scispace - formally typeset
Search or ask a question

Showing papers on "Phase (matter) published in 1981"


Journal ArticleDOI
TL;DR: The partition of proteins during phase separation in solutions of Triton X-114 is investigated and integral membrane proteins with an amphiphilic nature are recovered in the detergent phase.

3,150 citations


Journal ArticleDOI
TL;DR: In this article, the temperature dependence of positron lifetimes in both the brittle and plastic phases of trimethylacetic (pivalic) acid was examined using the positron lifetime technique.

1,640 citations


Journal ArticleDOI
TL;DR: In this paper, a theory of the cholesteric blue phase is presented, assuming a first-order Cholesteric-isotropic transition, and it is shown that the planar helix structure becomes unstable at temperatures near the transition point.
Abstract: We present a theory of the cholesteric blue phase, assuming a first-order cholesteric-isotropic transition. We show, on the basis of the Oseen-Frank elasticity equations, that the planar helix structure, generally associated with the cholesteric phase, becomes unstable at temperatures near the transition point. It transforms into a phase characterized by a network of disclination lines.

1,286 citations


Journal ArticleDOI
TL;DR: In this paper, the phase behavior of aqueous solutions of poly(ethylene oxide), PEO, is analyzed by means of a structural model of the system and a simple statistical-mechanical model based thereupon.
Abstract: The phase behaviour of aqueous solutions of poly(ethylene oxide), PEO, is analysed by means of a structural model of the system and a simple statistical-mechanical model based thereupon. The intention is to elucidate the structural questions involved in the water–PEO coupling and to gain some insight in possible consequences of this coupling. The experimental partial molar enthalpy and entropy of water can be reproduced, at least in fairly dilute solutions, if a zone with increased structuring of the water is assumed to exist around the PEO chain. The phase separation that takes place at high temperatures is traced back to the increase in total extension of the zones of enhanced water structure that occurs when the water content is increased. The chain-length dependence of the location of the solubility gap is mainly determined by the combinatorial entropy of the chains. The water solubility of PEO, which is unique in this respect among the polyethers, can be explained in terms of a good strutural fit between the water and the polymer.

689 citations


Journal ArticleDOI
TL;DR: In this paper, a molecular theory for the dynamics of rod-like polymers in concentrated solutions is presented, which describes the rotational motion of rods in both the isotropic phase and the liquid crystalline phase.
Abstract: A molecular theory is presented for the dynamics of rodlike polymers in concentrated solutions. The theory describes the rotational motion of rods in both the isotropic phase and the liquid crystalline phase. Combined with the molecular expression of the stress tensor, it also gives a unified rheological constitutive equation which predicts the nonlinear viscoelasticity in both phases. As an illustrative example, the steady-state viscosity η at zero-shear-rate is calculated. The predicted dependence of η on molecular weight and concentration agrees fairly well with experiments.

624 citations


Journal ArticleDOI
TL;DR: In this paper, an order parameter theory of the solid-liquid interface using structural information about the uniform liquid phase is presented. But this theory is restricted to the flat interface and the spherical ball.
Abstract: We present an order parameter theory of the solid–liquid interface which uses structural information about the uniform liquid phase. The order parameters are the coefficients of a Fourier expansion of the nonuniform density in terms of reciprocal lattice vectors characteristic of the uniform solid phase. The theory provides explicit formulas for the interfacial density profile and the surface free energy. Connection is made with recent theories of freezing and of the liquid–vapor interface. Two special cases of particular interest are considered: the flat interface, for which numerical simulations have been attempted, and the spherical ball, which is important in theories of liquid–solid nucleation.

333 citations



Journal ArticleDOI
TL;DR: In this paper, the deformation rate of polycrystalline ceramics that contain a residual glass phase is analyzed in terms of material transport through the liquid phase, where molecules are transported and deposited in the direction of the positive normal traction gradient along the interfaces.

275 citations


Journal ArticleDOI
TL;DR: In this article, two different mechanisms are observed depending on the source of silica and the Si/Al, Al/Na and (Si + A1)/TPA ratios in the reaction mixture.

258 citations


Journal ArticleDOI
TL;DR: The phase transitions in the ZrO2-YzO3 system have been investigated as a function of temperature using Raman scattering and the cubic phase was found to be structurally disordered and the spectrum has been compared with a one phonon density of states derived from a rigid ion model.

