Phase diagrams of blends of azide-containing polyoxetanes

The mutual solubility of polymers based on the azide-containing oxetane monomers 3,3-bis(azidomethyl)oxetane and 3-azidomethyl-3-methyloxetane is studied. The temperatures of melting, crystallization, glass transition; the upper critical solution temperature; and the compositions of coexisting phases for blends of polymers with different molecular masses are determined via differential scanning calorimetry and multiple-beam microinterferometry. On the basis of these data, the phase diagrams of blends are constructed. The melting regions and the metastable and heterogeneous states are determined. The studied systems are shown to have a complex amorphous-crystalline equilibrium and to differ in the location of boundary curves on the phase diagram, depending on the molecular mass of the components. Amorphous separation below the liquidus line in the metastable region with respect to the crystalline equilibrium is experimentally detected. The motion of the figurative point in different regions of the diagram is thoroughly considered. The specifics of structural and morphological organization of systems are examined via electron microscopy.     

The prediction of isobaric phase equilibria for non-ideal multicomponent mixtures from heat of mixing data

A method for predicting isobaric binary and ternary vapor—liquid equilibrium data using only isothermal binary heat of mixing data and pure component vapor pressure data is presented. Three binary and two ternary hydrocarbon liquid mixtures were studied. The method consists of evaluating the parameters of the NRTL equation from isothermal heat of mixing data for the constituent binary pairs. These parameters are then used in the multicomponent NRTL equation to compute isobaric vapor—liquid equilibrium data for the ternary mixture. No ternary or higher order interaction terms are needed in the ternary calculations because of the nature of the NRTL equation. NRTL parameters derived from heat of mixing data at one temperature can be used to predict vapor—liquid equilibrium data at other temperatures up to the boiling temperature of the liquid mixture.For the systems studied this method predicted the composition of the vapor phase with a standard deviation ranging from 1–8% for the binary systems and from 4–12% for the ternary systems.     

Metastable Equilibria with the Participation of Superheated Crystal Phases in Binary Oxide Systems

Experimental diagrams of binary systems, including compounds that melt upon decomposition, sometimes display the metastable congruent melting of such compounds above the peritectic equilibrium temperature. Conditions in which the occurrence of superheated states of binary systems is possible are analyzed. Thermodynamic and kinetic interpretations of such phenomena are presented.     

The equilibrium phase properties of selected naphthenic binary systems: Carbon dioxide-methylcyclohexane,hydrogen sulfide-methylcyclohexane

Vapor and liquid equilibrium phase compositions have been determined at temperatures ranging from 310 to 478 K for two binary systems. Measurements were made at 311.0, 338.9, 394.0, and 477.2 K for the carbon dioxide—methylcyclohexane system and at 310.9, 352.6, 394.3 and 477.6 K for the hydrogen sulfide—methylcyclohexane system. At each temperature, pressures ranged from the vapor pressure of methylcyclohexane to the vapor pressure of hydrogen sulfide, or to a pressure near the critical for the system, whichever was higher. The data were used to calculate equilibrium ratios for each component in the binary system.     

Vapor-liquid equilibrium in selected aromatic binary systems: m-xylene-hydrogen sulfide and mesitylene-hydrogen sulfide

Huang, S.S.-S. and Robinson, D.B., 1984. Vapor—liquid equilibrium in selected aromatic binary systems: m-xylene—hydrogen sulfide and mesitylene—hydrogen sulfide. Fluid Phase Equilibria, 17: 373–382.Vapor and liquid equilibrium phase compositions have been determined for the m-xylene-hydrogen sulfide and mesitylene—hydrogen sulfide binary systems at temperatures of 310.9, 352.6, 394.3 and 477.6 K and at several pressures from the vapor pressure of the less volatile component to the vapor pressure of hydrogen sulfide or to the critical pressure for the system, whichever was higher. The data have been used to calculate equilibrium ratios for each of the components in the binary systems. The results of Eakin and DeVaney (1974) for the mesitylene—hydrogen sulfide system at 310.9 and 477.6 K are also included for comparison.The data presented are useful in evaluating the properties of condensate reservoir fluids containing hydrogen sulfide and aromatic compounds.     

