Miscible Solutions Research Articles

Hanging aqueous polyelectrolyte “Dropbags” at liquid surface for Bio-inspired systems

Water surfaces serve as habitats for numerous creatures and have inspired a wide range of innovations. Herein, we demonstrate the fabrication of bag-shaped hanging droplets (dropbags) at the liquid surface using miscible polyelectrolyte aqueous solutions. The surface tension at the liquid-liquid interface maintains the top-opening structure of the dropbag, and the coacervate layer, formed rapidly by electrostatic interactions, inhibits the diffusion of large molecules, providing the dropbag with a flexible shape. Particularly, the "scattered dropbags-in-dropbag" (SDID) system was employed to accelerate the hatching of brine shrimp, such diverse compartmentalized structures and biophilic materials have the potential to be used for the cultivation and research of various creatures.

Effects of Inorganic Salts on the Phase Separation of Partially Miscible Solutes.

Partially miscible solutions with a lower critical solution temperature have promising applications in the field of physical chemistry. To better guide the utilization of these solutions in practice, we conduct an in-depth study about the phase separation behavior of the solution added with inorganic salts. The addition of the inorganic salts into the solution is found to consequently reduce the phase separation temperature. The variation of concentrations of inorganic salts does not notably affect the mass fraction of the separation. Moreover, the addition of inorganic salts in the solutions at lower mass fractions improves the separation mass fraction, while the addition of inorganic salts decreases the separation mass fraction at the mass fractions above 30%. It sheds light on selecting the proper mass fractions and inorganic salt concentrations. Furthermore, we explore the phase separation behavior of mixed solutions under different inorganic salt additions by means of a high-speed camera. The phase separation behavior under different inorganic salt systems shows a similar trend. However, calcium ions and Fe3+ ions in the solutions can greatly decrease the rate of droplet coalescence and result in an increase in phase separation. For better regulating the solutions with a lower critical solution temperature through inorganic salts, sodium chloride or potassium chloride is recommended with an appropriate concentration.

Field-induced interfacial instabilities in a two-phase ferrofluid flow

Forming a stable ferrofluid and non-magnetic interface in a microchannel is essential for biomedical applications with two miscible aqueous solutions. Here, we report the interface profile and its instability of aqueous ferrofluid and water co-flow in a microchannel under the influence of a magnetic field. The scaling law related to diffusion width and dimensionless Pe number is introduced by solving the momentum and diffusion equation and combining the experimental results. It is found that the dimensionless number of diffusion width δ/h ∝ X/Peα, when core flow concentration cf, residual magnetic flux density Br, sheath flow and core flow ratio Qw/Qf, and core flow velocity Qf are changed, α is 0.633–1.071, α ∝ Qβ, β = −0.059,0.147, 0.019 and −0.101, respectively. Altering the core flow velocity and magnetic field intensity can quickly impact the interface's stability by improving the transport efficiency by 32.9 % and counteracting the impacts of material diffusion by 51.8 %, respectively. Elevating the proportion of sheath flow to core flow and magnetic field will impede the diffusion of core flow. This will result in a drop of 11.9 % in the magnetic convection effect and a 20.8 % counteraction of material diffusion effects.

Interfacial energy as an approach to designing amphipathic surfaces during photopolymerization curing.

Photopolymerization induced phase separation (PIPS) is a platform capable of creating heterogeneous materials from initially miscible resin solutions, where both the reaction's governing thermodynamics and kinetics significantly influence the resulting phase composition and morphology. Here, PIPS is used to develop materials in a single photopolymerization step that are hydrophobic on one face and hydrophilic on the other. These two faces possess a water contact angle difference of 50°, bridged by a bulk-scale chemical gradient. The impact of the PIPS-triggering inert additive is investigated by increasing the loading of poly(methyl methacrylate) (PMMA) in an acrylonitrile/1,6-hexanediol diacrylate comonomer resin. The extent of phase separation in the sample network depends on this loading, with increasing PMMA corresponding to macroscale domains that are more chemically and mechanically distinct. A significant period between the onsets of phase separation and reaction deceleration, determined using in situ FT-IR, facilitates this enhanced phase segregation in PMMA-modified samples. Spatially directed domain formation can be further promoted using multiple interface types in the sample mold, here, glass and stainless steel. With multiple interface types, interfacial rearrangements to minimize surface energy during resin photopolymerization result in a hydrophobic face that is nitrile-rich and a hydrophilic face that is nitrile-poor (e.g., acrylate-rich). Using this strategy, patterned wettability on a single face can also be engineered. This study illustrates the capabilities of PIPS for complex surface design and in applications requiring stark differences in surface character without sharp interfaces.

