Miscible Solutions Research Articles

Tracking the Micro-Heterogeneity and Hydrogen-Bonding Interactions in Hydroxyl-Functionalized Ionic Liquid Solutions: A Combined Experimental and Computational Study.

Ionic liquids (ILs) are an important class of media that are usually used in combination with polar solvents to reduce costs and tune their physicochemical properties. In this regard, it is essential to understand the influence of adding solvents on the properties of ILs. In this work, the micro-heterogeneity and H-bonding interactions between a hydroxyl-functionalized IL, [HOEmim][TFSI], and acetonitrile (ACN) were investigated by attenuated total reflection Fourier transform infrared spectroscopy and molecular simulations. All studied IL-ACN mixtures were found to deviate from the ideal mixtures. The degree of deviations reaches the maximum at about x(ACN)=0.7 with the presence of both homogeneous clusters of pure IL/ACN and heterogeneous clusters of IL-ACN. With the addition of ACN to IL, the mixtures undergo the transformation from "ACN solvated in [HOEmim][TFSI]" to "[HOEmim][TFSI] solvated in ACN". It is found that the newly formed H-bonding interactions between the IL and ACN is the main factor that contributes to the red shifts of O-H, C2 -H, C4,5 -H, and Calkyl -H of [HOEmim]+ cation, and the blue shifts of C-D, C≡N of ACN, and C-F, S=O of [TFSI]- anion. These in-depth studies on the mixtures of hydroxyl-functionalized IL and acetonitrile would help to understand the micro-heterogeneity and H-bonding interactions of miscible solutions and shed light on exploring their applications.

Phase equilibria of Al2O3–TiOx system under various oxygen partial pressure: Emphasis on stability of Al2TiO5–Ti3O5 pseudobrookite solid solution

Phase equilibria of Al2O3–TiOx system were experimentally determined in a wide range of T and PO2: 1300 °C ≤T≤ 1600 °C and −16.6≤logPO2≤−8.0 (in atm). X-Ray diffraction and electron probe micro-analysis were employed to obtain equilibrium phases and compositions. Corundum (Al2O3 with limited Ti2O3), rutile (TiO2 with limited Al2O3), and pseudobrookite (Al2TiO5–Ti3O5) solid solutions were found. The liquid oxide phase was not found up to 1650 °C. At each temperature, the cationic ratio of the pseudobrookite solid solution (RTi = nTi/(nAl + Ti)) increased as PO2, thereby forming a wide range of solid solution from Al2TiO5 (RTi = 1/3) to Ti3O5 (RTi = 1.0). The pseudobrookite solid solution was a complete miscible solution at 1600 °C, while it exhibited a small miscibility gap at 1500 °C. Based on the results obtained in the present study, the behavior of Al2TiO5 was discussed in two aspects: (1) changes in physical properties and (2) evolution of Al–Ti complex oxide inclusions in liquid steel.

Addition of V2O5 and V2O3 to the CaO–FeO–Fe2O3–MgO–SiO2 database for vanadium distribution and viscosity calculations

Vanadium oxides were added to the existing GTOx database because of its important role in the ferro-titanium metallurgy as well as in petroleum coke gasification. The CaO–FeO–Fe2O3–MgO–SiO2 system is a part of GTOx database and is chosen because of the existence of experimentally determined vanadium distributions between vanadium ferroalloys and metallurgical slags. The CaO–FeO–Fe2O3–MgO–SiO2–V2O3–V2O5 system including all binary and ternary sub-systems was thermodynamically assessed using all available experimental data. Vanadium was introduced into the thermodynamic description of solid solution phases such as MeO, Spinel, Corundum and Ca2SiO4-α using available experimental information. Particular attention was given to the phase Spinel which forms the wide completely miscible solid solution Fe3O4–FeV2O4–MgV2O4–MgFe2O4. The thermodynamic description of the metallic vanadium containing systems was taken from the SGTE alloy database. With the knowledge about the complex behavior of vanadium in slags as well as in liquid metal alloys it is possible to calculate the vanadium distribution ratios (V)/[V] between iron melts and slags in a wide range of temperatures and compositions, corroborating the validity of the model under reducing conditions. The additionally developed viscosity model shows good agreement between the calculated and experimental values in vanadium-containing slags.

