Search Results (15)

Bacterially produced poly[(R)-3-hydroxybutyrate] (P3HB) was subjected to an alcoholysis reaction to produce low-molecular-weight (M_n ≈ 10,000 g mol⁻¹) hydroxy-terminated P3HB (LMPHB). Using diethyl zinc as a catalyst, LMPHB was reacted with the cyclic monomers ε-caprolactone and l-lactide in separate ring-opening polymerization (ROP) reactions to produce PHB-b-PCL (PHBCL) and PHB-b-PLA (PHBLA) AB-type crystalline–crystalline diblock copolymers with varying PCL and PLA block lengths. ¹H NMR and GPC were used to confirm the structure of the polymers. DSC was used to measure the thermal properties as well as assessing crystallization. A single-shifting T_g for PHBLA showed the two blocks to be miscible in the melt. The TGA results indicate enhanced thermal stability over the homopolymer P3HB. A study of the crystallization was undertaken by combining WAXD, a second DSC heating regime, and POM. POM showed that the crystallization in PHBCL to be dependent on the crystallization temperature more so than PHBLA, whose composition appeared to be the more definitive factor determining the spherulitic morphology. The results informed the crystallization temperatures used in the production of the melt-crystallized thin films that were imaged using AFM. AFM images showed unique surface morphologies dependent on the diblock copolymer composition, block length, and crystallization temperature. Finally, the enzymatic degradation studies showed these unique surface morphologies to influence how these block copolymers were degraded by enzymes. Full article

A better understanding of mixing times for mixed solvent systems in laboratory-scale vessels is crucial for improving mixing-sensitive processes such as antisolvent crystallisation. Whilst mixing in agitated vessels has been extensively studied using solutions of additives in the same solvent, there is very limited literature on the mixing of different miscible solvents and none which would be relevant to antisolvent crystallisation processes. In this work, the mixing times of water–ethanol systems in a 1 litre vessel, agitated by a pitched blade impeller with probes used as baffles, were investigated in the transitional flow regime using both experimental and computational fluid dynamics (CFD) approaches. We studied two scenarios: adding sodium chloride tracer to premixed water–ethanol solutions and adding ethanol containing a tracer to water. Mixing was investigated experimentally through conductivity measurements and computationally using large eddy simulations with the M-Star CFD software package. Empirical correlations from the Dynochem engineering toolbox were also used for comparison. The results showed significant run-to-run variability in the mixing times from both experiments and CFD simulations, with experimental ranges being notably wider than CFD ones under the given conditions. While the CFD simulations showed consistent mixing times across different solvent compositions, the experimental mixing times decreased with increasing ethanol content. The mixing times were approximately inversely proportional to the impeller speed. The CFD simulations indicated that 25–40 impeller rotations were required for homogenisation, while the experiments needed 25–100 rotations. The Dynochem correlations predicted 40 rotations, independent of speed, but could not capture the inherent variability of the mixing times. Full article

Longitudinal dispersion coefficient is a key parameter governing solute transport in porous media, with significant implications for various industrial processes. However, the impact of microfractures on the longitudinal dispersion coefficient remains insufficiently understood. In this study, pore-scale direct numerical simulations are performed to analyze solute transport in microfractured porous media during unstable miscible displacement. Spatiotemporal concentration profiles were fitted to the analytical solution of the convection–dispersion equation to quantify the longitudinal dispersion coefficient across different microfracture configurations. The results indicate that the longitudinal dispersion coefficient is highly sensitive to microfracture characteristics. Specifically, an increased projection length of microfractures in the flow direction and a reduced lateral projection length enhance longitudinal dispersion at the outlet. When Peclet number ≥1, the longitudinal dispersion coefficient follows a three-stage variation pattern along the flow direction, with microfracture connectivity and orientation dominating its scale sensitivity. Furthermore, both diffusion-dominated and mixed advective-diffusion regimes are observed. In diffusion-dominated regimes, significant channeling alters the applicability of traditional scaling laws, with the relationship between longitudinal dispersion coefficient and porosity holding only when the Peclet number is below 0.07. These results provide a comprehensive scale-up framework for CO₂ miscible flooding in unconventional reservoirs and CO₂ storage in saline aquifers, offering valuable insights for the numerical modeling of heterogeneous reservoir development. Full article