Electron-impact ionization of the metastable Mg(...2p63s3p3P0,2) atoms

Electron-impact ionization of Mg atoms from metastable states was investigated. The method and tech-nique of crossed atomic and electron beam studies are described. The value of the total ionization cross section from the 3s3p ³P_j metastable states for 4... 21 eV incident electron energy was determined. It was found that ionization cross sections from the metastable and ground states differ considerably. This is mainly due to the different mechanisms of ion formation from the metastable and ground states. The results obtained are compared with those calculated in the classical mechanics binary approximation.     

Isobars of the boiling temperature and isotherms of excess thermodynamic functions of isobutanol-alkyl ketone solutions

The boiling temperatures for solutions of five binary systems are measured via ebulliometry in the pressure range of 5.333–101.3 kPa. The isotherms constructed for the pressure of saturated vapor serve as the base for computing the compositions of equilibrium vapor phases of the systems. The excess Gibbs energies, enthalpies, and entropies of solutions are computed from the data on liquid-vapor equilibrium. The laws of changes in the phase equilibria and thermodynamic properties of solutions are determined depending on the composition and temperature of the systems. The vapor-liquid equilibrium of the systems is described by Wilson and NRTL equations.     

Estimation of the liquid-vapor spinodal from interfacial properties obtained from molecular dynamics and lattice Boltzmann simulations

Interfacial pressure and density profiles are calculated from molecular dynamics and lattice Boltzmann simulations of a liquid film in equilibrium with its vapor. The set of local values of tangential pressure and density along an interface exhibits a van der Waals-type loop; starting from the stable vapor bulk phase one passes through metastable and unstable states to the stable liquid bulk phase. The minimum and maximum values of the profile of tangential pressure are related to the liquid and vapor spinodal states, respectively. The spinodal pressures turn out to be linearly related to the extreme values of the tangential pressure in the interface. The comparison with equations of state shows good agreement with the simulation results of the spinodals. In addition the properties of the metastable region are obtained. Based on this investigation a method is proposed for the estimation of the liquid spinodal from experimentally obtained interfacial properties. Estimations for water and helium are presented.     

Size effects during phase transformations in stratifying systems

Size effects during phase transitions in binary stratifying mixtures with small systems are simulated by means of equilibrium chemical thermodynamics. Conditions are described under which stable and metastable thermodynamically equilibrium heterogeneous states exist. It is established that degeneracy is split in nanosize and submicron systems and the inversion of equilibrium and metastable states is possible. It is shown that size effects include a change and shift of the heterogeneity region in the phase diagram. It is concluded that in the limiting case, reducing the size of a system can homogenize a stratifying mixture of any composition.     

Can the speed of sound be used for detecting critical states of fluid mixtures?

The phenomenology of sound speeds in fluid mixtures is examined near and across critical lines. Using literature data for binary and ternary mixtures, it is shown that the ultrasound speed along an isotherm-isopleth passes through a minimum value in the form of an angular (or V-shaped) point at critical states. The relation between critical and pseudo-critical coordinates is discussed. For nonazeotropic fixed-composition fluid mixtures, pseudo-critical temperatures and pressures are found to be lower than the corresponding critical temperatures and pressures. The analysis shows that unstable pseudo-critical states cannot be detected using acoustic methods. The thermodynamic link between sound speeds and isochoric heat capacities is formulated and discussed in terms of p-Vm-T derivatives capable of being calculated using cubic equations of state. Based on the Griffiths-Wheeler theory of critical phenomena, a new specific link between critical sound speeds and critical isochoric heat capacities is deduced in terms of the rate of change of critical pressures and critical temperatures along the p-T projection of the critical locus of binary fluid mixtures. It is shown that the latter link can be used to obtain estimates of critical isochoric heat capacities from the experimental determination of critical speeds of sound. The applicability domain of the new link does not include binary systems at compositions along the critical line for which the rate of change in pressure with temperature changes sign. The new equation is combined with thermodynamic data to provide approximate numerical estimates for the speed of sound in two mixtures of carbon dioxide and ethane at different temperatures along their critical isochores. A clear decrease in the sound speed is found at critical points. A similar behavior is suggested by available critical heat capacity data for several binary fluid mixtures. Using an acoustic technique, the critical temperature and pressure were determined for three different mixtures of methane and propane, and compared with literature data obtained using conventional methods. It is concluded that acoustic-based techniques are reliable to determine, for the most part, critical surfaces of fluid mixtures. The remaining few cases where the present analysis cannot be applied could be tested by the thermodynamic calculation of critical sound speeds using crossover equations of state in conjunction with experimentally determined critical isochoric heat capacities.     

