Phase Behavior Of Binary Mixtures Research Articles

Phase Behavior of Isobutane + CO2 and Isobutane + H2 at Temperatures Between 190 and 400 K and at Pressures Up to 20 MPa

Mixtures containing isobutane, carbon dioxide, and/or hydrogen are found in various industrial processes, green refrigerant systems, and the growing hydrogen industry. Understanding the thermophysical properties of these mixtures is essential for these processes, and depends on reliable experimental data. Making use of an automated static-analytical apparatus, measurements were made of the phase behavior of binary mixtures of isobutane with CO2 and with H2, extending the range of available data for both mixtures. Measurements of the system isobutane + CO2 were carried out along three isotherms at temperatures of (240, 280, and 310) K with pressures from the lower limit of the sampling system (~ 0.5 MPa) to the mixture critical pressure. The results exhibit good agreement with literature data. Measurements on isobutane + H2 were carried out along nine isotherms at temperatures of (190, 240, 280, 311, 339, 363, 375, 390, and 400) K with pressures up to 20 MPa, covering a much broader range of conditions than the one prior investigation. The results have been used to optimize temperature-dependent binary parameters in the Peng–Robinson equation of state with two different mixing rules. This approach was found to perform well in comparison to alternative models.

Solid-fluid phase behaviour in binary mixtures: A new classification focused on paraffinic systems

The solid-fluid phase behavior of mixtures is important in a variety of real situations of industrial interest, including paraffin precipitation from hydrocarbon reservoir fluids, supercritical extraction or precipitation processes, and cryogenic processes among others. In the case of binary mixtures with the presence of fluid and solid phases, such behaviors can yield different topologies in terms of critical lines, three-phase lines, critical end points and quadruple points. The classification proposed by Yamamoto et al. in 1989 for those topologies is probably the best known and most used one, besides being more complete than others when considering experimentally observed behaviors. Nevertheless, a number of publications and in particular two recent PhD theses developed in our groups, found other topologies which deviate from the types considered in Yamamoto's et al. classification. These two theses employed different modelling approaches, using equation of state models for describing fluid phases and differing essentially in considering each solid phase as either made of the heavy compound in pure state or made of a solid solution. The deviations from the types in Yamamoto's et al. classification are compiled and analyzed in this work. Moreover, a new classification is proposed for binary systems with varying degrees of asymmetry. Being motivated by the study of paraffin precipitation from reservoir fluids, this new classification, in contrast to Yamamoto's et al. classification, leaves out of consideration the lower temperature range (up to the triple point of the light component) while, on the other hand, it incorporates some possible behavior variations, in the temperature range of more practical interest, which are not accounted for in Yamamoto's et al. classification. The new classification is shown to cover all possible phase behavior evolutions in the binary series of methane or ethane or propane with a heavier n-alkane and also of carbon dioxide with a n-alkane, considering both, what is known so far in terms of experimental data, and some features predicted with different modelling approaches, which have not been confirmed yet at the experimental level.

Microstructural diversity, nucleation paths, and phase behavior in binary mixtures of charged colloidal spheres.

We study low-salt, binary aqueous suspensions of charged colloidal spheres of size ratio Γ = 0.57, number densities below the eutectic number density nE, and number fractions of p = 1.00-0.40. The typical phase obtained by solidification from a homogeneous shear-melt is a substitutional alloy with a body centered cubic structure. In strictly gas-tight vials, the polycrystalline solid is stable against melting and further phase transformation for extended times. For comparison, we also prepare the same samples by slow, mechanically undisturbed deionization in commercial slit cells. These cells feature a complex but well reproducible sequence of global and local gradients in salt concentration, number density, and composition as induced by successive deionization, phoretic transport, and differential settling of the components, respectively. Moreover, they provide an extended bottom surface suitable for heterogeneous nucleation of the β-phase. We give a detailed qualitative characterization of the crystallization processes using imaging and optical microscopy. By contrast to the bulk samples, the initial alloy formation is not volume-filling, and we now observe also α- and β-phases with low solubility of the odd component. In addition to the initial homogeneous nucleation route, the interplay of gradients opens various further crystallization and transformation pathways leading to a great diversity of microstructures. Upon a subsequent increase in salt concentration, the crystals melt again. Wall-based, pebble-shaped β-phase crystals and facetted α-crystals melt last. Our observations suggest that the substitutional alloys formed in bulk experiments by homogeneous nucleation and subsequent growth are mechanically stable in the absence of solid-fluid interfaces but thermodynamically metastable.

