Phase Behavior Research Articles

Phase behavior of the carbon dioxide/toluene/poly(methyl methacrylate) ternary system

Carbon dioxide/organic polymer/solvent systems have several industrial applications, including supercritical polymerization. Various process parameters affect the phase behavior of these systems, thereby influencing the process design. Accordingly, the phase behavior of a carbon dioxide (CO2)/toluene (Tol)/poly(methyl methacrylate) (PMMA) ternary system was investigated in this study. Measurements were performed using a synthetic method combined with laser displacement and turbidity measurement. Bubble points (vapor–liquid phase separation) were determined from changes in the piston displacement, whereas cloud points (liquid–liquid (LL) phase separation) were determined from changes in the turbidity The phase boundaries of CO2 mass fractions ranging from 0.098 to 0.577 were measured by varying the Tol/PMMA ratio. The homogeneous phase area decreased when the ratio of PMMA to Tol increased, molecular weight of PMMA increased, and/or temperature decreased. These changes in the LL phase separation behavior were explained with reference to the free volume (vf) and solubility parameter (δ) estimated using the Sanchez–Lacombe equation of state. The estimation of vf and δ is expected to be helpful in comprehensively understanding the phase diagram and in predicting the phase behavior of CO2/organic solvent/polymer systems.

High temperature oxidation behavior of liquid phases sintered SiC ceramics with ZrB2 addition

The oxidation property of liquid-phase sintered silicon carbide (LPS-SiC) ceramics with ZrB2 addition was studied after oxidation test in air at 1400 °C. The results indicate that the addition of ZrB2 decreased the degree of polymerization (DOP) of the silicate networks in the oxide layer, suppressing the additional oxidation caused by residual bubbles in the oxide layer of LPS-SiC, which bypassed the layer and directly corroded the material internally. After 100 h of oxidation, the additional oxidation depth was found to be 125 μm in the sample without ZrB2 and 0 μm in those containing 10 wt% ZrB2. Simultaneously, the decrease in DOP facilitates the migration of crystalline phases. The generated ZrSiO4 can migrate and aggregate at the interface between the surface oxide layer and the SiC/ZrB2 matrix, forming a continuous ZrSiO4 barrier. This impedes the diffusion of the oxidant and enhances the oxidation resistance. However, an insufficient ZrB2 content leads to a discontinuous ZrSiO4 layer, thereby weakening its protective effect. Simultaneously, a decrease in DOP increases the rate of oxygen diffusion, resulting in an increase in the oxidation layer thickness. This study contributes to a better understanding of the failure mechanisms of LPS-SiC in oxidizing environments and provide a reference for the design of oxidation-resistant LPS-SiC materials.

Interfacial rheology of polyelectrolyte microgel monolayers: Correlation between mechanical properties and phase behavior at oil-water interfaces

Microgels are confined to fluid interfaces in numerous applications, yet many aspects of the microgel-covered interface remain unclear. In this work, we use interfacial shear and dilatational rheology to study the effects of electrostatics on the mechanical characteristics of polyelectrolyte microgel monolayers at oil-water interfaces as a function of the microgel interfacial concentration. We find a clear correlation between the influence of charges on the mechanical properties of the monolayers and the influence of charges on their two-dimensional phase behavior. At lower microgel interfacial concentrations, the moduli of uncharged monolayers are larger than those of charged monolayers. Consistent with our previous findings on the phase behavior, here, the mechanical response of the interfacial layer is controlled by in-plane interactions of the microgels within the interface. At higher microgel interfacial concentrations, the moduli of charged monolayers are larger than those of uncharged monolayers. The mechanical response becomes dominated by out-of-plane interactions between the fractions of the adsorbed microgels further from the interface. Evidently, electrostatic interactions do not contribute directly to the mechanical response of the interfacial layer, that is, through charge repulsion, but indirectly through the difference in the swelling properties of uncharged and charged microgels. These results advance our understanding of how the charge-dependent microstructure of the interfacial layer affects its mechanical properties, which is not only important from a fundamental point of view but is also relevant to applications where polyelectrolyte microgels are used as responsive emulsion stabilizers.

