Phase Behavior Of Systems Research Articles

Phase behavior of rotationally asymmetric Brownian kites containing 90° internal angles* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11874277 and 21621004, and 11704276) and the Natural Science Foundation of Tianjin, China (Grant No. 19JCQNJC14900).

Previous Monte Carlo simulations have shown that ordered tetratic phases can emerge in a dense two-dimensional Brownian system of rotationally asymmetric hard kites having 90° internal angles. However, there have been no experimental investigations yet to compare with these simulation results. Here, we have fabricated two types of micron-sized kites having internal angles of 72°–90°–108°–90° and 72°–99°–90°–99°, respectively, and we have experimentally studied their phase behavior in two-dimensional systems. Interestingly and in contrast to the Monte Carlo simulations, the experimental results show a phase sequence of isotropic fluid-hexagonal rotator crystal-square crystal as the area fraction ϕ A increases for both types of kites. The observed square crystal displays not only a quasi-long-range translational order but also (quasi-)long-range 4-fold bond- and molecular-orientational order; these characteristics confirm that tetratic order can emerge even in dense Brownian systems of rotationally asymmetric particles. A model based on local polymorphic configurations (LPCs) is proposed to understand the origin of the square lattice order in these dense kite systems. The results in this study provide a new route to realize custom-designed self-assembly of colloids by controlling LPCs.

Phase Transitions in Two-Dimensional Systems of Janus-like Particles on a Triangular Lattice.

We studied the phase behavior of two-dimensional systems of Janus-like particles on a triangular lattice using Monte Carlo methods. The model assumes that each particle can take on one of the six orientations with respect to the lattice, and the interactions between neighboring particles were weighted depending on the degree to which their A and B halves overlap. In this work, we assumed that the AA interaction was fixed and attractive, while the AB and BB interactions varied. We demonstrated that the phase behavior of the systems considered strongly depended on the magnitude of the interaction energies between the AB and BB halves. Here, we considered systems with non-repulsive interactions only and determined phase diagrams for several systems. We demonstrated that the phase diagram topology depends on the temperature at which the close-packed systems undergo the orientational order–disorder transition.

Solid-liquid transition induced by the anisotropic diffusion of colloidal particles

We numerically study the phase behaviors of colloids with anisotropic diffusion in two dimensions. It is found that the diffusion anisotropy of colloidal particles plays an important role in the phase transitions. A strong diffusion anisotropy induces the large vibration of particles, subsequently, the system goes into a disordered state. In the presence of the strong-coupling, particles with weak diffusion anisotropy can freeze into hexagonal crystals. Thus, there exists a solid-liquid transition. With the degree of diffusion anisotropy increasing, the transition points are shifted to the stronger-coupled region. A competition between the degree of diffusion anisotropy and coupling strength widens the transition region where the heterogeneous structures coexist, which results in a broad-peak probability distribution curve for the local order parameter. Our study may be helpful for the experiments related to the phase behavior in statistical physics, materials science and biophysical systems.

Curvature-assisted self-assembly of Brownian squares on cylindrical surfaces

HypothesisWe hypothesize that curved surfaces, including cylindrical surfaces, which go beyond prior experiments using flat surfaces, can significantly influence and alter the phase behavior and self-assembly of dense two-dimensional systems of Brownian colloids. ExperimentsHere, we report a first experimental study regarding the self-assembly of Brownian square platelets with an edge length L = 2.3 μm on cylindrical surfaces having different curvatures; these platelets are subjected to a depletion attraction in order to form a monolayer above the cylindrical surface, yet have nearly hard interactions within the monolayer. Simulations are also performed to confirm and explain the experimental observations. FindingsPhase diagrams as a function of curvature are determined experimentally. Interestingly, hexagonal rotator crystal structures are observed for tubes having radii > 10.9L, but a tetratic phase is seen instead for the 10.9L tube at the corresponding platelet area fractions. We show that this transition is caused by the curvature-induced orientation-dependence of the depletion attraction between the squares and the underlying cylindrical surface. Brownian dynamics simulation results confirm the experimental observations and also illustrate helical structures formed by squares packing on cylinders. Our results demonstrate a way towards control over the self-assembly of anisotropic particles through curvature and depletion-attraction-induced orientational confinement.

