Study Of Phase Behavior Research Articles

Supramolecular Assembly of Biobased Graphene Oxide Quantum Dots Controls the Morphology of and Induces Mineralization on Poly(ε-caprolactone) Films.

Biobased 2D graphene oxide quantum dots (GOQDs) were synthesized from waste paper via carbon nanosphere intermediates and evaluated as property-enhancing additives for poly(ε-caprolactone) (PCL). The morphology of PCL films was controlled by supramolecular assembly of the small, 2D GOQDs in the polymer matrix. Phase behavior studies of PCL-GOQD in the solid state indicated concentration-dependent self-association of GOQD sheets, which was confirmed by SEM observations. Depending on the GOQD concentration, the formation of, e.g., spheres and stacked sheets was observed. GOQDs also induced mineralization on the surface of the films. A calcium phosphate (CaP) mineralization test revealed that the density of growing CaP crystals was controlled by the type of GOQD aggregates formed. Thus, utilization of the aggregation behavior of small GOQD sheets in polymeric matrices paves the way for tuning the morphology and properties of nanocomposites.

Study of phase behavior and physical properties of a natural gas reservoir with high carbon dioxide content

AbstractThe discovery of natural gas reservoirs with high and varying CO2 content (5% to 98%) in China has attracted worldwide attention. In this paper, the phase diagram of natural gas with different CO2 content was calculated and drawn by PVT Sim 100 which was fitted by experimental data based on the Ruska PVT 2730 apparatus. Both the real critical parameters and the pseudo‐critical para­meters were calculated and compared. Also, the phase state of natural gas along the wellbore in a representative well under both shut‐in and flowing conditions was analyzed. In addition, to clarifying the phase transition process, videos of a gas sample showed variation between supercritical state to gas‐liquid state with isobaric cooling and heating up between 35°C and 25°C. Moreover, the compressibility factor (Z‐factor) of the natural gas with different CO2 content was chosen as one of the key physical parameters of natural gas to measure at pressures ranging from atmospheric pressure to 45 MPa and temperatures ranging from 40°C to 140°C experimentally. Results show that the Z factor decreases with the increase of CO2 content in natural gas at isothermal conditions, and increases with the increase of temperature. Furthermore, a new model is proposed to predict pressure and Z factor. The varying CO2‐CH4 concentrations of this reservoir are relevant to gas compositions which may arise in depleted natural gas reservoirs used for geologic carbon sequestration. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd

Perturbation of the Experimental Phase Diagram of a Diblock Copolymer by Blending with an Ionic Liquid

Understanding the phase behavior of block copolymer/ionic liquid mixtures is an important step toward their implementation in commercial devices. Here we report a high throughput and systematic small-angle X-ray scattering study of the lyotropic phase behavior of a series of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymers in the ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide (EMIM Tf2N). The ionic liquid induces disorder–order transitions for a number of low molecular weight systems, and the onset points of these transitions are used to calculate the dependence of the effective Flory–Huggins interaction parameter (χeff) on the ionic liquid concentration. This enabled construction of an experimental phase diagram, which reveals that after taking volumetric swelling into account, at higher ionic liquid concentrations, the experimental phase boundaries shift significantly when compared to theoretical calculations for block copolymer melts. It is also demons...

A Simulation Study of Phase Behavior of Double-Hydrophilic Block Copolymers in Aqueous Solutions

The phase behavior of double-hydrophilic AB diblock copolymers in concentrated aqueous solutions is investigated using a simulated annealing technique. Phase diagrams of the system are constructed as a function of the volume fraction and concentration of the copolymer (Φ) as well as the hydrophilicity difference between the two blocks. Rich phase transition sequences, especially reentrant phase transitions, such as lamellae → gyroid → hexagonally packed cylinders → gyroid → lamellae → disorder, are observed for a given copolymer with decreasing Φ. By analyzing the variations of the average contact numbers between the A or B monomers and solvents, and of the effective volume fractions, the mechanisms of the reentrant, the order–order, and the order–disorder transitions are elucidated. The difference in hydrophilicity or in volume fraction can be used to tune the degree of swelling of the two blocks, resulting in a nonmonotonic variation of the effective volume fraction of the A (or B)-rich domain with the ...

