Phase Diagram Of Solutions Research Articles

Lower critical solution temperature and hydrophobic hydration in aqueous polymer solutions

Phase diagrams of aqueous solutions of poly(N-vinyl caprolactam) (PVCL), N-vinyl caprolactam copolymer with vinylamine (3.8 mol%) (CP(VCL-VA)), and poly(N-vinyl propylacetamide) (PVPA) were shown to be binodal curves with lower critical solution temperatures (LCST) in the range 304–313.5 K and critical concentrations in the range of 0.02–0.08 polymer weight fraction. Aqueous solutions of N-vinyl caprolactam copolymer with N-vinyl pyrrolidone (80 mol%) (CP(VCL-VP)) remained homogeneous in the entire region of the liquid state of water. The enthalpy of mixing with water of PVPA and CP(VCL-VP) was negative and the curve was concave over the entire range of composition at 298 and 308 K. The excessive heat capacity and partial heat capacity at infinite dilution of PVPA were positive, proving the hydrophobic character of hydration of this polymer. In contrast, these parameters were negative for CP(VCL-VP), revealing hydrophilic hydration. Hydrophilic hydration was predominant in solutions which were homogeneous over a wide temperature range, whereas hydrophobic hydration predominated in solution of polymers with LCST.

Phase Diagrams of Aqueous Solutions of Polycarboxylates in the Presence of Divalent Cations

Phase separation and gelation phenomena induced by addition of divalent cations in aqueous solutions of synthetic and natural polycarboxylates have been investigated by comparison of their phase diagrams. Three major types of behavior may be identified on the basis of the position and shape of the demixing line in the phase diagram, regardless of the chemical structure of the polymer. We propose a model for quantitative prediction of the demixing and sol-gel transition. The relevant parameters introduced are the neutral units, the charge density, and the cation/polyanion affinity, all of which are responsible for inter- and intramolecular complexes. Besides this general scheme, the local configuration of the backbone in natural polymers seems to promote intermolecular cross-links, leading to a large gel phase.

Liquid—liquid phase diagrams for binary polymer solutions from a perturbed hard-sphere-chain equation of state

The perturbed hard-sphere-chain (PHSC) equation of state for multicomponent mixtures is presented as a generalization from the equation of state for pure fluids. The reference term, based on Chiew's equation of state for hard-sphere chains, requires no mixing rules. Only the attractive perturbation requires van der Waals one-fluid mixing rules. Cross parameters needed in the perturbation are obtained using pure-fluid parameters and simple combining rules. The simplifying physical assumptions required to reduce the perturbation term to the Flory χ parameter are given. Specific interactions are included by adapting the model of ten Brinke and Karasz. Model calculations for binary mixtures demonstrate that the PHSC equation can predict lower critical solution temperatures, upper critical solution temperatures and closed partial-miscibility loops. Special attention is given to the effects of polymer molecular weight, pressure, differences in segment size and differences in segment interaction energy.

Peculiarities of ferro-antiferroelectric phase transitions

Abstract The peculiarities of FE-AFE phase transitions are analyzed on the basis of a model of two interaction order parameters taking into account the anharmonicity of elastic energy. The obtained results are compared with experimental phase diagrams for PZT-based solid solutions.

Liquid crystallinity of levan/water/starch solutions

Transmitted light measurements performed with a UV-visible spectrophotometer were used to characterize how starch affects the position of boundaries on the phase diagram for dilute aqueous solutions of levan (a branched polymer of fructose). Data were collected in the range 15 to 70°C; the minimum concentrations required for separation of a nematic phase and the minimum concentration required for a fully nematic solution were identified within this range. While “hard” interactions (repulsion between rod-like molecular segments) dictate the formation of a liquid crystalline phase at and above ambient temperature in the absence of starch, “soft” interactions become more significant as solutions are cooled toward ambient when starch is present. Small amounts of starch might be used as a filler to modify the mechanical properties (while retaining the process-related benefits) of levan films cast from liquid crystalline solution.

