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PubMed2006

Phase separation in the itinerant metamagnetic transition of Sr4Ru3O10.

We have investigated the electronic transport properties of the triple-layered ruthenate Sr4Ru3O10. We observed surprising anomalous features near its itinerant metamagnetic transition, including ultrasharp magnetoresistivity steps, a nonmetallic temperature dependence in resistivity for upward field sweeps, and a resistivity drop in temperature dependence for downward field sweeps. These features suggest that the metamagnetic transition of Sr4Ru3O10 occurs via an electronic phase separation process with magnetic domain formation.

Journal Article↗

PubMed2004

Modeling phase separation in nonstoichiometric silica.

We have modeled the decomposition of nonstoichiometric amorphous SiOx upon annealing into silicon and stoichiometric silica, using a new method based on mapping Metropolis Monte Carlo simulations onto rate equations. The concentrations of all oxidation states of silicon are derived as a function of time and found to attain steady-state values at long times dependent on temperature T and oxygen content x. The degree of phase separation and the sizes of Si particles are predicted as a function of T and x, enabling greater control over the size of silicon quantum dots in silica matrices.

Journal Article↗

PubMed2003

Phase-separating binary fluids under oscillatory shear.

We apply the lattice Boltzmann methods to study the segregation of binary fluid mixtures under oscillatory shear flow in two dimensions. The algorithm allows to simulate systems whose dynamics is described by the Navier-Stokes and the convection-diffusion equations. The interplay between several time scales produces a rich and complex phenomenology. We investigate the effects of different oscillation frequencies and viscosities on the morphology of the phase separating domains. We find that at high frequencies the evolution is almost isotropic with growth exponents 2/3 and 1/3 in the inertial (low viscosity) and diffusive (high viscosity) regimes, respectively. When the period of the applied shear flow becomes of the same order of the relaxation time T(R) of the shear velocity profile, anisotropic effects are clearly observable. In correspondence with nonlinear patterns for the velocity profiles, we find configurations where lamellar order close to the walls coexists with isotropic domains in the middle of the system. For particular values of frequency and viscosity it can also happen that the convective effects induced by the oscillations cause an interruption or a slowing of the segregation process, as found in some experiments. Finally, at very low frequencies, the morphology of domains is characterized by lamellar order everywhere in the system resembling what happens in the case with steady shear.

Journal Article↗

PubMed2005

Investigation of a cylindrical chemosorptive denuder for sampling and phase separation of toluene diisocyanate aerosols.

A cylindrical chemosorptive denuder in series with a glass fibre filter has been evaluated for sampling toluene diisocyanate (TDI) aerosols. The sampler is designed for measuring personal exposure to diisocyanates. Several denuder coatings and derivatising reagents were investigated. Dimethylpolysiloxane (SE-30) and 5% phenyl dimethylpolysiloxane (SE-54) with either dibutylamine (DBA) or dipentylamine (DPeA) as derivatising reagents yielded the lowest vapour breakthrough (the amount (%) of the vapour that passes through the denuder), close to values predicted by theory. Immobilisation of the SE-30 denuder coating by in-situ cross-linking yielded comparable results. With an SE-30/DBA-coated denuder operating within an airflow range of 100-500 mL min(-1), the phase separation was shown to be consistent with theoretical predictions derived by use of the Gormley-Kennedy equation. This provides a means of calculating the vapour breakthrough and correcting experimentally obtained values with regard to vapour-particulate phase distribution, suggesting that the denuder can provide accurate phase-distribution measurements. The SE-30/DBA denuder can be used over a concentration range spanning nearly six orders of magnitude. Its capacity is sufficient to perform 15-min exposure measurements of a TDI aerosol with air concentrations as high as 1,700 microg m(-3), 40 times higher than the Swedish occupational exposure limit (OEL). At the other end of the range, the estimated limit of detection (LOD) was less than 2 ng m(-3) for both the vapour and the aerosol phases when LC-ESI-MS-MS was used for chemical analysis.

Adsorption↗

PubMed1977

Molecular interactions between lecithin and sphingomyelin. Temperature- and composition-dependent phase separation.

