMIs are strongly enriched in incompatible trace elements (mostly U, Th, La, Zr) and display a slight negative Hf anomaly. The development of zoned pyroxenes, as well as the entrapment of primary SMIs in the clinopyroxene rims, happened after partial melting and subsequent crystallization of clinopyroxenes, most probably due to an interaction between hot volatile-bearing evolved melt and mantle wall-rocks. This silicate melt filled microfractures in orthopyroxenes (and rarely spinels) resulting in secondary SMIs. [source]

Melt spun thermoresponsive shape memory fibers based on polyurethanes: Effect of drawing and heat-setting on fiber morphology and properties

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007
Jasmeet Kaursoin
Abstract Thermoresponsive shape memory (SMP) fibers were prepared by melt spinning from a polyester polyol-based polyurethane shape memory polymer (SMP) and were subjected to different postspinning operations to modify their structure. The effect of drawing and heat-setting operations on the shape memory behavior, mechanical properties, and structure of the fibers was studied. In contrast to the as-spun fibers, which were found to show low stress built up on straining to temporary shape and incomplete recovery to the permanent shape, the drawn and heat-set fibers showed significantly higher stresses and complete recovery. The fibers drawn at a DR of 3.0 and heat-set at 100°C gave stress values that were about 10 times higher than the as-spun fibers at the same strain and showed complete recovery on repeated cycling. This improvement was likely due to the transformation brought about in the morphology of the permanent shape of the SMP fibers from randomly oriented weakly linked regions of hard and soft segments to the well-segregated, oriented and strongly H-bonded regions of hard-segments. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2172,2182, 2007 [source]

Effect of Oxygen Partial Pressure on the Formation of Metastable Phases from an Undercooled YbFeO3 Melt Using an Aerodynamic Levitator

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2009
Malahalli S. Vijaya Kumar
The Yb2O3,Fe2O3 system was studied to investigate the effect of oxygen partial pressure on the formation of metastable phases over a wide range of oxygen partial pressures from 105 to 10,1 Pa. Two kinds of metastable phases, with space groups of P63cm and P63/mmc, were found through rapid solidification of an undercooled YbFeO3 melt in an atmosphere with reduced Po2. The crystal structure of the as-solidified samples changed from orthorhombic Pbnm to hexagonal P63cm and P63/mmc with decreasing Po2. X-ray diffractometric and scanning electron microscopic results confirmed the existence of various phases in the as-solidified samples. The stabilities of each phase were studied by annealing the bulk sample in the thermogravimetric,differential thermal analysis (TG-DTA) furnace up to 1673 K, and the equilibrium phase diagram was constructed for the Yb,Fe,O system at 1473 K. TG analysis showed an increase of the sample mass during annealing and revealed that the existence of Fe2+, which has an ionic radius larger than that of Fe3+, decreases the tolerance factor and therefore destabilizes the perovskite structure. [source]

Metastable Phase Formation from an Undercooled Rare-Earth Orthoferrite Melt

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2002
Kosuke Nagashio
High-speed digital imaging was conducted during the containerless solidification of rare-earth orthoferrites (RE = La, Sm, Dy, Y, Yb, and Lu) with the perovskite structure to determine the metastable phase and elucidate its growth behavior. Observation using a high-speed video camera revealed that the formation of the metastable phase became pronounced, and double recalescence from the metastable phase to a stable phase occurred, as the ionic radius of the rare-earth element decreased. In the present paper, the formation of the metastable phase is discussed systematically in view of the stability of the perovskite structure and the activation energy of nucleation. [source]

Miscibility in Blends of Isotactic/Syndiotactic Polystyrenes at Melt or Quenched Amorphous Solid State