Study of the phase separation in polymer solutions using the pair approximation of the CVM: analytical solution of the problem

The phase diagrams of polymer solutions are studied using the pair approximation of the Cluster Variational Method (CVM). In this model the solvent (oligomers) and the solute (polymers) are chains with different lengths. In particular, the dependence of the phase diagram on the lengths of the components of the mixture, on the lattice, and on the relative size of the components of the mixture is investigated. The critical temperature and the critical concentration are also studied. Some comparison of our results with the Flory and Guggenheim approximations are done for the symmetric case (when oligomer chains and polymer chains have the same length) and the asymmetric case (when oligomer chains and polymer chains have different length). A novel technique to solve the set of equations derived from the CVM is presented, and an analytical solution of the problem is given

Nuclear magnetic resonance approach to the characterization of the phase diagram of polyacrylonitrile in ternary solutions

This work deals with the properties of the temperature-concentration phase diagram of ternary poly-acrylonitrile solutions that were mainly observed from the transverse magnetic relaxation of protons attached to polymer chains, used to disclose the presence of solid-state domains. The binary solvent was a mixture of dimethylformamide (DMF) and water; the molar fraction of monomeric units was varied from 0 to 0.5, while the relative molar fractions of DMF and water were 1:1 or 2:1. The solvent quality was found to decrease upon addition of water. A curve (liquidus) that relates the temperature of formation of solid-state domains to the initial polymer concentration in solution was drawn from nuclear magnetic resonance (n.m.r.). The demixing part of the liquidus, determined as a plateau from n.m.r., was identified on observing a cloud-point curve. The main feature of the phase diagram concerns the specific behaviour of solutions observed whenever the concentration of disordered segments becomes lower than half the initial polymer concentration.

Phase Diagram and Rayleigh-Brillouin Scattering in Binary Solutions of Organic Compounds with Miscibility Gap

Abstract The phase diagrams of binary solutions of C6H14—CH3OH and C6H12—CH3OH have been determined. The thermodynamic quantities of mixing, such as concentration-concentration fluctuation in the long wavelength limit, Scc (O, c, T), have been derived by using the treatment of Bhatia and March. The Rayleigh-Brillouin scattering has also been investigated for these solutions. Scc (O, c, T)'s obtained by Rayleigh-Brillouin experiments were in agreement with those obtained by thermodynamical treatment of the phase diagram. The Rayleigh peak intensity of C6H14—CH3OH system shows a weak position dependence from the interfacial boundary, in the case of the coexistence of two phases, while that of C6H12—CH3OH does not shown such an unusual behavior. These different behaviors are discussed in terms of the densities of the components.

Flame Luminosity of Methanol/Additive Fuel Mixtures

Abstract Luminosity of pool fires from methanol/additive mixtures is investigated theoretically and experimentally. Phase diagrams of solutions are used to explain the transient behavior of flame luminosity of binary fuel mixtures. A model, based on solution theory, is developed to quantify the flame luminosity of methanol/additive binary fuel mixtures from the luminosities of the individual components and an interaction coefficient. The theoretical results agree well with the experimental data. The luminosity of methanol additive mixtures is found to be a function of the mixture's carbon/hydrogen (C/H) ratio. Flame luminosity increases with increasing mixture C/H ratio to a maximum (occurring around C/H = 0.35), and then decreases slightly beyond that point. Additives that form positive azeotropes with methanol and that have high C/H ratio are found to be the best candidates for enhancing the luminosity of methanol flames.