X-ray diffraction, scanning calorimetry, and polarizing light microscopy have used to determine the complete ternary phase diagram egg yolk lecithin/bovine brain sphingomyelin/water over the temperature range 10-44 degrees. The phase diagram shows that lateral separation of phospholipid bilayer phases can arise from variations in both composition and temperature. At 44 degrees in excess water, lecithin and sphingomyelin are miscible at all ratios in a lamellar liquid crystal bilayer phase. For samples containing greater than 33 mol % sphingomyelin, colling to 20 degrees results in the progressive lateral separation of an ordered chain sphingomyelin lamellar gel phase from the lecithin/sphingomyelin liquid crystal bilayer phase. At 20 degrees and below, the spingomyelin gel phase co-exists with an ordered bilayer phase, a stoichiometric peritectic molecular compound (66 mol % lecithin, 33 mol % sphingomyelin). Cooling mixtures containing less than 33 mol % sphingomyelin ultimately separates the compound from a lecithin liquid crystal bilayer phase containing small amounts of sphingomyelin. Although singificant variations in the lecithin/sphingomyelin ratio occur in normal and pathological membranes, at 37 degrees our results would suggest complete bilayer phase and lateral phase separation of the "ordered" sphingomyelin gel phase appears uplikely.

Calorimetry, Differential Scanning↗

PubMed2002

Ground states of SU(2)-symmetric confined bose gas: quantum superposition of the phase-separated classical condensates.

Conservation of the total isotopic spin S of a two-component Bose gas-such as 87Rb-has a dramatic impact on the structure of the ground state. In the case when S is much smaller than the total number of particles N, the condensation of each of the two components occurs into at least two single-particle modes. The quantum wave function of such a ground state is a quantum superposition of the phase separated classical condensates, the most "probable" state in the superposition corresponding to the classical ground state in the sector of given N and S.

Journal Article↗

PubMed2005

Phase separation of saturated and mono-unsaturated lipids as determined from a microscopic model.

A molecular model is proposed of a bilayer consisting of fully saturated dipalmitoylphosphatidylcholine (DPPC) and mono-unsaturated dioleoylphosphatidylcholine (DOPC). The model not only encompasses the constant density within the hydrophobic core of the bilayer, but also the tendency of chain segments to align. It is solved within self-consistent field theory. A model bilayer of DPPC undergoes a main-chain transition to a gel phase, while a bilayer of DOPC does not do so above zero degrees centigrade because of the double bond which disrupts order. We examine structural and thermodynamic properties of these membranes and find our results in reasonable accord with experiment. In particular, order-parameter profiles are in good agreement with NMR experiments. A phase diagram is obtained for mixtures of these lipids in a membrane at zero tension. The system undergoes phase separation below the main-chain transition temperature of the saturated lipid. Extensions to the ternary DPPC, DOPC, and cholesterol system are outlined.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2004

Gelation of PEO-PLGA-PEO triblock copolymers induced by macroscopic phase separation.

The gelation behavior of aqueous solutions of poly(ethylene oxide-b-(DL-lactic acid-co-glycolic acid)-b-ethylene oxide) (PEO-PLGA-PEO) triblock copolymer containing short hydrophilic PEO end blocks is investigated using dynamic light scattering, rheology, small-angle neutron scattering (SANS), and differential scanning calorimetry (DSC). For polymer concentrations between 5 and 35 wt %, four distinct regions of the turbidity change depending on temperature were observed. Interestingly, in the turbid solution region, gel phase is formed for polymer concentrations above 14 wt % and an extremely slow relaxation was detected. In fact, a power law, which takes into account the dynamics of percolation clusters, dominates the correlation function. In rheological measurements, the local maximum in G' is observed at around the temperature of maximum turbidity. We further found that G" > G' and G' is highly dependent on frequency at the gel state implying viscoelastic characteristics, which is quite different from general concepts of gels, typically formed by the micellar packing. SANS profiles showing multiple peaks in the sol state rather than in the gel state as well as a DSC exotherm at the temperature of gels can also serve as the evidence of different gel states. Based upon the experimental data obtained in the present study, a new gelation mechanism induced by the macroscopic phase separation of triblock copolymers containing short hydrophilic PEO end blocks such as PEO-PLGA-PEO is proposed. The effect of the type ofhydrophobic middle blocks on the gelation is also discussed.

Journal Article↗

PubMed2004

Cloud-point temperature and liquid-liquid phase separation of supersaturated lysozyme solution.