Gas miscible flooding, especially CO₂ miscible flooding, is a key method for enhanced oil recovery. However, the high Minimum Miscibility Pressure (MMP) often makes true-miscible flooding impractical. A number of studies confirm the existence of a near-miscible region that also ensures high recovery. However, the exact boundary for near miscibility remains unclear, with various speculative definitions based on experimental data or by experience. In this work, a molecular-level understanding of miscibility and near miscibility and the role of the MMP reducer are achieved using the molecular dynamics method. It is found that the traditional criterion of interfacial tension being zero is not valid for the molecular dynamics method, and that the interaction energy between oil molecules suggests distinct boundary between near-miscibility and miscibility regimes. MMP reducers were found to bring the two regions closer in terms of energy, rather than actually reducing the MMP. Full article

Numerical modeling of gas flows in rarefied regimes is crucial in understanding fluid behavior in microscale applications. Rarefied regimes are characterized by a decrease in molecular collisions, and they lead to unusual phenomena such as gas phase separation, which is not acknowledged in hydrodynamic equations. In this work, numerical investigation of miscible gaseous mixtures in the rarefied regime is performed using a modified lattice Boltzmann model. Slip boundary conditions are adapted to arbitrary geometries. A ray-tracing algorithm-based wall function is implemented to model the non-equilibrium effects in the transition flow regime. The molecular free flow defined by the Knudsen diffusion coefficient is integrated through an effective and asymmetrical binary diffusion coefficient. The numerical model is validated with mass flow measurements through microchannels of different cross-section shapes from the near-continuum to the transition regimes, and gas phase separation is studied within a staggered arrangement of spheres. The influence of porosity and mixture composition on the gas separation effect are analyzed. Numerical results highlight the increase in the degree of gas phase separation with the rarefaction rate and the molecular mass ratio. The various simulations also indicate that geometrical features in porous media have a greater impact on gaseous mixtures’ effective permeability at highly rarefied regimes. Finally, a permeability enhancement factor based on the lightest species of the gaseous mixture is derived. Full article

The present review focuses on the recent studies carried out in passive micromixers for understanding the hydrodynamics and transport phenomena of miscible liquid–liquid (LL) systems in terms of pressure drop and mixing indices. First, the passive micromixers have been categorized based on the type of complexity in shape, size, and configuration. It is observed that the use of different aspect ratios of the microchannel width, presence of obstructions, flow and operating conditions, and fluid properties majorly affect the mixing characteristics and pressure drop in passive micromixers. A regime map for the micromixer selection based on optimization of mixing index (MI) and pressure drop has been identified based on the literature data for the Reynolds number (Re) range (1 ≤ Re ≤ 100). The map comprehensively summarizes the favorable, moderately favorable, or non-operable regimes of a micromixer. Further, regions for special applications of complex micromixer shapes and micromixers operating at low Re have been identified. Similarly, the operable limits for a micromixer based on pressure drop for Re range 0.1 < Re < 100,000 have been identified. A comparison of measured pressure drop with fundamentally derived analytical expressions show that Category 3 and 4 micromixers mostly have higher pressure drops, except for a few efficient ones. An MI regime map comprising diffusion, chaotic advection, and mixed advection-dominated zones has also been devised. An empirical correlation for pressure drop as a function of Reynolds number has been developed and a corresponding friction factor has been obtained. Predictions on heat and mass transfer based on analogies in micromixers have also been proposed. Full article

This study explores the potential application of microfluidics in the field of bioenergy, with a particular focus on the energy potential of biogas derived from vine shoots, a locally abundant waste material. The enhanced mixing capability of a micromixer has been analyzed to make it suitable for microfluidic energy applications. Mixing index, pressure drop, and kinematic measurements within the T-micromixer with helical elements and their related mixing performances have been studied and validated using CFD for different values of Reynolds number (0.1–60) for laminar Newtonian miscible fluid. Geometrical characteristics were further examined to improve the mixing performance. Various values of twisted angles were evaluated and compared to choose the optimal angle. A new parameter, Q, was introduced to represent the ratio of vorticity square over the sum of vorticity square and deformation square intensities. Furthermore, the results of the numerical simulation were compared with the given data in the literature, showing a significant agreement, in addition to the fact that a high-quality mixture can be created with a geometry angle of 90°, and a mixing index above 0.99 can be obtained at low Reynolds numbers. The numerical investigation of the flow regimes of miscible fluid in the T-microkenics with the proposed angle can be utilized to develop the mixing performance of the micromixers in a wide variety of processes. Full article

