Existence Of Phase Separation Research Articles

Barriers to Diffusion in Cells: Visualization of Membraneless Particles in the Nucleus.

Transient barriers are fundamental to cell supramolecular organization and assembly. Discontinuities between spaces can be generated by a physical barrier but also by thermodynamic barriers achieved by phase separation of molecules. However, because of the transient nature and the lack of a visible barrier, the existence of phase separation is difficult to demonstrate experimentally. We describe an approach based on the 2-dimensional pair correlation function (2D-pCF) analysis of the spatial connectivity in a cell. The educational aim of the article is to present both a model suitable for explaining diffusion barrier measurements to a broad range of courses and examples of biological situations. If there are no barriers to diffusion, particles could diffuse equally in all directions. In this situation the pair correlation function introduced in this article is independent of the direction and is uniform in all directions. However, in the presence of obstacles, the shape of the 2D-pCF is distorted to reflect how the obstacle position and orientation change the flow of molecules. In the example shown in this article, measurements of diffusion of enhanced green fluorescent protein moving in live cells show the lack of connectivity at the nucleolus surface for shorter distances. We also observe a gradual increase in the connectivity for longer distances or times, presumably because of molecular trajectories around the nucleolus.

Investigation of the phase separation property in [formula omitted][formula omitted][formula omitted][formula omitted] manganite

We report a comprehensive investigation of La0.2Pr0.4Ca0.4MnO3 to clarify the micrometre scale phase separation phenomenon in the mixed valent manganite (La,Pr,Ca)MnO3. The compound shows multiple magnetic transitions, in which the charge-ordered state is converted into a ferromagnetic state in steps with the application of a magnetic field. The ac susceptibility measurements show that the glassy transition at low temperatures does not depend on the frequency, thus indicating the absence of any spin glass behaviour. Magnetization as well as heat capacity measurements indicate that this low temperature transition is magnetic field dependent. The field dependent resistivity at 2 K shows a sharp drop indicating that the sample behaviour changes from a high resistive state to a low resistive state, corroborating the conversion of charge-ordered insulating (COI) phase to a ferromagnetic metallic (FMM) phase. Our results point towards the existence of phase separation, rigidity of the low temperature glassy-like phase as well as the conversion of COI phase to FMM phase by the application of magnetic fields.

Toughening modification of cyanate ester with amino-terminated polyoxypropylene

An amino-terminated polyoxypropylene (DA2000) was used to modify a bisphenol A-type cyanate ester resin (BADCy). A series of BADCy/DA2000 resins with different DA2000 contents were prepared and investigated by mechanical tests, dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM). The results of mechanical tests demonstrated that the addition of DA2000 improved the bending and tensile strength of the modified resins. Compared with those of pure BADCy, the K IC and G IC values of the modified resins increased, indicating an improvement in toughness of the resin system. The DMA curves of modified resins showed that the storage moduli dropped with the increase in temperature and the T g values decreased with the increase in modifier content. Simultaneously, the moduli showed different changing trend at different temperature stages, indicating the existence of phase separation, which was also demonstrated by the fracture morphologies. At 20 wt% of DA2000 content, the fracture surface showed its characteristic strong ductile tear. Based on the above results, it was concluded that the –NH2 groups of DA2000 reacted with the –OCN groups of triazine ring to form flexible segments, which were embedded into the main chains of the curing network; the distance between the triazine rings increased, the cross-link density decreased and the yield deformation of the system was enhanced. Meanwhile, DA2000 reacted with BADCy monomers to form linear macromolecular chains, which interpenetrated into the network matrix, and enhanced the plastic deformation of the system. The formation of flexible segments, low cross-link density and the yield and plastics properties led to toughened cyanate ester (CE) resins.

