Evidence Of Phase Separation Research Articles

Study on the Mechanical Relaxations of a Zr36Ti24Be40 Amorphous Alloy by Time–Temperature Superposition Principle

In order to investigate the mechanical relaxation behavior of the Zr 36 Ti 24 Be 40 amorphous alloy, the dynamic mechanical properties were measured using dynamic mechanical analyzer (DMA). From the data collected during isothermal multi-frequency dynamic mechanical measurements, the master curves for storage and loss moduli over a broad range of temperature were constructed using the time–temperature superposition (TTS) principle. The temperature dependence of the shift factor was found to follow the Arrhenius relationship and the activation energies, calculated from the Arrhenius relationship, were about 93 and 390 kJ/mol for low temperature mechanical relaxation and viscous flow, respectively. According to the temperature dependence of the shift factor above T g , no evidence for phase separation was found. The fragility index was also calculated from the relationship between shift factors and temperature and was found to be m ≈34, suggesting that the Zr 36 Ti 24 Be 40 amorphous alloy can be classified...

Synthesis and Characterization of Bioconjugates of S-Layer Proteins

The self-assembling proteins that form crystalline surface layers (S-layers) on many microbial species have found numerous applications due to their nanostructured nature. To devise a new method to construct surface displays that exploit S-layer self-assembly activity and nanostructural properties, we have constructed polymer bioconjugates of S-layer proteins. The conjugates formed are similar in function to the monomer alkanethiols that form self-assembled monolayers (SAMs) on gold surfaces. However, the self-assembly is driven by the protein "headgroup" that positions polymer-tethered endgroups on a surface. This paper examines the integration of protein purification, conjugation, and surface assembly that has led to the development of this new method for the formation of nanostructured surfaces. Purified S-layer proteins from Lactobacillus brevis were conjugated with small molecule probes and polymers using amine-based reactions. To keep multiple labeling of protein amine groups to acceptable levels, the conjugations were performed at pH 6.5, allowing for limited yields (24-39%) as determined by mass spectrometry and SDS-polyacrylamide gel electrophoresis. As the presence of high levels of unlabeled S-layer proteins is undesired, we have developed a protocol for further purification that employs monomeric avidin affinity chromatography. The surface self-assembly of the polymer bioconjugates onto amine-terminated microspheres was studied using epi-fluorescence, confocal, and scanning electron microscopy. The surfaces obtained exhibited homogeneous distributions of tethered molecules. Also, in cases where the modular assembly of two distinct types of tethered endgroups was accomplished, there was no evidence for phase separation in the surfaces. The modular assembly method will provide a potential route to controlling surface display density as the starting assembly conditions guide displayed endgroup concentrations in mixed molecular monolayers.

The evidence of phase separation in perovskite manganites aboveT c

A series of bulk ceramic samples of La1−x CaxMn03 and Y1−x CaxMnO3 was prepared by the conventional solid state reaction method, and the samples of x = 1/3 were investigated particularly. The colossal magnetoresistance phenomenon and the properties of magnetic and transport were studied in detail by the experiments of magnetic susceptibility and low temperature resistance. Small angle X-ray scattering (SAXS) was used to investigate the charge inhomogeneities in our samples at room temperature for the first time, and phase separation and colossal magnetoresistance phenomena induced by charge inhomogeneities above Tc were discovered.

Chemical Force Microscopy of Mixed Self-Assembled Monolayers of Alkanethiols on Gold: Evidence for Phase Separation

Mixed self-assembled monolayers formed by the coadsorption of hydroxyl- and methyl-terminated alkanethiols with similar chain lengths have been characterized by friction force microscopy. Friction coefficients have been determined by assuming a fit to Amonton's law. The friction coefficients vary linearly with the fraction of polar-terminated adsorbates in the self-assembled monolayer (SAM). With carboxylic acid-terminated tips, the coefficient of friction increases with the fraction of hydroxyl-terminated thiols, while with methyl-terminated tips it decreases. Similar trends are observed for pull-off forces, which increase and decrease as a function of the fraction of polar-terminated adsorbates for carboxylic acid- and methyl-terminated adsorbates, respectively. Analysis of histograms of adhesion forces has yielded insights into the phase structure of mixed SAMs. Single-component monolayers yield histograms that may be fitted to symmetric Gaussian distributions, irrespective of the nature of the terminal group on either the tip or the SAM. However, mixed monolayers yield broad, asymmetric distributions that could not be fitted with a Gaussian distribution. The best explanation for these data is that mixed SAMs of hydroxyl- and methyl-terminated alkanethiols of similar chain length form phase-separated structures.