Nonequilibrium solidification velocity, recalescence degree and grain refinement of highly undercooled Ni-based single-phase alloys

The solidification velocity-undercooling relationship of infinite miscible solid solution Ni-Cu alloys was established. The research shows that the growth velocity follows four stages of “exponential growth—platform period—linear growth—platform period” within the undercooling range. The solute trapping occurs in the linear growth stage with a discontinuity velocity jump which makes the migration interface smooth and solidification uniform. According to the recalescence degree-undercooling function, the relationship among solute composition, non-equilibrium solidification degree and grain refinement was established. It is found that higher recalescence degree enhances the non-equilibrium solidification effect and the primary solid fraction formed is higher, which makes it easier for grain refinement to occur at high undercooling. By using EBSD characterization, the obvious misorientation and high-density twin boundaries were observed in the crystal structure at high undercooling. The microhardness decreases sharply after critical undercooling, and HRTEM analysis shows that the structural orientation of adjoining grains is totally different, which can provide comprehensive and reliable evidence for recrystallization mechanism.

Manipulation of toroidal-spiral particles internal structure by fluid flow

We report on the precise manipulation of the fine structures of toroidal-spiral particles (TSPs) generated by a self-assembly process of droplet sedimentation at low Reynolds numbers in a miscible bulk solution followed by solidification. The biocompatible polymeric TSP can serve as a device for drug delivery and in vivo therapeutic cell expansion, activation, and delivery, for which highly tunable and reproducible structures are essential to design dosages and release kinetics. TSP formation can be divided into two stages: initial infusion of the drop vs its subsequent sedimentation, deformation, and entrainment of the surrounding bulk solution. The infusion rate affects the drop shape and tail length. These two features represent crucial initial conditions for subsequent shape evolution, which determines the overall morphology of the TSP and fine structure of the internal channel. Our computer simulations of drop dynamics add a new capability to the swarm-of-Stokeslets technique: unequal viscosities of the drop and bulk phases (i.e., non-unit viscosity ratio). During sedimentation, the density difference between the droplet and the bulk solution played a more pronounced role than the viscosity ratio, which was revealed both by experimental observations and numerical simulations. Understanding the fundamental hydrodynamics and developing a flow map will ultimately aid in the design of TSPs with tunable empty channels toward drug delivery and cell encapsulation.

Simultaneous formation of inclusion complex and microparticles containing Albendazole and β-Cyclodextrin by supercritical antisolvent co-precipitation

Albendazole (ABZ) is an effective anthelmintic and an anticancer candidate. Due to the low oral bioavailability associated with its poor aqueous solubility, high doses are required, and dose-related side effects are reported. To enhance ABZ dissolution different formulation approaches were proposed, among others, its combination with cyclodextrins. In this work, co-precipitation of β-cyclodextrin and ABZ was performed by supercritical antisolvent technique as an alternative preparation method. The operating temperature and pressure of the experiments were selected by thermodynamic modeling with the purpose of obtaining a miscible solution between solvent mixture (DMSO + acetone) and CO2. Precipitated microparticles were characterized by spectroscopic, thermal, and crystallographic analysis in order to demonstrate the formation of a new solid form. The characterization evidenced that tautomer II of ABZ was obtained by precipitation in supercritical CO2 medium. The change of the crystalline phase was discussed in light of the results reported in the literature. Composite microparticles were obtained with a mean diameter ranging from 0.45 to 1.4 μm. An increase of about 4 times in the ABZ dissolution rate was measured for the particles with a 3:1 ABZ:β-cyclodextrin molar ratio with respect to the corresponding physical mixture and pure ABZ obtained by the same method. The dissolution improvement was attributed to the formation of the inclusion complex and a synergetic effect between both components, rather than the increase obtained for the change of ABZ to polymorphic form II.