Gas/liquid mass transfer phenomena in micellar multiphase systems

Micellar multiphase systems are versatile examples for smart solvent systems, which can be applied to intensify important process aspects like reaction rate and product separation. Choosing different temperatures and compositions, the phase behaviour of micellar multiphase systems can be changed, and the reaction conditions altered. Due to the changing phase behaviour, mass transfer is affected, i.e., by altered interfacial areas which can influence the rate of a reaction. Up to two liquid dispersed phases can appear. For fast reactions with a gaseous component, the dispersion conditions and mass transfer are, therefore, complex. In this work, the gas/liquid mass transfer in two and three-phase micellar multiphase systems was observed to gain a better understanding of the transport mechanisms in such systems. The phase behaviour was found to influence the mass transfer strongly. When a microemulsion formed the continuous phase, the mass transfer was enhanced by a factor up to 2.4. Whenever a second liquid phase appeared, the volumetric mass transfer coefficient was decreased. While the mass transfer of the gas to a pure single liquid phase could be predicted by known theory, current mass transfer equations fail to capture the effect in micellar multiphase systems.

Using Microemulsion Phase Behavior as a Predictive Model for Lecithin-Tween 80 Marine Oil Dispersant Effectiveness.

Marine oil dispersants typically contain blends of surfactants dissolved in solvents. When introduced to the crude oil-seawater interface, dispersants facilitate the breakup of crude oil into droplets that can disperse in the water column. Recently, questions about the environmental persistence and toxicity of commercial dispersants have led to the development of "greener" dispersants consisting solely of food-grade surfactants such as l-α-phosphatidylcholine (lecithin, L) and polyoxyethylenated sorbitan monooleate (Tween 80, T). Individually, neither L nor T is effective at dispersing crude oil, but mixtures of the two (LT blends) work synergistically to ensure effective dispersion. The reasons for this synergy remain unexplained. More broadly, an unresolved challenge is to be able to predict whether a given surfactant (or a blend) can serve as an effective dispersant. Herein, we investigate whether the LT dispersant effectiveness can be correlated with thermodynamic phase behavior in model systems. Specifically, we study ternary "DOW" systems comprising LT dispersant (D) + a model oil (hexadecane, O) + synthetic seawater (W), with the D formulation being systematically varied (across 0:100, 20:80, 40:60, 60:40, 80:20, and 100:0 L:T weight ratios). We find that the most effective LT dispersants (60:40 and 80:20 L:T) induce broad Winsor III microemulsion regions in the DOW phase diagrams (Winsor III implies that the microemulsion coexists with aqueous and oil phases). This correlation is generally consistent with expectations from hydrophilic-lipophilic deviation (HLD) calculations, but specific exceptions are seen. This study then outlines a protocol that allows the phase behavior to be observed on short time scales (ca. hours) and provides a set of guidelines to interpret the results. The complementary use of HLD calculations and the outlined fast protocol are expected to be used as a predictive model for effective dispersant blends, providing a tool to guide the efficient formulation of future marine oil dispersants.

Ordering and Dynamics of Interacting Colloidal Particles under Soft Confinement

Confinement can induce substantial changes in the physical properties of macromolecules in suspension. Soft confinement is a particular class of restriction where the boundaries that constraint the particles in a region of the space are not well-defined. This scenario leads to a broader structural and dynamical behavior than observed in systems enclosed between rigid walls. In this contribution, we study the ordering and diffusive properties of a two-dimensional colloidal model system subjected to a one-dimensional parabolic trap. Increasing the trap strength makes it possible to go through weak to strong confinement, allowing a dimensional transition from two- to one-dimension. The non-monotonic response of the static and dynamical properties to the gradual dimensionality change affects the system phase behavior. We find that the particle dynamics are connected to the structural transitions induced by the parabolic trap. In particular, at low and intermediate confinement regimes, complex structural and dynamical scenarios arise, where the softness of the external potential induces melting and freezing, resulting in faster and slower particle diffusion, respectively. Besides, at strong confinements, colloids move basically along one direction, and the whole system behaves structurally and dynamically similar to a one-dimensional colloidal system.