Solid–Liquid Phase Behaviors of Binary Mixtures of Various Partial Acylglycerols by Differential Scanning Calorimetry

AbstractMonoacylglycerol (MAG), diacylglycerol (DAG), and triacylglycerol (TAG) are impurities in biodiesel and a major cause of precipitation. Understanding the behavior of such acylglycerols is essential for predicting biodiesel cold flow properties (CFPs). The previous study on MAG/MAG binary mixtures shows that they tend to solidify by forming molecular compounds. In contrast, TAG/TAG mixtures, which have been studied extensively, are commonly eutectic or monotectic systems, in which each component solidifies separately. The present study focuses on binary mixtures of DAG/DAG and different acylglycerol pairs (MAG/DAG, TAG/MAG, and DAG/TAG), and determination of their solid–liquid phase behavior by differential scanning calorimetry. These mixtures are found to behave as eutectic or monotectic systems with no sign of compound formation. As DAG and TAG have lower contents than MAG in biodiesel and they are unlikely to form molecular compounds with MAG, it is suggested that DAG and TAG have little effect on the biodiesel CFPs.Practical Applications: Biodiesel has attracted much interest because its blending with conventional fossil diesel has become more standard with biofuel mandates. From an energy perspective, the solid–liquid phase behavior of acylglycerols will contribute to building prediction models for biodiesel CFPs.

Coarse-Grained Modeling of On-Surface Self-Assembly of Mixtures Comprising Di-Substituted Polyphenyl-Like Compounds and Metal Atoms of Different Sizes.

We use coarse-grained molecular dynamics simulations to investigate the phase behavior of binary mixtures of di-substituted polyphenyl-like compounds and metal atoms of different sizes. We have estimated the possible on-surface behavior that could be useful for the target design of particular ordered networks. We have found that due to the variation of system conditions, we can observe the formation of the parallel, square, and triangular networks, Archimedean tessellation, and “spaghetti wires.” All of these structures have been characterized by various order parameters.

Vapor-liquid equilibria for binary systems carbon dioxide + 1,1,1,2,3,3-hexafluoro-3-(2,2,2-trifluoroethoxy)propane or 1-ethoxy-1,1,2,2,3,3,4,4,4-nonafluorobutane at 303.15–323.15 K

The phase behavior of binary mixtures of carbon dioxide (CO2) and hydrofluoroethers (HFEs) has been studied. In particular, experimental vapor-liquid equilibrium (VLE) data for CO2 + 1,1,1,2,3,3-hexafluoro-3-(2,2,2-trifluoroethoxy)propane (HFE-449mec-f) and 1-ethoxy-1,1,2,2,3,3,4,4,4-nonafluorobutane (HFE-7200) at temperatures of 303.15, 313.15, and 323.15 K are reported. The VLE data were measured using a static-type apparatus and then correlated using the Peng-Robinson equation of state with the van der Waals one fluid and Wong-Sandler-NRTL mixing rules. Reasonable correlation results were obtained from the Peng-Robinson equation of state with both the van der Waals one fluid and the Wong-Sandler-NRTL mixing rules. The GC-SAFT-VR equation also gave good predictions of the phase behavior. Additionally, the group contribution SAFT-VR (GC-SAFT-VR) equation was used to predict the experimental VLE in good agreement with the experimental data, as well as the full p,T phase diagram for both systems.