Electrochemical Analysis in Charge-Transfer Science: Polarity at Electrode Surfaces Affect Electrochemical Analyses for Charge-Transfer Systems

Electrochemical analysis is a vital component of the science of charge transfer (CT), and its importance cannot be overstated. Many fields, including energy science, photoredox and electrocatalysis, biomedical sensor development, environmental engineering, and electronics, rely heavily on CT and require accurate electrochemistry. [Phys. Chem. Chem. Phys. 2020, 22, 21583-21629] As a result, it is critical to pay close attention to the details of collecting, implementing, and interpreting electrochemical results to advance this broad field of science and engineering. [Current Opinion in Electrochemistry 2022, 31, 100862]The interfaces of an electrochemical cell present specific challenges for the interpretation and applicability of the analysis. The polarity of the medium on the electrode surface is not the same as the polarity of the bulk medium, and this has a significant influence on the behavior of charged and dipole species. Solvation in a condensed medium controls the dynamics of processes involving CT, including intramolecular redistribution of electron density. Polarity affects several properties of solvated species, including solubility, reactivity, electrochemical potential, and spectral transitions. [J. Phys. Chem. B 2023, 127, 6, 1443–1458]To understand changes in electrochemical potential during oxidation and reduction, it is important to analyze the relationship between the bulk electrolyte concentration and the Born microenvironmental polarity experienced by the species analyzed in the diffuse Helmholtz layer and at the surface of the working electrode during the heterogeneous steps of CT. This analysis can be used to assess the polarity experienced by redox species on the surface of polarizing working electrodes.Another critical issue in electrochemical analysis is the liquid junction that connects two different solutions, typically through a porous medium. Differences in the transport properties and activity of ions on both sides of the junction create a potential, known as the liquid potential (ELJ), which contributes to the measured voltage. To minimize ELJs, a miscible solvent solution and an electrolyte composed of ions with the same mobility throughout the transition can be used. ELJs can also be eliminated using a cell configuration with a pseudo-reference electrode that does not contain a liquid interface. However, the potential of pseudo-reference electrodes depends on the composition of the sample solution in which they are immersed, so care must be taken when interpreting the measured values.Overall, electrochemical analysis is a complex and critical part of CT science, and its accurate implementation is essential in advancing this broad field of science and engineering. Understanding the influence of the polarity of the medium, the relationship between the bulk electrolyte concentration and the Born microenvironmental polarity, and the liquid junction is crucial for interpreting electrochemical results and evaluating CT thermodynamics.

Diffusive–layered convection in Y-shaped continuous-flow microreactor

Efficient and rapid mixing of fluids in continuous-flow microfluidic devices plays an important role in a wide range of applications. Although there are many different methods to enhance mixing in such reactors, the potential of natural convection to mix fluids has been overlooked because of its possible limitations at the microscale. Recent studies have challenged this statement by demonstrating the significance of both gravity-dependent and gravity-independent types of natural convection in improving mixing efficiency. It was shown that inducing double-diffusive convection, Marangoni convection, or Rayleigh–Taylor convection can greatly enhance the mixing of two aqueous solutions in a continuous-flow microreactor. In this study, we experimentally investigate the influence of another type of differential-diffusion instability, known as diffusive–layered convection, on the mixing of two aqueous solutions of chemically inert substances in a Y-shaped continuous-flow microreactor. We consider the scenario when two miscible solutions flow into the main channel through distinct tubes, in which they come into contact and mix, thus causing the onset of diffusive–layered convection. We used two experimental methods, including laser interferometry and dye visualization, to analyse the mixing process. Surprisingly, despite the vigorous convective motion driven by diffusive–layered convection, the intensity of mixing of pumped fluids remains comparable to the scenario when solutions mix only via a diffusion mechanism. We explain this unexpected result by the unique structure of the convective motion, which prevents system homogenization. A comparison with the results previously obtained for double-diffusive convection is performed, and pure diffusive mixing scenarios are implemented.

