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PubMed2006

Photochemical phase transition versus photochemical phase separation.

When a nematic liquid crystal is doped with a large amount of a liquid crystalline azobenzene compound (15 wt %), the photoisomerization of azobenzene under UV and visible light irradiation can give rise to reversible and interconvertible photochemical phase transition and photochemical phase separation. Both normal and reverse modes of photocontrolled switching of transmittance through crossed polarizers can be realized with the same mixture of liquid crystal/azobenzene dopant.

Journal Article↗

PubMed2001

Dynamics of late-stage phase separation in crystalline solids.

The dynamics of Ostwald ripening in elastically stressed crystalline solids is determined through large-scale numerical simulations. Using the insight provided by the simulations, a theory for the dynamics of late-stage phase separation in elastically anisotropic homogeneous solids is developed. Both the theory and simulations show that for the systems considered elastic stress does not alter the exponent of the temporal power law for the average particle size but does affect the amplitude of the power law in a manner that is only a function of the symmetry of the particle morphology.

Journal Article↗

PubMed2006

Phase separation, interface properties, and charge density waves in a simplified model for a macroion suspension.

A simplified density functional theory for a macroion suspension is examined, where the correlation free energy corresponds to the macroion self-energy, treated within a linearized or Debye-Hückel approximation. The model possesses a miscibility gap (liquid-liquid phase separation) at low ionic strength. Within the gap, density profiles, electrical structure, and surface tension are calculated for the interface between coexisting phases, using a variational approximation. Additionally, structure factors are calculated for the homogeneous system. As one approaches the critical points, the structure factors can diverge at a nonzero wave vector, signaling the onset of charge density wave phases. Although the quantitative results should be treated with care, the results may be indicative of the rich phenomenology that can arise in asymmetric charged systems.

Journal Article↗

PubMed2000

Macroscopic phase separation in high-temperature superconductors.

High-temperature superconductivity is recovered by introducing extra holes to the Cu-O planes, which initially are insulating with antiferromagnetism. In this paper I present data to show the macroscopic electronic phase separation that is caused by either mobile doping or electronic instability in the overdoped region. My results clearly demonstrate that the electronic inhomogeneity is probably a general feature of high-temperature superconductors.

Journal Article↗

PubMed2006

Nanoscale phase separation in mixed poly(tert-butyl acrylate)/polystyrene brushes on silica nanoparticles under equilibrium melt conditions.

This communication reports on the study of microphase separation of well-defined mixed poly(tert-butyl acrylate) (PtBA)/polystyrene (PS) brushes on silica nanoparticles under equilibrium melt conditions. Mixed PtBA/PS brushes were synthesized from an asymmetric, difunctional initiator-terminated self-assembled monolayer by combining atom transfer radical polymerization and nitroxide-mediated radical polymerization. Two symmetric PtBA/PS mixed brush samples with different molecular weights were used in this study and were thermally annealed in vacuum at 150 degrees C. For the mixed brushes with number average molecular weights (Mn) of 24 200 g/mol for PtBA and 23 000 g/mol for PS, two glass transitions were observed in the differential scanning calorimetry analysis. Transmission electron microscopy study showed that the two grafted polymers underwent a lateral microphase separation, forming a random worm-like pattern with a feature size of approximately 10 nm on the silica particle surfaces. In contrast, the mixed brushes with a Mn of 10,400 g/mol for PtBA and 11,900 g/mol for PS did not microphase separate. Although the mixed brushes are on curved substrates, this work provides results consistent with the theoretical prediction that symmetric mixed homopolymer brushes undergo lateral rather than vertical phase separation under equilibrium melt conditions.

Journal Article↗

PubMed2004

Colossal magnetoresistance without phase separation: disorder-induced spin glass state and nanometer scale orbital-charge correlation in half doped manganites.

The magnetic and electrical properties of high-quality single crystals of A-site disordered (solid solution) Ln0.5Ba0.5MnO3 are investigated near the phase boundary between the spin-glass insulator and colossal-magnetoresistive ferromagnetic metal, locating near Ln=Sm. The temperature dependence of the ac susceptibility and the x-ray diffuse scattering of Eu0.5Ba0.5MnO3 are analyzed in detail. The uniformity of the random potential perturbation in Ln0.5Ba0.5MnO3 crystals with a small bandwidth yields, rather than the phase separation, an homogeneous short ranged charge or orbital order which gives rise to a nearly atomic spin-glass state. Remarkably, this microscopically disordered "charge-exchange-glass" state alone is able to bring forth the colossal magnetoresistance.