The detailed understanding of the structure of biological macromolecules reveals their functions, and is thus important in the design of new medicines and for engineering molecules with improved properties for industrial applications. Although techniques used for protein crystallization have been progressing greatly, protein crystallization may still be considered an art rather than a science, and successful crystallization remains largely empirical and operator-dependent. In this work, a microcalorimetric technique has been utilized to investigate liquid-liquid phase separation through measuring cloud-point temperature T(cloud) for supersaturated lysozyme solution. The effects of ionic strength and glycerol on the cloud-point temperature are studied in detail. Over the entire range of salt concentrations studied, the cloud-point temperature increases monotonically with the concentration of sodium chloride. When glycerol is added as additive, the solubility of lysozyme is increased, whereas the cloud-point temperature is decreased.

Calorimetry, Differential Scanning↗

PubMed2005

Dispersion and phase separation of carbon nanotubes in ultrathin polymer films.

The inner structure and nanoscale distribution of the stiffness was studied for polymer-single-wall carbon nanotube composites. Dispersion of nanotubes in a polystyrene and polyurethane polymer matrix was achieved by a proper choice of the organic solvent (NMP) and sonification of polymer/SWNT solutions. Ultrathin nanocomposite films were prepared through a dip-coating procedure and possessed a noticeable degree of nanotube orientation in the direction of the applied shear force. Peculiarities of the phase separation in the films were studied by atomic force microscopy (with application of force modulation mode to map the nanotube distribution within the polymer matrix) and Raman spectroscopy.

Journal Article↗

PubMed2005

Supersolids versus phase separation in two-dimensional lattice bosons.

We study the nature of the ground state of the two-dimensional extended boson Hubbard model on a square lattice by quantum Monte Carlo methods. We demonstrate that strong but finite on-site interaction U along with a comparable nearest-neighbor repulsion V result in a thermodynamically stable supersolid ground state for densities larger than 1/2, in contrast to fillings less than 1/2 or for very large U, where the checkerboard supersolid is unstable towards phase separation. We discuss the relevance of our results to realizations of supersolids using cold bosonic atoms in optical lattices.

Journal Article↗

PubMed1984

Lateral diffusion and phase separation in two-dimensional solutions of polymerized butadiene lipid in dimyristoylphosphatidylcholine bilayers. A photobleaching and freeze fracture study.

Mixed vesicles of dimyristoylphosphatidylcholine (DMPC) and a polymerizable lipid containing one diene group per chain are studied by freeze fracture electron microscopy and by the photobleaching (fluorescence recovery after photobleaching) technique. Large thin-walled vesicles of some micron in diameter become more stable after photochemical polymerization. Before polymerization bilayers of the diene lipid exhibit a liquid crystal-to-gel transition at Tg = 31 degrees C. Upon polymerization the transition remains but shifts to a slightly higher temperature (Tg* = 34 degrees C). The transitions in both cases are accompanied by a freezing in of the lateral mobilities. The mixed vesicle exhibits lateral phase separation after polymerization. Before polymerization the two lipids appear miscible at all compositions in the fluid state and at DMPC concentrations at or below 50 mol % in the solid state. After polymerization a two-dimensional solution of the polymer in DMPC is obtained at T greater than Tg*, while lateral phase segregation into DMPC-rich domains and patches of the polymer is observed at T less than Tg*. The domain structure appears identical irrespective of whether polymerization is performed at T greater than Tg or at T less than Tg. A typical value of the diameter of the polymerized lipid domains (approximately 400 A) indicates a rather small aggregation number (N less than 100 monomers). The lateral diffusion coefficient in butadiene-lipid bilayers only decreases from D1 = 3.10(-7) cm2/s to D1 = 8.10(-8) cm2/s (that is by a factor of 4) upon polymerization. This is consistent with the freeze fracture finding of a small aggregation number. We point out the similarities of the mixed vesicles with plasma membranes coupled to the cytoskeleton.

Butadienes↗

PubMed2003

Alternating layer and island growth of Pb on Si by spontaneous quantum phase separation.

Real-time in situ x-ray studies of continuous Pb deposition on Si(111)-(7x7) at 180 K reveal an unusual growth behavior. A wetting layer forms first to cover the entire surface. Then islands of a fairly uniform height of about five monolayers form on top of the wetting layer and grow to fill the surface. The growth then switches to a layer-by-layer mode upon further deposition. This behavior of alternating layer and island growth can be attributed to spontaneous quantum phase separation based on a first-principles calculation of the system energy.

Journal Article↗

PubMed1990

Lanthanide(III)-phosphatidic acid complexes: binding site heterogeneity and phase separation.