Characterization of phase and diffusion behaviors of oil, surfactant, and co-surfactant ternary systems for lipid-based delivery carriers

The phase and diffusion characteristics of ternary mixture (oil, surfactant, and co-surfactant) were investigated for their utilization as a precursor for the fabrication of lipid-based delivery carriers. Different types of phases (W/O microemulsion, bicontinuous, liquid crystal, gel and O/W conventional emulsion phases) were generated depending on the content of the co-surfactant aqueous solution. A suspension with the smallest lipid particle was obtained from the bicontinuous phase, followed by the W/O microemulsion, liquid crystal, O/W conventional emulsion, and gel. The W/O microemulsion and bicontinuous phases showing a phase transition into the hexagonal phase of lyotropic liquid crystal, were found to be suitable for lipid-based delivery carriers with small particle size distribution and quercetin encapsulation efficiency. Thus, the ternary mixtures of oil, surfactant and co-surfactant could be utilized as a precursor for the production of lipid-based delivery carriers with various particle sizes.

Adsorption, selectivity, and phase behavior in organic nanopores for shale gas and oil development

In a shale gas and oil reservoir, hydrocarbon fluids are stored in organic nanopores with sizes on the order of ∼1–100 nm. The adsorption, selectivity, and phase behavior of hydrocarbons in the nanopores are crucial for estimating the gas-in-place and predicting the productivity. In this study, to understand the characteristics of the phase behavior of multicomponent hydrocarbon systems in shale reservoirs, the phase behavior of a CH4/n-C4H10 binary mixture in graphite nanopores was investigated by Grand Canonical Monte Carlo (GCMC) molecular simulation. The method for determining the dew-point pressure and bubble-point pressure in the nanopores was explored. The condensation phenomenon was observed owing to the difference in the adsorption selectivities of the hydrocarbon molecules on the nanopore surfaces, and hence the dew-point pressure (and bubble-point pressure) of hydrocarbon mixtures in the nanopores significantly shifted. The GCMC simulations reproduced both the higher and lower bubble-point pressures in nanopores in previous studies. This work highlights the crucial role of the selectivity in the phase behavior of hydrocarbons in nanopores.

Phase Behavior of Aqueous Biphasic Systems with Choline Alkanoate Ionic Liquids and Phosphate Solutions: The Influence of pH.

Aqueous biphasic systems (ABS) composed of the choline alkanoate ionic liquids (ILs) choline acetate [Cho][OAc], choline propanoate [Cho][Pro], choline butyrate [Cho][But], and choline hexanoate [Cho][Hex], mixed with K3PO4 solutions at pH 7.2 and 14.5, were prepared and their phase diagrams were compared. The ability to form ABS with alkaline K3PO4 solutions decreased in the order [Cho][OAc] ≈ [Cho][Pro] > [Cho][But] > [Cho][Hex], while with neutral K3PO4 solutions, [Cho][OAc] could not form an ABS, and the other three ILs performed similarly. All of the biphasic regions of the ABS decreased with the increase in pH. 1H-NMR data indicated anion exchange between phases in ABS at neutral pH. The ABS at neutral pH were evaluated to extract the triazine herbicides simazine, cyanazine, and atrazine, and the ABS formed by [Cho][Pro] and the pH 7.2 K3PO4 solution has shown extraction recoveries higher than 90%.

Modeling the equilibrium of two and three-phase systems including water, alcohol, and hydrocarbons with CPA EOS and its improvement for electrolytic systems by Debye-Huckel equation

Calculation of the phase equilibrium of hydrocarbons in the presence of electrolyte solutions is one of the most important and practical topics in chemical and petroleum engineering. The aim is to obtain an improved thermodynamic model that can predict the phase behavior of hydrocarbons along with electrolyte solution and alcohol with a good approximation. In this work, various equilibrium data published by previous researchers were collected, and then phase behavior of different systems including water, alcohol, and hydrocarbons was modeled using cubic plus association equation of state. Moreover, modified cubic plus association equation of state by Debye-Huckel equation was utilized for the prediction of the phase behavior of different systems containing salt. The results showed, for systems without electrolyte components, the cubic plus association equation of state predicts the phase behavior of these mixtures very well and the absolute average deviation value in these mixtures was between 1 and 10% for different systems. In recent decades, several equations of state have been proposed to predict the behavior of electrolyte mixture but, to the best of our knowledge, they did not consider all four components (hydrocarbon, water, alcohol, and salt) at the same time. In this research, an equation of state was presented to predict the phase behavior of systems that simultaneously contain hydrocarbons, water, alcohol, and salt in a mixture that considers both hydrogen bonds and ion interactions. The electrolytic cubic plus association equation is an equation that considers the effect of hydrogen bonds between different components as well as the effect of forces between existing ions. The results obtained for predicting electrolyte systems using the electrolytic cubic plus association equation showed that this equation can predict the phase behavior of these mixtures satisfactorily. The error value obtained for electrolytic systems and tangible components was between 1 and 12%.

