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Results for “Phase Separation”

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PubMed2003

Observation of liquid-liquid phase separation for eye lens gammaS-crystallin.

gammaS-crystallin (gammaS) is an important human and bovine eye lens protein involved in maintaining the transparency of the eye. By adding small amounts of polyethylene glycol (PEG) to the binary aqueous bovine gammaS solutions, we have observed liquid-liquid phase separation (LLPS) at -8 degrees C and revealed that, in the binary gammaS-water system, this phase transition would occur at -28 degrees C. We have measured both the effect of PEG concentration on the LLPS temperature and proteinPEG partitioning between the two liquid coexisting phases. We use our measurements of proteinPEG partitioning to determine the nature and the magnitude of the gammaS-PEG interactions and to quantitatively assess the effectiveness of PEG as a crystallizing agent for gammaS. We use our measurements of LLPS temperature as a function of protein and PEG concentration to successfully determine the location of the critical point for the binary gammaS-water system. This phase transition cannot be observed in the absence of PEG because it is inaccessible due to the freezing of the system. Our findings indicate that the effective interactions between gammaS molecules in the binary gammaS-water system are attractive. We compare the magnitude of the attraction found for gammaS with the results obtained for the other gamma-crystallins for which the critical temperature is located above the freezing point of the system. This work suggests that PEG can be used to reveal the existence of LLPS for a much wider range of binary protein-water systems than known previously.

Animals↗

PubMed2003

Evolution of 3D structures in a phase-separating polymer blend film confined by symmetric flat walls.

The recently extended imaging mode of dynamic Secondary Ion Mass Spectroscopy as well as its depth profiling variant were used to study three-dimensional structures in a phase-separating polymer blend film. Formation of layered morphology and its further reorganisation into columns were observed in a system confined by symmetric flat surfaces. The integral-geometry-based morphological image analysis provided a quantitative description of the evolution of the phase morphology.

Journal Article↗

PubMed1984

Formation of encapsulated hydrophilic polymer beads by combined techniques of bead polymerization and phase separation.

A novel and rapid procedure for the preparation of hydrophilic polymer beads coated with ethyl cellulose has been developed. The coated polymer beads were prepared by combining techniques of bead polymerization and phase separation into a single step procedure. The final product has a size range of 200-1000 micrograms and consists of the core copolymer of 2-hydroxyethyl methacrylate-acrylamide and the barrier membrane of ethyl cellulose. Examination of beads in which amaranth dye was used as a model of active ingredient showed the dye to be uniformly distributed throughout the polymer matrix. Microscopic examination indicated that ethyl cellulose coated the core matrix. The effects of ethyl cellulose concentration, degree of agitation and molar ratio of monomers on the size of coated beads were investigated.

Cellulose↗

PubMed2005

Monomer-solvent phase separation in one-step self-etch adhesives.

One-step adhesives bond less effectively to enamel/dentin than do their multi-step versions. To investigate whether this might be due to phase separation between adhesive ingredients, we characterized the interaction of 5 experimental and 3 commercial self-etch adhesives with dentin using transmission electron microscopy. All adhesives were examined for homogeneity by light microscopy. Bonding effectiveness to dentin was determined with the use of a micro-tensile bond-strength protocol. The lower bond strength of the one-step adhesives was associated with light-microscopic observation of multiple droplets that disappeared slowly. Interfacial analysis confirmed the entrapment of droplets within the adhesive layer. The prompt disappearance of droplets upon application of a small amount of HEMA (2-hydroxyethyl methacrylate) or a HEMA-containing bonding agent, as well as the absence of droplets at the interface of all HEMA-containing adhesives, strongly suggests that the adhesive monomers separate from water upon evaporation of ethanol/acetone. Upon polymerization, the droplets become entrapped within the adhesive, potentially jeopardizing bond durability. This can be avoided by strong air-drying of the adhesive, thereby removing interfacial water and thus improving bonding effectiveness.