Journal Article↗

PubMed1989

Novel procedure for extraction of a latent grape polyphenoloxidase using temperature-induced phase separation in triton x-114.

Polyphenoloxidase from grape berries is extracted only by nonionic detergents with a hydrophilic-lipophilic balance between 12.4 and 13.5. The enzyme was partially purified in latent form, free of phenolics and chlorophylls, by using temperature phase partitioning in a solution of Triton X-114. This method permits the purification of the enzyme with the same fold purification as the commonly used method, but with a yield three times higher and a 90% reduction in time needed. The latent enzyme can be activated by different treatments, including trypsin and cationic and anionic detergents. Cetyltrimethylamonium bromide was found to be the most effective detergent activator, followed by sodium dodecyl sulfate. Polyphenoloxidase in grape berries, in spite of being an integral membrane protein, had an anomalous interaction with Triton X-114, remaining in the detergent-poor phase after phase separation. This could be explained by its having a short hydrophobic tail that anchors it to the membrane.

Journal Article↗

PubMed1986

Spin label study of local anesthetic-lipid membrane interactions. Phase separation of the uncharged form and bilayer micellization by the charged form of tetracaine.

The interaction between tetracaine and egg phosphatidylcholine (egg PC) multibilayers was examined. ESR spectra of an ester spin label indicate that at low uncharged anesthetic: lipid ratios, membrane organization decreases. At higher ratios, saturation and phase separation occur, as suggested by a second spectral component which appears when the water solubility of tetracaine is reached. However, experiments with the drug in the absence and in the presence of membranes, making use of a phospholipid spin label, suggest that the new phase does not consist of solid tetracaine alone. Location of the new phase in the membrane would require a change in partition coefficient, while its location outside would imply a mechanism whereby the anesthetic would come off the membrane as an aggregate containing spin probe and phospholipid. Charged tetracaine forms micelles which disrupt-unilamellar egg PC vesicles (Fernandez, M.S. (1981) Biochim. Biophys. Acta 646, 27-30). Micellar tetracaine added to bilayers containing a PC spin probe changes the spectrum from one typical of a bilayer into one typical of micelles, indicating the formation of a tetracaine-egg PC mixed micelle. The effect is reversible upon dilution to concentrations below the critical micelle concentration of tetracaine. When membranes are prepared in the presence of a water-soluble spin label, TEMPOcholine, ascorbate destroys the signal of untrapped label; when mixed phospholipid-tetracaine are formed by addition of micellar tetracaine, this leads to a complete loss of the ESR signal. High drug concentrations are often used for anesthesia and could be related to morphological nerve damage caused by large doses of anesthetics.

Anesthetics, Local↗

PubMedDate not supplied

Preparation and properties of thermoreversible, phase-separating enzyme-oligo(N-isopropylacrylamide) conjugates.

A thermoreversible N-isopropylacrylamide (NIPAAm) oligomer with an N-hydroxysuccinimide (NHS) ester functional end group has been prepared for coupling to an enzyme, beta-D-glucosidase, to form a thermoreversible, phase-separating polymer-enzyme conjugate. This conjugate can be used for separation, recovery, and recycle of an enzyme simply by applying small temperature changes to the reaction medium. In contrast to the random polymer-enzyme conjugates previously reported by us and others in the literature, in this study the conjugate is formed by a single, end attachment of each oligomer chain to the enzyme. Preliminary studies show that the conjugated enzyme exhibits very high retention of activity, even higher than native enzyme, and shows improved thermal stability compared to native enzyme.

Acrylamides↗

PubMed1977

Significant structure theory applied to phase separation.

The significant structure theory of liquids has been applied to the partially miscible system of the O(3)-O(2) mixture, which exhibits partial miscibility in the temperature range from -195.5 degrees C to -179.9 degrees C. The thermodynamic condition for phase separation is given by the following inequality: [Formula: see text] A partition function for the binary liquid mixture is developed using significant liquid structure theory. Here X(i) is the mole fraction of either of the two components. We obtain the coexistence curve of the O(3)-O(2) system by varying the mole fractions of the components to find the temperature at which the two liquids separate. The agreement between theory and experiment is satisfactory.

