Miscibility Temperature Research Articles

The liquid–liquid phase diagram of sulfur+biphenyl

We have studied the liquid–liquid phase diagram of sulfur+biphenyl. Larkin, Katz, and Scott [J. Phys. Chem. 71, 352 (1967)] reported a liquid–liquid phase separation with an upper critical solution point (UCSP) at 381 K, complete miscibility between 381 K and a lower critical solution point (LCSP) at 494 K, and a polymerization line between the polymerization point of pure sulfur at 432 K and a point on the high temperature coexistence curve near the LCSP. We found that the phase transition temperatures for the higher temperature miscibility gap increased with time. We attribute this shift to chemical reaction between the sulfur and the biphenyl. Therefore, the transition temperatures which we obtain are necessarily upper limits to the true transition temperatures, but are in agreement with the results of Larkin et al. We find that the polymerization line meets the coexistence curve at 0.730±0.005 mole fraction sulfur and 498±2 K, whereas the LCSP, as indicated by the ratio of volumes of coexisting phases, is at 0.750±0.005 mole fraction sulfur and 496±3 K. Such a shift of the LCSP away from the end of the polymerization line is consistent with proximity to a nonsymmetrical tricritical point [Wheeler, J. Chem. Phys. 81, 3635 (1984), and references therein]. If we describe the shape of a branch of the high temperature coexistence curve by ‖x−xc ‖/xc =Bt β, where x is the mole fraction of sulfur, xc is the mole fraction at the critical point, and t is the reduced temperature ‖T−Tc ‖/Tc (with T the temperature and Tc the critical temperature), then the polymer-rich branch for sulfur+biphenyl is described well with β=0.25, the value appropriate for a nonsymmetrical tricritical point. The polymer-poor branch could not be described by any of the values of β thought to be possible (i.e., 0.25, 0.325, 0.50, 0.67, or 1.00). We searched carefully for a three-phase region near the LCSP and found none.

A Comparison of Tem and Apfim to the Interpretation of Modulated Microstructures

Interpretation of fine-scale microstructures containing high volume fractions of second phase is complex. In particular, microstructures developed through decomposition within low temperature miscibility gaps may be extremely fine. This paper compares the morphological interpretations of such complex microstructures by the high-resolution techniques of TEM and atom probe field-ion microscopy (APFIM).The Fe-25 at% Be alloy selected for this study was aged within the low temperature miscibility gap to form a <100> aligned two-phase microstructure. This triaxially modulated microstructure is composed of an Fe-rich ferrite phase and a B2-ordered Be-enriched phase. The microstructural characterization through conventional bright-field TEM is inadequate because of the many contributions to image contrast. The ordering reaction which accompanies spinodal decomposition in this alloy permits simplification of the image by the use of the centered dark field technique to image just one phase. A CDF image formed with a B2 superlattice reflection is shown in fig. 1. In this CDF micrograph, the the B2-ordered Be-enriched phase appears as bright regions in the darkly-imaging ferrite. By examining the specimen in a [001] orientation, the <100> nature of the modulations is evident.

Investigation of phase equilibria in mixtures of polypropylene oxide and water

Mixtures of polyxypropylene polyols with water are typical systems with a lower critical miscibility temperature whose position is proportional to the concentration of end hydroxyl groups independently of the degree of branching of the polyethers. Replacement of low-molecular products with water. The polydispersity of the specimens of the polyoxypropylene polyols has a substantial effect on the phase diagrams, whose shapes are principally determined by the presence of the high-molecular fractions.

Investigation of the nature of phase separation in the system polydimethoxyethylene—water

The method of temperature spectroturbidimetric titration has been used to study the solubility of two specimens of polydimethoxyethylene in water. It has been shown that the reduction in the solubility of polydimethoxyethylene in water when heated to 50–60°C is connected with phase separation of the liquid-liquid type with a lower critical miscibility temperature. The maximum fraction of precipitated polymer that is reached has been found to be directly proportional to the concentration of the initial solution. For the specified system and the PET turbidimeter, the optimum conditions have been found for carrying out the spectroturbidimetric titration: these ensure the most complete transformation of the polymer into a colloidally dispersed condition whose parameters, in the method of turbidimetric titration, give information about solubility and the molecular weight distribution of the polymer, which is connected with the solubility. An increase in the degree of stereoregularity of polydimethoxyethylene increases its solubility in water.

