Miscible Solutions Research Articles

Effect of water content on the corrosiveness of imidazolium‐based ionic liquids

Ionic liquids (ILs) are gaining attention in CO2 absorption, thanks to their favorable selectivity towards CO2 and physical characteristics, yet their corrosion behavior towards metallic equipment needs deeper evaluation, especially when approaching potential working conditions. Here we investigate the behavior of carbon steel and stainless steel in imidazolium based ILs with different alkyl chain lengths, mixed with various water contents. Oxygen reduction is identified as cathodic process, with limiting current density affected by fluid viscosity, oxygen solubility and diffusivity. The effect of water on ILs corrosiveness changes with its quantity and depends on the formation of a miscible solution or phase separation. Moreover, dissociation of ILs anions releases fluoride ions in water phase, increasing electrolyte aggressiveness.

Mussel-inspired modification of PTFE membranes in a miscible THF-Tris buffer mixture for oil-in-water emulsions separation

Traditional polymer membranes suffer from low flux and oil fouling when utilized for separating oil/water emulsion. Herein, a novel and simple method is exploited to design a novel polymer composite membrane with superhydrophilic and underwater superoleophobic property for oil in water emulsion separation by depositing polydopamine (PDA) on hydrophobic polytetrafluoroethylene(PTFE) membrane surface in tetrahydrofuran (THF)-Tris buffer mixture. In comparison with the traditional PDA coating on hydrophobic membrane in a Tris buffer solution, a PDA layer with mass of hydrophilic carboxyl groups and nano-microspheres hierarchical structure is formed on hydrophobic PTFE membrane by PDA coating in a miscible THF-Tris buffer mixed solution, and endows PTFE membranes with excellent superhydrophilic and underwater superoleophobic property. Therefore, the as-prepared membranes can be applied in varieties of oil-in-water emulsions separation with ultrahigh permeate flux (above 2250 L/m2 h) under ultralow operating pressure (only 0.04 MPa) and excellent oil rejection. Finally, thanks to the low oil adhesion of the PDA layer, the resulting membranes display outstanding antifouling performance and reusability for oil water separation. On the whole, a novel rational methodology is provided to tailor PDA coatings with superhydrophilic and underwater superoleophobic property on hydrophobic membrane surface in tetrahydrofuran-Tris buffer mixture.

Electrospinning of Polycaprolactone/Pluronic F127 dissolved in glacial acetic acid: fibrous scaffolds fabrication, characterization and in vitro evaluation

sThe Polycaprolactone (PCL) fibrous scaffolds in nano to micro scale have been considered as excellent templates for cell culture and tissue growth. The hydrophobic nature of the PCL, however, yields low initial cell seeding density, heterogeneous cell spreading and slow cell growth rate. Therefore, in this study the surface hydrophilic fibrous scaffolds were directly fabricated by the electrospinning of PCL solutions with small quantities (0.5–5%) of Pluronic F127 (PEO100-PPO65-PEO100) dissolved in benign solvent of glacial acetic acid. The clear and miscible solutions were achieved by controlling the proper F127 content in the blend solutions. The continuous and smooth fibers with average diameters from 0.71 to 1.43 μm made up the fibrous scaffolds in non-woven mode. Then the water wetting angle of the scaffolds could be adjusted from 126° to 0° by varying F127 content owing to its hydrophilic PEO chains presented on surface the blended fibers. Finally, it was demonstrated that the blended fibrous scaffolds with the F127 content less than 1% exhibited better cell attachment, proliferation and spreading performance than those of pure PCL scaffolds.