Selection of microemulsion composition via study of phase behavior for synthesis of stable monodisperse platinum nanoparticles and optimization of experimental parameters

ABSTRACTMonodisperse platinum nanoparticles were synthesized by microemulsion technique. Feasibility of formation of microemulsion with chosen proportions of components is a common problem with this method. Here, prior to preparation of microemulsion for synthesis purpose, systematic study was carried to check the suitability of selected microemulsion system by establishing phase diagram for ternary system at constant temperature on triangular coordinates. Temperature dependency of microemulsion was studied by preparing phase diagram of temperature against mass fraction of aqueous phase in ternary mixture. Both these triangular coordinate diagram at constant temperature and temperature dependency plots helped to choose proper concentrations of components in the system. Effects of molar concentration of water-to-surfactant ratio, platinum salt concentration, continuous oil phase concentration, and presence of cosurfactant with surfactant on particle size were investigated for selected system of components. Synthesized platinum nanoparticles were characterized by dynamic light scattering and transmission electron microscope. Light backscattering profiles obtained by Turbiscan were used to judge the stability of microemulsions. Further, partial weightage of affecting parameters on size of synthesized particle were studied by Taguchi orthogonal array method.

The role of lipid-based drug delivery systems for enhancing solubility of highly selective antiviral agent acyclovir

The study aimed to improve the aqueous solubility and dissolution rate of acyclovir (ACV) using self-emulsifying lipid formulations (SEDDS/SMEDDS). ACV was formulated in various SEDDS/SMEDDS using wide ranges of oils (mono-/di-/triglycerides), nonionic surfactants and water-soluble cosolvents with the aid of phase behavior studies. The drug solubility was determined in anhydrous, 10% and 99% diluted formulations. Drug precipitation and release profiles of the SEDDS/SMEDDS were also investigated. The ACV was highly soluble in the formulations containing high concentration of hydrophilic materials. The addition of propylene glycol (PG) significantly enhanced the drug solubility. In addition, with only 1% 0.1 M HCl, the drug solubility improved 10-fold higher without any precipitation. In the dissolution studies, the representative SEDDS/SMEDDS showed superior release profiles (>90% ACV released) than marketed Zovirax® suspension (<26% released). Formulations containing water-soluble cosolvent (e.g. PG), were the most suitable systems for ACV due to the extensive drug solubilization and release profile.

ASP flood of a viscous oil in a carbonate rock

The goal of this work is to develop an alkaline–surfactant–polymer (ASP) formulation for a viscous oil (105 cP at the reservoir temperature) and compare secondary and tertiary ASP floods. Phase behavior studies were performed to find an ultralow interfacial tension (IFT) ASP formulation for the viscous oil. Static surfactant adsorption experiments were performed to compare the effectiveness of different alkalis in reducing adsorption. The surfactant formulation was tested with an outcrop vuggy dolomite core in both tertiary and secondary modes. Lab coreflood results were modeled in UTCHEM which used EQBATCH to model sodium metaborate geochemical reactions in a carbonate rock. Sodium carbonate and sodium metaborate were both found to be equally effective in reducing surfactant adsorption on crushed dolomite. Waterflood recovered about 47.8% of the oil in place and reduced the oil saturation to 43.8%. The tertiary surfactant flood increased the cumulative oil recovery to 92.7% whereby the oil saturation was reduced to 6.1%. The secondary surfactant flood was even more effective than the tertiary; the oil saturation was reduced to 3.1% and the oil recovery was 95.6% OOIP. Very low surfactant retention was observed in the ASP corefloods. UTCHEM simulations showed a reasonable match with the experimental results. Experimental data for surfactant phase behavior, polymer viscosity, and surfactant adsorption were critical in modeling the experimental results.