Effects of Polydispersity on the Phase Behavior of Additive Hard Spheres in Solution.

The ability to separate enzymes, nucleic acids, cells, and viruses is an important asset in life sciences. This can be realised by using their spontaneous asymmetric partitioning over two macromolecular aqueous phases in equilibrium with one another. Such phases can already form while mixing two different types of macromolecules in water. We investigate the effect of polydispersity of the macromolecules on the two-phase formation. We study theoretically the phase behavior of a model polydisperse system: an asymmetric binary mixture of hard spheres, of which the smaller component is monodisperse and the larger component is polydisperse. The interactions are modelled in terms of the second virial coefficient and are assumed to be additive hard sphere interactions. The polydisperse component is subdivided into sub-components and has an average size ten times the size of the monodisperse component. We calculate the theoretical liquid–liquid phase separation boundary (the binodal), the critical point, and the spinodal. We vary the distribution of the polydisperse component in terms of skewness, modality, polydispersity, and number of sub-components. We compare the phase behavior of the polydisperse mixtures with their concomittant monodisperse mixtures. We find that the largest species in the larger (polydisperse) component causes the largest shift in the position of the phase boundary, critical point, and spinodal compared to the binary monodisperse binary mixtures. The polydisperse component also shows fractionation. The smaller species of the polydisperse component favor the phase enriched in the smaller component. This phase also has a higher-volume fraction compared to the monodisperse mixture.

Forecast of the Effect of Condensation Water on Reservoir Losses of Hydrocarbons in the T1-A Field of the Srednetungsky Field

Experimental PVT studies of the gas condensate mixture of the Srednetyungskoye field for the determination of the reservoir losses of hydrocarbons with the availability of condensation water have been conducted on recombined samples of separator gas, deposit water and saturated condensate. The bed samples were taken during field research of wells operating the T1-A deposit of the Srednetyungskoye oil and gas condensate field. T1-A bed has been sunk by all wells drilled in the field. The gas condensate pool was opened by thirteen wells, three of which (No. 225, 230, 240) made it possible to determine the position of the газоводяной контакт (ГBK) gas-water contact (GWC) of the deposit. Experimental modeling of phase behavior of gas-condensate bed systems at different thermodynamic states was carried out to determine the influence of condensation water on the value of condensate recovery during the development.

Membrane Protein Structures in Lipid Bilayers; Small-Angle Neutron Scattering With Contrast-Matched Bicontinuous Cubic Phases.

This perspective describes advances in determining membrane protein structures in lipid bilayers using small-angle neutron scattering (SANS). Differentially labeled detergents with a homogeneous scattering length density facilitate contrast matching of detergent micelles; this has previously been used successfully to obtain the structures of membrane proteins. However, detergent micelles do not mimic the lipid bilayer environment of the cell membrane in vivo. Deuterated vesicles can be used to obtain the radius of gyration of membrane proteins, but protein-protein interference effects within the vesicles severely limits this method such that the protein structure cannot be modeled. We show herein that different membrane protein conformations can be distinguished within the lipid bilayer of the bicontinuous cubic phase using contrast-matching. Time-resolved studies performed using SANS illustrate the complex phase behavior in lyotropic liquid crystalline systems and emphasize the importance of this development. We believe that studying membrane protein structures and phase behavior in contrast-matched lipid bilayers will advance both biological and pharmaceutical applications of membrane-associated proteins, biosensors and food science.

Influence of sucrose on the phase behaviour of phospholipid model systems

This article focuses on the influence of sucrose on the properties of SOPC (1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine) lipid systems. Differential scanning calorimetry is used to investigate the phase behaviour of the lipid system in the presence of sucrose. This method is appropriate and widely used to study the phase transitions parameters for organic compounds, in particular, lipids and the influence of various admixtures on these properties. Research results reveal that sucrose affects both, mechanical and physico-chemical characteristics of lipid systems. There are tangible differences in the bending elasticity moduli and enthalpies of the phase transitions due the addition of sucrose.