Epoxy Networks Modified by a New Class of Oligomeric Silsesquioxanes Bearing Multiple Intramolecular Rings Formed through SiOC Bonds

AbstractSummary: A new class of silsesquioxane (SSO), containing species with two to nine Si atoms bearing multiple intramolecular rings formed through SiOC bonds, was synthesized as a glassy powder. It was characterized by UV‐MALDI‐TOF MS, 29Si NMR and FT IR. Solutions containing different amounts of SSO in the diglycidyl ether of bisphenol A (DGEBA), were homopolymerized in the presence of (4‐dimethylamino)pyridine (DMAP) as initiator, leading to SSO‐modified epoxy networks. SSO species were covalently bonded to the epoxy network without any evidence of phase separation. The SSO addition provoked an increase in the elastic modulus in the glassy state explained by an increase in the cohesive energy density. The SSO addition gave also place to an increase in the intensity of tan δ and a decrease in both the glass transition temperature and the elastic modulus in the rubbery state. This was explained by a decrease in crosslink density associated with the flexibility of SSO structures. DMAP was much more effective than other usual initiators (like benzyldimethylamine, BDMA), in increasing the crosslink density of the resulting epoxy network. This led to high values of the glass transition temperature and the elastic modulus in the rubbery state.Schematic representation of the chemical structure of the most significant species containing three Si atoms, present in the silsesquioxane.imageSchematic representation of the chemical structure of the most significant species containing three Si atoms, present in the silsesquioxane.

Aggregation of soy/milk mixes during acidification

In spite of the increasing demand for food products containing soy protein, very little is known about the behavior of soy proteins when used as ingredients in foods. This research focused on the changes occurring in soy and milk protein mixtures during acidification. Acid gels were prepared by addition of glucono-δ-lactone. Dynamic oscillatory measurements carried out on soy/milk mixes acidified in situ demonstrated that soy protein affected the gelation behavior of the protein matrix. Confocal microscopy revealed network structures in all the soy/milk mixes, with large pore sizes in the presence of soy proteins. No evidence of phase separation was observed in any of the mixes. Dynamic light scattering measurements carried out on samples diluted in simulated milk ultrafiltrate during acidification showed no differences on the pH onset of aggregation between heated and unheated mixtures. The higher pH of aggregation of milk/soy gels compared to that of milk was attributed to the instability of soy proteins at pH 6.0 and to the presence of calcium ions.

Biodegradable Poly[bis(ethyl alanato)phosphazene] - Poly(lactide-co-glycolide) Blends: Miscibility and Osteocompatibility Evaluations

ABSTRACTWe have previously demonstrated that blending biodegradable glycine co-substituted polyphosphazenes with poly(lactide-co-glycolide) (PLAGA) results in novel biomaterials with versatile properties. The study showed that the degradation rate of polyphosphazene/PLAGA blends can be effectively controlled by varying the blend composition while at the same time the degradation products of polyphosphazenes effectively neutralized the acidic degradation products of PLAGA. In the present study, novel blends of hydrophobic, biodegradable polyphosphazene, poly[bis(ethyl alanato) phosphazene] (PNEA) and PLAGA (LA: GA; 85:15) were developed as candidates for bone tissue engineering applications. Two different blend compositions were developed by blending PNEA and PLAGA having weight ratios of 25:75 (Blend-1) and 50:50 (Blend-2) by the mutual solvent technique using dichloromethane as the solvent. The miscibility of the blends was determined using differential scanning calorimetry (DSC), fourier transform-infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). Surface analysis of the blends by SEM revealed a smooth uniform surface for Blend-1, whereas Blend-2 showed evidence of phase separation. PNEA is not completely miscible with PLAGA, as evidenced from DSC and FT-IR measurements. The osteocompatibilities of Blend-1 and Blend-2 were compared to those of parent polymers by following the adhesion and proliferation of primary rat osteoblast cells on two dimensional (2-D) polymer and blend films over a 21 day period in culture. Blend films showed significantly higher cell numbers on the surface compared to PLAGA and PNEA films.