A practical hybrid machine learning method for predicting the flash point of complex ternary alcohol-based mixtures

The flash point (FP) modeling of ternary mixtures containing partially miscible regions, even by known models, is still challenging. This work proposes a practical and easy-to-use hybrid machine learning method, which combines artificial neural networks (ANNs) with the genetic algorithm (GA), to calculate the FPs of complex alcohol-based mixtures, particularly aqueous solutions of low-carbon alcohols. For this purpose, multilayer perceptron (MLP), radial basis function (RBF), and group method of data handling (GMDH) ANNs, were trained using the FPs of totally miscible region while the FPs of the partially miscible region were predicted by the trained ANN. By applying this approach, the FPs of partially miscible region of water-ethanol-1-butanol, water-ethanol-2-butanol, water-1-butanol-2-butanol, and methanol + toluene + 2,2,4-trimethylpentane were predicted. Another method was implemented by which the FPs of water-1-butanol-2-butanol mixture were predicted by only those of other mixtures, i.e., water-ethanol-1-butanol and water-ethanol-2-butanol. To the best of our knowledge, two applied approaches have not been previously used. Moreover, the FPs of two totally miscible aqueous solutions, namely water-methanol-ethanol and water-ethanol-isopropanol, were evaluated by different proposed ANNs in a usual way. The highest and lowest absolute average errors obtained by the applied methods for testing data were 5.09 and 0.45 °C, respectively.

Исследование равновесия жидкость-пар бинарных растворов спиртов в рамках кластерной модели

The vapor-liquid equilibrium was analyzed for infinitely miscible binary solutions of alcohols exhibiting positive deviations from the Raoult’s law on the basis of the cluster model. The considered substances were by-products of the Fischer --- Tropsch process and various additives to the biofuel. Cluster model equation was provided to describe concentration dependences of vapor pressure over the solution on composition of the liquid phase. The model applicability included non-electrolyte solutions, which deviation from ideality was caused by preferential association of one of the solution components. The model equations parameters were the mathematical expectations of the associates’ distribution in standard state and dispersion of the association number. It is shown that the model equations adequately describe experimental data on vapor pressure for mixtures of various aliphatic alcohols with diethyl carbonate and ketones. For mixtures of hydrocarbons with pentanol isomers, the previously formalized method for simulating vapor pressure along concentration dependences of the mixture excess molar characteristics on the liquid phase composition was applied. It was established that solutions obtained by various methods are in good agreement with each other and adequately describe concentration dependences of the vapor pressure on composition of the liquid phase

Reorientation of the interface between two miscible solutions of equal density

Horizontally stratified flows of two liquids present unique opportunities in diverse applications in microfluidics, but they also introduce new complexity into these systems; there are many microfluidic applications that fail to transition from a simplified single-phase prototype to the two-phase regime. This paper reports experimental and numerical observations that show that the quasi-interface in horizontally stratified flows might rotate even if the density is completely homogenous at the inlet and transversal diffusion is not dominant. Subsequently, based on the results it is proposes that a chain of events beginning with diffusion at the interface and resulting from simultaneous effects of diffusion, density, changes in diffusion and density due to concentration of solutes, and gravitational forces give rise to this so far unreported rotation. Simplifications that ignore any one link in the phenomena chain will break the chain of events and are hence unable to predict their combined effect. Furthermore, the flow along the channel was characterized for various values of density and velocity and one possible method to counter this phenomenon is proposed. Rotations as great as 15° were observed at Ṕeclet numbers of order 1000, which is much greater than current common practice in the field indicates. The authors believe that understanding this phenomenon and finding strategies to compensate for this effect are necessary to achieve highly efficient microfluidic devices that incorporate interfaces of miscible liquids into their design.