Options for refractive index and viscosity matching to study variable density flows

Variable density flows are often studied by mixing two miscible aqueous solutions of different densities. To perform optical diagnostics in such environments, the refractive index of the fluids must be matched, which can be achieved by carefully choosing the two solutes and the concentration of the solutions. To separate the effects of buoyancy forces and viscosity variations, it is desirable to match the viscosity of the two solutions in addition to their refractive index. In this manuscript, several pairs of index matched fluids are compared in terms of viscosity matching, monetary cost, and practical use. Two fluid pairs are studied in detail, with two aqueous solutions (binary solutions of water and a salt or alcohol) mixed into a ternary solution. In each case: an aqueous solution of isopropanol mixed with an aqueous solution of sodium chloride (NaCl) and an aqueous solution of glycerol mixed with an aqueous solution of sodium sulfate ( $$\hbox {Na}_2\hbox {SO}_4$$ ). The first fluid pair allows reaching high-density differences at low cost, but brings a large difference in dynamic viscosity. The second allows matching dynamic viscosity and refractive index simultaneously, at reasonable cost. For each of these four solutes, the density, kinematic viscosity, and refractive index are measured versus concentration and temperature, as well as wavelength for the refractive index. To investigate non-linear effects when two index-matched, binary solutions are mixed, the ternary solutions formed are also analyzed. Results show that density and refractive index follow a linear variation with concentration. However, the viscosity of the isopropanol and NaCl pair deviates from the linear law and has to be considered. Empirical correlations and their coefficients are given to create index-matched fluids at a chosen temperature and wavelength. Finally, the effectiveness of the refractive index matching is illustrated with particle image velocimetry measurements performed for a buoyant jet in a linearly stratified environment. The creation of the index-matched solutions and linear stratification in a large-scale experimental facility are detailed, as well as the practical challenges to obtain precise refractive index matching.

Control of two-phase flow in microfluidics using out-of-phase electroconvective streaming

We propose herein to make use of rotating electric fields for achieving flexible control on the hydrodynamic behavior of two miscible co-flowing water solutions in straight microchannels, in the context of a new manipulation tool for stratified liquid contents of microfluidic systems. Our theoretical analysis indicates that, while fluids of distinct electrical conductivities and identical permittivity are parallel pumped into the mainchannel, a circularly traveling field, as emitted from a four-phase electrode array surrounding the channel sidewalls, can direct the deflection of diffusing phase interface between the side-by-side miscible electrolyte streams asynchronously at half of the interfacial relaxation frequency, where the co-field electrorotational torque becomes most appreciable. An immediate application of the out-of-phase electroconvective streaming is that time required for electrolyte mixing is reduced because the area of two-phase contact interface is dramatically enlarged, and a serial combination of several rotating electrode arrays of alternate propagating directions can further rectify the mixing of microfluidics by inducing chaotic advection.

Initial Collision Process of Two Miscible Droplets.

Dynamic properties of the metastable interface between two miscible solutions are investigated by the collision of two droplets. A clear interface is observed between the two colliding droplets. The interface moves in the colliding droplet toward the side where the original droplet has a lower surface tension. The interface is set to the middle of the colliding droplet by controlling the surface tension of the droplets to observe the chemical reactions at the droplet interface by cavity-enhanced Raman spectroscopy. This study provides a foundation for further research on the initial process of the chemical reactions of two miscible solutions.

Core-Shell Fibers Electrospun from Phase-Separated Blend Solutions: Fiber Formation Mechanism and Unique Energy Dissipation for Synergistic Fiber Toughness.