Candidate phases for SU(2) adjoint QCD$_4$ with two flavors from $\mathcal{N}=2$ supersymmetric Yang-Mills theory

We study four-dimensional adjoint QCD with gauge group SU(2)SU(2) and two Weyl fermion flavors, which has an SU(2)_RSU(2)R chiral symmetry. The infrared behavior of this theory is not firmly established. We explore candidate infrared phases by embedding adjoint QCD into {\mathcal N}=2𝒩=2 supersymmetric Yang-Mills theory deformed by a supersymmetry-breaking scalar mass MM that preserves all global symmetries and ’t Hooft anomalies. This includes ’t Hooft anomalies that are only visible when the theory is placed on manifolds that do not admit a spin structure. The consistency of this procedure is guaranteed by a nonabelian spin-charge relation involving the SU(2)_RSU(2)R symmetry that is familiar from topologically twisted {\mathcal N}=2𝒩=2 theories. Since every vacuum on the Coulomb branch of the {\mathcal N}=2𝒩=2 theory necessarily matches all ’t Hooft anomalies, we can generate candidate phases for adjoint QCD by deforming the theories in these vacua while preserving all symmetries and ’t Hooft anomalies. One such deformation is the supersymmetry-breaking scalar mass MM itself, which can be reliably analyzed when MM is small. In this regime it gives rise to an exotic Coulomb phase without chiral symmetry breaking. By contrast, the theory near the monopole and dyon points can be deformed to realize a candidate phase with monopole-induced confinement and chiral symmetry breaking. The low-energy theory consists of two copies of a \mathbb{CP}^1ℂℙ1 sigma model, which we analyze in detail. Certain topological couplings that are likely to be present in this \mathbb{CP}^1ℂℙ1 model turn the confining solitonic string of the model into a topological insulator. We also examine the behavior of various candidate phases under fermion mass deformations. We speculate on the possible large-MM behavior of the deformed {\mathcal N}=2𝒩=2 theory and conjecture that the \mathbb{CP}^1ℂℙ1 phase eventually becomes dominant.

MYC phase separation selectively modulates the transcriptome.

Dysregulation and enhanced expression of MYC transcription factors (TFs) including MYC and MYCN contribute to the majority of human cancers. For example, MYCN is amplified up to several hundredfold in high-risk neuroblastoma. The resulting overexpression of N-myc aberrantly activates genes that are not activated at low N-myc levels and drives cell proliferation. Whether increasing N-myc levels simply mediates binding to lower-affinity binding sites in the genome or fundamentally changes the activation process remains unclear. One such activation mechanism that could become important above threshold levels of N-myc is the formation of aberrant transcriptional condensates through phase separation. Phase separation has recently been linked to transcriptional regulation, but the extent to which it contributes to gene activation remains an open question. Here we characterized the phase behavior of N-myc and showed that it can form dynamic condensates that have transcriptional hallmarks. We tested the role of phase separation in N-myc-regulated transcription by using a chemogenetic tool that allowed us to compare non-phase-separated and phase-separated conditions at equivalent N-myc levels, both of which showed a strong impact on gene expression compared to no N-myc expression. Interestingly, we discovered that only a small percentage (<3%) of N-myc-regulated genes is further modulated by phase separation but that these events include the activation of key oncogenes and the repression of tumor suppressors. Indeed, phase separation increases cell proliferation, corroborating the biological effects of the transcriptional changes. However, our results also show that >97% of N-myc-regulated genes are not affected by N-myc phase separation, demonstrating that soluble complexes of TFs with the transcriptional machinery are sufficient to activate transcription.

Testing mixing rules for structural and dynamical quantities in multi-component crowded protein solutions.

Crowding effects significantly influence the phase behavior and the structural and dynamic properties of the concentrated protein mixtures present in the cytoplasm of cells or in the blood serum. This poses enormous difficulties for our theoretical understanding and our ability to predict the behavior of these systems. While the use of course grained colloid-inspired models allows us to reproduce the key physical solution properties of concentrated monodisperse solutions of individual proteins, we lack corresponding theories for complex polydisperse mixtures. Here, we test the applicability of simple mixing rules in order to predict solution properties of protein mixtures. We use binary mixtures of the well-characterized bovine eye lens proteins α and γB crystallin as model systems. Combining microrheology with static and dynamic scattering techniques and observations of the phase diagram for liquid-liquid phase separation, we show that reasonably accurate descriptions are possible for macroscopic and mesoscopic signatures, while information on the length scale of the individual protein size requires more information on cross-component interaction.

Unraveling the collinearity in short-range order parameters for lattice configurations arising from topological constraints.