Chemoconvection of miscible solutions in an inclined layer

This paper presents an experimental and numerical investigation of the chemoconvective flow of two miscible reacting solutions that generate a plain layer oriented at some angle to the gravity field. In the experiments, the aqueous solutions of nitric acid and sodium hydroxide were used. The system evolves from an initial state, in which each homogeneous solution occupies half of the layer, and the contact surface between the layers is flat. When the reacting solutions come into contact with each other, an acid-base neutralization reaction occurs, forming salt and water. The system configuration is chosen so that the acid solution of lower density rests on top of the denser base. This excludes the development of the Rayleigh–Taylor instability. The experiments were performed for such initial concentrations of the reagents at which a wave regime is realized in the system. The wave comprises a density jump rapidly advancing in the direction of gravity and separating the immobile alkali solution and the layer of acid and salt mixture, the convective motion of which feeds the frontal reaction with fresh acid. The visualization of the flow in the experiments was performed using a Fizeau interferometer. The numerical study of a complete three-dimensional problem was carried out using the ANSYS CFX hydrodynamic simulation program. We studied the flow evolution at a gradual increase in the angle of inclination from 0° to 70°. We found that the layer inclination leads to a significant change in the structure and intensity of the convective motion. Already at small inclination angles (up to 30°), the flow becomes three-dimensional, which makes the Hele-Shaw approximation inapplicable to this case. We show that there is a spontaneous stratification of salt and acid concentration fields in the cocurrent wave flow. With an increase in the angle of inclination, the wave velocity decreases, and chemoconvection in the cocurrent flow becomes less intense and acquires a certain vortex structure. At larger angles (from 50° to 70°), the wave front is strongly deformed or the wave breaks up. We demonstrate that an up-and-down fluid flow develops in the layer above the density jump. This flow eventually loses its stability with respect to the vertical rolls of solutal Rayleigh convection. There is a good agreement between the experimental measurements and the results of numerical simulation of the 3D problem.

Spatial inhomogeneity and molecular aggregation behavior in aqueous binary liquid mixtures

The component molecules in aqueous mixtures tend to aggregate with increasing concentration, and it has been conclusively reported that their spatial distribution is no longer uniform. Here, we attempt to measure the spatial inhomogeneity of constituent molecules in the cosolvent-water mixture by calculating the h value wherein the time-varying molecular configurations are obtained from molecular dynamics (MD) simulations conducted at various concentrations and temperatures. The results reveal that the miscible methanol solutions have a small h value, indicating the homogeneous distribution of components, while the immiscible dichloromethane-water mixtures have a relatively large h value, representing the localization of components due to the formation of two separated liquid phases. In the butanol-water mixture, the h value decreases significantly with increasing temperature, which reflects a temperature-dependent phase change from two liquid phases to a single phase, resulting in uniform distribution of molecular components at high temperatures. Meanwhile, in the graph theoretical analysis of cosolvent aggregates and water H-bond network, two prominent types of aggregation behavior are shown in the investigated binary liquid system, i.e., self-associated or spatially extended aggregates. The growth of self-associated cosolvent aggregates facilitates the liquid-liquid phase separation, resulting in a heterogeneous distribution of components with high h values. The development of a spatially extended network enables fully mixing with water H-bond network, bringing about the homogeneous distribution of constituent molecules and thus resulting in low h values. The concept of spatial inhomogeneity and bifurcating hypothesis on aggregation behavior is anticipated to contribute significantly to understanding the underlying issues, such as miscibility and liquid-liquid phase separation in aqueous mixtures.