Multi-Stacked Supported Lipid Bilayer Micropatterning through Polymer Stencil Lift-Off.

Complex multi-lamellar structures play a critical role in biological systems, where they are present as lamellar bodies, and as part of biological assemblies that control energy transduction processes. Multi-lamellar lipid layers not only provide interesting systems for fundamental research on membrane structure and bilayer-associated polypeptides, but can also serve as components in bioinspired materials or devices. Although the ability to pattern stacked lipid bilayers at the micron scale is of importance for these purposes, limited work has been done in developing such patterning techniques. Here, we present a simple and direct approach to pattern stacked supported lipid bilayers (SLBs) using polymer stencil lift-off and the electrostatic interactions between cationic and anionic lipids. Both homogeneous and phase-segregated stacked SLB patterns were produced, demonstrating that the stacked lipid bilayers retain lateral diffusivity. We demonstrate patterned SLB stacks of up to four bilayers, where fluorescence resonance energy transfer (FRET) and quenching was used to probe the interactions between lipid bilayers. Furthermore, the study of lipid phase behaviour showed that gel phase domains align between adjacent layers. The proposed stacked SLB pattern platform provides a robust model for studying lipid behaviour with a controlled number of bilayers, and an attractive means towards building functional bioinspired materials or devices.

Effects of graphene oxide and salinity on sodium deoxycholate hydrogels and their applications in dye absorption

Sodium deoxycholate/graphene oxide (NaDC/GO) composite hydrogels were prepared in varying salinity. The hydrogels were characterized in detail by phase behavior study, transmission electron microscopy (TEM) observations, scanning electron microscopy (SEM) observations, X-ray powder diffraction (XRD) mesurements, Fourier transform infrared (FT-IR) spectra and rheological measurements. It was found that the introduction of GO to NaDC hydrogel enhances the mechanical strength of the composite hydrogel. When contacted with methylene blue solution, methylene blue can be absorbed inside the gel accompanied with a swelling of the gel. On the contrary, the hydrogel forms by NaDC only dissolves in methylene blue solution, forming a homegeous solution. Further study reveals that the gelation of NaDC/GO composite gel can be accelerated by an increase in salinity. This work may open the door for a variety of applications of NaDC/GO composite hydrogels such as in biotechnology, drug delivery and sewage treatment.

Mesoscale solubilization and critical phenomena in binary and quasi-binary solutions of hydrotropes

Hydrotropes are substances consisting of amphiphilic molecules that are too small to self-assemble in equilibrium structures in aqueous solutions, but can form dynamic molecular clusters H-bonded with water molecules. Some hydrotropes, such as low-molecular-weight alcohols and amines, can solubilize hydrophobic compounds in aqueous solutions at a mesoscopic scale (∼100nm) with formation of long-lived mesoscale droplets. In this work, we report on the studies of near-critical and phase behavior of binary (2,6-lutidine–H2O) and quasibinary (2,6-lutidine–H2O/D2O and tert-butanol/2-butanol–H2O) solutions in the presence of a solubilized hydrophobic impurity (cyclohexane). In additional to visual observation of fluid-phase equilibria, two experimental techniques were used: light scattering and small-angle neutron scattering. It was found that the increase of the tert-butanol/2-butanol ratio affects the liquid–liquid equilibria in the quasi-binary system at ambient pressure in the same way as the increase of pressure modifies the phase behavior of binary 2-butanol–H2O solutions. The correlation length of critical fluctuations near the liquid–liquid separation and the size of mesoscale droplets of solubilized cyclohexane were obtained by dynamic light scattering and by small-angle neutron scattering. It is shown that the effect of the presence of small amounts of cyclohexane on the near-critical phase behavior is twofold: (1) the transition temperature changes toward increasing the two-phase domain; (2) long-lived mesoscopic inhomogeneities emerge in the macroscopically homogeneous domain. These homogeneities remain unchanged upon approach to the critical point of macroscopic phase separation and do not alter the universal nature of criticality. However, a larger amount of cyclohexane generates additional liquid–liquid phase separation at lower temperatures.

