Fluid Theory Research Articles

Influence of excipients on solubility of oxcarbazepine: Modeling and prediction based on thermodynamic models

In this work, the solubility of oxcarbazepine in polymers (PEG 6000, PEG 20,000, PVP K25, and PVP K30) and their aqueous solutions was investigated by experimental measurement and thermodynamic modeling. Firstly, the solubility of oxcarbazepine in water and polymers was modeled and the corresponding binary interaction parameters (oxcarbazepine + water and oxcarbazepine + polymer) were determined based on the experimental phase equilibrium data. Furthermore, the solubility of oxcarbazepine in the polymer aqueous solution (the mass ratios of polymers in water were 2 %, 4 %, and 6 %) was predicted by the solid-liquid equilibrium (SLE) coupled with the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT). It was observed that the predicted results agreed well with the experimental data, and the average relative deviation (ARD) was <7 %. In this study, the solubility of oxcarbazepine in polymer aqueous solution was successfully predicted through the SLE coupled with the PC-SAFT, which was expected to provide theoretical guidance for the selection of pharmaceutical excipients and the rational design of preparations.

Density functional theory for responsive hard-sphere fluids

We investigate the equilibrium properties of responsive hard-sphere fluids, where the particle size is a coarse-grained property that fluctuates within an internal free-energy landscape, responding to changes in concentration or the application of external fields. For this purpose, we employ a generalised density functional theory for responsive colloids based on the fundamental measure theory for polydisperse hard-sphere mixtures. We find that increasing particle softness yields a substantial reduction in mean particle size, volume fraction and pressure. We also examine the density profiles and size segregation of responsive hard-sphere fluids subjected to three representative external potentials: a planar hard wall, gravitational and Archimedes buoyant fields. We observe that increasing stiffness or particle concentration enhances density oscillations, converging to the behaviour of a monodisperse fluid. In a gravitational field, size segregation occurs, with smaller particles accumulating at the bottom due to sedimentation. This effect is more pronounced when the Archimedes force is included, causing larger colloids to accumulate at the top, leading to density oscillations in this region that intensify with particle softness, an effect not observed in monodisperse systems. Finally, we demonstrate that responsiveness leads to distinct behaviour compared to conventional polydisperse non-responsive fluids, in which particle compression is not allowed.

Does exposure to continuous and fluid theories of sexual orientation influence heterosexuals’ evaluations toward bisexual or gay/lesbian people?

Does exposure to continuous and fluid theories of sexual orientation influence heterosexuals’ evaluations toward bisexual or gay/lesbian people?

Predicting the Release Mechanism of Amorphous Solid Dispersions: A Combination of Thermodynamic Modeling and In Silico Molecular Simulation

Background: During the dissolution of amorphous solid dispersion (ASD) formulations, the drug load (DL) often impacts the release mechanism and the occurrence of loss of release (LoR). The ASD/water interfacial gel layer and its specific phase behavior in connection with DL strongly dictate the release mechanism and LoR of ASDs, as reported in the literature. Thermodynamically driven liquid-liquid phase separation (LLPS) and/or drug crystallization at the interface are the key phase transformations that drive LoR. Methods: In this study, a combination of Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) thermodynamic modeling and in silico molecular simulation was applied to investigate the release mechanism and the occurrence LoR of an ASD formulation consisting of ritonavir as the active pharmaceutical ingredient (API) and the polymer, polyvinylpyrrolidone-co-vinyl acetate (PVPVA64). A thermodynamically modeled ternary phase diagram of ritonavir (PVPVA64) and water was applied to predict DL-dependent LLPS in the ASD/water interfacial gel layer. Microscopic Erosion Time Testing (METT) was used to experimentally validate the phase diagram predictions. Additionally, in silico molecular simulation was applied to provide further insights into the phase separation, the release mechanism, and aggregation behavior on a molecular level. Results: Thermodynamic modeling, molecular simulation, and experimental results were consistent and complementary, providing evidence that ASD/water interactions and phase separation are essential factors driving the dissolution behavior and LoR at 40 wt% DL of the investigated ritonavir/PVPVA64 ASD system, consistent with previous studies. Conclusions: This study provides insights into the potential of blending thermodynamic modeling, molecular simulation, and experimental research to comprehensively understand ASD formulations. Such a combined approach can be leveraged as a computational framework to gain insights into the ASD dissolution mechanism, thereby facilitating in silico screening, designing, and optimization of formulations with the benefit of significantly reducing the number of experimental tests.