Flexible Humidity Sensitive Fiber with Swellable Metal–Organic Frameworks

Humidity sensors have become an essential need for improving daily life quality. Here, a novel humidity sensitive fiber was fabricated using the soft polydimethylsiloxane (PDMS) as the core layer and the non-swellable polyvinylidenedifluoride (PVDF) embedded with a swellable MIL-88A as the outer layer. Noticeably, the PDMS fiber was chosen as a carrier due to its smoothness, softness and good tensile properties. The isoreticular FeIII dicarboxylate MIL-88 family with swellable metal–organic frameworks (MOFs) can undergo reversible dynamic structural transformations with a response to external humidity change. The resulted fiber with swellable MOFs showed three kinds of deformation for a single solvent and also had good deformation performance for two-component miscible solution with different volume ratios. As a proof of concept, a shape-memory effect at relative humidity from 10 to 90% and the simulated salt solutions instead of relative humidity changes were used to evaluate humidity change. In addition, a deep insight into the self-shape-change mechanism among those phenomena was investigated, wherein expansion deformation of the PDMS fiber as well as the structural transformation of the MIL-88A worked in different conditions.

Mixing control in a continuous-flow microreactor using electro-osmotic flow

In recent years, pharmaceutical production has been stimulating the gradual miniaturization of continuous-flow chemical reactors. This process eventually resulted in the emergence of a new generation of microreactors. The advantages of these new reactor types are the flexible production that allows us to quickly reconfigure the scheme, small reactant quantities used for the synthesis, the control of the main reaction parameters with high accuracy. Nevertheless, a decrease in the thickness of the channels where the species contact and react forces us to search for new non-mechanical mechanisms for mixing. This problem is relevant for the slow reaction occurring in a slot where diffusion alone cannot provide mixing at reasonable distances from the entrance. It is also true for the fast reaction that takes place in a frontal manner. In this work, we consider the efficiency of mixing the reactants induced by electro-osmotic flow in a Hele-Shaw configuration with non-uniform zeta potential distribution. As a test reaction, we take the neutralization reaction with simple albeit non-linear kinetics. The reaction occurs between two miscible solutions, which are initially separated in space and come into contact in a continuous-flow microreactor. The reaction proceeds frontally, which prevents the efficient mixing of the reactants due to diffusion. Using direct numerical simulations of 2D and 3D flows, we demonstrate that the zeta potential applied to boundaries can effectively control the mixing rate of fluids by lengthening the front of the reaction. This approach makes it possible to increase the yield of the reaction product.

On the instability of buoyancy-driven flows in porous media

The interface between two miscible solutions in porous media and Hele-Shaw cells (two glass plates separated by a thin gap) in a gravity field can destabilise due to buoyancy-driven and double-diffusive effects. In this paper the conditions for instability to arise are presented within an analytical framework by considering the eigenvalue problem based on the tools used extensively by Chandrasekhar. The model considered here is Darcy’s law coupled to evolution equations for the concentrations of different solutes. We have shown that, when there is an interval in the spatial domain where the first derivative of the base-state density profile is negative, the flows are unstable to stationary or oscillatory modes. Whereas for base-state density profiles that are strictly monotonically increasing downwards such that the first derivative of the base-state density profile is positive throughout the domain (for instance, when a lighter solution containing a species A overlies a denser solution containing another species B), a necessary and sufficient condition for instability is the presence of a point on either side of the initial interface where the second derivative of the base-state density profile is zero such that it changes sign. In such regimes the instability arises as non-oscillatory modes (real eigenvalues). The neutral stability curve, which delimits the stable from the unstable regime, that follows from the discussion presented here along with the other results are in agreement with earlier observations made using numerical computations. The analytical approach adopted in this work could be extended to other instabilities arising in porous media.