Chemical synthesis of hydroxyapatite/poly(ε-caprolactone) composites

Hydroxyapatite (Ca 10(PO 4) 6(OH) 2)—biodegradable polymer composites as bone replacement scaffolds were synthesized by a colloidal non-aqueous precipitation technique at room temperature. The starting materials used for synthesizing hydroxyapatite (HA) were Ca(NO 3) 2·4H 2O and H 3PO 4 with a Ca/P ratio of 1.67 while poly(ε-caprolactone) (PCL) was used as the biodegradable polymer. The composites were prepared containing up to 34.5 wt.% HA and PCL polymer without any evidence of phase separation. This paper describes, the synthesis and structure of the HA/PCL composites. In addition, the pH changes during precipitation, the yield of the chemical reaction, and the possible existence of any bond between the ceramic and the polymer including the microstructure of the composites were studied. Finally, the mechanical and thermal properties of the composites were investigated. The results of these studies are described and discussed.

Two-fluid demixing theory predictions of stress-induced turbidity of polystyrene solutions in dioctyl phthalate

Stress induced demixing of a polymer solution is predicted by a two fluid theory reformulated to be able to impose all the interface boundary conditions required. The theory has now been applied to the data on solutions of polystyrene in dioctylphthalate of Rangel-Nafaile et al. [Macromolecules 17, 1187–1195 (1984)] at one molecular weight at various temperatures, to additional unpublished data at various molecular weights, and to various published experiments in which there was evidence for phase separation. The dependence of elastic compliance on concentration was approximated by an equation which permitted the analytic differentiations and integrations required for the equations of the theory. The prediction of visual cloud point stresses at various temperatures were excellent within the concentration range over which the compliances had been fitted. The calculated demixing stresses were somewhat higher than those measured by extrapolation of photometric data to onset of turbidity, possibly because the...

Oxygen-ion-induced ripple formation on silicon: evidence for phase separation and tentative model

We have investigated the ripple topography on silicon surfaces developed by 2–10 keV O 2 + bombardment at an impact angle of 45°. The ripple amplitude increased with the depth of erosion and finally became comparable with the ripple wavelength. This caused the local impact angle of ripples facing the oxygen-ion beam to reach the critical angle of SiO 2 formation, promoting the phase separation between silicon dioxide and silicon. As observed before, the critical depth for SiO 2 formation decreased with decreasing the primary ion energy. This appears to be related to the amount of erosion necessary to reach the critical angle of SiO 2 formation. The decrease of wavelength at lower primary ion energies is interpreted as the result of reduced surface diffusivity which is enhanced by ion bombardment.

Etude de stabilisation de verres a base de YF 3

New fluoride glasses were obtained in the InF 3-BaF 2-YF 3 system. Evidence for phase separation was found in this basic ternary system, suggesting that glasses based on yttrium fluoride could be formed. Indeed such glasses could be prepared by fast cooling. The mean sample thickness was 2–3 mm. Glass transition, crystallization and melting temperatures were measured.

Compatibility studies on some rubber blend systems by ultrasonic techniques

Longitudinal ultrasonic velocity, and ultrasonic attenuation, were measured in Adiprene CM–NBR, Adiprene CM–NR, Adiprene E–NR, Adiprene E–NBR blend systems at room temperature, using pulse echo technique. The densities of the blend samples were measured by the immersion method. Glass transition temperatures were measured experimentally using ultrasonic and differential scanning calorimetry (DSC). Glass transition temperatures were also calculated theoretically. Results showed that the variation of both longitudinal ultrasonic velocity and density with composition is linear with Adiprene CM–NBR, Adiprene CM–NR, and Adiprene E–NBR blends indicating compatible systems. For Adiprene E–NR, the plots of ultrasonic velocity and density vs. composition deviate from linearity according to the incompatibility degree of this system. Results obtained from ultrasonic attenuation measurements showed that the excess variation of ultrasonic attenuation with composition in rubber blend samples is of relaxational type and only one maxima or minima appeared in case of compatible blends and two or more maxima or minima appeared in case of incompatible blends. The presence of a single transition temperatures observed in DSC thermograms and ultrasonic attenuation–temperature relation is a decisive confirmation of the formation of one single phase and therefore the compatibility behaviour of this blend. On the other hand, the presence of two transition temperatures is taken as evidence of phase separation and consequently the formation of two phases with incompatible behaviour of the blend system.

