Miscible Mixtures Research Articles

Numerical Simulation of Magnetic Nanoparticles Injection into Two–phase Flow in a Porous Medium

In this paper, the problem of magnetic nanoparticles injection into a water–oil two–phase flow under an external permanent magnetic field is investigated. The mathematical model of the problem under consideration has been developed. We treat the water-nanoparticles suspension as a miscible mixture while it is immiscible with the oil phase. The magnetized phase pressure includes an additional pressure term with the conventional thermodynamic pressure. The countercurrent imbibition flow problem is taken as an example. Physical variables including water–nanoparticles suspension saturation, nanoparticles concentration, and pore wall/throat deposited nanoparticles are investigated under the influence of the magnetic field.

Modeling and Analysis of Magnetic Nanoparticles Injection in Water-Oil Two-Phase Flow in Porous Media under Magnetic Field Effect

In this paper, the magnetic nanoparticles are injected into a water-oil, two-phase system under the influence of an external permanent magnetic field. We lay down the mathematical model and provide a set of numerical exercises of hypothetical cases to show how an external magnetic field can influence the transport of nanoparticles in the proposed two-phase system in porous media. We treat the water-nanoparticles suspension as a miscible mixture, whereas it is immiscible with the oil phase. The magnetization properties, the density, and the viscosity of the ferrofluids are obtained based on mixture theory relationships. In the mathematical model, the phase pressure contains additional term to account for the extra pressures due to fluid magnetization effect and the magnetostrictive effect. As a proof of concept, the proposed model is applied on a countercurrent imbibition flow system in which both the displacing and the displaced fluids move in opposite directions. Physical variables, including water-nanoparticles suspension saturation, nanoparticles concentration, and pore wall/throat concentrations of deposited nanoparticles, are investigated under the influence of the magnetic field. Two different locations of the magnet are studied numerically, and variations in permeability and porosity are considered.

Phase Behavior of Dried – DDA Liposomal Formulation Dispersed in HPMC Matrix in the presence of Saccharides

The present study describes the effect of saccharides and hydroxypropyl methylcellulose (HPMC) matrix on phase behavior of dehydrated cationic dimethyl- dioctadecylammonium (DDA)-based liposomes. Saccharides such as sucrose, lactose and mannitol,have been reportedpreserve the lipid membranes during drying, whilst HPMC matrix is widely used in solid dispersion to prevent aggregation and/or recrystallization.The study revealed that addition of sucrose and HPMCin the formulation demonstrated a miscible mixture that might construct a stable dried liposomal formulation. DTA data showed that sucrose (5%w/v) and HPMC added to DDA liposomal formulation were relatively more miscible with the mixtures; whereas lactose and mannitol at the same concentration of 5% showed phase separation from the mixtures in the dehydrated state. Furthermore, XRD and SEM analysis exhibited supporting evidences in which formulation using sucrose and lactose showedrelatively less crystalline-forming properties compared to formulation using mannitol. Recrystallization that cause phase separation might trigger leakage and further affect the efficacy of the entrapped drug/antigen. From these data, it might be concluded that a driedliposomal formulation can be prepared in the presence of sucrose (lyoprotectant) that is dispersed in HPMC matrix. The protective mechanism of sucrose (5%w/v) and HPMC matrix is proposed through inhibition of the recrystallization which causes phase separation; indicated by DTA, SEM and XRDdata. The present study revealed prospective advantages of using sucrose and HPMC in development of dried – DDA liposomal formulations. Keywords : Liposomes, DDA, Sucrose, Lactose, Mannitol, HPMC, Phase Separation.

Mutual diffusion governed by kinetics and thermodynamics in the partially miscible mixture methanol + cyclohexane.

To gain an understanding of the transport and thermodynamic behavior of the highly non-ideal mixture methanol + cyclohexane, three complementary approaches, i.e. experiment, molecular simulation and predictive equations, are employed. The temperature and composition dependence of different diffusion coefficients is studied around the miscibility gap at ambient pressure. On the one hand Fick diffusion coefficients are measured experimentally by interferometric probing and on the other hand Maxwell-Stefan diffusion coefficients and intradiffusion coefficients are sampled by equilibrium molecular dynamics simulation at five temperatures below the upper critical temperature of ∼319 K. The spinodal curve is determined from extrapolation of the experimental Fick diffusion coefficient data and compared to predictions from excess Gibbs energy models. It is found that these models are not capable to correctly describe the activity coefficients over the whole composition range of the studied mixture. Thus, different parameter sets for a modified Wilson model are used for calculations of the thermodynamic factor, which is needed to transform Maxwell-Stefan into Fick diffusion coefficients and vice versa. Further, predictive equations for the Maxwell-Stefan diffusion coefficient, which are based on intradiffusion coefficients, are compared to simulation results. Using different approaches provides a clearer understanding of the relations between kinetic and thermodynamic properties contributing to the diffusion behavior of partially miscible mixtures.