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2006
Shu Hsien Li
Abstract Summary: Miscibility in amorphous phase and behavior in a crystalline phase of blends of two semicrystalline and isomeric polymers, isotactic polystyrene (iPS) and syndiotactic polystyrene (sPS), was probed. Optical and scanning electron microscopy results indicate no discernible heterogeneity in iPS/sPS blends in either melt state or rapidly quenched amorphous super-cooled state, while the Tg behavior of the quenched amorphous blends shows an intimately mixed state of two polymer chains. The crystal forms of the blends were further analyzed to provide additional evidence of miscibility in the amorphous domain. The sPS in the iPS/sPS blends upon melt crystallization was found to predominantly exist as the more stable , -form (rather than mixed , -form and , -form in neat sPS), which also suggests evidence of miscibility in the iPS/sPS blends. The melting behavior of semicrystalline sPS in the iPS/sPS mixtures was analyzed using the Flory-Huggins approach for estimation of interactions. By measuring the equilibrium melting point of the higher-melting sPS species in the sPS/iPS blends, a small negative value, for the interaction parameter (,,,,,0.11) was found. Further, by introducing a third polymer, poly(2,6-dimethyl- p -phenylene oxide) (PPO), a ternary iPS/sPS/PPO blend system was also proven miscible, which constituted a further test for stable phase miscibility in the iPS/sPS blend. General nature of miscibility in blends composed of two crystalline isomeric polymers is discussed. Issues in dealing with blends of polymers of the same chemical repeat unit but different tacticities were addressed. X-ray diffractograms for neat sPS and iPS/sPS blends, each having been isothermally crystallized at 245,°C for 4 h. [source]

Hydrolytic Degradation and Monomer Recovery of Poly(butylene succinate) and Poly(butylene succinate/adipate) in the Melt

MACROMOLECULAR REACTION ENGINEERING, Issue 6 2008
Hideto Tsuji
Abstract Aliphatic dicarboxylic acid/aliphatic diol-derived polyesters, poly(butylene succinate) and poly(butylene succinate/adipate), have been hydrolytically degraded in the melt in high-temperature and high-pressure water over a wide temperature range of 180,300,°C for periods of up to 30 min. The formation/decomposition of succinic acid (SA), adipic acid (AA), and butane-1,4-diol (BD), plus the molecular weight change of PBS and PBSA were then investigated. SA and AA were recovered at maximum yields of 65,80%, whereas BD was recovered at a maximum yield of only 30%, probably because of its decomposition. The obtained results were compared with those reported for aliphatic hydroxycarboxylic acid-derived polyesters and aromatic dicarboxylic acid/aliphatic diol-derived polyesters. [source]

Linear and Nonlinear Viscoelasticity of a Model Unentangled Polymer Melt: Molecular Dynamics and Rouse Modes Analysis

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 3 2006
Mihail Vladkov
Abstract Summary: Using molecular dynamics simulations, we determine the linear and nonlinear viscoelastic properties of a model polymer melt in the unentangled regime. Several approaches are compared for the computation of linear moduli and viscosity, including Green-Kubo and nonequilibrium molecular dynamics (NEMD). An alternative approach, based on the use of the Rouse modes, is also discussed. This approach could be used to assess local viscoelastic properties in inhomogeneous systems. We also focus on the contributions of different interactions to the viscoelastic moduli and explain the microscopic mechanisms involved in the mechanical response of the melt to external solicitation. [source]

Stretching induced phase transformations in melt extruded poly(vinylidene fluoride) cast films: Effect of cast roll temperature and speed

POLYMER ENGINEERING & SCIENCE, Issue 12 2007
Milind V. Mhalgi
Melt extruded poly(vinylidene fluoride) cast films were prepared at different cast roll temperatures and speeds to study the effect of casting temperature and preorientation of the melt on the ,- to ,-phase transformation in these films after uniaxial stretching. X-ray and fourier transform infrared spectroscopy were used to identify the crystalline phases. The unstretched films were characterized using small angle light scattering (SALS). The films were stretched to a stretch ratio of 4.2 and at 80°C. Birefringence of the films and the fraction of ,-phase [F(,)] formed after uniaxial stretching increased with stretch ratio. The films showed increased crystallinity after stretching. For the films prepared at different cast roll temperatures, there was little change in F(,) in the films having a cast roll temperature between 75 and 120°C, but for the film with a cast roll temperature of 130°C F(,) decreased considerably. For the films prepared at different cast roll speeds, the F(,) increased with stretch ratio as well as with cast roll speed for a fixed stretch ratio. The primary effect of changing both the parameters is a change in the average spherulitic radius (R), in the unstretched films measured using SALS. The F(,) obtained correlated well with R and lower spherulitic radii resulted in the higher conversion to the ,-phase. POLYM. ENG. SCI., 47:1992,2004, 2007. © 2007 Society of Plastics Engineers [source]