Glass Transition Study of Nile Tilapia Myofibrillar Protein Films Plasticized by Glycerin and Water

Studies on glass transition of myofibrillar proteins based edible films are scarce. This work aimed to determine the T g of edible films from Nile Tilapia myofibrillar proteins as a function of water content. Films with 30 or 70 g of glycerol/100 g of protein and several water content, were analyzed with a DSC TA 2010. Samples conditioned at water activity between 0.11 and 0.75, clearly showed one glass transition at low temperatures (<223 K), and another transition, less visible, above 273 K. DSC curves of samples conditioned ata w=0.84, also showed an endothermic peak below 273 K. These results rendered evidence of phase separation within edible films.

Optical Characterization of InGaN/GaN MQW Structures without In Phase Separation

Photoluminescence and cathodoluminescence spectroscopies are used to investigate the properties of the band edge emission of InGaN/(In)GaN multiple quantum well (MQW) structures which do not show evidence of phase separation in high resolution electron microscopy. The data still show a clear low energy peak in the spectra, about 0.1 eV below the main exciton peak. Possible interpretations of this second peak are discussed.

Combined strain and high-pressure oxygen treatment effects and phase separation in La0.67Ca0.33MnO3 thin films

Evidence for phase separation in high-pressure oxygen-treated La0.67Ca0.33MnO3/(100)MgO thin films is presented. This phase-separated state is not observed for the x=0.33 classical doping level either for bulk material or for as-prepared thin films. It originates from the combined influence of two factors: large strains due to the film-substrate lattice mismatch and high-pressure (100 bar) annealing in oxygen. These factors weaken double exchange, drastically enhance low-field magnetoresistance, and lead to hysteresis phenomena. The experimental results are interpreted in terms of phase separation of the film volume into the ferromagnetic conductive matrix with inclusions of spin-glass-like clusters.

Fluorinated Vesicles Allow Intrabilayer Polymerization of a Hydrophobic Monomer, Yielding Polymerized Microcapsules

Intrabilayer polymerization of hydrophobic monomers has been attempted as a way to strengthen the structure of vesicles and producing polymer microcapsules. However, no clear evidence has been provided that demonstrates the formation of polymerized vesicles. On the contrary, it has recently been shown that polymerization of hydrophobic monomers within a vesicular bilayer did not yield the expected capsules but led to the formation of hybrid surfactant−polymer particles constituted by a polymer latex lump attached to the vesicle. We now report that use of highly ordered, microcompartmentalized fluorinated vesicles, i.e., made from fluorinated lipids, allows to achieve true intrabilayer polymerization. We have studied the thermally induced free radical polymerization of isodecyl acrylate (ISODAC) in small unilamellar vesicles (SUVs) made from a perfluoroalkylated phosphatidylcholine (F-PC) and compared it to polymerization of ISODAC in vesicles made from standard egg phospholipids (EggPC). Cryogenic transmission electron microscopy (cryo-TEM) confirmed that extended polymer/bilayer phase separation occurred in the EggPC vesicles. On the other hand, no evidence of phase separation was observed in the case of F-PC vesicles. The polymer, poly(isodecyl acrylate) (poly(ISODAC)), was homogeneously distributed within the bilayer. In addition, the rate of polymerization in F-PC vesicles, as monitored by 1H NMR, was higher than in EggPC vesicles. The molecular weight of poly(ISODAC), as determined by size exclusion chromatography (SEC), was smaller when obtained in F-PC than in EggPC vesicles. The internal fluorinated core present in F-PC vesicles significantly reduces the space available for polymerization, the monomer being excluded from the central core and confined in the two tight, nonexpandable lipophilic regions of the vesicles. Such conditions of confinement, which likely result both in an increase in local monomer concentration and in probability of polymerization termination steps, may explain the observed higher reaction rate and lower polymer molecular weight.

H−Tmagnetic phase diagrams of electron-dopedSm1−xCaxMnO3: Evidence for phase separation and metamagnetic transitions

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Molecular organization in two-dimensional films of liquid I. Langmuir films of binary mixtures of liquid crystals with a crystalline mixtures terminal cyano group

The Langmuir films of two liquid crystal materials, 4-octyl-4'-cyanobiphenyl (8CB) and 4-pentyl-4"-cyano-p-terphenyl (5CT), and of their mixtures have been studied by recording surface pressure-area isotherms and Brewster angle microscopy (BAM) images. The pure liquid crystals revealed very different characters of the surface pressure-area isotherms indicating different organization of the molecules and different molecular interactions in the monolayer at the water-air interface. The surface pressure-area isotherms of Langmuir films formed from 8CB/5CT mixtures give evidence for phase separation of the components over the whole range of molar fractions. Similar conclusions have been drawn on the basis of BAM image analysis.