In multicomponent lattice problems, for example, in alloys and at crystalline surfaces and interfaces, atomic arrangements exhibit spatial correlations that dictate the kinetic and thermodynamic phase behavior. These correlations emerge from interparticle interactions and are frequently reported in terms of the short-range order (SRO) parameter. Expressed usually in terms of pair distributions and other cluster probabilities, the SRO parameter gives the likelihood of finding atoms/molecules of a particular type in the vicinity of other atoms. This study focuses on fundamental constraints involving the SRO parameters that are imposed by the underlying lattice topology. Using a data-driven approach, we uncover the interrelationships between different SRO parameters (e.g., pairs, triplets, and quadruplets) on a lattice. The main finding is that while some SRO parameters are independent, the remaining are collinear, i.e., the latter are dictated by the independent ones through linear relationships. A kinetic and thermodynamic modeling framework based on these constraints is introduced.

Liquid-Liquid Phase Behavior of Acetonitrile and Normal Alkanes

Liquid-Liquid Phase Behavior of Acetonitrile and Normal Alkanes

Structural characteristics, mechanical properties, electronic behavior, and lattice thermal conductivities for novel LaX phases (X = P, As, Sb)

Rare-earth-metal monopnictides have rich high-pressure structures, magnetism, and topological properties, but there is still relatively little research related to them, especially in recent years. We here predict a new group of LaX (X = P, As, Sb) phases (HR-type) by means of the particle swarm optimization method. Their stabilities can be verified by dynamic, thermodynamic, and mechanical calculations. By utilizing the density functional and semiclassical Boltzmann transport theory, we investigate their mechanic, electronic, and thermal transport properties. These HR-type LaX are rather soft with lower than 6 GPa of Vickers hardness, and exhibit the obvious mechanical anisotropy. These HR-type LaX also exhibit amazing topological properties, owning a mostly flat surface band between two bulk Dirac cones. Based on the calculations of gaps in energy dispersion planes and Z2 invariants, we prove that these HR-type LaX should be the nodal-line semimetals. We compute their lattice thermal conductivities, and find that HR-type LaAs own the largest lattice thermal conductivity of 6.34 (22.34) W/mK along x (y) direction at 300 K. This mean free path of the pertinent heat-carrying phonons in the HR-type LaX are also predicted. Our research might offer new perspectives on the various allotropes of rare-earth-metal monopnictides.

On the isomeric purity of endcap molecules in cholesteric liquid crystal oligomers for near-infrared thermochromic coatings

ABSTRACT Structurally coloured responsive materials provide an interesting avenue for the development of autonomous temperature regulating window films. One interesting class of such thermochromic materials is cholesteric liquid crystals. However, cholesteric liquid crystals have rarely been applied in coatings for smart window applications. In this work, we report the synthesis of endcapped cholesteric liquid crystal oligomers and its application as near-infrared thermochromic coatings for windows. Two isomerically pure monoacrylate endcapping molecules and its isomeric mixture are synthesised. The molecules are used to synthesise a variety of endcapped cholesteric liquid crystal oligomers to study the effect of the isomeric purity on the thermochromic properties of the coatings. It is found that while the oligomers are almost identical in composition and phase behaviour, only one isomer produces a clear transparent coating, highlighting the significance of minute isomeric differences. Remarkably, the thermochromic behaviour of the coatings for all oligomers is the same. The best performing oligomer is able to reversibly blueshift by 250 nanometres when heated from room temperature to 100°C, opening the way of cholesteric liquid crystals for use in temperature regulating window films.

Propane-Induced Inversion of the Pressure Dependence of Highly Efficient Microemulsions: Phase Behavior and Its Prediction via HLD

Propane-Induced Inversion of the Pressure Dependence of Highly Efficient Microemulsions: Phase Behavior and Its Prediction via HLD

Ising Paradigm in Isobaric Ensembles.

We review recent work on Ising-like models with "compressible cells" of fluctuating volume that, as such, are naturally treated in NpT and μpT ensembles. Besides volumetric phenomena, local entropic effects crucially underlie the models. We focus on "compressible cell gases" (CCG), namely, lattice gases with fluctuating cell volumes, and "compressible cell liquids" (CCL) with singly occupied cells and fluctuating cell volumes. CCGs contemplate singular diameters and "Yang-Yang features" predicted by the "complete scaling" formulation of asymmetric fluid criticality, with a specific version incorporating "ice-like" hydrogen bonding further describing the "singularity-free scenario" for the low-temperature unusual thermodynamics of supercooled water. In turn, suitable CCL variants constitute adequate prototypes of water-like liquid-liquid criticality and the freezing transition of a system of hard spheres. On incorporating vacant cells to such two-state CCL variants, one obtains three-state, BEG-like models providing a satisfactory description of water's "second-critical-point scenario" and the whole phase behavior of a simple substance like argon. Future challenges comprise water's crystal-fluid phase behavior and metastable states.