An Integrated View of the Influence of Temperature, Pressure, and Humidity on the Stability of Trimorphic Cysteamine Hydrochloride.

Understanding the phase behavior of pharmaceuticals is important for dosage form development and regulatory requirements, in particular after the incident with ritonavir. In the present paper, a comprehensive study of the solid-state phase behavior of cysteamine hydrochloride used in the treatment of nephropathic cystinosis and recently granted orphan designation by the European Commission is presented employing (high-pressure) calorimetry, water vapor sorption, and X-ray diffraction as a function of temperature. A new crystal form (I2/a, form III) has been discovered, and its structure has been solved by X-ray powder diffraction, while two other crystalline forms are already known. The relative thermodynamic stabilities of the commercial form I and of the newly discovered form III have been established; they possess an overall enantiotropic phase relationship, with form I stable at room temperature and form III stable above 37 °C. Its melting temperature was found at 67.3 ± 0.5 °C. Cysteamine hydrochloride is hygroscopic and immediately forms a concentrated saturated solution in water with a surprisingly high concentration of 47.5 mol % above a relative humidity of 35%. No hydrate has been observed. A temperature-composition phase diagram is presented that has been obtained with the unary pressure-temperature phase diagram, measurements, and calculations. For development, form I would be the best form to use in any solid dosage form, which should be thoroughly protected against humidity.

Effect of PE-g-MA compatibilizer on the structure and performance of HDPE/EVA blend membranes fabricated via TIPS method

Neat and compatibilized high density polyethylene and ethylene vinyl acetate blend membranes were fabricated via thermally induced phase separation method. ATR-FTIR results confirmed that existence of PE-g-MA as compatibilizer keeps EVA molecules in the bulk of the membrane. Phase behavior studies showed that addition of compatibilizer improves the compatibility of the blend; therefore any cloud point was observed. Leafy structure obtained by SEM images also confirmed that a solid–liquid phase separation was occurred for all ranges of blending ratios. Pure water flux (PWF) and porosity analyses showed that compatibilized HDPE/EVA blend membrane with EVA content of 10wt.%, exhibits the best results in which PWF increases more than 2.8 folds in comparison with both neat blend and pure membranes.The results show that the tensile strength as well as elongation at breaks for compatiblized blend membrane is improved. The fouling behavior of compatiblized blend membranes with optimum composition of EVA in BSA protein filtration showed that maximum flux recovery of 71%, which was 18% and 86% higher than that of neat blend and pure HDPE membranes, respectively. Addition of compatibilizer decreased the portion of irreversible fouling ratio and increased the portion of reversible fouling ratio.

Thermal and phase behaviour studies of hydrogen-bonded compounds (SA:nOBA) using POM, DSC and image-processing techniques

A novel series of hydrogen-bonded liquid crystals are synthesised. The hydrogen bond is formed between non-mesogenic salicylic acid and the mesogenic p-n-alkoxy benzoic acids with n = 4–8, 10–12 and 16. The formation of hydrogen bond is confirmed from infrared studies. The transition temperatures and the phase identification are made with the use of polarising microscope (POM) attached with a hot stage. Further, the heats of transition and enthalpies are obtained by employing the differential scanning calorimeter (DSC). Along with POM and DSC, textural image analysis is done by image-processing techniques using MATLAB software and transition temperatures are identified. The results reveal that the compounds with the chain number n = 7, 8, 10–12 show the manifestation of smectic-B phase by quenching smectic-C phase.