Phase separation behaviour of a metal-organic derived sodium silicate glass

The phase separation behaviour of an 18.56 mol % Na2O-SiO2 glass prepared via the standard glass preparation technique and the metallic-organic derived (MOD) method have been studied and contrasted. Our results suggest that at this composition the miscibility temperature is significantly elevated when a MOD preparation procedure is used. The origin of this effect appears to be related to the enhanced water content in the glass prepared by the MOD procedure.

The role of diffusion in determining the controlling creep mechanisms in Al-Zn solid-solutions: Part II

The theoretically appropriate diffusion coefficients for creep in binary solid solutions are verified in Part I. Furthermore it is observed that the observed composition dependence of the steady-state creep rate for Al-Zn alloys may be described by these diffusion coefficients. Part II further examines the creep behavior of the Al-Zn system. Stress exponent and activation energy measurements indicate that a transition from climb-controlled to glide-controlled creep occurs as the Zn concentration increases. It is found that the observed creep behavior can be explained by a combination of climb and glide controlled creep processes. Glide creep is dependent on the chemical diffusivity which approaches zero at the miscibility gap composition and temperature. This causes a minimum in the creep rate at the miscibility gap composition. By using a sequential summation of a semiempirical climb equation and the Cottrell-Jaswon glide equation, the absolute magnitude of the observed creep rate can be rationalized for all compositions. The observed behavior of the stress exponent and activation energy is also predicted.

Comparison of Methods for the Assay of Ethanol in Pharmaceutical Preparations, Cosmetics, and Alcoholic Beverages

Abstract Different methods, dichromate (iodometric and colorimetric), vanadate (spectrophotometric), critical miscibility temperature, and gas chromatography, were investigated for the determination of ethanol in various products. The results were compared with those from the official specific gravity method (USP and Egyptian Pharmacopoeia). The advantages and disadvantages, as well as the precision, are given for each method.

Effects of Components Except the Alkalies on the Phase Separation of Alkali Silicate Glasses

As basic compositions, 15Na2O⋅85SiO2 (Na glass) and 25Li2O⋅75SiO2 or 30Li2O⋅70SiO2 (Li glass) were selected and the effects of addition or substitution of the components such as MgO, CaO, BaO, ZnO, CdO, PbO, Al2O3, B2O3, TiO2, ZrO2, SiO2, GeO2 and P2O5 on miscibility temperature (Tm), viscosity, texture of phase separated glass etc. were examined.The addition of small amount of the divalent components lowered Tm of Na glass in the order CaO<BaO<CdO<ZnO<MgO<PbO. But even in the case of CaO the introduction to the amount contained in commercial soda-lime-silica glasses (e. g. sheet glass) prevented the phase separation occurring. Among the polyvalent components, the effects of P2O5 and Al2O3 on Tm were especially remarkable, the former raised and the latter lowered it. B2O3 lowered Tm at first and then raised it with increasing amount of the addition, for viscosity B2O3 gave reverse change, though. In the glasses added the components which raised Tm, the interconnected two phase structures were liable to be observed after heat treatment. Similar results were also obtained in Li glass.It was showed from the plot of Tm of 15Na2O⋅85SiO2+2.5ROx glasses against ionic field strength of added cations that (i) in case of the network modifiers, Tm rose with increasing ionic field strength of added cation, (ii) this was also true for network formers, but (iii) this relation became inverse for intermediates. The possible reason was discussed from the point of the effects of added cations on the compatibility between SiO2 and Na containing phase.Moreover it was pointed out that the chemical durability was low in the glass with high Tm.