Co-sorption of volatile components in polymer-based pharmaceutical formulations

Amorphous Solid Dispersions (ASDs) are mixtures of active pharmaceutical ingredients (APIs) and polymers aiming to increase API aqueous solubility and bioavailability. ASDs are often produced using solvent-based manufacturing, such as spray drying. Due to solubility or miscibility limitations in one solvent, solvent mixtures are frequently used for this purpose. Drying solvents or solvent mixtures from polymer-based products like ASDs is an energy-intensive and time-consuming process. Designing and optimising this drying process requires knowledge of the sorption isotherms of the solvent(s) in these polymer-based products. In this work, we developed a novel approach for measuring the simultaneous absorption/desorption of two solvents in a polymer. Combining classical dynamic vapour sorption (DVS) measurements with Raman spectroscopy, this innovative approach provides a more detailed and accurate measurement of the sorption isotherms than common methods. Moreover, we developed an approach for precisely predicting the sorption equilibria in three-component systems just based on sorption data of the corresponding binary subsystems. Our modelling approach combines the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) with the Non-Equilibrium Thermodynamics of Glassy Polymers (NET-GP). Building on the description of the sorption isotherms of either water or ethanol in poly(vinylpyrrolidone-co-vinyl acetate) (PVPVA64) and in indomethacin (IND), we were able to quantitatively predict the simultaneous sorption of water and ethanol in PVPVA64 and the one of ethanol in an IND/PVPVA64 ASD.

Modelling of wall-bounded cavitating flow and spray mixing in multi-component environments using the PC-SAFT equation of state

This work introduces a numerical multiphase model for multi-component mixtures, utilizing tabulated data for physical and transport properties across a spectrum of conditions from near-vacuum pressures to supercritical states. The property data are derived using Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT), vapor-liquid equilibrium (VLE) calculations, entropy scaling methodologies, and Group Contribution (GC) methods. These techniques accurately reflect the thermodynamic behaviors of real fluids, avoiding the empirical estimation of Equation of State (EoS) input parameters. Implemented in OpenFOAM, the fluid dynamics solver is designed to address the three-dimensional Navier-Stokes equations for multi-component mixtures. The methodology integrates operator splitting to manage hyperbolic and parabolic steps distinctively. Hyperbolic terms are solved using the HLLC (Harten-Lax-van Leer-Contact) solver with temporal integration performed via a third-order Strong-Stability-Preserving Runge–Kutta (SSP-RK3) method. Viscous stress tensor contributions in the momentum equation are handled through an implicit velocity correction equation, while parabolic terms in the energy equation are explicitly solved. The simulation efficiency is further enhanced by adaptive Local Time Stepping and the Immersed Boundary (IB) method, which addresses interactions between the fluid and solid boundaries. Turbulence is resolved using the Wall Adaptive Large Eddy (WALE) model. Applied to high-pressure diesel fuel spray injections into non-reacting (nitrogen) gas environments, the model has been validated against Engine Combustion Network (ECN) data for the Spray-C configuration, featuring a fully cavitating multi-hole orifice. Results demonstrate that the model achieves accurate predictions across a broad range of tested conditions without the need for tuning or calibration parameters.

Study on plasma expansion model of primary discharge on spacecraft solar array

In the space plasma environment, primary discharge may occur on the solar array and evolve into a destructive sustained arc, which threatens the safe operation of the spacecraft. Based on the plasma expansion fluid theory, a new multicomponent plasma expansion model is proposed in this study, which takes into account the effects of ion species, ion number, initial discharge current, and Low Earth Orbit (LEO) plasma environment. The expansion simulation of single-component and multicomponent ions is carried out respectively, and the variations of plasma number density, expansion distance, and speed during the expansion process are obtained. Compared with the experimental results, the evolution of propagation distance and speed is closed and the error is within a reasonable range, which verifies the validity and rationality of the model. The propagation characteristics of the primary discharge on the solar array surface and the influence of the initial value on the maximum propagation distance and the propagation current peaks are investigated. This study can provide important theoretical support for the propagation and evolution of the primary discharge and the key behavior of the transition to secondary discharge on spacecraft solar array.