Acid Etching, Dental↗

PubMed2004

Combined negative dielectrophoresis and phase separation in nondilute suspensions subject to a high-gradient ac electric field.

Experiments were conducted on concentrated suspensions of neutrally buoyant particles which exhibit negative dielectrophoresis. We found that, due to interparticle electrical interactions, such suspensions undergo a phase separation when subjected to a high-gradient ac field (approximately kV/mm) and form a propagating distinct front between the regions enriched with and depleted of particles. A generalization of our theory for the thermodynamics of the field-induced phase transitions in suspensions of polarized particles [Phys. Rev. E 52, 1669 (1995); 54, 5428 (1996); 60, 3015 (1999)] is proposed for the front propagation, and its predictions are shown to be consistent with the experiments even though the model contains no fitting parameters. The combination of field-induced dielectrophoresis and phase transition provides a method for strongly concentrating particles in prespecified regions of dielectrophoretic devices.

Journal Article↗

PubMed2005

Phase separation of the Widom-Rowlinson mixture in confined geometry.

The behavior of binary Widom-Rowlinson [J. Chem. Phys. 52, 1670 (1970)] mixture in confined geometry is investigated. The influence of confinement on phase separation is examined. Coexistence curves for the mixture in slitlike pores and pores of complex geometry are calculated in Monte Carlo simulations. Finite size scaling analysis is used to determine precisely the location of critical point for the bulk mixture.

Journal Article↗

PubMed2000

Simulation of enzymatic cellular reactions complicated by phase separation.

We present two-dimensional Monte Carlo simulations of enzymatic cellular reaction occurring via the Michaelis-Menten scheme in the case of attractive interactions between the reaction products. The model employed predicts phase separation in the cell provided that the reaction is relatively fast. The shape of the corresponding patterns varies from a few separate islands to a large patch located in the center of the cell. The fluctuations of the reaction rate during such regimes are found to be much higher than those predicted by the Poissonian distribution.

Algorithms↗

PubMed2003

Phase separation in asymmetrical fermion superfluids.

Motivated by recent developments on cold atom traps and high density QCD we consider fermionic systems composed of two particle species with different densities. We argue that a mixed phase composed of normal and superfluid components is the energetically favored ground state. We suggest how this phase separation can be used as a probe of fermion superfluidity in atomic traps.

Journal Article↗

PubMed2005

Intergranular giant magnetoresistance in a spontaneously phase separated perovskite oxide.

We present small-angle neutron scattering data proving that, on the insulating side of the metal-insulator transition, the doped perovskite cobaltite La(1-x)Sr(x)CoO(3) phase separates into ferromagnetic metallic clusters embedded in a nonferromagnetic matrix. This induces a hysteretic magnetoresistance, with temperature and field dependence characteristic of intergranular giant magnetoresistance (GMR). We argue that this system is a natural analog to the artificial structures fabricated by depositing nanoscale ferromagnetic particles in a metallic or insulating matrix; i.e., this material displays a GMR effect without the deliberate introduction of chemical interfaces.

Journal Article↗

PubMedDate not supplied

Gradation of microcapsule wall porosity by deposition of polymer mixtures (Eudragit RL and Eudragit RS). Phase separation of polymer mixtures and effects of external media and conditions on release.

With the aim of increasing flexibility in controlling release from microcapsules, mixtures of wall polymers varying in porosity were investigated by phase separation. Eudragit RL and RS (polymethylmethacrylate linear backbone polymers) mixtures differing in polar substituent content and porosity were used as the wall material and were deposited using a non-solvent addition method. Release rates increased with polar group content of the mixtures, using theophylline, potassium dichromate or sodium chloride as model core materials. Theophylline release rate had the same relationship to polar group content as found earlier for urea permeation of cast mixed-polymer films. Release was generally accelerated in these systems when the external medium contained sodium lauryl sulphate as a wetting agent but not consistently, decreasing unexpectedly for RL-theophylline microcapsules. Localized dissolution of core substance was visible microscopically during release from single microcapsules. The release rate was sensitive to agitation intensity only at low wall to core ratios. Temperature change revealed only a single release mechanism for sodium chloride by Arrhenius equation treatment. Buffer ions penetrated coatings readily, changing theophylline release rates and providing clear evidence of diffusion via a pore-capillary mechanism.