Demixing and tetratic ordering in some binary mixtures of hard superellipses.

We examine the fluid phase behavior of binary mixtures of hard superellipses using the scaled particle theory. The superellipse is a general two-dimensional convex object that can be tuned between the elliptical and rectangular shapes continuously at a given aspect ratio. We find that the shape of the particle affects strongly the stability of isotropic, nematic, and tetratic phases in the mixture even if the side lengths of both species are fixed. While the isotropic-isotropic demixing transition can be ruled out using the scaled particle theory, the first order isotropic-nematic and the nematic-nematic demixing transition can be stabilized with strong fractionation between the components. It is observed that the demixing tendency is strongest in small rectangle-large ellipse mixtures. Interestingly, it is possible to stabilize the tetratic order at lower densities in the mixture of hard squares and rectangles where the long rectangles form a nematic phase, while the squares stay in the tetratic order.

Modulating the crystallization of phytosterols with monoglycerides in the binary mixture systems: mixing behavior and eutectic formation

Phytosterols (PSs) are insoluble in water and poorly soluble in oil, which hampers their potential as cholesterol level regulator in human. To mitigate this problem, monoglycerides (MGs) were used to modulates the crystallization behavior of PSs. Therefore, the understanding on mixing behavior provides the insight into different aspects of crystallization and the resultant effects. The effects on thermal, morphology, diffraction, and spectroscopy behavior were investigated for binary mixtures of 11 different ratios (100:0 to 0:100 MGs:PSs). The phase behavior of binary mixtures of commercial MGs and PSs exhibited complexity with the formation of eutectic mixtures at 90:10 and 80:20 (MGs:PSs) combinations. These combinations revealed a single melting profile and reduced melting enthalpy, though after a month of storage at 5 °C. Conversely, two separate melting regions were observed in others. Furthermore, powder X-ray diffraction (PXRD) analysis of selected combinations revealed a change in crystalline forms with changes in the peaks located between 18-19° (2θ) and 25-26° (2θ). Accordingly, Raman spectroscopy results revealed changes in intensities and peak shape. Therefore, the change in crystalline forms or behavior correlated well to the change in thermal properties. Overall, the characterizations revealed the formation of eutectic mixtures between MGs and PSs at 90:10 and 80:20 (MGs:PSs) in which MGs modified the crystallization of PSs and changed the crystal forms thus, thermal behaviors. This study provides new insight into the mixing behavior of MGs and PSs which supports other research. Therefore, the results of this study are beneficial for the improvement of formulation of phytosterols in food and pharmaceutical products. Nonetheless, this study reveals a simple technique to alter crystal forms of phytosterols through simple complexation with monoglycerides.

Saddle-splay-induced periodic edge undulations in smectic-A disks immersed in a nematic medium.

We report experimental studies on the phase behavior of binary mixtures of 1″,7″-bis(4-cyanobiphenyl-4'-yl)heptane (CB7CB) and 4,4-diheptyloxyazoxybenzene, which exhibit, apart from the nematic (N) and twist-bend nematic (N_{TB}) phases, the induced smectic-A (Sm-A) phase for weight fraction of CB7CB between 0.05 and 0.70. In planar nematic layers, the N_{TB} phase separates as droplets of tactoidlike planform; the chirality of droplets manifests in the optical dissimilarity between their opposite angular ends. Our main result is that, in the appropriate two phase region, Sm-A nuclei with positive dielectric anisotropy change over to disks immersed in the nematic above some electric field, their edges decorated by periodic bright spots, a result which was earlier reported in another binary system exhibiting the induced Sm-A phase [R. Pratibha and N. V. Madhusudana, Physica A 224, 9 (1996)10.1016/0378-4371(95)00311-8]. We develop a simple theory for the threshold of this distortion, which is a periodic undulation of the edge of the disk, demonstrating that it arises from saddle-splay elasticity of Sm-A, the low Sm-A-N interfacial tension unable to suppress the distortion. The observed increases in the number of bright spots with field, and with the radius of the disk at a given field, in both the experimental systems are also accounted for by the model. The distortion, which results in the most direct visualization of saddle splay in Sm-A, is also exhibited by disks nucleating on surfaces treated for homeotropic anchoring.