Replica theory of the rigidity of structural glasses

We present a first principle scheme to compute the rigidity, i.e., the shear-modulus of structural glasses at finite temperatures using the cloned liquid theory, which combines the replica theory and the liquid theory. With the aid of the replica method which enables disentanglement of thermal fluctuations in liquids into intra-state and inter-state fluctuations, we extract the rigidity of metastable amorphous solid states in the supercooled liquid and glass phases. The result can be understood intuitively without replicas. As a test case, we apply the scheme to the supercooled and glassy state of a binary mixture of soft-spheres. The result compares well with the shear-modulus obtained by a previous molecular dynamic simulation. The rigidity of metastable states is significantly reduced with respect to the instantaneous rigidity, namely, the Born term, due to non-affine responses caused by displacements of particles inside cages at all temperatures down to T = 0. It becomes nearly independent of temperature below the Kauzmann temperature T(K). At higher temperatures in the supercooled liquid state, the non-affine correction to the rigidity becomes stronger suggesting melting of the metastable solid state. Inter-state part of the static response implies jerky, intermittent stress-strain curves with static analogue of yielding at mesoscopic scales.     

Free-energy landscape of nucleation with an intermediate metastable phase studied using capillarity approximation

Capillarity approximation is used to study the free-energy landscape of nucleation when an intermediate metastable phase exists. The critical nucleus that corresponds to the saddle point of the free-energy landscape as well as the whole free-energy landscape can be studied using this capillarity approximation, and various scenarios of nucleation and growth can be elucidated. In this study, we consider a model in which a stable solid phase nucleates within a metastable vapor phase when an intermediate metastable liquid phase exists. We predict that a composite critical nucleus that consists of a solid core and a liquid wetting layer as well as pure liquid and pure solid critical nuclei can exist depending not only on the supersaturation of the liquid phase relative to that of the vapor phase but also on the wetting behavior of the liquid surrounding the solid. The existence of liquid critical nucleus indicates that the phase transformation from metastable vapor to stable solid occurs via the intermediate metastable liquid phase, which is quite similar to the scenario of nucleation observed in proteins and colloidal systems. By studying the minimum-free-energy path on the free-energy landscape, we can study the evolution of the composition of solid and liquid within nuclei which is not limited to the critical nucleus.     

Phase equilibria in phospholipid-water systems

This work is a critical account of phase studies of phospholipid-water mixtures. The Phase Rule and equations of thermodynamics of heterogeneous systems are applied in the analysis of calorimetric and dilatometric results for these systems. It is inferred that the approach in which a lipid-water mixture of low lipid content is regarded as a one-component system is misleading and unhelpful. A mixture containing water and a pure synthetic phospholipid is a binary system, and the Phase Rule can be applied to it in a straightforward manner. Non-isothermal transitions and invariant three-phase reactions of the eutectic, peritectic and polytectic type can be encountered in lipid-water systems, like in other binary mixtures. The concentration dependence of the enthalpy of the isothermal three-phase transition yields a well-known Tammann triangle. For the volume change at such transition an analog of the Tammann triangle can be drafted which can be useful in interpretation of dilatometric and densitometric data for heterogeneous binary systems.The literature thermodynamic data for the aqueous lipids are analyzed on the basis of the phase diagram of the DPPC-water system. The measured values of the transition enthalpy and volume change at the pre- and main transitions refer to invariant phase reactions. The measured heat capacities and thermal coefficients of expansion actually characterize the biphasic lipid-water mixtures and may reflect phenomena specific for heterogeneous binary systems only. A reinterpretation of the literature DSC data for the DPPC-water system at temperatures below zero is suggested.Experience gained in the study of equilibrium phase diagram, kinetic and colloidal aspects of phase behaviour of dioctadecyldimethylammonium chloride-water system indicates that the common procedures of the sample preparation of lipid-water mixtures may lead to the states which are non-equilibrium in two respects: the system contains a metastable phase, and the phase is dispersed to such an extent that an irreversible colloidal structure is formed. Definitive phase studies of the phase behaviour of phospholipid-water systems in the whole concentration range are urgently needed.     