Mixing and finger morphologies in miscible non-Newtonian solution displacement

Unexpected interface complexities were found resulting from the miscible displacement of saltwater by a miscible shear-thinning solution (xanthan gum) in a radial Hele-Shaw cell, for both convergent and divergent flow. Such complex patterns have not been described before for either Newtonian or non-Newtonian solutions. A more viscous solution was injected into the cell to displace a less viscous solution (divergent flow) and then withdrawn at the injection site (convergent flow). A variegated mixing fringe between the solutions developed during the injection phase, against the stabilizing viscous effects, which would tend to promote a stable piston-like displacement. This interface geometry is markedly different from what is seen in displacement experiments performed with glycerol under otherwise similar viscosity contrast and flow conditions. The concentration field heterogeneity resulting from the presence of the fringe, quantified using a spatial autocorrelation measure, is mostly controlled by the applied shear rate, or equivalently, by the ratio of the volumetric flow rate to the flow cell’s aperture. It is significantly correlated with the radial width of the mixing zone. In addition to producing a large volume of blended solution during the injection phase, the mixing fringe impacted the development of viscous fingers (VFs) during the withdrawal phase. Such VFs are expected due to the viscosity ratio, but the initial roughness of the interface from which they develop and, hence, their later dynamics are controlled by the geometry of the mixing fringe at the end of the injection. We characterize the dynamics as a function of the imposed flow rate and cell thickness. The observed complexities of miscible displacement involving shear-thinning solutions have implications for subsurface engineering applications such as oil recovery and groundwater remediation.

Chitosan/iota-carrageenan/curcumin-based materials performed by precipitating miscible solutions prepared in ionic liquid

Curcumin (CUR) is a hydrophobic drug which has been loaded into polymeric carrier matrices by using experimental strategies with many steps, as well as by using conventional and volatile organic solvents. For the first time, this study reports the use of an ionic liquid ([Hmim][HSO4−]) to solubilize polycation-polyanion polymer pairs and hydrophobic CUR in the same system. By using the [Hmim][HSO4−] as an appropriated solvent, CUR (ca. 10% wt) is loaded into a polyelectrolyte complex (PEC) based on chitosan and commercial iota-carrageenan, following a straightforward method (in-situ approach). A solution containing chitosan, iota-carrageenan, and CUR is produced in [Hmim][HSO4−] and subsequently precipitated in an ice-water bath to form the CUR-loaded PEC. The ionic liquid is synthesized following a straightforward experimental route, and after PEC production, it is recovered and reused. X-ray photoelectron spectroscopy analysis shows that chitosan and iota-carrageenan are principally interacting by coulombic forces. Also, X-ray photoelectron spectroscopy and infrared spectroscopy analyses confirm that CUR is loaded into the PEC structure. Wide-angle X-ray scattering, scanning electron microscopy, and differential scanning calorimetry also confirm that CUR loaded PEC (ca. 105 mg g−1) comprise a more disorganized structure when compared to the pristine drug. The CUR is released in simulated gastric fluid (SGF, pH 1.2) because the PEC material increases 3.3-fold its solubility in SGF when compared to the raw curcumin. The ionic liquid can remain in the PEC structure, potentially imparting cytotoxicity. A simple aqueous washing step is sufficient to remove the residual [Hmim][HSO4−] and promote cytocompatibility. Cell viability assay performed on bone marrow-derived stem cells demonstrates that CUR significantly increases the cell viability promoted by the PEC.

More than a Liquid Junction: Effect of Stirring, Flow Rate, and Inward and Outward Electrolyte Diffusion on Reference Electrodes with Salt Bridges Contained in Nanoporous Glass

The Henderson equation is usually used to calculate liquid-junction potentials between miscible electrolyte solutions. However, the potentials of reference electrodes that comprise an electrolyte-filled nanoporous glass frit may also be affected by charge screening. As reported previously, when the Debye length approaches or surpasses the glass pore diameter, reference potentials depend on the composition of the bridge electrolyte, the pore size of the frit, and the concentration of electrolyte in the sample. We report here that stirring of samples may alter the reference potential as it affects the electrolyte concentration in the section of the nanoporous glass frit that is facing the sample solution. When the flow rate of bridge electrolyte into the sample is small, convective mass transport of sample into the nanoporous frit occurs. The depth of penetration into the frit is only a few nanometers but, despite the use of concentrated salt bridges, this is enough to affect the extent of electrostatic screening when samples of low ionic strength are measured. Mixing of sample and salt bridge solutions-and in particular penetration of sample components into the frit-was optically monitored by observation of a deeply colored Fe[(SCN)(H2O)5]2+ complex that formed in situ exclusively in the region where the sample and salt bridge mixed. Importantly, because flow through nanoporous frits is very slow, mass transport through these frits is dominated by diffusion. Consequently, over as little as 1 h, reference electrode frits with low flow rates become contaminated with sample components and undergo depletion of electrolyte within the frit to a depth of several millimeters, which can negatively affect subsequent experiments.