Liquid–Liquid Phase Behavior of Solutions of 1,3-Diethylimidazolium Bis((trifluoromethyl)sulfonyl)amide in n-Alkyl Alcohols

The cloud point method is applied for the characterization of the limited miscibility of ionic liquid (IL) solutions. Here, we report the phase behavior of binary mixtures of the ionic liquid 1,3-d...

Phase Behavior of Binary Mixtures of Tripalmitin, Triolein, and Trilinolein

Phase Behavior of Binary Mixtures of Tripalmitin, Triolein, and Trilinolein

P.570 Effects of ginseng and ginsenosides on mutant huntingtin aggregation, cellular apoptosis, mitochondrial dysfunction and motor impairment of Huntington's disease model

The phase behavior of binary mixtures of non-crystallizable racemic poly (d, l-lactic acid) (PDLLA) and the mosquito-repellent/drug N,N-diethyl-3-methylbenzamide (DEET) was analyzed with respect to the effect of the polymer molar mass on the liquid-liquid (L–L) phase separation characteristics, by cloud-point measurements and differential scanning calorimetry. The PDLLA/DEET system shows a subambient upper critical solution temperature (UCST), with the critical temperature decreasing and critical polymer concentration increasing with decreasing molar mass of PDLLA. The obtained L–L phase separation curves were used to estimate the temperature-dependence of the interaction parameter, confirming that the enhanced miscibility of the system components in case of low molar mass PDLLA is due to increased entropy of mixing.

Understanding the thermal behaviour of blends of biodiesel and diesel: Phase behaviour of binary mixtures of alkanes and FAMEs

The study of the phase behaviour of binary mixtures of fatty acid methyl esters (FAME) and alkanes are here studied to understand the behaviour of the mineral diesel/biodiesel blends. Six binary mixtures of the most common saturated methyl esters (methyl stearate or methyl palmitate) with a saturated alkane (hexadecane, octadecane or eicosane) were evaluated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and optical microscopy. The binary mixtures studied show a more complex phase behaviour than previously reported, which it is shown to be dependent of the size difference between the alkyl chain length of the esters and the alkanes. It was found that in mixtures with equal alkyl chain length a co-crystal is formed, and when the alkane chain length is larger than in the FAME by two methylene groups the formation of a solid-solution increasing significantly the solid phase stability is observed. The results and conclusions derived from the phase behaviour of this set of binary mixtures, between alkanes and methyl esters, can be used as a model for the interpretation of the cloud and pour points increase in biodiesel blends (in special the ones with a rich fraction of methyl palmitate or methyl stearate when combined with mineral diesel with high content of octadecane or eicosane respectively).

Effect of Isomerism on the Liquid–Liquid Phase Behavior of Mixtures of 1-Alkyl-3-methylimidazolium Bis((trifluoromethyl)sulfonyl)amide Ionic Liquids with Heptanol

Systematic investigations on the liquid–liquid phase behavior of binary mixtures of ionic liquids (IL) of the type 1-alkyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide (CxmimNTf2, x = 2, 4, 6, 8, and 10) with n-heptanol and its branched isomers 3-ethyl-3-pentanol and 2,4-dimethyl-3-pentanol have been performed. The phase diagrams were determined at atmospheric pressure in the temperature range (T) of 263–448 K by applying the cloud point method. The phase diagrams are analyzed in terms of well-established numerical concepts based on Ising criticality. The results are discussed, and trends and explanations for the shifts of the range of solubility are given. The systems show partial miscibility with upper critical solution temperatures. Comparing the solutions in branched alcohols with those in the linear isomer, the critical solution points are found to be remarkably shifted toward higher temperatures and lower IL contents. The trend becomes more pronounced for ILs with shorter alkyl side chains where also a change of the shape of the phase diagrams is observed.