Through single-tube electrospinning, the biodegradable core-shell fibers of poly(3-hydroxybutyrate) (PHB) and poly(d,l-lactic acid) (PDLLA) were obtained from blend solutions with different compositions at a total polymer concentration of 7 wt %. Regardless whether PHB is the major or minor component (PHB/PDLLA = 90/10, 75/25, 50/50, and 25/75 wt. ratio), these phase-separated solutions all yielded core-shell fibers with PHB as core and PDLLA as shell. A new scenario of core-shell fiber formation was proposed on the basis of the relative magnitude of the intrinsic relaxation rate of fluids and external extension rate during electrospinning. The effects of blend compositions on the morphologies of the Taylor cone, whipping jet, and as-spun fibers were investigated. The diameters of core-shell fibers can be tailored by simply varying the PHB/PDLLA ratios. Two scaling laws describing the apparent viscosity (ηo) dependence of the outer fiber diameter (dfo) and core fiber diameter (dfc) were derived. That is, dfo ∼ ηo0.38 and dfc ∼ ηo0.86. The microstructures of the as-spun fibers were determined by differential scanning calorimetry, Fourier transform infrared spectroscopy, and synchrotron wide-angle and small-angle X-ray scatterings. Results showed that the PDLLA component was in the amorphous state, and the crystallizability of PHB component remained unchanged, except the amorphous 10/90 fibers electrospun from a miscible solution state. The synergistic mechanical properties of the core-shell fibers were obtained, along with the ductile PDLLA shell enclosing the brittle PHB core. The enhanced toughness was attributed to the fragmentation of the brittle PHB core and necking fracture of the ductile PDLLA shell, which served as an effective route for energy dissipation. Compared with the neat PHB fiber, the 90/10 and 75/25 core-shell fibers possessed larger elastic moduli, which was attributed to the high PHB crystal orientation in their core sections despite the reduced PHB crystallinity. By contrast, the crystal c-axis of PHB in the 25/75 core-shell fibers was preferentially perpendicular to the fiber axis, suggesting the significant stretching of developing PHB crystals during electrospinning.

Nonlinear simulation of miscible displacements with concentration-dependent diffusion coefficient in homogeneous porous media

The nonlinear dynamics of miscible flow displacements in homogeneous porous media are examined for the special case of concentration-dependent diffusion coefficient (CDDC) models. Highly accurate numerical methods are used to simulate the time evolution of fingering with both mobility and diffusion coefficient contrasts of two components in a fully miscible solution system. The simulations revealed that, when compared with a constant diffusion coefficient (CDC), the CDDC models show drastically different viscous fingering structures and mixing of the two components. In particular, for a pure diffusion process with a stable front, using a CDDC results in less mixing, with a non-symmetric concentration gradient. While for the unstable displacements with relatively large mobility contrasts, it is found that using a CDDC tends to trigger fingers at the very beginning of the displacements. The diffusion-dominated period is therefore very short and can nearly be neglected. Moreover, the fingers reach the downstream boundary much earlier with fingering structures about 2–4 times more complex than the CDC case. Quantitative analysis indicates that the exponential CDDC models can enhance the mixing by shortening the diffusive regime but not change the growth rate of mixing in the convective regime. In addition, in contrast with the CDC case, the time required for the appearance of fingers for the CDDC seems to be independent of Peclet number Pe at a relatively large log mobility ratios R. As Pe increases for the CDDC cases, more complex dynamics of the fingers are observed, which can only be found at very high Pe and R values for the CDC case. In addition, a small increase in R is able to significantly enhance the instabilities since it can result in not only larger mobility contrast but also a steeper diffusion gradient.

Phase and interface determination in computer simulations of liquid mixtures with high partial miscibility.

Partially miscible solutions can represent a challenge from the computer simulation standpoint, especially if the mutual solubility of the components is so large that their concentrations do not change much from one phase to another. In this case, identifying which molecules belong to which phase becomes a complicated task. Here, we propose a density-based clustering approach with self-tuning capabilities and apply it to the case of the mixture of an ionic liquid with benzene. The almost linear scaling of the algorithm makes it suitable for the analysis of long Molecular Dynamics or Monte Carlo trajectories.