Preliminary Fluid Inclusion Constraints on Fluid Evolution in the Bayan Obo Fe-REE-Nb Deposit, Inner Mongolia, China

The Bayan Obo Fe-REE-Nb deposit, Inner Mongolia, China, is the world’s largest REE resource and is also exploited as a major Fe oxide deposit. The deposit consists of replacement bodies hosted in dolomite marble and of magnetite, hematite, and REE minerals associated with apatite, aegirine, amphibole, fluorite, calcite, and barite. Fluid inclusions from monazite-(Ce), bastnasite-(Ce), apatite, aegirine, fluorite, and barite were studied from eight samples to provide new constraints on ore genesis. During early disseminated monazite mineralization the fluids are best represented by the system H 2 O-CO 2 -NaCl, with salinities ranging from 1 to 5 wt percent NaCl equiv and X (CO 2 ) values from 0.3 to 0.45, at temperatures of >280° to 330°C and pressures of >0.7 kbar. Fluids in apatite and bastnasite from the main-stage banded ores were initially aqueous, with salinities ranging from 6 to 10 wt percent NaCl equiv. They developed significant CO 2 contents (X (CO 2 ) = 0.1–0.3) due to carbonate dissolution at temperatures of >400° to ~300°C and pressures of >0.9 to 1.4 kbars. Evidence for phase separation from coexisting brine and CO 2 -rich fluid inclusions in vein fluorite indicates pressures of 0.8 to 1.0 kbar during vein formation. These pressures can be used to infer temperatures of 430° to 460°C for aegirine alteration and of 340° to 240°C for apatite, bastnasite, and fluorite vein fill. Fluids responsible for aegirine alteration were dominantly aqueous, with salinities from 5 to 15 wt percent NaCl equiv, whereas those responsible for apatite and bastnasite mineralization had salinities of 1 to 6 wt percent NaCl equiv and X (CO 2 ) values from 0.25 to 0.75. Inclusions in late-stage fluorite and barite have homogenization temperatures from 240° to 150° and 200° to 130°C, respectively. The general salinity trend in these inclusions suggests dilution from around 15 to 5 wt percent NaCl equiv down to very low salinities (<1 wt % NaCl equiv) during barite precipitation. Halite-bearing inclusions may indicate episodes of boiling or aqueous-carbonic fluid immiscibility. These fluids are similar to those in some carbonatitic, alkaline igneous, and other igneous-related REE- and Fe-rich magmatic hydrothermal systems. However, they are different from fluids in igneous-related Fe oxide-Cu-Au-U-REE deposits, which have previously been compared to those at Bayan Obo.

Structural study of the electron-doped manganites Sm0.1Ca0.9MnO3 and Pr0.1Sr0.9MnO3: Evidence of phase separation

The investigation of two perovskite manganites with the same carrier concentration of 0.1 electron per Mn has been performed using neutron powder diffraction and electron microscopy, and completed with transport and magnetic measurements. For ${\mathrm{Sm}}_{0.1}{\mathrm{Ca}}_{0.9}{\mathrm{MnO}}_{3},$ whatever the temperature (from 2 to 300 K), a unique crystalline structure (Pnma space group) is observed. The magnetic state below ${T}_{N}{=T}_{C}=110\mathrm{K}$ is phase separated, consisting of ferromagnetic domains of different sizes ranging from small clusters to macroscopic regions, which are embedded in an antiferromagnetic G-type matrix. The high conductivity observed in ${\mathrm{Sm}}_{0.1}{\mathrm{Ca}}_{0.9}{\mathrm{MnO}}_{3}$ at low temperature is established through a percolation of the ferromagnetic domains. At room temperature, the structure of the analogous compound ${\mathrm{Pr}}_{0.1}{\mathrm{Sr}}_{0.9}{\mathrm{MnO}}_{3}$ is cubic $(Pm3m$ space group). At low temperature $(Tl200\mathrm{K}),$ this manganite exhibits a complex microstructure, consisting of an intergrowth of G and C-type antiferromagnetically ordered layers, both from tetragonal $I4/mcm$ structure, with appreciable lattice distortion. In agreement with the insulating behavior of ${\mathrm{Pr}}_{0.1}{\mathrm{Sr}}_{0.9}{\mathrm{MnO}}_{3}$ at low temperature, no ferromagnetism is observed.