Melt processed microporous films from compatibilized immiscible blends with potential as membranes

POLYMER ENGINEERING & SCIENCE, Issue 4 2002
M. Xanthos
Microporous flat films with potential as membranes were produced via melt processing and post-extrusion drawing from immiscible polypropylene/polystyrene blends containing a compatibilizing copolymer. The blends were first compounded in a co-rotating twin-screw extruder and subsequently extruded through a sheet die to obtain the precursor films. These were uniaxially drawn (100%,500%) with respect to the original dimensions to induce porosity and then post-treated at elevated temperatures to stabilize the resultant structure, which consisted of uniform microcracks in the order of a few nanometers in width. The effects of blend composition and extrusion process parameters on surface and cross-sectional porosity and solvent permeability of the prepared films are presented and related to specific microstructural features of the films before and after drawing. Finite element modeling of the stretching operation in the solid state yielded a successful interpretation of the blend response to uniaxial tension that resulted in microcrack formation. Comparison of some of the novel microporous structures of this work with commercial membranes prepared by solvent-based phase inversion processes suggests comparable pore size and porosity ranges, with narrower pore size distribution. [source]

Melt flow properties, mechanical properties, thermal properties and morphology of polycarbonate/highly branched polystyrene blends

POLYMER INTERNATIONAL, Issue 5 2006
Aiying Li
Abstract A highly branched polystyrene (HBPS) was synthesized via the copolymerization of 4-(chloromethyl) styrene with styrene using the self-condensing atom transfer radical polymerization method. The addition of HBPS as a melt modifier for polycarbonate (PC) was attempted. Melt flow properties, mechanical properties, thermal properties and morphology of the blends were studied. The results showed that a significant drop in the blend viscosity occurs immediately on addition of HBPS. Impact strength, tensile strength and glass transition temperature (Tg) of all the blends have not been significantly reduced compared with those of pure PC. The TGA analyses showed that an initial weight loss temperature of all the blends is above 458 °C and slightly low compared with that of pure PC, but all the blends still have excellent thermal stability. Morphological studies using SEM showed that a two-phase morphology is characteristic of all the blends, with more or less spherical droplets of the minor HBPS phase dispersed in the continuous PC phase. Copyright © 2006 Society of Chemical Industry [source]

Mechanical properties and thermal analysis of low-density polyethylene,+,polypropylene blends with dialkyl peroxide

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 4 2010
Kamil, irin
Abstract Polypropylene,+,low density polyethylene (PP,+,LDPE) blends involving 0, 25, 50, 75 and 100,wt% of PP with dialkyl peroxide (DAP) were prepared by melt blending in a single-screw extruder. The effects of adding dialkyl peroxide on mechanical and thermal properties of PP,+,LDPE blends have been studied. It was found that at lower concentrations of peroxide (e.g., 0,0.08,wt% of dialkyl peroxide) LDPE component is cross-linked and Polypropylene (PP) is degraded in all compositions of PP,+,LDPE blends. Mechanical properties (Tensile strength at break, at yield and elongation at break), Melt flow index (MFI), hardness, Scanning Electron Microscope (SEM) and thermal analyses (DSC) of these blends were examined. Because of serious degradation or cross-linking the mechanical properties and the crystallinty (%) of those products were decreased as a result of increasing peroxide content. Copyright © 2009 John Wiley & Sons, Ltd. [source]