Effect of natural convection and diffusion on liquid-liquid phase separation behaviors of partially miscible solutions with lower critical solution temperature

Partially miscible solutions with lower critical solution temperature (LCST) have significant potential in improving the cooling performance of microchannel heat sinks, reducing pressure drop, and ensuring stable operation of the cooling system. Thereby, it is essential and meaningful to clearly understand the liquid-liquid phase separation process driven by natural convection and diffusion to enhance the cooling performance in microchannels further. In this paper, the liquid-liquid phase separation behaviors of 2-Butoxyethanol/water solutions in a slit cavity were visually investigated. Moreover, the effect of driven force was discussed on the temperature distribution, motion of boundaries and phase separation rate. Furthermore, the effect of the mass fraction was discussed on the phase separation temperature range and phase separation rate. The results proved that the phase separation rate was kept at 0.39%·s−1 on average in the whole slit cavity by the natural convection, whereas the driving force of diffusion was so weak that the phase separation rate rapidly decreased along the vertical direction. That means reasonable enhancements of the disturbance in the microchannel could significantly increase the phase separation rate. Moreover, the phase separation rate increased with an increase in the mass fraction, and the solution with the best cooling performance could be found at 27.4%≤ω2-BE≤35%. The results are expected to provide theoretical guidance to prepare solutions with suitable phase separation temperature range and excellent cooling performance.

Non-isoplethic measurement on the solid-liquid-vapor equilibrium of binary mixtures at cryogenic temperatures.

We measured the solid-liquid-vapor (SLV) equilibrium of binary mixtures during experiments that alternated between cooling the mixture and injecting the more-volatile component into the sample chamber; thus, the composition of the mixture changed (non-isoplethic) throughout the experiment. Four binary mixtures were used in the experiments to represent mixtures with miscible solid phases (N2/CO) and barely miscible solid solutions (N2/C2H6), as well as mixtures with intermediate solid miscibility (N2/CH4 and CO/CH4). We measured new SLV pressure data for the binary mixtures, except for N2/CH4, which are also available in the literature for verification in this work. While these mixtures are of great interest in planetary science and cryogenics, the resulting pressure data are also needed for modeling purposes. We found the results for N2/CH4 to be consistent with the literature. The resulting new SLV curve for CO/CH4 shows similarities to N2/CH4. Both have two density inversion points (bracketing the temperature range where the solid floats). This result is important for places such as Pluto, Triton, and Titan, where these mixtures exist in vapor, liquid, and solid phases. Based on our experiments, the presence of a eutectic is unlikely for the N2/CH4 and CO/CH4 systems. An azeotrope with or without a peritectic is likely, but further investigations are needed to confirm. The N2/CO system does not have a density inversion point, as the ice always sinks in its liquid. For N2/C2H6, new SLV pressure data were measured near each triple point of the pure components.

Моделирование давления пара в бинарных растворах неэлектролитов по избыточным функциям

The paper considers simulating thermodynamic properties of completely miscible binary non-electrolyte solutions characterised by a positive deviation from ideality due to association concerning one of the solution components in general. We used a cluster-based mathematical model. The paper provides a cluster model equation to describe concentration dependences of vapor pressure over the solution as functions of the liquid phase composition. The model equation parameters are the expected value of associate distribution in the standard state and the variance of associates. We present a formalised method for simulating vapor pressure using concentration dependences of excess molar characteristics of the mixture as functions of the liquid phase composition. We derived concentration dependences of vapour pressure for binary solutions of alcohols in haloalkanes directly from the experimental data and analytically from the excess molar enthalpy and excess molar volume. These results, though derived by different methods, agree well with each other and appropriately describe vapor pressure concentration dependences as functions of the liquid phase composition. We demonstrate that varying cluster model equation parameters in a temperature range will successfully match patterns of association found in systems prone to hydrogen bond formation