Journal Article↗

PubMedDate not supplied

Effect of the solvent-non-solvent pairs on the surface morphology and release behaviour of ethylcellulose microcapsules prepared by non-solvent-addition phase separation method.

Four solvent-non-solvent pairs (ethyl-acetate-cyclohexane, dichloromethane-cyclohexane, acetone-cyclohexane and dichloromethane-n-hexane) with different solubility parameter differences were chosen to prepare ethylcellulose microcapsules containing theophylline by using non-solvent-addition phase separation method. The results showed that the surface morphology and release behaviour of microcapsules were greatly affected by different solvent-non-solvent pairs. The surface of the microcapsules prepared from the system of high solubility parameter difference was more smooth than those from the systems of low solubility parameter difference. The release rate of the drug from microcapsules decreased with increasing solubility parameter difference of the preparative system. The determination of the wall thickness and porosity of the microcapsules could reasonably explain the release characteristics. The porosity of the microcapsules decreased with the increase of solubility parameter difference of the preparative system, but the wall thickness of the microcapsules showed a corresponding increase. The release of the drug from various ethylcellulose microcapsules fitted first-order kinetics with biphasic release profiles.

Cellulose↗

PubMed2002

Nonequilibrium phenomena in the phase separation of a two-component lipid bilayer.

Lipid bilayers composed of two phospholipids with significant acyl-chain mismatch behave as nonideal mixtures. Although many of these systems are well characterized from the equilibrium point of view, studies concerning their nonequilibrium dynamics are still rare. The kinetics of lipid demixing (phase separation) was studied in model membranes (large unilamellar vesicles of 1:1 dilauroylphosphatidylcholine (C(12) acyl chain) and distearoylphosphatidylcholine (C(18) acyl chain)). For this purpose, photophysical techniques (fluorescence intensity, anisotropy, and fluorescence resonance energy transfer) were applied using suitable probes (gel phase probe trans-parinaric acid and fluid phase probe N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-dilauroylphosphatidylethanolamine). The nonequilibrium situation was induced by a sudden thermal quench from a one-fluid phase equilibrium situation (higher temperature) to the gel/fluid coexistence range (lower temperature). We verified that the attainment of equilibrium is a very slow process (occurs in a time scale of hours), leading to large domains at infinite time. The nonequilibrium structure stabilization is due essentially to temporarily rigidified C(12) chains in the interface between gel/fluid domains, which decrease the interfacial tension by acting as surfactants. The relaxation process becomes faster with the increase of the temperature drop. In addition, heterogeneity is already present in the supposed homogeneous fluid mixture at the higher temperature.

Anisotropy↗

PubMed1983

Phase separation and lens cell age.

Using laser light scattering spectroscopy, we are studying age-related changes in the microstructure of lens cytoplasm. We have established in animal models that one of the earliest identifiable stages in cataract development is the presence of a phase transition in the lens cytoplasm. As a result of the phase transition, the cytoplasm separates into microvolumes that differ in their protein concentration. These microvolumes scatter light and cause the lens to become opaque. This phase separation occurs in normal lens cells at a characteristic temperature, Tcat, which varies across the lens with the cell age. As the animal becomes older, the Tcat for the nuclear cells decreases to a value well below body temperature. In X-irradiated eyes, however, Tcat increases with animal age until the phase separation occurs at or near body temperature. At this point, a well-developed nuclear cataract appears. We are now attempting to understand the biochemical basis for the differences between Tcat of normal and Tcat of X-irradiated lens cells during the aging process.

Aging↗

PubMed2005

The microstructure of di-alkyl chain cationic/nonionic surfactant mixtures: observation of coexisting lamellar and micellar phases and depletion induced phase separation.

The evolution of the microstructure and composition occurring in the aqueous solutions of di-alkyl chain cationic/nonionic surfactant mixtures has been studied in detail using small angle neutron scattering, SANS. For all the systems studied we observe an evolution from a predominantly lamellar phase, for solutions rich in di-alkyl chain cationic surfactant, to mixed cationic/nonionic micelles, for solutions rich in the nonionic surfactant. At intermediate solution compositions there is a region of coexistence of lamellar and micellar phases, where the relative amounts change with solution composition. A number of different di-alkyl chain cationic surfactants, DHDAB, 2HT, DHTAC, DHTA methyl sulfate, and DISDA methyl sulfate, and nonionic surfactants, C12E12 and C12E23, are investigated. For these systems the differences in phase behavior is discussed, and for the mixture DHDAB/C12E12 a direct comparison with theoretical predictions of phase behavior is made. It is shown that the phase separation that can occur in these mixed systems is induced by a depletion force arising from the micellar component, and that the size and volume fraction of the micelles are critical factors.