Acrylic Resins↗

PubMed1997

Reversed-phase separations of nitrogenous phospholipids on an octadecanoyl poly(vinyl alcohol) phase.

Molecular species of nitrogenous phospholipids (PLs) phosphatidylcholine (PC), phosphatidylethanolamine (PE), PE-derivatives and sphingomyelin (SP) were separated on an octadecanoyl poly(vinyl alcohol) (ODPVA) column by reversed-phase HPLC with UV and evaporative light scattering detection (ELSD). Mobile phases employed variable proportions of acetonitrile, methanol and water. HPLC-UV of the polar lipids yield components with peak intensities somewhat different from those obtained by HPLC-ELSD despite discernible similarity in the peak profiles observed in the two detection systems. Incorporation of ammonium hydroxide in mobile phases resulted in a decrease in analyte retention. The mobile phase basicity effect on capacity factors of PE species was significantly greater than that of PC counterparts. The new ODPVA-HPLC-ELSD technique was applied to the analysis of PC and PE molecular species in vegetable oils.

Ammonium Hydroxide↗

PubMed2006

Monte Carlo study of supramolecular polymer fractionation: selective removal of chain stoppers by phase separation.

Supramolecular polymers consist of bifunctional monomers that join and break reversibly. Supramolecular polymer solutions are often polluted by monofunctional contaminants, which drastically reduce the chain-forming capabilities of the system. Unfortunately, the monofunctional contaminants are difficult to remove due to the physical and chemical resemblance with the bifunctional counterparts. In this paper, we present a method to specifically remove the monofunctional contaminants from a supramolecular polymer solution. The general idea is to induce phase separation by decreasing the solvent quality and to remove the most dilute phase. This concept is explored by means of a recently developed Monte Carlo scheme to calculate the compositions of the coexisting liquid phases. The simulations provide a proof of principle that the proposed purification method is suitable to remove the monofunctional contaminants efficiently. The calculations indicate that, at the right experimental conditions, the vast majority of the monofunctional contaminants can be removed in this way while retaining most of the bifunctional monomers. Because of the general nature of the arguments presented here, it is to be expected that the results are applicable to a large variety of supramolecular systems. Moreover, the method is very suitable for large-scale applications because only solvent is added and no tedious chromatographic steps are required.

Journal Article↗

PubMed1999

Porous biodegradable polymeric scaffolds prepared by thermally induced phase separation.

Poly(L-lactic acid) and its copolymers with D-lactic and glycolic acid were used to fabricate various porous biodegradable scaffolds suitable for tissue engineering and drug delivery based on a thermally induced phase separation (TIPS) technique. A variety of parameters involved in TIPS process, such as types of polymers, polymer concentration, solvent/nonsolvent ratio, and quenching temperature, were examined in detail to produce a wide array of micro- and macroporous structures. A mixture of dioxane and water was used for a binary composition of solvent and nonsolvent, respectively. In particular, the coarsening effect of pore enlargement affected by controlling the quenching temperature was used for the generation of a macroporous open cellular structure with pore diameters above 100 microm. The use of amorphous polymers with a slow cooling rate resulted in a macroporous open cellular structure, whereas that of semicrystalline polymers with a fast cooling rate generated a microporous closed cellular structure. The fabricated porous devices loaded with recombinant human growth hormone (rhGH) were tested for the controlled delivery of rhGH, as a potential additional means to cell delivery.

Biocompatible Materials↗

PubMed1989

Phase separated membrane bioreactor: results from model system studies.