Chain Architecture and Hydrogen Bonding Induced Co-Ordering and Segregation of Block Copolymer/Graft Copolymer Blends

We investigated the effects of chain architecture and hydrogen-bonding interaction on the phase behavior of binary mixtures containing nearly symmetric polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer and highly asymmetric polystyrene-graft-poly(acrylic acid) (PS-g-PAA) graft copolymer. When PS-g-PAA was added to PS-b-P2VP, hydrogen bonds between PAA and P2VP chains improved the miscibility of the copolymers and facilitated localization of PS-g-PAA at the PS-b-P2VP interface, which reduced the interfacial free energy of the blends. However, positioning PS-g-PAA with one PS main chain and two PAA grafted chains at the PS-b-P2VP interface increased the stretching free energy of PS-b-P2VP. Consequently, the interfacial coverage of PS-g-PAA reached saturation. Residual PS-g-PAA was segregated into the PS microdomains formed by PS-b-P2VP to regain translational entropy and reduce the stretching free energy. When the molecular weight ratio of PS-b-P2VP to PS-g-PAA (R) was smaller than 8, PS-g-PAA could not swell the PS microdomains formed by PS-b-P2VP. Therefore, the morphology of PS-b-P2VP/PS-g-PAA blends remained lamellar. By contrast, when R > 8, PS-g-PAA effectively swelled the PS microdomains formed by PS-b-P2VP. This behavior amplified the asymmetry effect caused by the branched-chain architecture of PS-g-PAA on altering the interfacial curvature of PS-b-P2VP. Consequently, the morphology of the blends transformed into a cylindrical structure.

GC-EoS extension to alkylphosphate imidazolium ionic liquids

In this work, the Group Contribution Equation of State (GC-EoS) is extended to model two new ionic liquid families, namely, 1-alkyl-3-methylimidazolium dimethylphosphate ([-MeIm]+[Me2PO4]-) and 1-alkyl-3-methylimidazolium diethylphosphate ([-MeIm]+[Et2PO4]-). Pure group parameters for the functional groups [-MeIm]+[Me2PO4]- and [-MeIm]+[Et2PO4]- and interaction parameters between these groups and the main paraffinic and aromatic subgroups (CH3, CH2, ACH, AC, ACCH3, CH2=CH) were estimated using infinite dilution activity coefficients from literature. In order to evaluate the performance of the new parameters, the model was compared with experimental data on the phase behavior of binary mixtures, showing an average relative deviation of 4.5%.

Induced smectic phase in binary mixtures of twist-bend nematogens.

The investigation of liquid crystal (LC) mixtures is of great interest in tailoring material properties for specific applications. The recent discovery of the twist-bend nematic phase (NTB) has sparked great interest in the scientific community, not only from a fundamental viewpoint, but also due to its potential for innovative applications. Here we report on the unexpected phase behaviour of a binary mixture of twist-bend nematogens. A binary phase diagram for mixtures of imino-linked cyanobiphenyl (CBI) dimer and imino-linked benzoyloxy-benzylidene (BB) dimer shows two distinct domains. While mixtures containing less than 35 mol % of BB possess a wide temperature range twist-bend nematic phase, the mixtures containing 55–80 mol % of BB exhibit a smectic phase despite that both pure compounds display a Iso–N–NTB–Cr phase sequence. The phase diagram shows that the addition of BB of up to 30 mol % significantly extends the temperature range of the NTB phase, maintaining the temperature range of the nematic phase. The periodicity, obtained by atomic force microscopy (AFM) imaging, is in the range of 6–7 nm. The induction of the smectic phase in the mixtures containing 55–80 mol % of BB was confirmed using polarising optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction. The origin of the intercalated smectic phase was unravelled by combined spectroscopic and computational methods and can be traced to conformational disorder of the terminal chains. These results show the importance of understanding the phase behaviour of binary mixtures, not only in targeting a wide temperature range but also in controlling the self-organizing processes.