Effects of Iron Oxide on the Crystallization of Calcium Alumino-Silicate Glass

Different amounts of iron oxide (Fe2O3) were added into a base calcium alumino-silicate glass (CaO 40, Al2O3 9, SiO2 51 wt%). The crystallization behavior of the glassed was investigated by DTA, XRD, SEM and optical microscopy. DTA analysis on the samples with and without the iron additions shows that the iron-containing glasses obviously absorb more heat energy than the base glass. All the glasses show two endothermal peaks correspondent to two transition temperatures, Tg1 and Tg2, indicating the existence of phase separation. Compared with the base glass, an initial addition of 5wt% Fe2O3 does not result in significant changes in Tg1, but a large decrease in Tg2 is observed. Further additions of 10 and 15wt% Fe2O3, both Tg1 and Tg2 decreases. The iron-containing glasses show two crystallization peaks in their DTA curves. Fe2O3 facilitates the crystallization of the calcium alumino-silicate glass indicated by the decreased activation energy and increased Avrami exponent. SEM observations evidenced that the crystallintes in the heat treated samples are nanosized. It is evidenced that the base glass and the glasses containing 5 and 10 wt% Fe2O3 are surface crystallized upon heat-treatment and the main crystalline phase is wollastonite. The surface crystallization layer and the grain size increase with Fe2O3. However, an addition of 15wt% Fe2O3 results in a bulk crystallization leading to the formation of iron-and aluminum-containing phases.

Overcoming the Phase Inhomogeneity in Chemically Functionalized Graphene: The Case of Graphene Oxides

The inhomogeneous phase, which usually exists in graphene oxides (GOs), is a long-standing problem that has severely restricted the use of GOs in various applications. By using first-principles based cluster expansion, we find that the existence of phase separation in conventional GOs is due to the extremely strong attractive interactions of oxygen atoms at different graphene sides. Our Monte Carlo simulations show that this kind of phase separation is not avoidable under the current experimental growth temperature. In this Letter, the idea of oxidizing graphene on a single side is proposed to eliminate the strong double-side oxygen attractions, and our calculations show that well-ordered GOs could be obtained at low oxygen concentrations. These ordered GOs behave as quasi-one-dimensional narrow-gap semiconductors with quite small electron effective masses, which can be useful in high-speed electronics. Our concept could be widely applied to overcome the phase inhomogeneity in various chemically functionalized two-dimensional systems.

Magnetic and dielectric study of Bi2CuO4

Magnetic and dielectric properties have been investigated for Bi2CuO4, which has the same chemical formula as that of the parent materials of cuprate superconductors R2CuO4 (R: rare earths). Magnetization measurements show the antiferromagnetic transition of the Cu2+ spins at ∼42K, as reported previously. Dielectric measurements for the frequencies of 1kHz to 1MHz show that the dielectric constants are 100–500 at room temperature. The dielectric dispersion reveals that the dielectric response lacks spatial coherence, a property which indicates the possible existence of phase separation as suggested for La2CuO4. The imaginary part of dielectric response gives the activation energy of 0.22eV, suggesting that the dielectric response is governed by the electron hopping between the Cu ions.

Study of phase separation and photo‐ luminescent emission in silicon nanostructured PECVD systems

AbstractIn this work two systems with total phase separation composed of alternated a‐Si/SiO2 and a‐Si/Si3N4 respectively along with silicon‐rich SiOxNy films were deposited by the PECVD technique and characterized by XANES, Raman, TEM and PL techniques. The multilayers were used to analyse the effects of phase separation in the XANES and Raman spectra as well as to determine the phase contrast in TEM images in order to elucidate upon the existence of phase separation in the silicon‐rich SiOxNy films and correlate it with the high photoluminescence intensity in the visible spectra region observed in the as deposited films. The results clearly indicate that the as deposited films present partial phase separation, which is crucial for the PL emission. The effect of high temperature annealing in the silicon‐rich SiOxNy films is also studied, Raman and XANES results show that heat treatments promote silicon aggregation and, in some cases, crystallization strongly influencing the PL emission. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Well-Controlled Synthesis of Block Copolythiophenes