On the efficiency of convective mixing in a Y-shaped channel

Continuous-flow microfluidic devices are widely used in microbiology, fine organic synthesis, pharmaceuticals, biomedicine, etc. Most applications require rapid mixing of the fluids that pass through the microfluidic chip. The mechanism of natural diffusion is not always efficient due to limitations on the length of the channel. In this work, we numerically study the efficiency of using various mechanisms of natural convection for the mixing of fluids entering the microfluidic chip. Solutions typically differ in buoyancy and diffusion rates of dissolved components, making them sensitive to gravity-dependent instabilities such as Rayleigh-Taylor convection, double diffusion and diffusion layer convection. We consider a Y-shaped microchannel, which is, on the one hand, the simplest, and, on the other hand, a typical element of a microfluidic network. We assume that two miscible solutions independently flow into a common channel where they come into contact. For each type of instability, we numerically estimated the characteristic channel length, after which complete mixing of the solutions occurs. The simulations were performed in the framework of both 2D and 3D models. Finally, we compare the numerical results with the experimental data obtained recently.

Strain-sensitive alginate/polyvinyl alcohol composite hydrogels with Janus hierarchy and conductivity mediated by tannic acid

To construct conductive hydrogels with a conductive and a non- or weakly conductive layer for comfortable and safe electronic application, marine biobased anionic polysaccharide sodium alginate (SA) and neutral polyvinyl alcohol (PVA) were employed as the hydrogel matrixes. Tannic acid (TA) was exploited to mediate the demixing of the miscible aqueous solution of SA and PVA in view of the much larger interaction strength of TA with PVA than both of TA with SA and PVA with SA calculated from the density functional theory (−40.21, −29.77 and −21.00 kcal·mol−1 respectively). The finally-fabricated alginate/PVA composite hydrogels not only possess a “Janus” hierarchy but manifest asymmetrical conductivity, i.e., one layer strongly conductive and another weakly conductive. The strongly conductive layer achieves a conductivity of more than 2.95 S·m−1, facilitating their application in soft electronic areas like human-machine interfaces, smart wearable devices and soft robots. The weakly conductive layer with the conductivity less than 0.60 S·m−1 and the thickness adjustable, constitutes a protective screen for another layer. The Janus hydrogels exhibit good mechanical performance, excellent strain-sensing performance and fatigue-resistant mechanics, conductivity and sensitivity.

Solubility determination and thermodynamic model of 6-hydroxy-3,4-dihydro-2(1H)-quinolone in ten pure solvents and four binary solvents at 278.15 to 323.15 K

6-hydroxy-3,4-dihydro-2(1H)-quinolone is an important chemical intermediate, which has important application value in the fields of medicinal chemistry and material chemistry. In this paper, the static counterpoise method integrated with HPLC was used to detected the solubility of sample in 10 pure solvents (1-Butanol, methanol, ethanol, isopropanol, tetrahydrofuran, 1-Propanol, methyl acetate, ethyl acetate, acetonitrile and isobutanol) and four binary solvents (ethanol + ethyl acetate, ethanol + acetonitrile, methanol + acetonitrile, and methanol + ethyl acetate). The results reveals that the sample has higher solubility in methanol and ethanol in pure solvents. In binary solvents, the solubility has a maximum value at xA = 0.7. At the same temperature, the binary system can improve the solubility of sample more than pure solvents. At 278.15–323.15 K, themole fraction solubility ranges of the 6-hydroxy-3,4-dihydro-2(1H)-quinolone respectively are 0.0018–0.0062 (1-Butanol), 0.0022–0.0084 (methanol), 0.0021–0.0076 (ethanol), 0.0019–0.0072 (isopropanol), 0.0025–0.0065 (tetrahydrofuran), 0.0017–0.0064 (1-Propanol), 0.0016–0.0039 (methyl acetate), 0.0007–0.0013 (ethyl acetate), 0.0003–0.0012 (acetonitrile), 0.0011–0.0049 (isobutanol), 0.0010–0.0090 (ethanol + ethyl acetate), 0.0006–0.0095 (ethanol + acetonitrile), 0.0007–0.0092 (methanol + acetonitrile), 0.0009–0.0102 (methanol + ethyl acetate). The five models, such as the SUN model, λ h model, CNIBS/R-K model, Jouyban-Acree model and modified Apelblat model, were used to fit the experimental data. The CNIBS/R-K model and modified Apelblat model fit the data better in miscible and single solution respectively. In addition, the KAT-LSER model was used to study the relationship between solute-solvent interaction and sample solubility.