The luminescent lanthanides are potentially useful probes of cation-induced events involving phospholipid membranes. In this work, the spectroscopic properties of Tb3+, Ce3+ and Eu3+ are shown to be complementary in defining three forms of complex with phosphatidic acid vesicles. Ce3+, in particular, is useful for studying dilute cation-lipid complexes because it has strong excitation bands in the near ultraviolet. In addition to providing a means for detecting chemically distinct forms of lanthanide-lipid complexes, the luminescence can be used to monitor cation-induced lateral segregation. Ce3+ to Tb3+ energy transfer was observed at lanthanide levels as low as 1:1000 Ln3+/phosphatidic acid, indicating clustering or phase separation. Initial clustering occurs on a subsecond timescale, followed by a much slower aggregation continuing for several minutes to hours. Addition of a chelator results in slow release of the lanthanides. In the case of the dioleoylphosphatidic acid complexes, release is bimodal and indicative of cation entrapment; dimyristoylphosphatidic acid complexes exhibit this behavior only at high temperatures. These observations are consistent with the relative tendencies of these two lipids to form the HII phase. This work sets the foundation for experiments designed to determine the size of nucleation sites for cation-induced events such as intramembrane inverted micelle formation and membrane fusion.

Cerium↗

PubMed2006

Effects of sugars on the cross-linking formation and phase separation of high-pressure induced gel of whey protein from bovine milk.

The effects of sugars (xylose, arabinose, fucose, fructose, galactose, glucose, sorbitol, maltose, sucrose, and lactose; 0-20% w/v) on the properties of the pressure-induced gel from a whey protein isolate (20%, 800 MPa, 30 degrees C, 10 min) were studied. All the sugars decreased the hardness, breaking stress and water-holding capacity of the gel at the same concentration of 55.5 mM. Increasing the sugar content changed the microstructure of the gel from a honeycomb-like structure to a stranded structure, while the strand thickness was progressively reduced. These results suggest that sugars decreased the degree of intermolecular S-S bonding of proteins and non-covalent interaction, and restrained the phase separation during gelation under high pressure.

Animals↗

PubMed1984

Phase separation induced in gelatin-base coacervation systems by addition of water-soluble nonionic polymers I: Microencapsulation.

A microencapsulation procedure in which water-soluble nonionic polymers (especially, polyethylene oxide or polyethylene glycol) were added to gelatin-base coacervation systems is described. The advantages of this method are: (a) The addition of a small amount of polyethylene glycol (PEG) or polyethylene oxide (PEO) to a complex coacervation system (e.g., gelatin-acacia) allows microencapsulation to occur over an expanded pH region (pH 2-9 in gelatin-acacia). (b) These polymers induce phase separation in an aqueous solution of gelatin alone and enable the preparation of gelatin-coated microcapsules not only in the vicinity of the isoelectric point (pH 9.0), but over a wide pH range (pH 5.5-9.5). (c) Spherical single-seeded microcapsules can be obtained.

Capsules↗

PubMed1986

Phase separation of miscible phospholipids by sonication of bilayer vesicles.

Sonication of phospholipid vesicles may result, according to their liquid or solid crystal state, in the generation of unilamellar vesicles or structural defects within their bilayers, respectively. The transition temperature Tm of the phospholipid bilayer is usually the threshold temperature delineating the physical effects of ultrasound. However, for vesicles made from a mixture of two miscible phospholipids, this threshold temperature was not found to be the intermediate Tm of the phospholipid mixture bilayers, but the Tm of the lowest melting component. This was due to a simultaneous lateral phase separation of the two phospholipids induced by the sonication as demonstrated by differential scanning calorimetry analysis.

Carbon Radioisotopes↗

PubMed2004

[Phase separation and transport behaviors in La(0.7 - x)Dy(x)Sr0.3MnO3 system].

The influence of Dy doping (0.00 < or = x < or = 0.30) on magnetic and electric properties of La0.7Sr0.3MnO3 was studied by measuring M-T curves, M-H curves, ESR curves, rho-T curves and MR-T curves of the samples. The experimental results indicate that all samples undergo the transition from paramagnetism to ferromagnetism at T(C). When T < T(C), the doped samples enter the cluster-spin glass state, and the antiferromagnetism is exhibited at lower temperature. For the samples x = 0.2, the phase separation occurs at the temperature far above T(C), the variation in magnetic structure caused by Dy doping leads to colossal magnetoresistance.

English Abstract↗