Boiling temperatures and excess thermodynamic functions of 2-propanol-n-alkyl propanoate solutions

Boiling temperatures of five binary systems are measured by ebuliometer in the pressure range of 5.333?C101.3 kPa. The compositions of equilibrium vapor phases in the systems are calculated using the constructed saturated vapor pressure isotherms as a base. The excess Gibbs energies, excess enthalpies, and excess entropies of solutions are calculated from our data on liquid-vapor equilibria. Regularities in the changes of phase equilibria and thermodynamic properties of solutions with the composition and temperature of the system are established. Vapor-liquid equilibria in the systems are described by the Wilson and NRTL equations.     

Formation of supercooled liquid solutions from nanoscale amorphous solid films of methanol and ethanol

Molecular beam techniques are used to create layered nanoscale composite films of amorphous methanol and ethanol at 20 K. The films are then heated, and temperature programed desorption and infrared spectroscopy are used to observe the mixing, desorption, and crystallization behavior from the initially unmixed amorphous layers. We find that the initially unmixed amorphous layers completely intermix to form a deeply supercooled liquid solution after heating above T(g). Modeling of the desorption kinetics shows that the supercooled liquid films behave as ideal solutions. The desorption rates from the supercooled and crystalline phases are then used to derive the binary solid-liquid phase diagram. Deviations from ideal solution desorption behavior are observed when the metastable supercooled solution remains for longer times in regions of the phase diagram when thermodynamically favored crystallization occurs. In those cases, the finite lifetime of the metastable solutions results in the precipitation of crystalline solids. Finally, in very thick films at temperatures and compositions where a stable liquid should exist, we unexpectedly observe deviations from ideal solution behavior. Visual inspection of the sample indicates that these apparent departures from ideality arise from dewetting of the liquid film from the substrate. We conclude that compositionally tailored nanoscale amorphous films provide a useful means for preparing and examining deeply supercooled solutions in metastable regions of the phase diagram.     

Direct calculation of solid-vapor coexistence points by thermodynamic integration: application to single component and binary systems

We present a new thermodynamic integration method that directly connects the vapor and solid phases by a reversible path. The thermodynamic integration in the isothermal-isobaric ensemble yields the Gibbs free energy difference between the two phases, from which the sublimation temperature can be easily calculated. The method extends to the binary mixture without any modification to the integration path simply by employing the isothermal-isobaric semigrand ensemble. The thermodynamic integration, in this case, yields the chemical potential difference between the solid and vapor phases for one of the components, from which the binary sublimation temperature can be calculated. The coexistence temperatures predicted by our method agree well with those in the literature for single component and binary Lennard-Jones systems.     

Phase equilibria and critical phenomena in the cesium nitrate-water-diethylamine ternary system

Phase equilibria and critical phenomena in the cesium nitrate-water-diethylamine ternary system were studied by the visual-polythermal method over the temperature range 60–150 °C, where the boundary binary liquid system was characterized by stratification with a lower critical solution temperature (LCST). The introduction of cesium nitrate into the water-diethylamine system decreased the LCST of this system from 146.1 to 69.3°C and lowered the mutual solubility of the components. The diethylamine distribution coefficients between the aqueous and organic phases were calculated for monotectic equilibria at various temperatures. The salting out of diethylamine with cesium nitrate grew stronger as the temperature increased. The conclusion was drawn that the isotherms of the phase states of the system substantiated the generalized scheme of topological transformations of phase diagrams for salt-binary solvent ternary systems with salting out. The salting out effects of cesium and potassium nitrates on the water-diethylamine binary system were compared.     

Extension of the exp-6 model to the simulation of vapor-liquid equilibria of primary alcohols and their mixtures

Configurational-biased Gibbs ensemble Monte Carlo simulations were performed to obtain the phase behavior of the homologous series of primary alcohols from ethanol to 1-heptanol. Molecular interactions in these systems are modeled by a newly developed exp-6 potential in combination with a Coulombic intermolecular potential. Some of exp-6 potential parameters required to describe these alcohols were taken from the previous literature data reported for methanol and n-alkanes. The oxygen's potential parameters were optimized to fit the coexistence curve of these alcohols to the experimental data. Simulated values of saturated liquid and vapor densities, vapor pressures and critical constants of the alcohols are in good agreement with experimental data. The efficiency of the new model in the prediction of binary phase diagram of water/ethanol and n-hexane/1-propanol mixtures is also evaluated. The calculated mole fractions in the vapor and liquid phases of these binary mixtures also show satisfactory agreement with the experimental data.