A pharmacokinetic study of piroxicam in children,

ANAESTHESIA, Issue 10 2004
P. Dix
Summary Feldene MeltTM (piroxicam) is commonly used for analgesia following day case surgery. The manufacturer's recommended paediatric dose is 0.4 mg.kg,1 once daily. In children, plasma piroxicam levels of 3,5 ,g.ml,1 are associated with effective analgesia. However, in adults a single dose of 20 mg piroxicam (0.4 mg.kg,1 for a 50-kg adult) produces plasma levels of only 1.5,2.2 ,g.ml,1. We therefore studied plasma levels achieved by 0.4 mg.kg,1 or 1.0 mg.kg,1 piroxicam in 22 children aged between 3 and 16 years, undergoing elective orthopaedic surgery, in order to investigate the adequacy of single dosing. The first 12 patients received 0.4 mg.kg,1 Feldene MeltTM pre-operatively. Following assay of plasma piroxicam levels, a further 10 patients received 1.0 mg.kg,1 Feldene MeltTM. In both groups, five blood samples were taken at 2-hourly intervals. The mean (95% CI) piroxicam level following 0.4 mg.kg,1 was 2.90 (2.33,3.54) ,g.ml,1, compared to 5.87 (4.58,7.16) ,g.ml,1 following 1.0 mg.kg,1 (p = 0.0003). [source]

Single Crystal Growth of Manganese Gallium Nitride Using Mn,Ga,Na Melt.

CHEMINFORM, Issue 13 2004
Masato Aoki
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

Description of the Structure and Properties of Atactic Polystyrene Melt Using Integral Equation Theory

CHINESE JOURNAL OF CHEMISTRY, Issue 12 2007
Lei ZHAO
Abstract The polymer reference interaction site model (PRISM) integral equation theory was used to describe the structure and thermodynamic properties of atactic polystyrene (aPS) melt, in which the monomer of aPS is represented with an eight-site model to characterize its microstructure. The intramolecular structure factors needed in the PRISM calculations were obtained from single chain MD simulations. The calculated results indicate that the results by the integral equation method agrees well with experiments, and can reflect the fine microscopic structure of real aPS melt. This work shows that the PRISM theory is a powerful tool for investigating the structure and properties of complex polymers. [source]

Crystallization of Highly Supercooled Silicate Melts

ADVANCED ENGINEERING MATERIALS, Issue 12 2006
M. Roskosz
Crystallization of liquids in the system CaO-MgO-Al2O3 -SiO2 at one atmosphere has been studied at temperatures between the glass transition (Tg) and the solidus. To determine the textures, compositions and unit-cell parameters of the crystalline phases, the authors have characterized the experimental charges over a wide range of length scales by scanning and transmission electron microscopy, electron microprobe analyses, X-ray diffraction, and Raman spectroscopy. With increasing temperature, crystals tend to reach the equilibrium composition, but the relative importance of thermodynamic and kinetic factors is a single function of T - Tg, regardless of liquid composition. This feature is of considerable practical interest as it provides the possibility, not only to predict, but also to control the composition of the crystallizing phases. [source]

Quantification of Chemical Striae in Inorganic Melts and Glasses through Picture Processing

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010
Martin Jensen
Chemical striations occur in various types of inorganic melts like lava and glass melts, and affect the physical properties of materials. This paper reports a quantitative study of the chemical striations in iron-rich aluminosilicate melts and glasses. In this study, an integrated method has been established, which consists of sample preparation, image acquiring, Fourier Transformation, and characteristic value determination. The principle of the established method is illustrated by picture processing-based simulation. The extent of the chemical striations and the diffusion length of the striae can be measured using this method. It is found that the extent of the chemical striations is rather sensitive to the melting technique. Furthermore, the impact of chemical diffusion and stirring on the extent of striations is revealed using the picture processing-based simulation approach. The diffusion process eliminates small striae and reduces the intensity of the larger ones. At a constant temperature, the diffusion determines the transformation rate of an inhomogeneous melt into a homogeneous one. During stirring, the size distribution of the large striae becomes broader, but the overall intensity of the striae becomes smaller. [source]