Pore-scale study on reactive mixing of miscible solutions with viscous fingering in porous media

In this paper, the reactive mixing process with viscous fingering of two miscible solutions is studied at pore scale using the lattice Boltzmann method. This single-phase flow obeys the Navier–Stokes equations with a concentration-dependent viscosity. The concentration transport is governed by the advection-diffusion-reaction equation, in which the interfacial reaction rate is described by a function of the concentration of a single reacting solute and admits two stable states separated by an unstable one. The reaction effects on mixing process with viscous fingering are explored in a single pore with different reaction rates, Péclet numbers and viscosity ratios. It is found that generally the reaction can suppress the mixing process significantly by sharping the solution interfaces. Such restriction is more obvious with increasing reaction rate, and even shares the similar fashion for different Péclet numbers and viscosity ratios. The reactive mixing process with viscous fingering is further investigated in artificial homogeneous and heterogeneous porous media with different parameters, and similar results are observed.

Band gap bowing in NixMg1-xO.

Epitaxial transparent oxide NixMg1−xO (0 ≤ x ≤ 1) thin films were grown on MgO(100) substrates by pulsed laser deposition. High-resolution synchrotron X-ray diffraction and high-resolution transmission electron microscopy analysis indicate that the thin films are compositionally and structurally homogeneous, forming a completely miscible solid solution. Nevertheless, the composition dependence of the NixMg1−xO optical band gap shows a strong non-parabolic bowing with a discontinuity at dilute NiO concentrations of x < 0.037. Density functional calculations of the NixMg1−xO band structure and the density of states demonstrate that deep Ni 3d levels are introduced into the MgO band gap, which significantly reduce the fundamental gap as confirmed by optical absorption spectra. These states broaden into a Ni 3d-derived conduction band for x > 0.074 and account for the anomalously large band gap narrowing in the NixMg1−xO solid solution system.

Tailoring the morphologies of PVDF nanofibers by interfacial diffusion during coaxial electrospinning

The morphology regulation of nanofiber (NF) plays an important role in its applications. In the present study, a simple method to tailor the cross-section morphology of polyvinylidene fluoride (PVDF) NFs by controlling the interfacial diffusion during coaxial electrospinning is presented. By choosing a soft bad-solvent of PVDF to prepare a partially miscible inner solution, the regulation of the interfacial diffusion can be simplified into the adjustment of the viscosity difference between the inner and outer solutions. When the viscosity of the inner solution surpassed that of the outer solution, the diffusion direction changed from outer-to-inner to inner-to-outer, which leaded to the change in the cross-section morphology of resultant NFs from a net-like to a hollow structure. Water contact angle also showed the effect caused by the interfacial diffusion. BET surface area of the as-prepared porous PVDF NFs can reach up to 42m2/g, which is almost the highest data ever reported in the literature for polymer nanofiber.

PEDOT:PSS-assisted polyindole hollow nanospheres modified carbon cloth as high performance electrochemical capacitor electrodes

The poor conductivity of polyindole (PIn) is a major factor to limit its application in supercapacitors. To solve the problem, a simple and efficient immersion method designed to obtain a binary nanocomposite, which composed of polyindole hollow nanospheres (PIn-NS) and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). PIn-NS with diameters of 300–600nm and shell thickness of about 50nm were prepared by the chemical oxidative polymerization of indole in the ethanol/H2O miscible solution using ammonium peroxydisulfate (APS) as oxidant agent without any surfactants. The pure PIn-NS modified carbon cloth (PIn-NS/CC) shows a low specific capacitance of 110Fg−1 at 0.5Ag−1 in 1.0M H2SO4 aqueous solution. By the immersion of PIn-NS/CC in PEDOT:PSS/ethanol solution, the obtained PIn-NS/CC-PEDOT:PSS shows a large improved specific capacitance of 623Fg−1 at 0.5Ag−1 and good stability with a cycling efficiency of 84.8% after 3000 cycles. The results demonstrate that the electrochemical properties of PIn-NS can be significantly improved with the assistance of PEDOT:PSS as electrically conductive connection. In addition, the symmetric PIn-NS/CC-PEDOT:PSS//PIn-NS/CC-PEDOT:PSS supercapacitor showed a high specific capacitance of 161Fg−1 at 0.5Ag−1 and the low equivalent series resistances (ESR) of 4.4ohm. Therefore, such binary composite is a promising material for application in the next generation high-performance supercapacitors.