255 citations


Journal ArticleDOI
TL;DR: In this article, a scaling model for the metal-insulator transition in amorphous materials is presented, which predicts a continuous phase transition at zero temperature with localized states and a correlation gap in the insulating phase.
Abstract: A scaling model is presented for the metal-insulator transition in amorphous materials which includes a localization, correlation, and screening. The model predicts a continuous phase transition at zero temperature with localized states and a correlation gap in the insulating phase.

Journal ArticleDOI
TL;DR: The paramagnetic resonance spectra of two spin-labels, 2,2,6,6-tetramethylpiperadinyl-1-oxy and a head-group spin-labeled phosphatidylethanolamine, have been used to study solid-liquid and liquid-liquid phase separations in binary mixtures of dimyristoylphosphatidylcholine and cholesterol.
Abstract: The paramagnetic resonance spectra of two spin-labels, 2,2,6,6-tetramethylpiperadinyl-1-oxy and a head-group spin-labeled phosphatidylethanolamine (L-alpha-dipalmitoylphosphatidyl-N-ethanolamine), have been used to study solid-liquid and liquid-liquid phase separations in binary mixtures of dimyristoylphosphatidylcholine and cholesterol. A quantitative analysis of these resonance spectra supports the view that at temperatures below theta m, the chain-melting temperature of the phospholipid, and at cholesterol mole fractions Xc less than 0.2, these mixtures consist of two phases, a solid phase of essentially pure dimyristoylphosphatidylcholine and a fluid phase having a mole fraction of cholesterol equal to 0.2. The spin-label data also provide evidence for fluid-fluid immiscibility in the bilayer membrane at temperatures above the chain melting transition temperature of dimyristoylphosphatidylcholine.

Journal ArticleDOI
01 Dec 1981
TL;DR: In this article, phase separations in dispersions of different types of spherical, lyophilic, monodisperse silica particles and polystyrene molecules in cyclohexane at the theta temperature were investigated.
Abstract: Phase separations in dispersions of different types of spherical, lyophilic, monodisperse silica particles and polystyrene molecules in cyclohexane at the theta temperature were investigated. We used silica particles stabilized with a chemically bonded layer of stearyl alcohol molecules and silica particles stabilized with tetraethylenepentamine-terminated polyisobutene molecules. At a fixed silica concentration (1.0 or 5.0% w/v) a liquid-liquid phase separation occurs above some limiting polystyrene concentration. The limiting concentration, c lim , usually is of the order of a few percent (w/v), and depends on the molar mass of the polymer. High-molar-mass polymers show a lower c lim value than low-molar-mass polymers. An increase in the concentration of the silica particles lowers the c lim value. The radius of the silica particles also influences c lim . The experimental results are interpreted in terms of a simple “hard sphere-cavity” model, with which a theory is worked out which is based on first principles only. Most experimental results can be reproduced by theoretical calculations on a semiquantitative scale. Discrepancies between theory and experiment only are found with the silica samples that obviously do not conform to the hard sphere model used.


Journal ArticleDOI
TL;DR: This work investigated membrane flow and lateral lipid diffusion in the membrane on the trough, and found the "liquid-condensed/liquid-expanded" region appears to be a homogeneous membrane where lateral diffusion and membrane flow are both rapid.


Journal ArticleDOI
TL;DR: Osakabe et al. as discussed by the authors observed the phase transition process of clean (111) silicon surfaces between the (7 × 7) and (1 × 1) structures at about 830°C.

Journal ArticleDOI
TL;DR: In this paper, an experimental study of the effect of boron in the water saturated Q-Or-Ab-B2O3-H2O system has been performed at P = 1 Kbar to provide experimental data and explain the role of bboron in some late magmatic and early hydrothermal events.
Abstract: An experimental study of the effect of boron in the water saturated Q-Or-Ab-B2O3-H2O system has been performed at P=1 Kbar to provide experimental data and explain the role of boron in some late magmatic and early hydrothermal events. Experiments were conducted between 500° C and 800° starting from a gel, or a previously crystallized gel, and variable amounts of boron (0 to 18% B2O3) added to water. The phases obtained were: quartz, sanidine, albite, silicate liquid quenched to glass, and aqueous vapour phase. Boric acids, borates and isotropic low index materials were found in the quenched vapour phase. An aluminium silicate-like mineral, not yet fully identified, is also present. The solidus temperature of the Q-Or-Ab composition is lowered by 60° C when 5 wt. % B2O3 is added and by more than 130° C when 17wt. % B2O3 is added. Compositions of equilibrated silicate melts and vapours were obtained between 780° C and 750° C for various B2O3 concentrations. The vapour phase is B and Si rich. It is also enriched in Na with respect to K, and in alkalis with respect to Al. Its silicate solute content is higher than in experiments with pure water. The solubility of water is increased by the addition of boron in Q-Or-Ab melts. Microprobe data show that the melts equilibrated with vapour phases become hyperaluminous and more potassic than sodic. The partition coefficient of boron is in favour of the vapour (k D=B2O3% in melt/B2O3% in vapour=0.33±0.02). The effect of the interaction between the silicate phases and the vapour is discussed. Comparison is made between the behaviour of boron and that of chlorine and fluorine. Geological applications are also provided, which concern the influence of boron on minimum melting, on muscovite stability and on the hypersolvus-subsolvus transition.