A Limited Review of Water Diffusivity and Solubility in Glasses and Melts

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2008
James E. Shelby
A limited review of the literature dealing with water solubility and diffusion in oxide glasses and melts is presented, with an emphasis on simple and commercial compositions and on work during the past decade. Several methods for determination of water solubilities and diffusivities are discussed. Experimental results are presented for silicate, borate, and germanate glasses and melts. Water diffusivities always increase with increasing temperature and modifier oxide content in these melts. Variations in water solubility and diffusivity with alkali and alkaline earth identity for otherwise identical compositions are small, while variations with the identity of the glass-forming oxide are large. Water solubility increases with increasing modifier oxide content in alkali silicate melts, but decreases with increasing modifier oxide content in alkali borate and germanate melts. [source]

Supercooled Barium Boric Oxide Melts: X-Ray Diffraction Measurements and Glass Formation

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2007
Seiichi Matsumura
It is well-known that oxide melts easily form a glass state from a supercooled state; however, it is difficult for some oxides to transform to the glass state from the corresponding supercooled state. ,-BaB2O4 (,-BBO) crystals are important materials for laser applications. The ,-BBO crystal easily grows from the supercooled melt, and it is therefore difficult to form the BBO glass state. We attempted to make BBO glass by a containerless technique using the conical nozzle gas-jet levitation (CNL) method. We were successful in making BBO glass with a diameter of 2 mm from a highly supercooled melt without rapid quenching. In order to clarify the phase selection mechanism of the BBO melt, we performed high-energy X-ray (113.6 keV) diffraction experiments on the glassy and supercooled liquid BBO using the CNL technique at the BL04B2 beamline of SPring-8. From these experiments, the structure factor S(Q) of BBO glasses and supercooled melts were found to have almost the same features. From these S(Q), we obtained the radial distribution function T(r)=4,rg(r). The analysis also showed that BBO glass and the BBO-supercooled melt have the same short-range distances. For phase selection between crystalline and glassy phases, we discuss a structure model of the BBO melt, including medium range structure based on the short-range structure obtained in this experiment. [source]

An Examination of Surface Tension of Binary Lithium Borate Melts as a Function of Composition and Temperature

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006
Xiumei Shi
Surface tensions of xLi2O,(1,x)B2O3 melts, where 0,x,0.68, have been measured systematically with a ring method from respective liquidus temperatures up to about 1450 K. For all of the investigated melts, the relationship between surface tension and temperature can be well described by quadratic polynomial functions. With increasing Li2O content, surface tension monotonously increased, whereas the temperature coefficient of surface tension increased slowly up to about x=0.1, changed sign from positive to negative at about x=0.2, and then remained negative with further increasing Li2O content. Together with the physical properties reported in our previous work, such as density, temperature coefficient of density, and volume expansion coefficient, etc., both surface tension and temperature coefficient of surface tension have been comparatively plotted as a function of Li/B molar ratio. Differentiated from the inflections of slope in the plots of physical properties vs. Li/B molar ratio, three characteristic regions have been found in the melts of this system. Within different regions, different effects of temperature and concentration on the physical properties of melts have been observed. [source]