Magnesium bis(trifluoromethanesulfonyl)amide complexes with triglyme and asymmetric homologues: phase behavior, coordination structures and melting point reduction.

The phase behavior of binary mixtures of triglyme (G3) and Mg[TFSA]2 (TFSA: bis(trifluoromethanesulfonyl)amide) was investigated, towards the development of a Mg2+-based room-temperature solvate ionic liquid (SIL) electrolyte. In a 1 : 1 molar ratio, G3 and Mg[TFSA]2 form a thermally stable complex (decomposition temperature, Td: 240 °C) with a melting point (Tm) of 70 °C, which is considerably lower than that of the analogous tetraglyme (G4) system (137 °C). X-ray crystallography of a single crystal of [Mg(G3)][TFSA]2 revealed that a single Mg2+ cation is coordinated by a single, distorted, tetradentate G3 molecule from one side, and two monodentate [TFSA]- anions, with transoid conformation, from the reverse side to form an ion pair. Raman spectra of [Mg(G3)][TFSA]2 in the molten state revealed the presence of different coordination structures, as the liquid exhibits changes in the vibrational modes corresponding to G3 and the [TFSA]- anion compared to those observed for the solid. Investigation of the ion pair stabilization energies by DFT calculations suggests that higher stability cation complexes and ion pairs co-exist in the molten state than those observed in the crystalline state. These results imply that the coordination structures of the ion pairs play a key role in providing SILs with low Tm. To decrease the Tm further, several asymmetric homologues of G3, which have higher conformational flexibility than G3, were investigated. Notably, a 1 : 1 mixture of Mg[TFSA]2 with G3Bu (where one of the terminal methyl groups of G3 is substituted for a butyl group) formed a thermally stable complex (Td: 251 °C) without any distinct Tm and showed reasonable ionic conductivity at room-temperature, indicating partial dissociation of ions. In this electrolyte, which showed high oxidative stability, quasi-reversible Mg deposition/dissolution was achieved, indicating that Mg2+-based room-temperature SILs can be utilized as a new class of Mg electrolyte.

Phase behavior of the polymer/drug system PLA/DEET: Effect of PLA molar mass on subambient liquid-liquid phase separation

The phase behavior of binary mixtures of non-crystallizable racemic poly (d, l-lactic acid) (PDLLA) and the mosquito-repellent/drug N,N-diethyl-3-methylbenzamide (DEET) was analyzed with respect to the effect of the polymer molar mass on the liquid-liquid (L–L) phase separation characteristics, by cloud-point measurements and differential scanning calorimetry. The PDLLA/DEET system shows a subambient upper critical solution temperature (UCST), with the critical temperature decreasing and critical polymer concentration increasing with decreasing molar mass of PDLLA. The obtained L–L phase separation curves were used to estimate the temperature-dependence of the interaction parameter, confirming that the enhanced miscibility of the system components in case of low molar mass PDLLA is due to increased entropy of mixing.

Binary Colloidal Crystal Films Grown by Vertical Evaporation of Silica Nanoparticle Suspensions

Despite intensive research efforts in the synthesis of binary colloidal crystals, the production of well ordered binary colloidal crystal films over large areas continues to be synthetically challenging. In this paper, we investigate the phase behavior of binary mixtures of l-arginine-stabilized 36 and 22 nm silica nanoparticles deposited as centimeter-scale thin films onto a vertical substrate via evaporative assembly. By adjusting the temperature and relative colloid composition under high humidity conditions, we controlled the order of the resultant colloidal crystal films. The domain size of the AB2 binary crystalline phase increased with an excess of small (B) particles and a very slow evaporation rate below 45 °C, with the best results obtained at 30° and 35 °C.