Journal Article↗

PubMed1999

Salt-induced liquid-liquid phase separation of protein-surfactant complexes.

We report the cloud-point curve determination of lysozyme-sodium-doderyl-sulfate (SDS) complexes in solution. By varying the pH, salt concentration, and relative ratio of lysozyme to SDS, the phenomenon of clouding and liquid-liquid phase separation is investigated under different solution conditions. For the temperature, concentration, and pH ranges used in this study, the clouding phenomenon appears to be controlled by the electrostatic interaction between the lysozyme-SDS complexes. Any change in the solution condition that leads to a decrease in the charge on the lysozyme-SDS complexes results in an increase in cloud-point temperature. A generalized Flory-Huggins theory for polydisperse polymers is used to describe the cloud-point curve.

Animals↗

PubMed2004

Evaluation of solubilizing ability of humic aggregate basing on the phase-separation model.

Solubilizing abilities of aggregates of humic acid (HA) to chlorinated benzenes (CBs) were investigated by means of the apparent water solubility enhancement. Both the water solubilities of 1,4-dichlorobenzene (DCB) and 1,2,4,5-tetrachlorobenzene (TeCB) linearly increased with increasing concentration of HA above the critical micelle concentration (CMC). Such solubilization behavior of CBs for HA was compatible with those for sodium dodecyl sulfate (SDS). These results indicate that the solubilization of CBs in the aqueous solution of HA above the CMC can be interpreted on the basis of the phase-separation model. Thus, the partition coefficients (K(mic)) of CBs between water and HA aggregate phases were calculated by assuming this model. The fact that the K(mic) value increased with increasing K(ow) of CBs supported the partition into the HA aggregate phase by hydrophobic interaction. The estimated K(mic) values of DCB were not dependent on the solution pH. Both K(mic) values of DCB and TeCB for the HA aggregate were found to be 4-5-fold lower than those of SDS.

Chlorobenzenes↗

PubMed2003

Phase separation in calcium alginate gels.

Alginates are polysaccharides consisting of beta-D-mannuronate and alpha-L-guluronate units. In the presence of bivalent cations like calcium the guluronate blocks form physically cross-linked gels. The gelation properties of alginates play an important role in the stability of extracellular polymer substances and in the food industry. When stock solutions of Ca2+ ions and alginate are mixed, the gelation starts before the Ca2+ ions are evenly distributed, which leads to non-uniform gels. In this contribution, Ca alginate gels were prepared by in situ gelation using glucono-delta-lactone and CaCO3. In this way, uniform gels could be prepared directly in the measuring cell. Below a critical concentration, highly viscous solutions were obtained, which were below the critical point of gel formation. In these solutions at low rotational speeds a Schlieren peak arose, which became smaller and steeper with increasing time until a new meniscus could be detected. This behaviour is in contrast to the peak broadening due to diffusion after a synthetic boundary was formed. Evaluation of the data leads to negative diffusion coefficients. It has been shown by others that the mutual diffusion coefficient must be negative in the spinodal region. This phenomena is known as uphill diffusion and leads to phase separation of a binary system. The formation of the gel phase in this case is therefore discussed as uphill diffusion.

Alginates↗

PubMed2002

BPTI liquid-liquid phase separation monitored by light and small angle X-ray scattering.

In the field of protein crystallization, a better knowledge of the nucleation process is essential to control the nucleation rate, the growth and therefore the size and the quality of crystals. With that aim, it becomes clear that the important stage is the determination of the protein phase diagram. We highlighted and investigated the bovine pancreatic trypsin inhibitor (BPTI) binary liquid-liquid phase separation in 350 mM KSCN solutions as a function of temperature. We measured the low concentration part of the binodal curve using light scattering and optical microscopy. We show, from small angle X-ray scattering experiments, that the high concentrated phase sediments in the bottom of the capillary and we analysed the low concentrated phase in terms of monomers/decamers equilibrium.

Animals↗