Well-controlled rod−rod block copolymers, poly(3-hexylthiophene)-b-poly(3-phenoxymethylthiophene)s, were successfully prepared by nickel-catalyzed coupling polymerization of 2-bromo-3-hexyl-5-iodothiophene followed by that of 2,5-dibromo-3-phenoxymethylthiophene. The homopolymerization of 2,5-dibromo-3-phenoxymethylthiophene was investigated in detail to determine the polymerization conditions. The structure of block copolymers was confirmed by FT-IR and 1H NMR spectroscopies, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), ultraviolet−visible (UV−vis), and fluorescence spectroscopies. The thin film formed on a silicon wafer and annealed at 40 °C for 3 days was analyzed using atomic force microscopy (AFM), and the results indicated the existence of phase separation.

Anomalous Diffusion of Water in [BMIM][TFSI] Room-Temperature Ionic Liquid

We have studied the self-diffusion properties of butyl-methyl-imidazolium bis(trifluoromethylsulfonyl)-imide ([BMIM][TFSI]) + water system. The self-diffusion coefficients of cations, anions, and water molecules were determined by pulsed field gradient NMR. These measures were performed with increased water quantity up to saturation (from 0.3 to 30 mol %). Unexpected variations have been observed. The self-diffusion coefficient of every species increases with the quantity of water but not in the same order of magnitude. Whereas very similar evolutions are observed for the anion and cation, the increase is 25 times greater for water molecules. We interpret our data by the existence of phase separation at microscopic scale.

Magnetic properties of La1−xCaxCoO3 single crystals

DC magnetization and optical measurements have been carried out for La1−xCaxCoO3 single crystals (x=0.1, 0.15, 0.2). The results indicate an inhomogeneous distribution of Ca2+ ions in a microscopic local scale, and existence of phase separation into a hole-rich ferromagnetic regions and a hole-poor host matrix. It was shown that with a temperature decrease the system evolves from a paramagnetic state of weakly interacting cobalt ions, through weakly interacting spin clusters, to the cluster glass state. The measured magnetic field dependences of magnetization have indicated that the volume of a hole-rich ferromagnetic cluster grows in magnetic field. These clusters can be considered as a precursor of the doping-induced ferromagnetic state. The analysis of the Curie–Weiss behavior at high temperature has shown that Ca doping stabilizes Co3+ ions in the intermediate spin state. Nevertheless, the small part of cobalt ions in the low spin state, up to about 10%, was suggested to exist for all levels of doping in paramagnetic phase up to room temperature. The long-time relaxation phenomena were found to follow a power law.

The Pr0.5Ca0.5Mn1−xCrxO3 series (0 ≤ x ≤ 0.5):evidence of steps in the magnetic and transport properties for a narrowcomposition range

The Pr0.5Ca0.5Mn1−xCrxO3 series has beeninvestigated up to x = 0.5. For lowdoping content (x ≤ 0.04),the introduction of Cr3+ favoursthe creation of ferromagnetic (FM) regions leading to phase-separation phenomena.Steps in the magnetic and transport properties measured versus field are observedand these properties strongly depend on the thermal history of the samples. Forx = 0.04–0.06,the samples are almost 100% FM. As the Cr3+concentration increases beyond this optimum doping level of 0.04–0.06, the FM fractionxFMslowly decreases, reflecting the fact that Cr3+is antiferromagnetically coupled to the Mn network, and reaches almost 0 forx = 0.5. Beyondthe optimum doping, the steps disappear. In a martensitic-like picture, the presence of stepsfor x < 0.04is consistent with the existence of phase separation. On theother hand, the disappearance of jumps beyond the optimumdoping shows that the nature of phase separation, if it exists forx > 0.04–0.06, is completelydifferent from the low-xside.