Synergistic local toughening of high performance epoxy-matrix composites using blended block copolymer-thermoplastic thin films

A new block copolymer-thermoplastic dual toughening concept for high performance RTM6 epoxy matrix composites is elaborated through a comprehensive microstructural study of well-defined model systems. A blend of phenoxy and MAM (copolymer of poly(methyl methacrylate) and poly(butyl acrylate)) increases the toughness of the corresponding carbon fiber reinforced composite by 125%, a five-fold synergistic improvement over the situation where the tougheners are used alone at the same total concentration. Selective intercalation of blended toughener thin films in the preform gives rise to a diffusion-induced composition gradient during the RTM process, which generates a morphology gradient upon curing. The observed microstructures results from MAM self-assembly in the miscible mixture of phenoxy and the epoxy resin precursor, followed by reaction induced phase separation, forming wormlike micelles, interconnected micelles and co-continuous morphologies. The resulting microstructures activate different toughening mechanisms responsible for the observed synergy.

Thermodynamic coarsening arrested by viscous fingering in partially miscible binary mixtures.

We study the evolution of binary mixtures far from equilibrium, and show that the interplay between phase separation and hydrodynamic instability can arrest the Ostwald ripening process characteristic of nonflowing mixtures. We describe a model binary system in a Hele-Shaw cell using a phase-field approach with explicit dependence of both phase fraction and mass concentration. When the viscosity contrast between phases is large (as is the case for gas and liquid phases), an imposed background flow leads to viscous fingering, phase branching, and pinch off. This dynamic flow disorder limits phase growth and arrests thermodynamic coarsening. As a result, the system reaches a regime of statistical steady state in which the binary mixture is permanently driven away from equilibrium.

Spinodal decomposition of chemically reactive binary mixtures.

We simulate the influence of a reversible isomerization reaction on the phase segregation process occurring after spinodal decomposition of a deeply quenched regular binary mixture, restricting attention to systems wherein material transport occurs solely by diffusion. Our theoretical approach follows a diffuse-interface model of partially miscible binary mixtures wherein the coupling between reaction and diffusion is addressed within the frame of nonequilibrium thermodynamics, leading to a linear dependence of the reaction rate on the chemical affinity. Ultimately, the rate for an elementary reaction depends on the local part of the chemical potential difference since reaction is an inherently local phenomenon. Based on two-dimensional simulation results, we express the competition between segregation and reaction as a function of the Damköhler number. For a phase-separating mixture with components having different physical properties, a skewed phase diagram leads, at large times, to a system converging to a single-phase equilibrium state, corresponding to the absolute minimum of the Gibbs free energy. This conclusion continues to hold for the critical phase separation of an ideally perfectly symmetric binary mixture, where the choice of final equilibrium state at large times depends on the initial mean concentration being slightly larger or less than the critical concentration.

Simple Engineering of Polymer–Nanoparticle Hybrid Nanocapsules

AbstractA general method to generate hybrid hollow capsules is reported. The process is based on the stabilization of solvent droplets by nanoparticles, in macroscopically miscible mixtures of tetrahydrofuran (THF) and water. After addition of a crosslinking polymer and removal of the solvent core, capsules of diameter ca 100 nm are obtained. This novel strategy does not require the use of block copolymers. In contrast, most methods reporting the formation of hybrid nanocapsules incorporate nanoparticles into block‐copolymer polymersomes or use nanoparticles tethered with block‐copolymers. The nanocapsules were characterized using a full set of techniques including nanoparticle tracking analysis, electron microscopy and liquid phase atomic force microscopy. Our results show that the vesicular shape of the nanocapsules is templated by the liquid droplets. Nanocapsules were prepared from quantum dots, gold nanoparticles, superparamagnetic iron oxide nanoparticles and mixtures of particles. The entrapment of a fluorescent dye was also demonstrated. Thus, nanocapsules with dual properties (e.g., magnetic and fluorescent) are easily obtained. Interestingly, the magnetic nanocapsules enable magnetic resonance imaging contrast enhancement of tumors in vivo.