Modeling Dipolar Molecules with PCP-SAFT: A Vector Group-Contribution Method.

Predicting thermodynamic equilibrium properties is essential to develop chemical and energy conversion processes in the absence of experimental data. For the modeling of thermodynamic properties, statistical associating fluid theory (SAFT)-based equations of state, such as perturbed-chain polar (PCP)-SAFT, have been proven powerful and found broad application. The PCP-SAFT parameters can be predicted by group-contribution (GC) methods. However, their application to the dipole term is substantially limited: current GC methods neglect the dipole term or only allow for a single dipolar group per substance to avoid handling the molecular dipole moment's symmetry effects. Still, substances with multiple dipolar groups are highly relevant, and their description substantially improves by including the dipole term in SAFT models. To overcome these limitations, this work proposes a vector-addition-based (Vector-)GC method for the dipole term of PCP-SAFT that accounts for molecular symmetry. The Vector-GC employs information on the substance's molecular 3D structure to predict the molecular dipole moment through a vector addition of bond contributions. Combining the proposed sum rule for dipole moments with established sum rules for the remaining parameters yields a consistent GC method for PCP-SAFT for dipolar substances. The prediction capabilities of the Vector-GC method are analyzed against experimental data for two substance classes: nonassociating oxygenated and halogenated substances. We demonstrate that the Vector-GC method improves vapor pressure and liquid density predictions compared to neglecting the dipole term. Moreover, we show that the Vector-GC method enables differentiation between cis- and trans-isomers. The Vector-GC method, hence, substantially increases the predictive capabilities and applicability domain of GC methods. All parameters are provided as JSON and CSV files, and the Vector-GC method is available through an open-source python package. Additionally, the developed regression framework for GC methods for PCP-SAFT is openly available. The regression framework can be employed to regress the Vector-GC method to other substance classes and is easily adaptable to other sum rules for PCP-SAFT.

Predicting phase coexistence and adsorption isotherms of classical and quantum fluids using the microcanonical-ensemble perturbation theory (MEPT)

The Microcanonical-Ensemble Perturbation Theory (MEPT) of Sastre et al. (2018) [7] has been extended to study the vapor-liquid phase coexistence of binary and ternary mixtures of fluids. The attractive interactions between chains of molecules are represented as monomer segments interacting via a square-well pair potential. Calculations for the thermodynamic properties and phase behavior of square-well monomer chains are considered and compared with experimental data. Molecular parameters have been obtained to model the phase behavior of real fluids such as n-alkanes (from C1 to C12), nitrogen, perfluoromethane, carbon dioxide, i-butane, i-pentane, neon, and hydrogen. Furthermore, the capability of the MEPT approach in predicting critical and azeotropic lines of binary and ternary mixtures is explored. The results demonstrate that the MEPT approach provides a robust description of the phase behavior of mixtures containing chains of fluids. Additionally, we have integrated the MEPT approach with the two-dimensional Statistical Associating Fluid Theory for fluids interacting via variable range potentials (SAFT-VR-2D) to investigate the effect of quantum contributions on both phase behavior and adsorption. Remarkable improvements are observed when both higher order perturbation terms of the Helmholtz free energy and quantum contributions are included in the predictions of the phase behavior of quantum fluids such as neon and hydrogen. In all cases, the theoretical results exhibit favorable comparisons with experimental data in a wide range of compositions, pressures, and temperatures.