Determination of .chi. from liquid-liquid phase data and the computation of phase diagrams for quasi-binary polymer solutions and blends

A generalized Flory-Huggins theory is described that permits the investigation of the phase behavior for quasi-binary polymer solutions or blends in which, for blends, both components may be polydisperse. A temperature- and concentration-dependent χ interaction parameter is used. Itis demonstrated that the χ parameter may be readily extracted from experimental phase data. This is illustrated by using a robust fitting procedure to obtain the composition and temperature dependence of χ for the cyclohexane/ polystyrene system from experimental phase data. The result (eq 22) is in excellent agreement with previous determinations of χ for this system, and the method employed here has several advantages over other approaches

Semi‐interpenetrating polymer networks with controllable morphology ‐ arrest of demixing by thermoreversible gelation

AbstractSemi‐interpenetrating polymer networks with well defined morphologies were obtained using a three‐step process, separating morphology formation and polymerization/crosslinking. Different phase textures were formed when (spinodal) liquid/liquid demixing of a solution of atactic polystyrene in methacrylate monomers was arrested by thermoreversible gelation (vitrification) of the polymer‐rich phase at a desired stage. Subsequent UV‐polymerization of the methacrylate allowed to study the morphology by transmission electron microscopy. Phase diagrams of polymer solutions with low and high viscosities are reported. Depending on the initial solution viscosities and the applied cooling conditions, morphologies both with a dispersed as well with a continuous polystyrene phase could be obtained at PS concentrations already below 10 %. Mechanical measurements indicated only partial demixing in the semi‐IPN's.

Magnetization, neutron-, and resonant x-ray-diffraction studies of U0.85Th0.15Sb.

The magnetic phase diagram of USb-ThSb solid solutions was reported 10 years ago, but we have reexamined single crystals of (nominal) U 0.85 Th 0.15 Sb following some unusual results found using synchrotron x-ray techniques. We show by magnetization that the material becomes antiferromagnetic at T N ∼190 K, but that a strong ferromagnetic moment develops below T C =145 K, and reaches 2.7 μB per U atom in high fields and at low temperature. Neutron diffraction (in zero field) on the same (and another) crystal indicates that the initial ordering near 190 K is incommensurate with q inc ∼0.44 reciprocal-lattice units (r.l.u)

Peculiarities of ferro-antiferroelectric phase transitions. 1. Effects initiated by elastic energy anharmonicity

On the base of the model of two interacting order parameters taking into account the anharmonicity of elastic energy the peculiarities of phase transitions between FE and AFE states are analyzed. The obtained results are compared with experimental phase diagrams for PZT-based solid solutions. Phase transitions in PLZT system are considered in detail. It is shown that the peculiarities of phase transitions in this system are described in the frames of the ideas of FE-AFE phase transitions developed in the present paper.

Phase diagrams of quasi-binary polymer solutions and blends

Abstract A generalized Flory-Huggins theory is presented for use in fitting and predicting liquid-liquid phase diagrams of quasi-binary polymer solutions and blends, in which one component may be polydisperse. A temperature- and concentration-dependent χ parameter is employed. As has been demonstrated previously for simple binary systems, the form chosen for χ is sufficient to fit phase diagrams having upper and lower critical solution temperatures (UCST and LCST), combination of the two with the LCST lying above the UCST, closed loop and hour-glass shapes. In extending this work to quasi-binary systems, the phase diagrams obtained are compared with those for binary solutions and blends. It is illustrated how polymer solutions, in which the polymeric component has the same weight-average molecular weight and even the same polydispersity index, although having identical spinodals, may exhibit markedly different cloud-point curves. Comparison is also made with experimental data determined on a model quasi-binary system. Such comparisons may be used to extract the temperature and concentration dependence of χ for the system.

Quantitative theory of the globule-to-coil transition. 4. Comparison of theoretical results with experimental data

Quantitative theoretical results are compared with the available data of real experiments and computer simulations on single chain gyration and hydrodynamic radii and on binodal and spinodal curves of a polymer solution phase diagram. The comparison manifests a rather good agreement of the mean-field theory with experiments. However, the question of the observation of equilibrium polystyrene-cyclohexane single chain globules before solution precipitation remains to be discussed. Criterion of the globularity of an experimentally observed chain is discussed

Phase diagrams of quasi-binary polymer systems with LCST/UCST spinodals and hour-glass cloud-point curves