Synthesis of silsesquioxane-linked polyester with liquid crystalline backbone chain

A novel procedure for the synthesis of a 3D network polyester bearing silsesquioxane cores was executed to prepare the ternary silsesquioxane-linked copolyester BNH (BNH4 and BNH8) based on 4-acetoxy benzoic acid (ABA), 6-acetoxy-2-naphthoxylic acid (ANA), and a silsesquioxane-cored monomer (CSQ-AHA4 or CSQ-AHA8). The thermal data and phase behavior indicated that moderate crosslinking would reduce the stacking of the backbones, thereby enhancing the mobility of the backbone. However, greater crosslinking would limit the movement of the backbone, while the 3D cross-linked structure enhanced the structural stability of the phase region and the uniformity of the crystal size distribution. The loose fiber bundles showed that the participation of the 3D configuration and silsesquioxane increased the chain flexibility, and facilitated the formation of strong polyester ultrafine fibers. It was possible to improve the lateral mechanical properties of the oriented polyester materials, probably improving the mechanical properties aspect ratio of thin film materials.

Wetting and emergence of long-range couplings in arrays of fluid cells.

Critical wetting is of crucial importance for the phase behavior of a simple fluid or Ising magnet confined between walls that exert opposing surface fields so that one wall favors liquid (spin up), while the other favors gas (spin down). We show that arrays of boxes filled with fluid and linked by channels with appropriately chosen opposing walls can exhibit long-range cooperative effects on a length scale far exceeding the bulk correlation length. We give the theoretical foundations of these long-range couplings by using a lattice gas (Ising model) description of a system.

Effect of Peptide-Polymer Host-Guest Electrostatic Interactions on Self-Assembling Peptide Hydrogels Structural and Mechanical Properties and Polymer Diffusivity.

Peptide-based supramolecular hydrogels are an attractive class of soft materials for biomedical applications when biocompatibility is a key requirement as they exploit the physical self-assembly of short self-assembling peptides avoiding the need for chemical cross-linking. Based on the knowledge developed through our previous work, we designed two novel peptides, E(FKFE)2 and K(FEFK)2, that form transparent hydrogels at pH 7. We characterized the phase behavior of these peptides and showed the clear link that exists between the charge carried by the peptides and the physical state of the samples. We subsequently demonstrate the cytocompatibility of the hydrogel and its suitability for 3D cell culture using 3T3 fibroblasts and human mesenchymal stem cells. We then loaded the hydrogels with two polymers, poly-l-lysine and dextran. When polymer and peptide fibers carry opposite charges, the size of the elemental fibril formed decreases, while the overall level of fiber aggregation and fiber bundle formation increases. This overall network topology change, and increase in cross-link stability and density, leads to an overall increase in the hydrogel mechanical properties and stability, i.e., resistance to swelling when placed in excess media. Finally, we investigate the diffusion of the polymers out of the hydrogels and show how electrostatic interactions can be used to control the release of large molecules. The work clearly shows how polymers can be used to tailor the properties of peptide hydrogels through guided intermolecular interactions and demonstrates the potential of these new soft hydrogels for use in the biomedical field in particular for delivery or large molecular payloads and cells as well as scaffolds for 3D cell culture.

Study on Emulsification Effect of Crude Oil in Brine Emulsions by Automated Demulsibility Tester

The purpose of the surfactants used is to greatly reduce the interfacial tension between the crude oil and brine, thereby decreasing the capillary number. The resulting oil-in-water emulsions are often grouped according to the Winsor theory. Oil recovery aims to produce Winsor type-III emulsions because they have the lowest interfacial tension values and the most favorable flow properties. The sensitivity of oil–water–surfactant systems to environmental influences (e.g., mixing speed and equilibration time) increases close to the favorable environmental range (temperature, brine total salt concentration, pressure, etc.) of the Winsor III type, the middle microemulsion phase, which is favorable for crude oil recovery. The tests aimed to investigate the quality and quantity of emulsions prepared with surfactants used in enhanced oil recovery (EOR) using an automatic device to characterize and select surfactants for industrial petroleum applications. An essential method for surfactant selection is to study the emulsifying effect and phase behavior. Phase behavior tests and emulsifying effect tests were performed on surfactants and surfactant packages as a function of mixing parameters. The mixing speed and mixing time can influence the results of the phase behavior and emulsifying effect tests, although during the investigations, other parameters were unchanged.