Breakup and deformation of a droplet falling in a miscible solution.

When a droplet with a higher density falls in a miscible solution, the droplet deforms and breaks up. The instability of a vortex ring, formed by droplet deformation during the falling process, causes the breakup. To determine the origin of the instability, the wavelengths and thicknesses of the vortex rings are investigated at the time when the instability occurs. The experimental results are almost in agreement with the calculated results for the Rayleigh-Taylor instability using the thickness of a higher-density solution. Furthermore, we performed simulations considering the torus shapes and circulations of the vortex ring. The simulations provided patterns similar to those observed experimentally for the breakup process, and showed that the circulations suppress the instability of the vortex ring. These results imply that the Rayleigh-Taylor instability plays a dominant role in the instability of vortex rings.

Effect of polymer molecular weight distribution on solute sequestration in two-phase partitioning bioreactors

Polymeric solids are effective absorbents in two-phase partitioning bioreactors (TPPBs) when they provide adequate absorptive capacity for the target solute, as well as the physical properties required by solid–liquid TPPB operations. This study demonstrates the influence of molecular weight distribution (MWD) on solute uptake, as measured by solute partition coefficient (PC), and mechanical strength, as measured by the polymer’s complex modulus (G∗). Experimental PC data for n-octanol absorption from aqueous solution by poly(dimethyl siloxane) (PDMS) demonstrate a decline in absorptive capacity with increasing number average molecular weight (Mn), in agreement with Flory–Huggins solution theory predictions. Importantly, MWD is shown to have no effect on solute uptake, with both unimodal and bimodal distributions generating the same PC at a given Mn. This is in contrast to G∗, whose MWD sensitivity is exploited to formulate bimodal mixtures of poly(isobutylene) (PIB) that provide high n-octanol PC values as well as satisfactory material strength. This bimodal MWD strategy to TPPB absorbent design is extended to miscible solutions of high MW PIB and cyclohexylbenzene, which are shown to generate superior n-octanol PC at a given G∗.

Simultaneous Formulation, Evaluation and Estimation of Self Emulsifying Drug Delivery System (SEDDS) of Ibuprofen Tablet Dosage form using Varied quantities of Goat Fat as an Excipient and Tween-60 as a Surfactant

The aim of present study confirmed that the SEDDS formulation can be used as a possible alternate to traditional or classical formulations of Ibuprofen to improve its bioavailability using varied quantities of goat fat as an excipient and tween 60 as a surfactant which is a drug in the nonsteroidal anti-inflammatory drug (NSAID) class used for treating pain, fever and inflammation which is also known to be isobutylphenylpropanoic acid. The investigation proved that the formulated dosage forms showed good release profile as well as acceptable tablet properties. The batches with higher tween60: goat fat content ratios gave better release rates. The SEDDS of Ibuprofen was successfully prepared and the tablets prepared passed the various evaluation tests conducted. This method has advantage of reliance on cheap raw materials such as goat fat with fewer processing steps, best suited for lipophilic drugs where the resulting emulsification gives faster dissolution rates and absorption. Invivo evaluation of this novel dosage form is currently in progress. Self-emulsifying drug delivery systems are a promising approach for the formulation of lipophilic drug compounds having poor aqueous solubility. The oral delivery of hydrophobic drugs can be made possible by SEDDSs which have been shown to improve oral bioavailability substantially. From the formulation point of view it is necessary to consider the emulsification properties of lipid base vehicle and the solubility of drug in the lipid surfactant mixture to form a completely miscible solution so as to solubilize adequate quantities of drug in lipid vehicle. Lipids have an important role in absorption process. Thus, SEDDS plays an important role in the formulation of poorly water soluble drugs and enhancing their bioavailability.