The influence of molecular weight distribution of industrial polystyrene on its melt extensional and ultimate properties

We analyze the linear viscoelastic behavior and the strain‐rate dependence of nonlinear viscoelastic as well as the ultimate extensional properties of industrially relevant linear polystyrene mixtures (PS). The studied materials comprise different miscible binary mixtures of a well entangled matrix and unentangled diluent resulting in bimodal molar mass distribution (MWD). We also analyze the effect of the diluent weight average molar mass (Mw) by comparison with a mixture having broad but monomodal MWD. We show that the dilution effect on linear rheological properties is in agreement with the theoretical value of unity for the dilution exponent. We further show that the processing window, expressed as the ability of the material to withstand a given load without loss of homogeneity during elongation or ultimate loss of cohesion, is affected differently depending on the diluent Mw and concentration. Finally, we conclude that the existence of strain hardening is not sufficient for complete characterization of extension dominated operations. Our results demonstrate that significant enhancement of strain hardening achieved by adding small‐Mw diluents is often accompanied by trade‐off with respect to failure behavior of these mixtures. POLYM. ENG. SCI. 56:1012–1020, 2016. © 2016 Society of Plastics Engineers

Critical conditions for the buoyancy-driven detachment of a wall-bound pendant drop

We investigate numerically the critical conditions for detachment of an isolated, wall-bound emulsion droplet acted upon by surface tension and wall-normal buoyancy forces alone. To that end, we present a simple extension of a diffuse-interface model for partially miscible binary mixtures that was previously employed for simulating several two-phase flow phenomena far and near the critical point [A. G. Lamorgese et al. “Phase-field approach to multiphase flow modeling,” Milan J. Math. 79(2), 597–642 (2011)] to allow for static contact angles other than 90°. We use the same formulation of the Cahn boundary condition as first proposed by Jacqmin [“Contact-line dynamics of a diffuse fluid interface,” J. Fluid Mech. 402, 57–88 (2000)], which accommodates a cubic (Hermite) interpolation of surface tensions between the wall and each phase at equilibrium. We show that this model can be successfully employed for simulating three-phase contact line problems in stable emulsions with nearly immiscible components. We also show a numerical determination of critical Bond numbers as a function of static contact angle by phase-field simulation.

Highlighting Diffusional Coupling Effects in Ternary Liquid Extraction and Comparisons with Distillation

Liquid extraction processes involve the separation of mixtures containing three or more species whose compositions are close to the binodal curve; this proximity causes the diffusion equilibration process to be strongly influenced by phase equilibrium thermodynamics. Due to thermodynamic factors, the interphase transfer flux of any component is influenced by the driving force of all the constituent species in the mixture, i.e. the diffusion process is strongly coupled. The transient diffusion equilibration process within spherical droplets dispersed within a continuous liquid phase is quantified by the classic Geddes model, used in combination with the Maxwell–Stefan diffusion formulation. For 13 different partially miscible ternary liquid mixtures, the equilibration trajectories in composition space are found to be curvilinear in shape. In all cases, the component Murphree efficiencies, Ei, are unequal to one another. The separations achieved are significantly different from those predicted by a simpler ...

Anthracene and pyrene photolysis kinetics in aqueous, organic, and mixed aqueous-organic phases

Condensed phases in the atmosphere, such as cloud droplets and aerosols, often contain both water and organic matter (OM). Reactivity can differ significantly between aqueous and organic phases. We have measured photolysis kinetics of the polycyclic aromatic hydrocarbons (PAHs) anthracene and pyrene in several organic solvents and in water, as well as in miscible and phase-separated aqueous-organic mixtures at atmospherically-relevant wavelengths. Photolysis rate constants generally increased with increasing solvent polarity; photolysis of both PAHs was more than ten times faster in water than in octanol. Local polarity had a much greater effect on PAH photolysis kinetics than changes in PAH absorptivity or singlet oxygen concentrations. Photolysis kinetics in homogeneous aqueous-organic mixtures varied monotonically with2 OM volume fraction. Kinetics in immiscible (phase-separated) solutions were more complex, with different dependences on OM content observed in stagnant and turbulent solutions. Our results suggest that OM could greatly affect the photochemical lifetimes of PAHs in atmospheric condensed phases such as aerosols, even if the OM does not itself absorb photons.