Interaction of miscible solutions and superhydrophobic surfaces

ABSTRACTThe complex composition in industrial pollutants includes immiscible liquid and miscible solution that present a great challenge to deal with the effluent. In this research, the interaction between super hydrophobic surface and the miscible solution is studied based on surface tension (ST) and contact angle. A superhydrophobic surface is fabricated by simple anodisation and self-assemble method. Then two different types of miscible solution are adopted to evaluate the property of the superhydrophobic surfaces. The obtained result shows that the wettability is closely related to ST of mixtures, which is controlled by the interface component. When the ST is less than 31.55 mN m−1, the critical pressure reduced from maximum value (6442.8 Pa) to negative number. In turn, the superhydrophobic film loses its repellency and shows affinity to the mixtures. This can provide an important supplement for utilising superhydrophobic materials, especially for the oil–water separation.

A new activity coefficient model for the solution of molecular solute + ionic liquid

Based on electrolyte non-random two-liquid (e-NRTL) equation, a new activity coefficient model is proposed for the solution of ionic liquid + molecular solute. In the new model, the sizes of particles have been taken into consideration by introducing volume elements into the new model. For easier application, the Pitzer-Debye-Hückel expression is cancelled in the new model, because ionic liquids work as solvents more frequently. To simplify the model, the assumptions (local electroneutrality and like-ion repulsion) have been made, which were adopted in Chen's e-NRTL model. As a result, the new model only needs 5 parameters like NRTL equation. Moreover, the new model can predict accurate results with fewer experiment data in comparison with NRTL for both totally miscible and partially miscible solutions, which has been proven with 19 kinds of solution.

Experimental Characterization of Acoustic Streaming in Gradients of Density and Compressibility

Suppression of boundary-driven Rayleigh streaming has recently been demonstrated for fluids of spatial inhomogeneity in density and compressibility owing to the competition between the boundary-layer-induced streaming stress and the inhomogeneity-induced acoustic body force. Here we characterize acoustic streaming by general defocusing particle tracking inside a half-wavelength acoustic resonator filled with two miscible aqueous solutions of different density and speed of sound controlled by the mass fraction of solute molecules. We follow the temporal evolution of the system as the solute molecules become homogenized by diffusion and advection. Acoustic streaming rolls is suppressed in the bulk of the microchannel for 70-200 seconds dependent on the choice of inhomogeneous solutions. From confocal measurements of the concentration field of fluorescently labelled Ficoll solute molecules, we conclude that the temporal evolution of the acoustic streaming depends on the diffusivity and the initial distribution of these molecules. Suppression and deformation of the streaming rolls are observed for inhomogeneities in the solute mass fraction down to 0.1 %.

Mode selection on breakup of a droplet falling into a miscible solution

A study of the breakup of a droplet falling into a miscible solution of lower density shows that a nondimensional parameter determines the breakup number. A mechanism of the mode-selection based on the Rayleigh-Taylor instability for the growing vortex ring is discussed.