In this work, slim tube displacement tests for minimum miscibility pressure MMP were carried out. Based on the displacement data, the MMP was calculated by statistical regression using linear and quadratic extrapolation with threshold values of 90% and 95% oil recovery as well as the intersection of trend lines for immiscible and miscible displacement regimes. The obtained data show a significant variation in the range of MMP values depending on the calculation method. To clarify the MMP value, an analysis of displacement dynamics was carried out. The ratio of the volume flow rate of reservoir oil to the volume flow rate of the injected gas—flow rates ratio (FFR)—was used as a new parameter. The MMP value calculated from the FRR value extrapolation was determined as 37.09 MPa. According to the results obtained, the proposed methodology based on the displacement dynamics can be useful as a criterion for clarifying the MMP value in slim tube displacement experiments. Full article

Miscible viscous fingering occurs when a less viscous fluid displaces a more viscous one in porous media or a Hele–Shaw cell. Such flow instabilities are of particular interest in a variety of applications in flows and displacements in subsurface energy and environment systems. In this study, we investigate the miscible viscous fingering dynamics experimentally using water to displace glycerol in a sealed Hele–Shaw cell with two wells located in it instead of at the boundary or corners. We comprehensively examine the spatial and temporal variations of fingering dynamics, different flow regimes, and how they are affected by the water injection rate and control of pressure or rate at the outlet. Alongside the widely recognized diffusion-dominated and convection-dominated flow regimes, we identify three new regimes: a slow expansion regime prior to breakthrough, a rapid shrinkage regime immediately after breakthrough, and a uniform, slow expansion regime without fingering instability. Each regime is characterized by interesting flow dynamics, which has not been reported previously. The duration of each regime depends on the water injection rate and whether constant pressure or a constant production rate is applied at the outlet. The variations of swept area, interfacial length, and count of fingers are also quantitatively examined. This study provides new insights into the fundamental mechanisms for miscible fluid displacements in a variety of applications such as CO₂ sequestration, hydrogen storage, enhanced oil recovery, and groundwater contaminate remediation. Full article

This study investigates the use of an ionic liquid obtained from fatty acids (FAIL) as an additive at 2 wt.% in two different base oils: a mineral oil (M1) and a polyol ester (E1). Physicochemical characterization of the base oil–FAIL blends confirmed the miscibility of the FAIL in the base oils. The addition of the FAIL hardly changed the density of the base oils and the viscosity slightly increased at lower temperatures. The tribological performance of the base oils and their blends with the FAIL was determined using three different tests: Stribeck curve determination and tribofilm formation tests, both under sliding/rolling motion, and reciprocating wear tests. The M1 + FAIL blend showed the lowest friction values under the mixed lubrication regime due to its higher viscosity, while the E1 + FAIL showed the lowest friction values under the elastohydrodynamic lubrication regime, which may well have been due to its higher polarity. Only the E1 + FAIL blend outperformed the antiwear behavior of the base oil, probably because it has better chemical affinity (higher polarity) for the metallic surface. SEM images showed that the predominant wear mechanism was adhesive-type with plastic deformation and XPS studies proved that the presence of increasing amounts of organic oxygen on the wear scar caused better antiwear performance when the E1 + FAIL blend was used. Full article

We studied the miscibility of two dipolar quantum gases in the limit of zero temperature. The system under study is composed of a mixture of two Bose gases with dominant dipolar interaction in a two-dimensional harmonic confinement. The dipolar moments are all considered to be perpendicular to the plane, turning the dipolar potential in a purely repulsive and isotropic model. Our analysis is carried out by using the diffusion Monte Carlo method, which allows for an exact solution to the many-body problem within some statistical noise. Our results show that the miscibility between the two species is rather constrained as a function of the relative dipolar moments and masses of the two components. A narrow regime is predicted where both species mix and we introduce an adimensional parameter whose value quite accurately predicts the miscibility of the two dipolar gases. Full article