Density, Surface Tension, and Viscosity of PbO-B2O3 -SiO2 Glass Melts

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2004
Shigeru Fujino
The density, surface tension, and viscosity of the melts from the PbO-B2O3 -SiO2 system have been measured at temperatures in the range 1073,1473 K. The effect of composition on these properties was also investigated. The density of the melt was found to increase linearly with increasing PbO content. Molar volume was derived from the density data, and its deviation from the additivity of partial molar volumes was calculated. These deviations in molar volume from those obtained from additivity rules have been used along with the ratio of various coordination numbers of boron (as reported by Bray) to discuss the structure of the melts. The surface tension was found to decrease with decreasing SiO2/B2O3 ratio, and to increase in the range of the PbO content between 30 and 60 mol%, showing a maximum at ,60 mol% PbO, and then decreased with further additions. This result suggested that the surface tension would be affected primarily by the B2O3 content in the range of the PbO content between 30,60 mol%, and mainly by the PbO content in the range of the PbO content >60 mol%, respectively. The viscosity of the melt was found to decrease linearly with increasing PbO content. The results obtained indicate that the increase in viscosity with B2O3 was half that of SiO2 (on a molar basis), and an empirical equation has been proposed for the viscosity as a function of mole fraction. [source]

Properties of Nitrogen-Containing Yttria,Alumina,Silica Melts and Glasses

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003
Noritaka Saito
The viscosity and solubility of nitrogen in Y2O3,Al2O3,SiO2 melts have been systematically examined. The effects of nitrogen content on viscosity for Y-Al-Si-O-N melts and on Vickers hardness of oxynitride glasses also have been examined. Although the viscosity of Y2O3,Al2O3,SiO2 melts was decreased, the solubility of nitrogen into the melts was increased with increased Y2O3 content. These results indicated that the yttrium ion behaved as a network modifier. Therefore, the structural units for viscous flow became small, and the amount of nonbridging oxygen increased in the melts when the Y2O3 content increased. The viscosity of Y-Al-Si-O-N melts and Vickers hardness of oxynitride glasses remarkably increased with increased nitrogen content. These results suggested that the substitution of nitrogen for oxygen in the melts may have led to a high average coordination of nonmetal atoms and that the increased cross-linking produced a more rigid glass network. [source]

Novel Dynamic Viscoelastic Measurements of Polyurethane Copolymer Melts and Their Implication to Tack Results

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2006
Sonia Florez
Abstract Summary: A series of polyurethane multiblock copolymers with different proportions of hard segments (urethane) to soft segments (polyadipate of hexane-1,6-diol), are investigated. Dynamic viscoelastic functions of homogeneous melts in the terminal zone are determined. For the first time, entanglement modulus values of such copolymers are reported, which allows estimation of the packing length. These parameters do not vary with changing the hard-to-soft segment ratio, a result that is explained by a compensating effect of the chain architecture. For samples of similar molecular weight, the relaxation time of the terminal zone increases as the hard-to-soft segment ratio augments. The adhesives obtained from PUR solutions show a correlation between the elastic modulus and the debonding stress-strain curves in tack experiments. The storage modulus of the adhesives as a function of frequency at 70,°C. [source]

Monte Carlo Simulation of ABA Triblock Copolymer Melts Confined in a Cylindrical Nanotube

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2007
Xingqing Xiao
Abstract Monte Carlo simulations were used to identify the microphase morphologies of ABA triblock copolymer melts confined in a cylindrical nanotube. The influences of the volume fraction of mid-block B (fB), the radius of nanotube (R) and the asymmetry of ABA triblock copolymer chain were discussed in detail. When fB varies, a series of double-continuous, three-layer concentric cylinder barrel, porous net, double helixes and the new multiplex structures were observed under different conditions. In addition, the stacked disk, catenoid-cylinder and multi-layer concentric cylinder barrel structures occur in turns at changing R. The relation between circular lamellae period L and layer number Nlayer of concentric cylinder barrel with the increase of R was investigated to further explain the put-off phenomenon of microphase transition of the multi-layer concentric cylinder barrel structures. As for the increase of the asymmetry of ABA triblock copolymer chain, it was concluded that the short AI segments tend to site at the interface between rich A and B circular lamellae. [source]