Asymmetric Phase Diagram of a Three Component Model Membrane Mixture Containing Sphingomyelin: Coupling of Lateral and Transverse Lipid Organization

Lipid asymmetry is a fundamental aspect of plasma membrane structure. Despite the importance of asymmetry, how the molecular features of individual lipids influence coupling between the leaflets is largely unexplored. We investigated the composition dependent phase behavior of ternary lipid system composed of egg sphingomyelin, DOPC, and cholesterol. Symmetric giant unilamellar vesicles (GUVs) were prepared by electroformation. Asymmetric GUVs were prepared by calcium induced hemifusion of the symmetric GUVs with a supported lipid bilayer composed of DOPC and cholesterol.

Hydrocarbon mixture phase behavior in multi-scale systems in relation to shale oil recovery: The effect of pore size distributions

Shale media contains a large amount of nano-scale pores, with their total pore volume comparable to that of the connected macropores and natural/hydraulic fractures (bulk). Previous work largely neglected the interplay between nanopores and bulk region as well as the effect of pore size distribution (PSD), where fluids can freely exchange between nanopores and bulk region. To accurately predict production and ultimate oil recovery, PSD effect should be taken into consideration. In this work, engineering density functional theory (DFT) is used to study phase behaviors of hydrocarbon mixtures in multi-scale nanoporous media with PSD effect during constant composition expansion (CCE) and constant volume depletion (CVD) processes. We found that under the PSD effect, due to the chemical equilibrium between various nanopores and connected bulk as well as competitive adsorption in nanopores, the interplay between nanopores and bulk region influences phase behaviors and properties of fluids in the multi-scale system. Phase transitions first occur in the bulk region, then the larger pores followed by the smaller pores. The bulk bubble point pressure increases as the volume ratio of the smaller pores in the system increases, while the bulk dew point decreases. When fluids in one specific pore begin to vaporize, in other pores, the heavier component would be adsorbed, while the lighter component would be released, which suppresses the phase transitions in the smaller pores because of the heavier component accumulation. The higher volume ratio of the smaller pores suppresses the heavier component production, when pressure is below the bulk dew point.

Machine learning for phase behavior in active matter systems.

We demonstrate that deep learning techniques can be used to predict motility-induced phase separation (MIPS) in suspensions of active Brownian particles (ABPs) by creating a notion of phase at the particle level. Using a fully connected network in conjunction with a graph neural network we use individual particle features to predict to which phase a particle belongs. From this, we are able to compute the fraction of dilute particles to determine if the system is in the homogeneous dilute, dense, or coexistence region. Our predictions are compared against the MIPS binodal computed from simulation. The strong agreement between the two suggests that machine learning provides an effective way to determine the phase behavior of ABPs and could prove useful for determining more complex phase diagrams.

Analysis of various approaches to accurately prediction of phase equilibrium of binary helium systems based on the Peng-Robinson equation of state

The paper presents a detailed algorithm for calculating the vapor-liquid phase equilibrium for multicomponent systems based on the Peng-Robinson equation of state. Various approaches are considered that make it possible to improve the quality of predicting phase equilibrium by the example of eight binary helium systems containing nitrogen, argon, carbon dioxide, methane, ethane, propane, isobutane, and n-butane. The influence of the acentric factor and the binary interaction parameter on the accuracy of the helium systems phase behavior predicting is analyzed. The optimal interaction coefficients for the presented systems are found under the assumption that this parameter does not depend on temperature. The temperature range of applicability of various approaches is determined, which makes it possible to maximize the description of the phase behavior of helium systems.

Molecular Thermodynamics for Aggregation of Surfactants with Alkylbenzene or Branched Alkane Tails: An Experimental-Modeling Approach

This work presents a molecular thermodynamic approach in which microemulsion properties are obtained by minimizing the total Gibbs energy of the system. Notably, this optimization process is carried out mainly based on the surfactant molecular structure and the solution conditions. Even though molecular thermodynamic modeling has been widely applied to oil-in-water (O/W) microemulsions, just a few studies are reported on water-in-oil (W/O) microemulsions mainly focused on ionic surfactants with linear alkyl tails. Here, we investigate the self-aggregation of different non-ionic surfactants with more complex structures acting as hydrophobic tails. In this context, we model the phase behavior of alkylphenol ethoxylate surfactant systems incorporating liquid-vapor and liquid-liquid data of alkylbenzenes from the literature. As a result, we can optimize the model parameters and describe the equilibrium micelle structure. The particle swarm optimization method was applied to minimize the Gibbs free energy for both O/W and W/O microemulsions. In order to evaluate the predictive performance of the model, we compared the experimental data with the computed critical micelle concentration and micelle size.