Foaming characteristics of sugar- and polyvinylpyrrolidone-alcohol solutions during vacuum foam drying: A rheological approach

Vacuum foam drying offers great perspectives to formulate solid-state encapsulated active drugs. Taking into account the specific need of pharmaceutical formulations to keep drug molecules active and dispersed, we show in this paper that vacuum drying of pharmaceutical formulations can be substantially improved by using original rheological approaches. Typically, our formulations totally dried-up in less than 5 min, a delay much shorter than the long hours of the traditional vacuum drying process. Steady-shear rheology was used to evaluate the solution’s specific viscosity against the solutions’ concentrations, in order to correlate the dilution regime to the foamabiltiy. This rheological approach indicated that in miscible solutions, spontaneous foaming occurred in the semi-dilute entangled regime, near the transition to the concentrated regime; for partially miscible solutions, it occurred in solutions at a concentration near to the percolation concentration. The proposed methodology is versatile, and should provide a simple way to assess the foamability of pharmaceutical formulations.

Design and operation of an enhanced pervaporation device with static mixers

AbstractPervaporation has a high potential for separating miscible solutions, particularly azeotropic mixtures. However, mass transfer limitations have long been a common concern in pervaporation device design. Therefore, in this work, we design a static mixer‐based pervaporation device using water–ethanol separation as a model system and further develop computational fluid dynamics tools to investigate systematically all the influencing parameters. In the experiments, we use three‐dimensional printed helical static mixers in the feed liquid channel to enhance mass transfer and implement a Sulzer pervaporation membrane for fast removal of water from ethanol. Using flow and mass‐transfer simulations, we fit the membrane mass transfer coefficient and provide predictive models for optimal process design. Our pervaporation assembly exhibits promising performance and potential toward pervaporation processes for the removal of water from organics and is preferably scaled out by using stackable designs.

Reaction induced interfacial instability of miscible fluids in a channel

When a less viscous miscible fluid displaces a more-viscous one under a pressure-driven channel flow, unstable Kelvin–Helmholtz (K–H)-type billows are formed at the miscible interface. In this paper, we investigate whether such instability can be induced by a simple ($\textbf {A}+ \textbf {B} \rightarrow \textbf {C}$)-type chemical reaction. Here a miscible solution of one reactant $\textbf {A}$ is displacing another isoviscous reactant $\textbf {B}$ and producing a more-viscous product $\textbf {C}$ at the reactive front. It is found that because of a local increase in viscosity gradient due to the formation of more-viscous product $\textbf {C}$, K–H-type billows are formed at the $\textbf {A}$–$\textbf {C}$ interface. The changes in dynamical properties of such billows are examined by varying the governing parameters such as the mobility ratio $R_{c}$, Damköhler number $Da$, Péclet number $Pe$ and Reynolds number $Re$. Interestingly, we have found that even at high reaction rates (sufficiently large $Da$) for $R_{c}=1$, the interface remains stable and for larger values of $R_{c} (=3, 5)$ the K–H billows are observed. It is also noticed that a laminar horseshoe-type vortex develops near the wall at the channel inlet where the less-viscous reactant pushes the more-viscous product. We have computed numerically the onset time ($t_{on}$) of instability to understand the early-stage developments of the K–H billows. For different values of $Da$, we have shown the unstable and stable time zones in the ($t_{on}$–$R_{c}$) space. The bipartite ($t_{on}$–$R_{c}$) space also depicts the critical ($Da$-, $Pe$- and $Re$-dependent) $R_{c}$ value for which instability can be triggered in a finite desirable time. The delay in the onset of instability is observed with increasing $Pe$. Further it is shown that $t_{on}$ can be linearly scaled with $Pe$ to have a modified onset time ($t^{*}_{on}$), which establishes a proportionate dynamics with respect to $Pe$ in the early stages of the instability. Moreover, a reverse dependency of onset on lower $R_{c}$ values for higher Reynolds numbers is observed.