Comprehensive study of medications solubility in supercritical CO2 with and without co-solvent; Laboratory, theoretical, and intelligent approaches

Determining the dissolution characteristics of medicines in supercritical CO2 is vital for formulating innovative drug delivery systems through an efficient supercritical process. This study investigates the solubility of three poorly bioavailable drugs −Topiramate, Meclizine, and Dimenhydrinate- in supercritical CO2, both with and without ethanol co-solvent, over a temperature range of 308 K to 348 K and pressures from 17 MPa to 41 MPa. The solubility of these medicines in supercritical CO2 (binary system) is notably low, ranging from 2.5 × 10-6 − 4.54 × 10-6, 0.26 × 10-5 − 2.3 × 10-5, and 0.20 × 10-5 − 1.91 × 10-5 in mole fraction, respectively. However, in the presence of ethanol (ternary system), their supercritical solubility significantly increases by factors of 2.75–5.84, 1.40–3.20, and 2.04–4.85, respectively.The supercritical solubility of the mentioned compounds are theoretically evaluated using several approaches, including empirical models, a machine learning methodology employing a multilayer perceptron neural network, thermodynamic models based on two cubic equations of state (Peng-Robinson (PR) and Soave–Redlich–Kwong (SRK)), and a non-cubic equation of state (perturbed chain-statistical associating fluid theory (PC-SAFT)), as well as two expanded liquid models (UNIQUAC and Wilson).The findings revealed that all the specified models demonstrate acceptable accuracy in correlating the experimental data of the specified drugs in both binary and ternary systems. Among these, the PR and SRK thermodynamic models, along with some empirical models, show the best results. Furthermore, the machine learning model exhibited outstanding accuracy in forecasting the supercritical solubility of the desired drugs, with over 99.9% alignment between their predicted and experimental data.

Adsorption Modeling Based on Classical Density Functional Theory and PC-SAFT: Temperature Extrapolation and Fluid Transfer.

Adsorption is at the heart of many processes from gas separation to cooling. The design of adsorption-based processes requires equilibrium adsorption properties. However, data for adsorption equilibria are limited, and therefore, a model is desirable that uses as little data as possible for its parametrization, while allowing for data interpolation or even extrapolation. This work presents a physics-based model for adsorption isotherms and other equilibrium adsorption properties. The model is based on one-dimensional classical density functional theory (1D-DFT) and the perturbed-chain statistical associating fluid theory (PC-SAFT). The physical processes inside the pores are considered in a thermodynamically consistent approach that is computationally efficient. Once parametrized with a single isotherm, the model is able to extrapolate to other temperatures and outperforms the extrapolation capabilities of state-of-the-art models, such as the empirical isotherm models from Langmuir or Toth. Furthermore, standard combining rules can be used to transfer parameters adjusted to an adsorbent/fluid pair to other fluids. These features are demonstrated for the adsorption of N2, CH4, and CO2 in metal-organic frameworks. Thereby, the presented model can calculate temperature-dependent isotherms for various fluids by using data limited to a single isotherm as input.

Resistive wall mode and fishbone mode in ITER steady state scenario: roles of fusion-born alphas and plasma flow

Drift-kinetic effects of fusion-born alpha particles on the n= 1 (n is the toroidal mode number) resistive wall mode (RWM) is numerically investigated for a recent design of the ITER 10 MA steady state plasma scenario, utilizing a magneto-hydrodynamic (MHD)-kinetic hybrid toroidal model. While the fluid theory predicts unstable RWM as the normalized plasma pressure β N exceeds the no-wall Troyon limit and with the mode growth rate monotonically increasing with β N, inclusion of the drift-kinetic contribution of trapped alphas qualitatively modifies the behavior by stabilizing the mode at high β N. In fact, a complete stabilization of the n= 1 RWM up to the ideal-wall Troyon limit is found. On the other hand, another unstable branch—the alpha-driven n = 1 fishbone mode (FB)—is identified in the high-β N regime, with the mode frequency matching that of the toroidal precession frequency of trapped alphas. Fast plasma toroidal flow however helps mitigate the FB instability. Kinetic stabilization of the RWM and flow stabilization of the (alpha-triggered) FB result in an enhancement of β N from the design value of 3.22–3.52 for the ITER scenario considered, while still maintaining stable plasma operation against the aforementioned MHD instabilities.