Journal ArticleDOI
TL;DR: In this paper, a structural model of the rotator phase can be deduced from x-ray experiments performed both on single domains and on powder samples of normal paraffins CnH2n+2 with n ranging from 17 to 21.
Abstract: We present here a study of the ’’rotator’’ phase displayed by the odd‐numbered normal paraffins CnH2n+2 with n ranging from 17 to 21. A structural model of the rotator phase can be deduced from x‐ray experiments performed both on single domains and on powder samples. Its structure very much looks like the crystalline phase structure, i.e., the molecules are packed within layers forming a bilayer structure with the molecular axes oriented perpendicularly to the layer planes. The comparison of the space group Ccmm with the steric dimensions of the molecules implies the appearance of an orientational disorder of the molecules around their long axes which is the main characteristic of the crystalline→rotator phase transition. Such a conclusion is in agreement with the dynamical measurements which state a uniaxial rotation of the molecules.

Journal ArticleDOI
TL;DR: HAL as discussed by the authors is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not, which may come from teaching and research institutions in France or abroad, or from public or private research centers.
Abstract: HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Two-dimensional ising model with competing interactions : floating phase, walls and dislocations J. Villain, P. Bak

Journal ArticleDOI
TL;DR: In this article, the electrical conductivity and the Hall effect were investigated in the temperature region from 77 to 1000 K on undoped ZnO single crystals grown by vapour phase transport.
Abstract: The electrical conductivity and the Hall effect are investigated in the temperature region from 77 to 1000 K on undoped ZnO single crystals grown by vapour phase transport. The growth conditions were systematically altered to get crystals with definite non-stoichiometry. The electrical properties are related to these growth conditions. The analysis of the Hall data yields the phase boundary ZnO/Zn and a formation enthalpy of 1.5 eV for the dominant native donor. This donor is suggested to be the oxygen vacancy. The Hall mobility is analysed with regard of new aspects giving a smaller anisotropy than in earlier analyses.

Journal ArticleDOI
TL;DR: In this paper, the surface tension of mixed solutions of cationic and anionic surfactants has been studied quantitatively for the system sodium dodecyl sulfate and trimethyl ammonium bromide.

Journal ArticleDOI
TL;DR: A brief overview of the important issues governing the behavior of polymer blends is presented in this paper, where the influence of melt processing conditions on the resulting properties and behavior of both miscible and immiscible blends is reviewed.
Abstract: A brief overview of the important issues governing the behavior of polymer blends is presented. Thermodynamic issues which determine the phase behavior of blends are reviewed and qualitatively related to physical interactions between blend components. The influence of melt processing conditions on the resulting properties and behavior of both miscible and immiscible blends is reviewed. The physical properties of blends are reviewed and illustrated by examples from recent work on miscible blends of polycarbonate with a copolyester and on the immiscible blends of polystyrene with high density polyethylene.

Journal ArticleDOI
TL;DR: In this paper, the surface excess description of a mixed mobile phase in a liquid-solid chromatographic column is used to measure the adsorption of solvent components from a mixture of acetonitrile and methanol on to reversed-phase packings.