Studies of Poly-2-vinylpyridine. VI. Thermodynamic Data on Solutions of Poly-2-vinylpyridine in Various Solvents

Abstract The viscosities of dilute solutions of several fractions of poly-2-vinylpyridine have been measured in methanol, isopropanol, chloroform, benzene, dioxane, and methyl ethyl ketone at different temperatures, ranging from 15 to 65°C. The osmotic pressures of dilute solutions of fractions of the polymer have been measured in dioxane at 10, 25, 40, and 65°C. The data have then been analysed using the theories of Flory and Fox and of Kurata and Stockmayer. The results obtained are as follows: (1) the entropy parameters, ψ1, for the solutions of poly-2-vinylpyridine in methanol and isopropanol are negative, while the critical miscibility temperatures, θ, are positive and extraordinary high; (2) ψ1 is positive and θ is negative in chloroform; (3) These parameters behave regularly in benzene and dioxane. Qualitatively the same results have also been obtained with the poly-4-vinylpyridine fraction in several solvents, including methanol and chloroform. These results show that in alcohols and chloroform the temperature coefficient of the solubility of polyvinylpyridines is negative, and indicate the presence of strong interaction between segments and solvents, probably due to hydrogen-bond formation.

Properties of dilute polymer solutions III: Intrinsic viscosity/temperature relationships for conventional polymethyl methacrylate

Intrinsic viscosity/temperature relationships from 0° to 120°C determined in a variety of solvents on sixteen fractions of conventional polymethyl methacrylate ranging in molecular weight from 10 5 to 2.6 × 10 6 yield, through comparison with existing theory, information on both the intrachain forces and the thermodynamic interactions with the solvent, and their effect on the average dimensions of the polymer coil. The observation that the viscosity at the critical miscibility temperature Θ is 4.8 × 10 −4M 1 2 independent of temperature, from 30° to 70° at least, indicates an average linear dimension for the polymer coil twice that expected for free rotation about the chain bonds; the observed temperature independence indicates that the trans and gauche minima in the potential energy profile on rotation have the same energy. The heat of mixing and the Θ-temperature for polyisobutylene, polystyrene, and polymethyl methacrylate in different solvents are shown to be generally related to (and to increase with) the difference between the Hildebrand solubility parameters for the polymer and the solvent, and other unknown factors which in specific instances play a dominant role. The abnormally low entropy of mixing observed for these solutions indicates a high degree of local order in the packing of solvent molecules and polymer segments as a result of specific interactions dependent on the chemical and geometrical structure of the polymer-solvent pair.

Column fractionation of polymers

AbstractMixtures of fractions of atactic polystyrene dissolved in cyclohexane were resolved by elution from a column at different temperatures. A coarse‐grained Ottawa sand was used to minimize the surface area of the support. Comparison with the critical miscibility temperature data of Schultz and Flory shows that the lower molecular weights are eluted from the column at a temperature somewhat below the critical miscibility temperature, as expected, but for molecular weights above 3 × 105 the elution temperature increases abruptly, and even exceeds the critical miscibility temperature. This rapid rise occurred at 1.5 × 105 when the surface area of the support was increased by use of a very fine Celite. We conclude that for the higher molecular weights additional thermal energy is required to desorb the polymer, and hence the partitioning of these species is not determined solely by solubility considerations. Concerning the efficiency of the column extraction, considerable resolution of each component was obtained, and attempts to determine the M̄w/M̄n ratios of the individual components were at least partially successful. As predicted by theory, for a given molecular weight interval the range of elution temperature was increased fivefold by the use of a mixed solvent, benzene–ethanol, in place of the single poor solvent, cyclohexane. Customary fractionation procedures are very inefficient when applied to high‐melting crystalline polymers. For these polymers we investigated selective precipitation upon a column having a temperature gradient, rather than elution from the column. For dilute solutions, amorphous phase separation may precede crystallization, particularly in the case of polymers whose rates of crystallization are low, owing to the presence of bulky side groups. The column precipitation method failed to give improved fractionation of polyacrylonitrile, owing to phase separation of the dimethylformamide–heptane mixture part way down the column. On the other hand, good resolution was obtained for an unfractionated sample of isotactic polystyrene up to 1.5 × 106. Molecular weights above this level were compressed into a narrow band at the top of the column. Thus, if the distribution is extremely broad, a second fractionation with a different solvent:‐ precipitant ratio may be required. Even so, a single pass through the column resulted in a better resolution than that obtained by a large‐scale, two‐stage extraction‐precipitation procedure, indicating that the column precipitation method does posses an advantage for the fractionation of crystalline polymers.