The operation and evaluation of a bioreactor designed for high intensity oxygen transfer in a microgravity environment is described. The reactor itself consists of a zero headspace liquid phase separated from the air supply by a long length of silicone rubber tubing through which the oxygen diffuses in and the carbon dioxide diffuses out. Mass transfer studies show that the oxygen is film diffusion controlled both externally and internally to the tubing and not by diffusion across the tube walls. Methods of upgrading the design to eliminate these resistances are proposed. Cell growth was obtained in the fermenter using Saccharomyces cerevisiae showing that this concept is capable of sustaining cell growth in the terrestrial [correction of terrestial] simulation.

Carbon Dioxide↗

PubMed2001

Microstructural effects on microbial survival: phase-separating dextran solutions.

Evolving microstructure in a model dextran solution is shown to exert a major influence on the survival of Escherichia coli K-12 frag 1 and Salmonella typhimurium LT2. The microstructure results from microscopic phase separation, which develops over several hours resulting in hardening of the solution into a glassy state. The microstructure is characterized by an array of physical methods including image analysis, electron spin resonance and bulk rheology, and it is shown that bacterial survival depends on the formation of microscopic. water-rich domains and not primarily on bulk water activity or hardness.

Colony Count, Microbial↗

PubMed1996

Ethanol-enhanced permeation of phosphatidylcholine/ phosphatidylethanolamine mixed liposomal membranes due to ethanol-induced lateral phase separation.

Effects of ethanol on permeability of large unilamellar vesicles (ca. 160 nm in diameter), composed of dipalmitoyl phosphatidylcholine/dilauroyl phosphatidylethanolamine (DLPE) mixture, were studied by monitoring leakage of the fluorescent dye, calcein, entrapped in the inner aqueous phase of the vesicles. In the presence of 2.1 M ethanol, permeabilities of membranes in various phases were G (bilayer gel) phase > L (bilayer liquid-crystalline) phase with a high mole fraction of DLPE and (I (ethanol-induced interdigitated gel phase) + G) phase > (I + L) at 20 mol % DLPE. Arrhenius plots of the leakage rate constants demonstrated that the permeability was greater with 2.1 M ethanol than without ethanol, especially in the temperature above 33 degrees C, suggesting that the presence of ethanol can induce lateral phase separation of liposomal membranes and cause them to have a high permeability even if they are stable and have low permeability in its absence.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1977

Lateral phase separations in binary mixtures of phospholipids having different charges and different crystalline structures.

Synthetic dipalmitoyl phosphatidylserine exhibits a sharp chain-melting transition temperature at 51 degrees C as judged by partitioning of the spin label 2,2,6,6-tetramethylpiperidine-1-oxyl. Phase diagrams representing lateral phase separations in binary mixtures of dipalmitoyl phosphatidylserine with dipalmitoyl phosphatidylcholine as well as with dimyristoyl phosphatidylcholine are derived from paramagnetic resonance determinations of 2,2,6,6,-tetramethylpiperidine-1-oxyl partitioning, freeze-fracture electron microscopic studies and theoretical arguments that limit the general form of acceptable phase diagrams. The reported phase diagrams are the first to describe binary mixtures in which one lipid is charged and the second lipid uncharged. These phase diagrams also are the first to include the problem of solid phases with different crystalline conformations as it relates to the occurrence of a pretransition in phosphatidylcholines and its absence in phosphatidylserines. In addition to the phase diagrams reported here for these two binary mixtures, a brief theoretical discussion is given of other possible phase diagrams that may be appropriate to other lipid mixtures with particular consideration given to the problem of crystalline phases of different structures and the possible occurrence of second-order phase transitions in these mixtures.

Crystallization↗

PubMed2004

Phase separation close to the density-driven Mott transition in the Hubbard-Holstein model.

The density-driven Mott transition is studied by means of dynamical mean-field theory in the Hubbard-Holstein model, where the Hubbard term leading to the Mott transition is supplemented by an electron-phonon (e-ph) term. We show that an intermediate e-ph coupling leads to a first-order transition at T=0, which is accompanied by a phase separation between a metal and an insulator. The compressibility in the metallic phase is substantially enhanced. At quite larger values of the coupling, a polaronic phase emerges coexisting with a nonpolaronic metal.

Journal Article↗