Buoyancy-driven instabilities around miscible A+B→C reaction fronts: a general classification.

Upon contact between miscible solutions of reactants A and B along a horizontal interface in the gravity field, various buoyancy-driven instabilities can develop when an A+B→C reaction takes place and the density varies with the concentrations of the various chemicals. To classify the possible convective instability scenarios, we analyze the spatial dependence of the large time asymptotic density profiles as a function of the key parameters of the problem, which are the ratios of diffusion coefficients and of solutal expansion coefficients of species A, B, and C. We find that 62 different density profiles can develop in the reactive problem, whereas only 6 of them can be obtained in the nonreactive one.

Comparative study on electrical properties of copper nanowire/polypropylene and carbon nanotube/polypropylene composites

Nanocomposites using copper nanowires (CuNWs) or carbon nanotubes (CNTs) as fillers with polypropylene (PP) as matrix were prepared by miscible solution mixing and precipitation method. Comparative studies on electrical conductivity and electromagnetic interference shielding properties were reported. On the conductivity curve, a plateau was found for both CuNW/PP composite and CNT/PP composite. The plateaus are located at a different concentration range for each composite type: for CuNW/PP composite, it is between 0.8 and 1.7 vol %, while for CNT/PP composite the plateau occurs in a narrower range between 0.4 and 0.6 vol %. The shielding effectiveness (SE) increases with increased concentration of fillers. CNT/PP composite has higher SE at concentrations less than 2 vol %; the two curves cross near 10 dB at this point and at concentrations higher than 2 vol %, CuNW/PP composite has higher SE. © 2014 American Institute of Chemical Engineers AIChE J, 61: 296–303, 2015

Wavelength Analysis of Interface between Two Miscible Solutions Observed in Formation of Fractal Pattern

When a droplet of a higher-density solution (HDS) is placed on top of a lower-density solution (LDS), the HDS draws a fractal pattern on the surface of the LDS. Before the fractal pattern is formed, a stick-like pattern with a periodic structure emerges in a region surrounding the surface pattern due to interfacial instability. We experimentally measure the wavelength of this stick-like pattern. The wavelength increases with the volume of the HDS and is independent of the viscosities of the two solutions. To understand the stick generation, we propose a model of miscible viscous fingering whose boundary conditions are similar to those of the experiments. The wavelength obtained from the model agrees with the experimentally obtained wavelength. The formation of the fractal pattern is discussed by comparing it with the viscous fingering.

Salt Bridges Contained in Nanoporous Glasses or Polymers: Improved Alternatives to Vycor

Nanoporous glass plugs are widely used to contain the electrolyte solution that forms a salt bridge between the sample and the reference electrode. Even though reference electrodes with plugs made of nanoporous glass (such as Vycor or CoralPor glass) are commercially available and are frequently used, the limits of their use were not explored until very recently [1]. It will be shown in this presentation that at ionic strengths lower than 100 mM, the half-cell potentials of reference electrodes with nanoporous glass plugs are not sample independent, as it would be desirable, but they depend on the ionic sample composition. Sample dependent shifts of more than 50 mV in the half cell potential were encountered. Reference potentials were found to be affected in aqueous solutions by HCl, NaCl, KCl, and CaCl2, and in acetonitrile by trifluoroacetic acid and the supporting electrolyte tetrabutylammonium perchlorate. These observations cannot be explained by the liquid junction potential between two mutually miscible electrolyte solutions, as commonly described with the Henderson equation. Instead, they result from the surface charge density on the glass surface and the resulting electrostatic screening of ion transfer into the glass pores when the latter have dimensions comparable to or smaller than the Debye length. Users of reference electrodes with nanoporous plugs at the junction to the sample need to be aware of these limitations to avoid substantial measurement errors.This presentation will also address how problems at the junction to nanoporous plugs can be avoided using novel plug materials and selecting electrolyte conditions judiciously.