GaAsSe Ternary Alloy Nanowires for Enhanced Photoconductivity

Alloyed semiconductor nanowires (NWs) are of great interest for next-generation integrated optoelectronic nanodevices owing to their tunable band gap and emission wavelength. In this study, we synthesized the GaAsSe ternary alloy nanowires (NWs) with various compositions between GaAs and Ga2Se3 using chemical vapor transport method. The band gap was continuously tuned in the range of 1.5–2.1 eV because of the completely miscible solid solution at all compositions. The alloy NWs (including Ga2Se3) consisted of a cubic phase with the [011] growth direction, in contrast with the GaAs NWs grown along the [111] direction. In particular, the GaAs1–xSex (x = 0.3) alloy NWs were grown from Ga-rich Au nanoparticles such as cubic-phase AuGa2 and had a defect-free single-crystalline nature. X-ray photoelectron spectroscopy analysis reveals much less surface oxide layers for x = 0.3, suggesting that Se incorporation at this composition effectively diminishes the surface defects. We fabricated photodetectors using the...

Viscous Fingering of Miscible Liquids in Porous and Swellable Media for Rapid Diagnostic Tests.

In lateral flow and colorimetric test strip diagnostics, the effects of capillary action and diffusion on speed and sensitivity have been well studied. However, another form of fluid motion can be generated due to stresses and instabilities generated in pores when two miscible liquids with different densities and viscosities come into contact. This study explored how a swellable test pad can be deployed for measuring urea in saliva by partially prefilling the pad with a miscible solution of greater viscosity and density. The resultant Korteweg stresses and viscous fingering patterns were analyzed using solutions with added food color through video analysis and image processing. Image analysis was simplified using the saturation channel after converting RGB image sequences to HSB. The kinetics of liquid mixing agreed with capillary displacement results for miscible liquids undergoing movement from Korteweg stresses. After capillary filling, there was significant movement of liquid due to these fluidic effects, which led to mixing of the saliva sample with an enzyme test solution. Owing to the simplicity and speed of this test method, urea can be analyzed with an electronic nose over a useful range for detecting salivary urea concentration for rapid and early detection of dehydration.

Microfluidic Inverted Flow of Ternary Water/Hydrophilic/Hydrophobic Organic Solvent Solution in a Y-Type Microchannel and a Proposal of the Response Microfluidic Analysis through the Experiment.

Two solutions that are individually fed at the same flow rate into two separate microchannels of a microchip, combine to form a single channel (a Y-type microchannel). This flow is either parallel for immiscible solutions or initially parallel, but then becomes homogeneous through diffusion, for miscible solutions. However, a new type of microfluidic behavior in a Y-type microchannel that was neither parallel nor homogeneous flow has been observed using, for example, water/acetonitrile (3:4.5, v/v) and acetonitrile/ethyl acetate (3.5:4, v/v) mixed solutions. Each mixed solution was marked with distinctive dyes and delivered at the same flow rate into a Y-type microchannel under laminar flow conditions. In the single channel, the two phases were initially observed to flow in parallel, but then apparently swapped to flow on the opposite wall while retaining parallel flow with a slight change in the components of the two phases. We have named this type of laminar flow "microfluidic inverted flow" for ternary water/hydrophilic/hydrophobic organic solvent mixed solutions. The inverted flow of a ternary water/acetonitrile/ethyl acetate system was examined in detail under various flow conditions. We also proposed a concept of response microfluidic analysis based on such microfluidic inverted flow.

Dynamics of polymers in concentrated solutions: A weaker self-concentration effect

We examine the validity of the Lodge-McLeish (LM) self-concentration model on polymer dynamics in concentrated polymer/small molecule solutions. Three solutions, 1,2-polybutadiene/2-ethylhexyl benzoate, 1,4-polyisoprene/phenyloctane, and polystyrene/2-ethylhexyl benzoate, are investigated by rheological technique. The temperature dependence of their normalized terminal relaxation times is fitted by the WLF equation to extract the effective glass transition temperature. The calculated self-concentration is found lower than the LM prediction, in contrast with the significant values in miscible polymer blends. According to the molecular dynamic simulation, this weak self-concentration effect is explained by the overestimation of the polymer's interchain concentration, which is postulated as the global average concentration in the original LM model. The lower interchain concentration in solutions is attributed to the higher probabilities for small molecules to fill the cooperative volume. Both experimental and simulation results may motivate the further theoretical modification on the interchain concentration in order to establish a self-consistent model predicting both miscible blends and polymer solutions.