Computational study of trimer self-assembly and fluid phase behavior

The fluid phase diagram of trimer particles composed of one central attractive bead and two repulsive beads was determined as a function of simple geometric parameters using flat-histogram Monte Carlo methods. A variety of self-assembled structures were obtained including spherical micelle-like clusters, elongated clusters, and densely packed cylinders, depending on both the state conditions and shape of the trimer. Advanced simulation techniques were employed to determine transitions between self-assembled structures and macroscopic phases using thermodynamic and structural definitions. Simple changes in particle geometry yield dramatic changes in phase behavior, ranging from macroscopic fluid phase separation to molecular-scale self-assembly. In special cases, both self-assembled, elongated clusters and bulk fluid phase separation occur simultaneously. Our work suggests that tuning particle shape and interactions can yield superstructures with controlled architecture.

Experimental and modeling studies of phase behavior for propane/Athabasca bitumen mixtures

Recent developments in heavy oil recovery methods indicate that the co-injection of solvent and steam can result in higher oil production rates. To investigate the performance and gain a better understanding of this newly developed process, it is essential to study the phase behavior of solvent/heavy crude oil mixtures and measure the saturated phase properties. This study attempts to provide insight into the phase behavior of propane/bitumen mixtures over wide ranges of temperatures and pressures, where the conditions would be applicable for both Vapex and ES-SAGD processes. Thus, phase behavior experiments for propane/Athabasca bitumen mixtures were conducted over temperature range of 323–473K and at pressures up to 10MPa. The results indicate that the mixture of propane and bitumen forms vapor–liquid and liquid–liquid phase separations over the studied temperature and pressure ranges. The variation of solubility with equilibrium pressure was found to be more significant at low temperatures. There were crossovers for gas-saturated bitumen density and viscosity which highlights the effect of solubility at low temperatures that is more significant than the effect of temperature on the bitumen density and viscosity. Thus, lower saturated properties were obtained at low temperatures and high pressures. The solubility and saturated liquid density were well predicted by Peng–Robinson equation of state and the saturated bitumen viscosities were reasonably correlated with Pedersen’s correlation.

Cold flow properties of biodiesel: a guide to getting an accurate analysis

Biodiesel has several advantages compared to conventional diesel fuel (petrodiesel). Nevertheless, biodiesel has poor cold flow properties that may restrict its use in moderate climates. It is essential that the cold flow properties of biodiesel and its blends with petrodiesel be measured as accurately as possible. This work provides an overview of the important cold flow properties and how they are analyzed. The utility of cloud point (CP), pour point (PP), and cold filter plugging point (CFPP) in evaluating biodiesel at low temperatures is discussed. Advantages and limitations of the experimental methods are evaluated. Finally, the use of sub-ambient differential scanning calorimetry (DSC) in the study of low temperature phase behavior of biodiesel is examined.

Assembly of Biological Nanostructures: Isotropic and Liquid Crystalline Phases of Neurofilament Hydrogels

Neurofilaments are the building blocks of the major cytoskeletal network found in the axons of vertebrate neurons. The filaments consist of three distinct molecular-weight subunits—neurofilament-low, neurofilament-medium, and neurofilament-high—which coassemble into 10-nm flexible rods with protruding intrinsically disordered C-terminal sidearms that mediate interfilament interactions and hydrogel formation. Molecular neuroscience research includes areas focused on elucidating the functions of each subunit in network formation, during which disruptions are a hallmark of motor-neuron diseases. Here, modern concepts and methods from soft condensed matter physics are combined to address the role of subunits as it relates to interfilament forces and phase behavior in neurofilament networks. Significantly, the phase behavior studies reveal that although neurofilament-medium subunits promote nematic liquid crystal hydrogel phase stability with parallel filament orientation, neurofilament-high subunits stabilize the hydrogel in the nematic phase close to the isotropic gel phase with random, crossed-filament orientation. This indicates a regulatory role for neurofilament-high subunits in filament orientational plasticity required for organelle (e.g., membrane-bound vesicle or mitochondrion) transport along microtubules embedded in neurofilament hydrogels. Future studies—for example, on neurofilament subunits mixed with tubulin and microtubule-associated proteins—should lead to a deeper understanding of forces and heterogeneous structures in neuronal cytoskeletons.