Solid Solution in Zinc Blende Type A2IIIB3VICompounds

Ranges of solid solution have been investigated in systems composed of either two A2 IIIB3VI compounds or one AIIIBV and one A2IIIB3VI compound. It is found that in practically all cases considered complete solid solution throughout the whole range of composition can be obtained, but that in some cases this equilibrium condition can only be reached under special conditions of temperature and time of annealing. The possibility of ordering and of the occurrence of low temperature miscibility gaps is investigated.

Solid Solution in AIIIBVCompounds

Ranges of solid solution have been investigated in systems composed of two AIIIBV compounds, particularly GaSb-InSb, GaAs-InAs and InAs-InSb. It is found that in practically all cases considered complete solid solution throughout the whole range of composition can be obtained, but that this equilibrium condition can only be reached under special conditions of temperature and time of annealing. The work includes the investigation of solidus curves and the possible presence of low temperature miscibility gaps. In all cases, it is found that if normal annealing methods are used, equilibrium can be attained with a reasonable length of time of anneal only in the case of compressed powder specimens. Consideration is given to the methods available for producing alloys in equilibrium in the solid form.

The influence of hydrophilic colloids on the miscibility of phenol and water

AbstractThe influence of certain hydrophilic materials on the miscibility of phenol and water is examined. The critical solution temperature (C.S.T.) is lowered by sodium stearate and tannin, and raised by colophony, starch, agar and gelatin. For stearate and tannin systems it is found that a linear relation obtains between the logarithm of the depression and the logarithm of the concentration. Small quantities of these solutes can be estimated by measuring the change in C.S.T. Precipitation occurs in systems containing starch, agar and gelatin, and dissolution temperatures corresponding to the production of a standard turbidity are determined. For colloidal materials of this kind, the observation of the miscibility and dissolution temperatures furnishes a method of identification.

Statistical Mechanics of Dilute Polymer Solutions. II

New thermodynamic relationships applicable to dilute solutions of heterogeneous high polymers are derived. The function previously given to express the interaction between two polymer molecules of equal size is modified to include chemically similar polymer molecules differing in size. With the aid of this more general pair partition function the mutually excluded volume for a pair of polymer molecules is easily computed. The osmotic pressure for a dilute solution of a heterogeneous polymer may be expressed in virial form through the application of conventional methods for treating imperfect gases. The second virial coefficient in the series expansion for the osmotic pressure is readily obtained but it is necessary to resort to the hard sphere approximation for estimation of the third coefficient. The third coefficient is much larger than was indicated by earlier theories now known to be inapplicable to dilute solutions, and plots of π/c vs. c must be appreciably curved if the slope is great. Similar expressions are derived for Hc/τ obtained from light scattering measurements. For a dilute solution of a homogeneous polymer the value of the second coefficient in either the osmotic pressure or light scattering expression is not entirely independent of molecular weight, as predicted by earlier theories. The effect of heterogeneity on the second coefficient in these expressions is investigated for the special case of a dilute solution of two polymers differing only in molecular weight, from which it follows that the ratio of the second coefficients in the light scattering and osmotic pressure relations may be either equal to two, or greater or less than that value, depending on the heterogeneity ratio. At the critical miscibility temperature Θ, the excluded volume vanishes and the present treatment becomes identical with previous theories. The latter should be valid for all concentrations only at the unique temperature T=Θ. The primary parameters κ1 and ψ1 governing the heat and entropy of interaction between polymer segments and solvent molecules are difficult to evaluate solely from thermodynamic measurements on dilute solutions except at T=Θ.

(9〜10)臺灣産石油の溶劑抽出に關する研究(第16〜17報)

(9〜10)臺灣産石油の溶劑抽出に關する研究(第16〜17報)

CCCLXVIII.—The influence of dissolved salts on the mutual miscibility temperature of the systems ethyl alcohol or methyl alcohol–paraffins

CCCLXVIII.—The influence of dissolved salts on the mutual miscibility temperature of the systems ethyl alcohol or methyl alcohol–paraffins