The miscibility and phase separation of poly(methyl methacrylate) (PMMA) and styrene-acrylonitrile (SAN) have already been investigated using various methods. However, these methods have limitations that often result in inconsistent characterization. Consequently, the reasons for the dependence of miscibility on composition as well as on processing temperature have not yet been proved. The phase separation of PMMA/SAN blends was therefore investigated for the first time using a novel technique, nanoscale AFM-IR. It couples nanoscale atomic force microscopy (AFM) with infrared (IR) spectroscopy. Therefore, the phase morphology can be chemically identified and precisely classified within the nm-regime. The PMMA/SAN blends, on the other hand, were analyzed of their changes in morphology under different thermal treatments. It was possible to visualize and define the phase separation, as well as dependence of the miscibility on the mixing ratio. In the miscible domain, no two individual phases could be detected down to the nanometer range. It was shown that with increasing temperature, the morphology changes and two different phases are formed, where the phase boundaries can be sharply defined. The onset of these changes could be identified at temperatures of about 100 °C. Full article

The effects of miscibility in interacting two-component classical fluids are relevant in a broad range of daily applications. When considering quantum systems, two-component Bose–Einstein condensates provide a well-controlled platform where the miscible–immiscible phase transition can be completely characterized. In homogeneous systems, this phase transition is governed only by the competition between intra- and inter-species interactions. However, in more conventional experiments dealing with trapped gases, the pressure of the confinement increases the role of the kinetic energy and makes the system more miscible. In the most general case, the miscibility phase diagram of unbalanced mixtures of different atomic species is strongly modified by the atom number ratio and the different gravitational sags. Here, we numerically investigate the ground-state of a ${}^{23}$Na–${}^{39}$K quantum mixture for different interaction strengths and atom number ratios considering realistic experimental parameters. Defining the spatial overlap between the resulting atomic clouds, we construct the phase diagram of the miscibility transition which could be directly measured in real experiments. Full article

We explain the composition of ternary nanowires nucleating from a quaternary liquid melt. The model we derive describes the evolution of the solid composition from the nucleated-limited composition to the kinetic one. The effect of the growth temperature, group V concentration and Au/III concentration ratio on the solid-liquid dependence is studied. It has been shown that the solid composition increases with increasing temperature and Au concentration in the droplet at the fixed In/Ga concentration ratio. The model does not depend on the site of nucleation and the geometry of monolayer growth and is applicable for nucleation and growth on a facet with finite radius. The case of a steady-state (or final) solid composition is considered and discussed separately. While the nucleation-limited liquid-solid composition dependence contains the miscibility gap at relevant temperatures for growth of In_xGa_1−xAs NWs, the miscibility gap may be suppressed completely in the steady-state growth regime at high supersaturation. The theoretical results are compared with available experimental data via the combination of the here described solid-liquid and a simple kinetic liquid-vapor model. Full article

The existence, stability, and dynamics of bound pairs of symbiotic matter waves in the form of dark-bright soliton pairs in two-component mixtures of atomic Bose–Einstein condensates is investigated. Motivated by the tunability of the atomic interactions in recent experiments, we explore in detail the impact that changes in the interaction strengths have on these bound pairs by considering significant deviations from the integrable limit. It is found that dark-bright soliton pairs exist as stable configurations in a wide parametric window spanning both the miscible and the immiscible regime of interactions. Outside this parameter interval, two unstable regions are identified and are associated with a supercritical and a subcritical pitchfork bifurcation, respectively. Dynamical manifestation of these instabilities gives rise to a redistribution of the bright density between the dark solitons, and also to symmetry-broken stationary states that are mass imbalanced (asymmetric) with respect to their bright soliton counterpart. The long-time dynamics of both the stable and the unstable balanced and imbalanced dark-bright soliton pairs is analyzed. Full article