Tuning the Dimensionality of Nitridosilicates in Lithium Melts,

ANGEWANDTE CHEMIE, Issue 34 2009
Sandro Pagano
Welche Dimension soll es sein? Der Zugang zu ein-, zwei- oder dreidimensionalen Nitridosilicaten lässt sich gezielt steuern, indem die Synthese in geschmolzenem Lithium in verschweißten Tantalampullen ausgeführt wird. Erhalten wurden Li4Ca3Si2N6 bestehend aus kantenverknüpften [Si2N6]10, -Einheiten, LiCa3Si2N5, das kantenverknüpfte Doppelketten und mit Li+ besetzte Kanäle aufweist, sowie Li2Sr4Si4N8O, das durch den Einschluss von Li2O eine Zeolith-analoge Struktur bildet (siehe Bild). [source]

Buchbesprechung: Industrial Crystallization of Melts.

CHEMIE-INGENIEUR-TECHNIK (CIT), Issue 3 2005
Von C. M. van't Land.
No abstract is available for this article. [source]

Produktdesign , Möglichkeiten der Produktgestaltung

CHEMIE-INGENIEUR-TECHNIK (CIT), Issue 8 2004
W. Rähse Dr.-Ing.Article first published online: 29 JUL 200
Abstract Die Entwicklung leistungsstarker, auf den Anwendungsfall zugeschnittener Chemieprodukte erfolgt einerseits über gezielte Veränderungen am Molekül (Product Engineering) und andererseits über zugesetzte Hilfsstoffe, Formulierungen oder Mischungen (Product Design). Das Produktdesign umfasst zusätzlich die optimierte Produkthandhabung und Gestaltung. Es wird für Feststoffe an den Beispielen der Granulierung und des Coatings erläutert sowie konkret für die Qualitätseinstellung in der Papierindustrie und für die Gestaltung von Teigwaren diskutiert. Aus Schmelzen lassen sich über die Extrusionstechnologie beliebige Formen realisieren, z.,B. Folien, Stränge, Fasern, Hohl- bzw. Vollkörper (Flaschen, Rohre, Profile), oder über das Vertropfen/Versprühen entstehen Pulver, Granulate, Schuppen, Kügelchen und Pastillen. Für Flüssigkeiten erfolgt die Beschreibung der Einstellung gewünschter Produktleistungen am Beispiel der Niotenside, das Produktdesign am Beispiel der Milch und eines Öls. Die Kombination beider Produktdimensionen ist für die Lackindustrie dargestellt. Einige Gestaltungsmöglichkeiten von Suspensionen, Pasten und Lösungen werden an der Trocknung matrixverkapselter Enzyme, an der Zeolithherstellung sowie an der Verarbeitung keramischer Massen aufgezeigt. Product Design , Possibilities of Product Design The development of high-performance chemical products tailored to a concrete application is done either by making deliberate changes to a particular molecular structure (product engineering) or by adding auxiliary agents, formulations or mixtures (product design). Product design, besides the design proper, also includes the optimized application of the product. For solids it is exemplified by granulation and coating and discussed in concrete terms for the quality adjustment in the paper industry, and for the design of pasta products. Melts can take any desired shape when extruded, such as films, strands, fibers, hollow or solid bodies (bottles, tubes, sections) or they can be processed by dropping/spraying to produce powders, granulates, flakes, pearls or lozenges. The adjustment the desired properties for liquid products is described for the example of non-ionic surfactants and product design is shown for milk and for an oil. The combination of the two product dimensions is presented for the paint industry. Some design possibilities for suspensions, pastes and solutions are demonstrated by the drying of matrix-encapsulated enzymes, the production of zeolite and the processing of ceramic compounds. [source]

ChemInform Abstract: Nitridogermanate Nitrides Sr7[GeN4]N2 and Ca7[GeN4]N2: Synthesis Employing Sodium Melts, Crystal Structure, and Density-Functional Theory Calculations.

CHEMINFORM, Issue 11 2009
Sebastian C. Junggeburth
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Structure of Silicate Glasses and Melts at High Pressure: Quantum Chemical Calculations and Solid-State NMR.

CHEMINFORM, Issue 28 2004
Sung Keun Lee
No abstract is available for this article. [source]