Interplay between the non-resonant streaming instability and self-generated pressure anisotropies

ABSTRACT The non-thermal particles escaping from collision-less shocks into the surrounding medium can trigger a non-resonant streaming instability that converts parts of their drift kinetic energy into large amplitude magnetic field perturbations, and promote the confinement and acceleration of high energy cosmic rays. We present simulations of the instability using an hybrid-Particle-in-Cell approach including Monte Carlo collisions, and demonstrate that the development of the non-resonant mode is associated with important ion pressure anisotropies in the background plasma. Depending on the initial conditions, the anisotropies may act on the instability by lowering its growth and trigger secondary micro-instabilities. Introducing collisions with neutrals yield a strong reduction of the magnetic field amplification as predicted by linear fluid theory. In contrast, Coulomb collisions in fully ionized plasmas are found to mitigate the self-generated pressure anisotropies and promote the growth of the magnetic field.

Configuration rearrangement of squalane induced by carbon dioxide dissolution: A molecular simulation study

Squalane has emerged as a desirable absorbent material for carbon capture, utilization, and storage solutions due to its tunable sorption properties, microscopic structures, and cost-effectiveness in response to the increasing demand. Moreover, a thorough understanding of the fundamental characteristics of hydrocarbons and dissolved gases involved in the Fischer–Tropsch industrial synthesis processes is also essential for researching industrial purification and separation. However, these macromolecules may experience varying degrees of induced alterations in their structural rearrangement when absorbing absorbates, which impacts the performance indicators of squalane. This study examined the solubility characteristics of absorbents made from squalane and their interaction with gaseous CO2 molecules. The perturbed chain statistical associated fluid theory (PC–SAFT) was employed to comprehensively evaluate the macroscopic thermodynamic experimental density and solubility data. Simultaneously, the Monte Carlo (MC) simulation approach was utilized to investigate the rearrangement and swelling features of the squalane chain induced by the presence of CO2 gas in a broad spectrum of temperature and pressure conditions. This work indicated that elevated temperatures increased flexibility in the molecular structure of squalane, leading to a more pronounced spatial dispersion, while higher pressures may lead to spatial homogeneity and enhanced capacity for carrying additional CO2 molecules. The examples and methodologies presented demonstrate the effectiveness of molecular simulations in comprehending absorption–based phenomena at an atomistic and molecular level and offer essential guidance in forecasting the potential for separation, storage, or catalytic.

A modified simplified SAFT EOS for VLE study of associating fluids

AbstractIn this study, the simplified version of statistical associating fluid theory (SAFT) equation of state (EOS) developed by Fu and Sandler is modified by replacing the dispersion term of this EOS with the Haghtalab–Mazloumi equation. This new SAFT‐based EOS has three adjustable parameters for non‐associating compounds and five adjustable parameters for associating compounds. The adjustable parameters of the new EOS are obtained by simultaneously fitting vapour pressures and liquid densities of pure substances. The new EOS shows better results in correlating vapour pressure and saturated liquid densities than SSAFT EOS for a selection of non‐associating and associating substances. Then, by using proper mixing rules, the new EOS is extended for mixtures. Both self‐associating and cross associating binary mixtures are used to test the capability of the new EOS in vapour–liquid equilibrium (VLE) calculations, and the results demonstrate good accuracy of the new EOS.

Firehose instability in heat-conducting solar wind plasmas including FLR corrections and electrical resistivity

The effects of finite Larmor radius (FLR) corrections and heat-flux vector are studied on the pressure anisotropy-driven firehose instability in finitely conducting solar wind plasmas described by the double-adiabatic Chew, Goldberger and Low (CGL) fluid theory. The fluid description of collisionless plasmas is governed through modified adiabatic equations due to the heat-flux vector and finite ion Larmor radius corrections. The analytical dispersion relation of the firehose instability has been derived using the normal mode analysis and discussed in the solar wind plasmas. In the transverse mode, the dispersion relation of the Alfvénic mode is modified due to electrical resistivity and FLR corrections. In the longitudinal mode, the effects of the heat-flux parameter and electrical resistivity are observed separately. The dispersion relation of the firehose mode is modified due to the combined effects of FLR corrections and electrical resistivity. The graphical illustrations show that finite electrical resistivity and ion Larmor frequency destabilize the growth rate of the firehose instability. The results are useful for analyzing the solar mission data to study the firehose instability in the solar wind plasmas.

Self-diffusion coefficient as a function of the thermodynamic factor.