Solubility Of CO2 and C2H6 in heavy Oil and its Sara fractions

Solvent‐based recovery is one of the most promising techniques to enhance heavy oil/bitumen recovery as an alternative to thermal methods. Phase behaviour study of light gases in heavy oil is therefore very important when designing operation and surface facilities for heavy oil recovery. In this study, the original oil (Cactus Lake) was first characterized into saturate, aromatic, resin, asphaltene, and maltene fractions (0.0 wt. % asphaltene). An intelligent gravimetric microbalance was used to measure the solubility of carbon dioxide and ethane in the heavy oil and its saturate, aromatic, resin, asphaltene, and maltene fractions. The measurements were carried out at 288, 294, 299, and 303 K, and at pressures from 200 to 2000 kPa. The standard Peng‐Robinson equation of state was used to correlate the experimental results. The associated Henry's law constants were regressed and reported. The adsorbed amounts of carbon dioxide and ethane on asphaltene were correlated using the Freundlich isotherm. As for the given heavy oil sample and its fractions, carbon dioxide showed lower solubility than ethane at constant temperature, even at high pressures. It was observed that the asphaltene content affects ethane solubility quite significantly in this heavy oil when compared to carbon dioxide.

A study of phase behavior and conductivity of mixtures of the organic ionic plastic crystal N-methyl-N-methyl-pyrrolidinium dicyanamide with sodium dicyanamide

We report on the thermal, structural and conductivity properties of the organic ionic plastic crystal (OIPC) N-methyl-N-methyl-pyrrolidinium dicyanamide [C1mpyr][N(CN)2] mixed with the sodium salt Na[N(CN)2]. The DSC thermal traces indicate that an isothermal transition, which may be a eutectic melting, occurs at ~89°C, below which all compositions are entirely in the solid phase. At 20mol% Na[N(CN)2], this transition is the final melt for this mixture, and a new liquidus peak grows beyond 20mol% Na[N(CN)2]. The III–>II solid–solid phase transition continues to be evident at ~−2°C. The microstructure for all the mixtures indicated a phase separated morphology where precipitates can be clearly observed. Most likely, these precipitates consist of a Na-rich second phase. This was also suggested from the vibrational spectroscopy and the 23Na NMR spectra. The lower concentrations of Na[N(CN)2] present complex 23Na MAS spectra, suggesting more than one sodium ion environment is present in these mixtures consistent with complex phase behavior. Unlike other OIPCs where the ionic conductivity usually increases upon doping or mixing in a second component, the conductivity of these mixtures remains relatively constant and above 10−4S⋅cm−1 at ~80°C, even in the solid state. Such high conductivities suggest these materials may be promising to be used for all solid-state electrochemical devices.

Mechanical instability at finite temperature.

Many physical systems including lattices near structural phase transitions, glasses, jammed solids and biopolymer gels have coordination numbers placing them at the edge of mechanical instability. Their properties are determined by an interplay between soft mechanical modes and thermal fluctuations. Here we report our investigation of the mechanical instability in a lattice model at finite temperature T. The model we used is a square lattice with a φ(4) potential between next-nearest-neighbour sites, whose quadratic coefficient κ can be tuned from positive to negative. Using analytical techniques and simulations, we obtain a phase diagram characterizing a first-order transition between the square and the rhombic phase and different regimes of elasticity, as well as an 'order-by-disorder' effect that favours the rhombic over other zigzagging configurations. We expect our study to provide a framework for the investigation of finite-T mechanical and phase behaviour of other systems with a large number of floppy modes.