Buoyancy-driven detachment of a wall-bound pendant drop: interface shape at pinchoff and nonequilibrium surface tension.

We present numerical results from phase-field simulations of the buoyancy-driven detachment of an isolated, wall-bound pendant emulsion droplet acted upon by surface tension and wall-normal buoyancy forces alone. Our theoretical approach follows a diffuse-interface model for partially miscible binary mixtures which has been extended to include the influence of static contact angles other than 90^{∘}, based on a Hermite interpolation formulation of the Cahn boundary condition as first proposed by Jacqmin [J. Fluid Mech. 402, 57 (2000)JFLSA70022-112010.1017/S0022112099006874]. In a previous work, this model has been successfully employed for simulating triphase contact line problems in stable emulsions with nearly immiscible components, and, in particular, applied to the determination of critical Bond numbers for buoyancy-driven detachment as a function of static contact angle. Herein, the shapes of interfaces at pinchoff are investigated as a function of static contact angle and distance to the critical condition. Furthermore, we show numerical results on the nonequilibrium surface tension that help to explain the discrepancy between our numerically determined static contact angle dependence of the critical Bond number and its sharp-interface counterpart based on a static stability analysis of equilibrium shapes after numerical integration of the Young-Laplace equation. Finally, we show the influence of static contact angle and distance to the critical condition on the temporal evolution of the minimum neck radius in the necking regime of drop detachment.

Low Mach number fluctuating hydrodynamics of binary liquid mixtures

Continuing on our previous work [ArXiv:1212.2644], we develop semi-implicit numerical methods for solving low Mach number fluctuating hydrodynamic equations appropriate for modeling diffusive mixing in isothermal mixtures of fluids with different densities and transport coefficients. We treat viscous dissipation implicitly using a recently-developed variable-coefficient Stokes solver [ArXiv:1308.4605]. This allows us to increase the time step size significantly compared to the earlier explicit temporal integrator. For viscous-dominated flows, such as flows at small scales, we develop a scheme for integrating the overdamped limit of the low Mach equations, in which inertia vanishes and the fluid motion can be described by a steady Stokes equation. We also describe how to incorporate advanced higher-order Godunov advection schemes in the numerical method, allowing for the treatment of fluids with high Schmidt number including the vanishing mass diffusion coefficient limit. We incorporate thermal fluctuations in the description in both the inertial and overdamped regimes. We apply our algorithms to model the development of giant concentration fluctuations during the diffusive mixing of water and glycerol, and compare numerical results with experimental measurements. We find good agreement between the two, and observe propagative (non-diffusive) modes at small wavenumbers (large spatial scales), not reported in published experimental measurements of concentration fluctuations in fluid mixtures. Our work forms the foundation for developing low Mach number fluctuating hydrodynamics methods for miscible multi-species mixtures of chemically reacting fluids.

Nanoparticle biphasic calcium phosphate loading on gelatin-pectin scaffold for improved bone regeneration.

Biphasic calcium phosphate (BCP) nanoparticles were loaded with porous gelatin-pectin (GE-P) scaffolds. The biodegradable gelatin-pectin-BCP scaffolds were produced as miscible mixtures with well-defined interconnected pores to facilitate osteoconductivity and enhance bone formation. It was observed that the compressive strength increased with the loading of BCP nanoparticles. From in vitro results, cell adhesion, viability, and proliferation were found in the GE-P-10 scaffolds in comparison with those without BCP, resulting in high alkaline phosphate (ALP), and osteopontin (OPN) expression at 21 days. Micro-computed tomography data, hematoxylin and eosin staining, and immunohistochemistry (OPN, OCN, COL I, and COL II) confirmed rapid new bone formation in rabbit models. Our results provide a novel and simple method to provide an adequate scaffold, and thus GE-P-BCP porous scaffolds may be appropriate candidates for bone tissue engineering.