Much effort has been put into developing theories for dense fluids; as a result of these efforts many theories work for a certain type of particle or in a certain concentration regime. Rosenfeld proposed a dependence of the self-diffusion coefficient on the excess entropy. Our proposal is similar to Rosenfeld's in that it also attempts to describe diffusion in terms of a thermodynamic function but, instead of the excess entropy, we use the thermodynamic factor or the excess chemical potential. Simulations were taken for hard spheres and our model was fitted with two free parameters. Simulations were then carried out for a Lennard-Jones gas and our model correctly described the new data with the value of the free parameters that we had obtained for hard spheres. This is a feature of our model that we wish to emphasize, since the usual situation is that parameters have to be readjusted for different interaction potentials. An experimental xenon self-diffusion data set was used as an example of where the model can be applied, especially in the high-density regime.

Experimental and modeling study of isothermal VLE properties of the supercritical C3H8 + benzylamine mixture

BackgroundsFor the design and development of a method utilizing SC C3H8 for the chemical synthesis like the production of active pharma ingredients (pharmaceutical applications) and crop protection agents, it is essential to understand the solubility and other properties of benzylamine as an industrial important compound in the SC C3H8. MethodsA high-temperature and high-pressure optical cell has been used to measure the phase equilibrium properties (PTxy) of the binary SC C3H8 + benzylamine mixture. The experimental and modeling studies of the isothermal VLE properties (solubility, PTxy relationship) of benzylamine in the supercritical (SC) C3H8 along the four selected constant temperatures of (393.15, 413.15, 433.15, and 473.15) K over the pressure range from (0.9 to 9.5) MPa have been performed in the present work. Significant FindingsIt was found the Perturbed-Chain Statistical Association Fluid Theory (PC-SAFT) is less accurate than its Critical Point-based revision (CP-PC-SAFT) in predicting the new VLE data in the C3H8 + benzylamine binary system with k12 = 0. Both models substantially deviate from the bubble point data at pressures below 2 MPa.

Bubble Point Measurements of cis-1,1,1,4,4,4-Hexafluorobutene [R-1336mzz(Z)] + trans-1,2-Dichloroethene [R-1130(E)] mixtures

Saturation pressures of pure R-1336mzz(Z) and R-1130(E) and bubble point pressures of three R-1336mzz(Z)/1130(E) blends were measured from 265 K to 360 K. For each pure refrigerant or refrigerant blend, a total of twenty unique saturation pressures or bubble points were measured. In total 100 unique state points were obtained. Presently, no Helmholtz-energy-explicit type equation of state (EoS) is available for R-1130(E). While an extended corresponding states EoS for R-1130(E) is available to estimate the properties of the R-1336mzz(Z)/1130(E) blend, this model does not resolve the azeotropic behavior of the mixture. Therefore, the perturbed-chain statistical-associating fluid theory (PC-SAFT) EoS is used to model the vapor–liquid equilibria of the R-1336mzz(Z)/1130(E) blend. PC-SAFT model parameters are reported, and the overall performance of the model is characterized by deviations from the experimental data.

Fluid energy theory of membrane

Membrane science is the key strategy to solve water shortage in the future, and its essence is energy and mass transfer. Due to the complexity and variety of the internal structure of membrane, the energy transfer theory of membrane is still a black box theory. Herein, a new fluid mechanics principle is introduced to establish the energy fluid theory of membrane, which is translated into the energy formula: such as the initial total pressure difference (ΔP), the flow rate of fluid exiting the membrane (v1 and v2), fluid density (ρ), and energy consumption by salt resistance (NSR): {ΔP2ΔPρ=ΔP2ΔPρ[1−v1ρ2ΔP]+NSR+[ΔPv1(v2v1)2−12ρv23]+12ρv23}. The theoretical framework is not only helpful for the data analysis of the energy transfer process of membranes, but also helps to allow for more in-depth and specific theoretical research. For instance, the relationship between NSR and the concentration difference (C) of salt can be expressed as NSR = aCb (a-product constant, b-exponential constant, R2>0.99). Hence, the basic theory can not only be widely applied to a variety of membranes with complex internal structure, but also have a profound impact on the application and research of membrane science.