A generalized Flory-Huggins theory is utilized to investigate liquid-liquid phase diagrams of quasi-binary polymer solutions and blends, in which one component may be polydisperse. A temperature and concentration dependent χ parameter is employed. It is illustrated that a polymer solution, in which the polymeric component has a Schulz-Zimm molecular weight distribution, may exhibit combined lower critical solution temperature/upper critical solution temperature spinodals and hour-glass cloud-point curves (CPCs). This is a direct consequence of the critical points being offset from the extrema of the CPCs and spinodals for quasi-binary systems, in contrast to true binary systems (such as solutions and blends of monodisperse polymers). Thus, for quasi-binary systems, it may be hazardous to infer the behaviour of spinodals from observations of CPCs or vice versa.

Transient phase diagram of ternary polyetherimide solutions: effect of polymer association

Effects of chain association on the demixing behaviour of ternary solutions containing a polyetherimide in a solvent-non-solvent mixture are investigated. Time evolution of the temperature of demixing of the solutions is observed over 1 month. It is ascribed to a slow dissociation process involving charge transfer and hydrogen bonding complexes in the system. The observed demixing curves are characterized by high values of the precipitation threshold. A model based on the Flory-Huggins theory of polymer solutions is developed to explain this effect, and an intermolecular association parameter is introduced into the discussion. Fairly good agreement is obtained between calculated and experimentally found demixing curves. The fraction of associated electron donor or acceptor groups of a polymer chain is predicted by the model.

Film formation of poly (p-phenylene terephthalamide) from sulphuric acid solution.

A novel process for the formation of poly (p-phenylene terephthalamide) (PPTA) film from liquid crystalline sulphuric acid solution was developed. A homogeneous and transparent PPTA film is very difficult to obtain from sulphuric acid solution owing to the highly anisotropic flow properties of the solution. A biaxially balanced PPTA film could be formed by using the optically anisotropic to isotropic transition appeared in the phase diagram of the PPTA sulphuric acid solution. The phase transition was generated by controlling temperature and/or polymer concentration of the solution. The anisotropic solution was cast on a flat glass plate. The cast dope was carried into a conditioning chamber (air oven) in which the phase transition occurred before it was immersed into the coagulation bath. The isotropic cast dope was coagulated and dried holding dimensions constant. The adjustment of temperature and water content of the cast dope plays an important role in the process and directly affects the properties of the film obtained. The conditioning at 100°C was suitable for the film properties in a series of experiments. The Young's modulus of 14 GPa and tensile strength of 450 MPa were obtained for the film heat-treated at 350°C during 20min. This process can be applied to a continuous large scale process.

Thermodynamic properties of aqueous solutions of ammonium Nitrate salts

We present Differential Scanning Calorimetry (DSC) results on Hydroxyl Ammonium Nitrate (HAN) solutions and Triethanol Ammonium Nitrate (TEAN) solutions with varying concentrations. These results are used to generate phase diagrams of these solutions. The results of the melting points of these liquids are compared with the theoretical calculations of the depression of melting points. The melting temperatures of the HAN solutions at some specified concentration range are predicted rather well using the two electrolyte assumption. The phase diagram of the TEAN solutions explains an instability with respect to phase separation of this liquid.

Behavior of Miscibility Gaps in the Phase Diagrams of III-V Semiconductor Solid Solutions: Quaternary Systems of the Type AxB1-xCyD1-y

The behavior of miscibility gaps in liquid-solid phase diagrams has been studied schematically for III-V semiconductor quaternary solutions of the type AxB1-xCyD1-y such as GaInPAs and AlInPAs. The topological features of the liquidus surface affected by solid immiscibility have been the focus of our examination. Liquidus surfaces below the melting temperatures of the constituent binary semiconductors are presented for typical geometric patterns of a miscibility gap. Liquidus surfaces around the melting temperatures are presented for two typical cases realized in systems such as GaInPAs and AlInAsSb.