Synthesis and characterization of poly(ether ketone ketone) (PEKK)/sodium sulfonated poly(arylene ether ketone) (S‐PAEK) block copolymers

AbstractA series of well‐defined poly(ether ketone ketone) (PEKK)/sodium sulfonated poly(aryl ether ketone) (S‐PAEK) block copolymers of high molecular weights was prepared by direct nucleophilic polymerization of hydroquinone with sodium 5,5′‐carbonylbis(2‐fluorobenzene sulfonate) (1) and PEKK oligomer (2). Varying the ratio of 1 to 2 used in polymerization can be used to control the degree of polymer sulfonation, which correspondingly affects the polymer solubility in solvents. Increasing content of 1 in the copolymers, slightly decreases their thermal stability which is nevertheless thermally stable up to 400 °C. Two Tg values, or one broad Tg, were observed in the DSC measurements of the block copolymers, indicating the existence of phase separation, which was further proved by phase‐separated morphologies as shown in atomic force microscopy images.© 2001 Society of Chemical Industry

The Equilibrium Properties and Microstructure of Mixtures of Colloidal Particles with Long-Range, Soft Repulsions

Osmotic pressure and elastic moduli of bimodal suspensions of particles experiencing long-range, soft repulsions were measured. At fixed osmotic pressure, the total suspension volume fraction, φ, varies linearly as the mixing ratio φl/φ is increased from 0 to 1. Here φlis the volume fraction of large particles based on total suspension volume. This result suggests the suspensions studied here are phase separated into domains containing primarily small and primarily large particles and is not expected for hard sphere suspensions where, at fixed osmotic pressure, φ passes through a maximum as φl/φ is increased. Elastic moduli are well described by a model based on a composite microstructure where the domains of pure large and small particles must have the same osmotic pressure which fixes the local particle volume fraction and hence the elastic modulus in each phase. The existence of phase separation is supported by electron micrographs taken on samples prepared by rapidly drying suspensions with volume fractions near 0.6.

Morphological changes in segmented polyurethane elastomers by varying the NCO/OH ratio

AbstractThe morphological changes induced to segmented polyurethane elastomers by varying the NCO/OH ratio during the second step of polymerization, while keeping constant the total hard‐segment content (∼ 30%), were studied by means of fourier transform infared spectroscopy (FTIR), differential scanning calorimetry (DSC), and the thermally stimulated depolarization current method (TSDC). The DSC results gave evidence for the existence of phase separation in thermoplastic polyurethanes, whereas the elastomerc ones appeared to form a more homogeneous network. The FTIR results gave additional evidence regarding phase separation be detecting the sterength of the hydrogen bonds. Moreover, an attempt was made to assess the relative contribution made to the hydrogen bonding in such systems by the two potential acceptors: ester and urethane carbonyls. The TSDC results gave a relaxation mechnism that is due to interfacial (Maxwell–Wagner–Sillars) polarization, providing evidence of the existence of an interfacial phase. The introduced secondary chemical cross‐links was found to affect mainly the irregularly packed hard domains and to form a more homegeneous network at higher values of the NCO/OH ratio. © 1994 John Wiley &amp; Sons, Inc.

Bounds for the ground-state energy in the Emery model determined by cluster calculations.

We present simple upper and lower bounds for the ground-state energy of the Emery model. These bounds are derived by partitioning the full Hamiltonian into a sum of sub-Hamiltonians that may be treated with the Lanczos algorithm. The energy bounds are used to derive bounds on the magnetization as a function of magnetic field and the hole density as a function of chemical potential. We improve upon the recent variational calculation of Carstensen and Dichtel [Phys. Rev. B 46, 11 040 (1992)], which suggested the existence of phase separation. Our results contain no evidence for phase separation.

Polyarylate/polyamide 6 blends: A calorimetric study

A calorimetric study has been done of the miscibility of blends composed of polyarylate (PAr) and poly(e-caprolactam) (polyamide 6, nylon 6). The thermal transitions of blends subjected to two different thermal treatments have been determined. Two glass transitions have been observed in the blends irrespective of the thermal history. These glass transitions indicate the existence of two amorphous phases in the blends, a practically pure nylon phase and a mixed PAr/nylon 6 phase. The variation of the melting temperature of nylon with the blend composition is in good agreement with the existence of phase separation in the blends. However, the melting heat shows a slightly positive deviation from linearity when it is represented against the blend composition.