Use of homeopathy in feeding piglets as an alternative to reduce fighting behavior in the nursery phase: effects on production and hematological, metabolic, and oxidative variables

Use of homeopathy in feeding piglets as an alternative to reduce fighting behavior in the nursery phase: effects on production and hematological, metabolic, and oxidative variables

Kinetic and Thermodynamic Interplay of Polymer-Mediated Liquid-Liquid Phase Separation for Poorly Water-Soluble Drugs.

Understanding the interplay between kinetics and thermodynamics of polymer-mediated liquid-liquid phase separation is crucial for designing and implementing an amorphous solid dispersion formulation strategy for poorly water-soluble drugs. This work investigates the phase behaviors of a poorly water-soluble model drug, celecoxib (CXB), in a supersaturated aqueous solution with and without polymeric additives (PVP, PVPVA, HPMCAS, and HPMCP). Drug-polymer-water ternary phase diagrams were also constructed to estimate the thermodynamic behaviors of the mixtures at room temperature. The liquid-liquid phase separation onset point for CXB was detected using an inline UV/vis spectrometer equipped with a fiber optic probe. Varying CXB concentrations were achieved using an accurate syringe pump throughout this study. The appearance of the transient nanodroplets was verified by cryo-EM and total internal reflection fluoresence microscopic techniques. The impacts of various factors, such as polymer composition, drug stock solution pumping rates, and the types of drug-polymer interactions, are tested against the onset points of the CXB liquid-liquid phase separation (LLPS). It was found that the types of drug-polymer interactions, i.e., hydrogen bonding and hydrophobic interactions, are vital to the position and shapes of LLPS in the supersaturation drug solution. A relation between the behaviors of LLPS and its location in the CXB-polymer-water ternary phase diagram was drawn from the findings.

Highly efficient hydrolysis of cellulose to sugars using supercritical CO2 as a green acid catalyst and solvent

Rapid depolymerization of cellulose into processable monomers (e.g., sugars) using solid acid catalysts is an important step for cost-effective biofuel and biochemical production, but has not yet been achieved due to the limited contact between solid cellulose and solid catalysts. Herein, the unique roles of supercritical CO2 (i.e., scCO2) as an in-situ acid catalyst and reaction solvent in achieving the ultra-fast full solid catalytic hydrolysis of cellulose are disclosed for the first time. When the ball-milling pretreated cellulose was hydrolyzed using oxidized carbon catalysts at 150 °C and 100–300 bar-CO2, the hydrolysis kinetics remarkably increased by 3× for conversion and 5× for glucose, resulting in ∼90% conversion and ∼85% total sugar selectivity at 20 min. The hydrolysis rate obtained with scCO2 here was higher than conventional ones with toxic and unrecyclable homogeneous catalysts (e.g., HCl) under harsh reaction conditions (i.e., 180–220 °C and pH of 1–2). A comprehensive reaction engineering study (e.g., temperature, CO2 pressure, stirring speed, catalyst acid properties) combined with the estimation of the solution pH by the CO2 phase equilibrium model and the in-situ and ex-situ monitoring of the phase behavior of the H2O/scCO2 solution were conducted to quantify the activity promotion by scCO2 and understand the acid-solvent roles of scCO2 toward the enhanced hydrolysis of cellulose. Specifically, the formation of the Pickering emulsions at the interface between scCO2 and water and their impact on the enhancement of the cellulose-carbon contact were proposed and verified in detail.

Switchability and synergistic effect of a CO2-responsive surfactant with co-surfactants at an O/W interface: A molecular insight

CO2-responsive surfactants are a promising technology with potential applications in various fields. Therefore, the design of their formulations must be carefully considered to ensure their effectiveness in each specific application. Herein, we employed molecular dynamics simulations to investigate an oil/water (O/W) interface stabilized by a surfactant mixture containing a CO2-responsive cationic primary surfactant and another co-surfactant. It has been discovered that formulating the CO2-responsive cationic surfactant with a typical anionic surfactant (sodium dodecyl sulfate, SDS) can lead to a distinct CO2-responsive mechanism of the surfactant mixture. To compare, the CO2-responsive mechanism remains unchanged if the CO2-responsive cationic surfactant is formulated with a typical cationic surfactant (dodecyl trimethylammonium bromide, DTAB). A nonionic co-surfactant can enhance the interface activity of the surfactant mixture but the synergistic effect is not strong enough to lead to a different CO2-responsive mechanism. The distinct phase behavior between two surfactant mixtures suggests that the CO2-responsive mechanism is dominated by the type of surfactants formulated with the CO2-switchable surfactant.