Journal ArticleDOI
01 Apr 1981
TL;DR: In this article, a thermodynamic model is proposed for the description of the amphiphile association behavior in ionic water systems, based on a model expression for the free energy G containing five contributions, a hydrophobic energy, a surface free energy of the aggregates, an electrostatic free energy calculated from the Poisson-Boltzmann equation, an entropy of mixing for the micellar aggregates.
Abstract: A thermodynamic model is proposed for the description of the amphiphile association behavior in ionic amphiphile-water systems. The treatment is based on a model expression for the free energy G containing five contributions, a hydrophobic energy, a surface free energy of the aggregates, an electrostatic free energy calculated from the Poisson-Boltzmann equation, an entropy of mixing for the micellar aggregates, and the condition that the aggregate size is, in at least one dimension, limited to the length of an extended amphiphile molecule. From the expression for G the chemical potentials, μi, of the different components, i, are determined by calculating (∂G∂ni)nj directly. The calculations are restricted to three aggregate geometries: spheres as in micellar solutions, infinite cylinders as in normal and reversed hexagonal phases, and lamellae as in lamellar liquid crystalline phases. For each type of aggregate the optimal thickness, b, is determined by requiring that (∂G∂b)nj = 0, which for the liquid crystalline phases implies that the surface free energy γA equals twice the energy of the ion-ion interactions. By comparing with X-ray diffraction data for a series of potassium carboxylate-water systems it is shown that the proportionality constant γ = 18 mN/m at 86°C. Using this value of γ in the expressions for μi, the stability regions of the different phases, including two-phase regions, are determined for several carboxylic soaps and good agreement with experiment is found. Calculations are also presented for the phase equilibria in the Aerosol OT-H2O system, where the amphiphile has two hydrocarbon chains. It is shown that the theory also can account for the formation of a lamellar phase without an extensive micellar region and for the fact that the system forms a reversed hexagonal phase at low water contents.

Journal ArticleDOI
TL;DR: A model is developed for the bilayer to nonbilayer phase transition in which it is proposed that the driving force which triggers this phase transition is the introduction of a degree of conformational disorder so high that the integrity of the bilayers surface can no longer be maintained.
Abstract: A Fourier-transform infrared spectroscopic study of the thermotropic behavior of egg yolk phosphatidylethanolamines is reported. Two phase changes were monitored, the gel to liquid-crystalline acyl chain melting transition, centered at 12 degrees C, and a transition from the liquid-crystalline to be inverted hexagonal phase, centered at 28 degrees C. It is demonstrated that the gel to liquid-crystalline phase transition results in a large increase in the conformational disorder of the acyl chains in the bilayer and that the nonbilayer phase contains a still higher degree of conformational disorder. It is shown that the transition to the inverted hexagonal phase is promoted by highly unsaturated acyl chains. A model is developed for the bilayer to nonbilayer phase transition in which it is proposed that the driving force which triggers this phase transition is the introduction of a degree of conformational disorder so high that the integrity of the bilayer surface can no longer be maintained, due to the volume requirements of the acyl chains. A number of previously reported data are rationalized in terms of this hypothesis.

Journal ArticleDOI
TL;DR: In this article, a reversed-phase system has been developed that permits the detection and quantification of down to 0.1 nmole of non-UV-absorbing cations and anions using a UV detector.

Journal ArticleDOI
TL;DR: In this article, a number of commercially available soybean lecithins were analyzed with respect to their phospholipid composition and emulsifying properties, and the minimal amount of emulsifier required to stabilize the emulsions was estimated, which corresponds to a thickness of two double lipid layers in the interfacial film.
Abstract: A number of commercially available soybean lecithins were analyzed with respect to their phospholipid composition and emulsifying properties. A phosphatidylcholine (PC) from soybean swells to a lamellar liquid crystalline phase which incorporates slightly less than 50% of water. The swelling behavior of the commercially available soybean lecithins may be different depending on the concentration of other phospholipids such as phosphatidylethanolamine (PE), phosphatidylinositol (PI) and phosphatidic acid (PA). In the presence of the negatively charged phospholipids PI and PA, the swelling of the lamellar phase of PC was dramatically enhanced while a lecithin with equal amounts of PC and PE and small quantities of PI and PA formed two liquid crystalline phases, i.e., a lamellar and a hexagonal phase. Stable o/w-emulsions can be prepared when the phospholipid composition is such that a lamellar liquid crystalline phase in equilibrium with the oil and water phases incorporates large amounts of water. The minimal amount of emulsifier required to stabilize the emulsions has been estimated to give an interfacial film of ca. 80 A thickness which corresponds to a thickness of two double lipid layers in the interfacial film. The incorporation of large amounts of water is obtained if the lamellar layers contain dissociated ionic groups.


Journal ArticleDOI
TL;DR: In this paper, it was shown that paraffin oil-in-water emulsions containing crystals became much more unstable during laminar flow, for instance by 4-6 orders of magnitude.