Flashpoint Prediction for Binary Mixtures of Alcohols with Water in Order to Improve their Safety

AbstractAqueous solutions of alcohols are of considerable interest for a wide range of scientists and technologists. Simple dimensionless experimental formulae based on rational reciprocal and polynomial functions are proposed for correlation of the flashpoint data of binary mixtures of two components. The formulae are based on data obtained from flashpoint experiments and predictions. The main results are the derived flashpoint approximated values and the model verification by comparing the predicted values with the experimental data for the studied mixtures. Potential application for the model concerns the assessment of fire and explosion hazards, and the development of inherently safer designs for chemical processes containing binary partially miscible mixtures of an aqueous‐organic system.

A new method for the prediction of flash points for ternary miscible mixtures

The flash point is one of the most important physicochemical parameters used to characterize the fire and explosion hazard for flammable liquids. The flash points of ternary miscible mixtures with different components and compositions were measured in this study. Four model input parameters, being normal boiling point, the standard enthalpy of vaporization, the average number of carbon atoms and the stoichiometric concentration of the gas phase for mixtures, were employed and calculated based on the theory of vapor–liquid equilibrium. Both multiple linear regression (MLR) and multiple nonlinear regression (MNR) methods were applied to develop prediction models for the flash points of ternary miscible mixtures. The developed predictive models were validated using data measured experimentally as well as taking data on flash points of ternairy mixtures from the literature. Results showed that the obtained average absolute error of both the MLR and the MNR model for all the datasets were within the range of experimental error of flash point measurements. It is shown that the presented models can be effectively used to predict the flash points of ternary mixtures with only some common physicochemical parameters.

Flash points measurements and prediction for binary miscible mixtures

Flash point is one of the most important parameters used to characterize the potential fire and explosion hazards for flammable liquids. In this study, flash points of twenty eight binary miscible mixtures comprised eighteen flammable pure components with different compositions were measured by using the closed cup apparatus. The obtained experimental data are further employed to develop simple and accurate models for predicting the flash points of binary miscible mixtures. Based on the vapor–liquid equilibrium theory, the normal boiling point, the standard enthalpy of vaporization, the average number of carbon atoms, and the stoichiometric concentration of the gas phase were selected as the dominant physicochemical parameters that were relevant to the overall flash point property of liquids. With these parameters for pure components as well as the compositions of mixtures, the new form of characteristic physicochemical parameters for mixtures were developed and used as the input parameters for the flash point prediction of mixtures. Both the modeling methods of multiple linear regression (MLR) and multiple nonlinear regression (MNR) were employed to model the possible quantitative relationships between the parameters for mixtures and the flash points of binary miscible mixtures. The resulted models showed satisfactory prediction ability, with the average absolute error for the external test set being 2.506 K for the MLR model and 2.537 K for the MNR model, respectively, both of which were within the range of the experimental error of FP measurements. Model validation was also performed to check the stability and predictivity of the presented models, and the results showed that both models were valid and predictive. The models were further compared to other previously published models. The results indicated the superiority of the presented models and revealed which can be effectively used to predict the FP of binary miscible mixtures, requiring only some common physicochemical parameters for the pure components other than any experimental flash point or flammability limit data as well as the use of the Le Chatelier law. This study can provide a simple, yet accurate way for engineering to predict the flash points of binary miscible mixtures as applied in the assessment of fire and explosion hazards and the development of inherently safer designs for chemical processes.

Experimental Study of Pool Boiling at Low Heat Flux in Water Miscible Binary Mixtures

Experimental studies are conducted to investigate pool boiling characteristics of water and its binary mixtures with ethanol and 2-propanol, at low heat fluxes. In-house fabricated experimental setup is used for the studies. Ethanol and 2-propanol are both water miscible and have a boiling point lower than that of pure water. The relation between the surface heat flux and degree of superheat for the above binary mixtures is obtained for low heat flux values in the range of 3kW/m2 to 30kW/m2. Variation of change in concentration and degree of superheat with time is reported for water miscible binary mixtures. The experimental results obtained are compared against the results predicted by correlations in the literature.

Preparation of polydopamine nanocapsules in a miscible tetrahydrofuran-buffer mixture.

A miscible tetrahydrofuran-tris buffer mixture has been used to fabricate polydopamine hollow capsules with a size of 200 nm and with a shell thickness of 40 nm. An unusual non-emulsion soft template mechanism has been disclosed to explain the formation of capsules. The results indicate that the capsule structure is highly dependent on the volume fraction of tetrahydrofuran as well as the solvent, and the shell thickness of capsules can be controlled by adjusting the reaction time and dopamine concentration.