Miscible Solutions Research Articles

On Numerical Classification of Solution Adsorption Isotherms

To numerically classify solution adsorption isotherms, a difference or deviation measure, DS(mc) (the relative difference between two sums of the adsorption maximum's characteristics of selectivity isotherms x 100), is derived. The measure is applicable to completely miscible binary solutions on solids. This quantity evaluates the difference between an adsorption system and the ideal adsorption system (ideal adsorbed and bulk phases, homogeneous surface, and equal molar area solution components) at the point of maximum adsorption. For model systems, DS(mc)s are calculated at several levels of surface heterogeneity (Gaussian distribution of surface energy) and for different signs of phase nonideality (regular solution phases) on a homogeneous surface and on a simple two-site-type heterogeneous surface. All heterogeneous surfaces have negative DS(mc) values, but nonideal phases have DS(mc)s with signs opposite to the sign of deviation from Raoult's law. DS(mc)s from both U- and S-shape isotherms are reported for 16 experimental systems consisting of hydrocarbon mixtures and both alcohol + hydrocarbon and alcohol + water solutions or acetone + carbon tetrachloride on several silica gels and a variety of carbons.

Visualization of the Reaction Zones Between Two Miscible Solutions with Potentiometric and Amperometric Microsensors

AbstractA strategy for visualizing the concentration gradients in the border zone between two miscible aqueous solutions of different composition is presented. To achieve this goal, potentiometric pH microsensors and disk‐shaped Pt microelectrode have been operated as scanning probes in a set‐up that combined conventional scanning electrochemical microscopy (SECM) equipment with an inverted optical microscope and a syringe pump for analyte injection. With the established system, complex gradients in proton concentration have been examined in the reaction zone between two aqueous solutions of different pH value, one of which being dispensed into the other at controlled flow rate. In addition to the local potentiometric measurements, Pt microelectrodes have been used as amperometric SECM tips to visualize the reaction zone at the diffuse boundary between a stream of H2O2 and a neighbouring catalase‐containing buffer solution.

The effect of mixed salts in gel-coated polymer electrolyte for advanced lithium battery

A miscible blend solution of poly(ethylene glycol diacrylate) (PEGDA)/poly(vinylidene fluoride) (PVdF)/poly(methyl methacrylate) (PMMA) was crosslinked on polypropylene (PP) separator by UV-irradiation. PEGDA/PVdF/PMMA(E/V/M)-coated electrolytes showed much better liquid electrolyte uptaking and retention than PEGDA/PP composite electrolyte because viscous ternary blend solution was more compatible with electrolyte system. Gel-coated membranes (GCE) containing a mixed lithium salts of LiPF 6/LiCF 3SO 3 (10/1 (w/w)) showed slightly lower maximum conductivity than those containing only LiPF 6, but their interfacial resistance much more stable than other salt compositions. In addition, it was found that γ-Al 2O 3 filler improved interfacial stability. As a result, 8 cm × 13 cm MCMB/LiCoO 2 cells composed of E/V/M-coated composite matrix and LiPF 6/LiCF 3SO 3 (10/1 (w/w)) delivered 99.6% initial capacity after 100 cycles at C/2 rate.

Lyophilization of polyethylene glycol mixtures

Lyophilization of cosolvent systems may be a beneficial way of enhancing both physical and chemical stability of a drug product. The objective of this research is to establish whether cosolvent systems commonly used in the formulation of poorly water‐soluble drugs can be successfully lyophilized. Polyethylene glycol (PEG) 400 was selected because it is widely used and can be easily frozen. The addition of PEG 400 to commonly used bulking agents, such as mannitol, sucrose, or polyvinylpyrrolidone, caused a significant change in the thermal properties of the bulking agents as observed by modulated differential scanning calorimetry. In addition, PEG 8000 was evaluated as a bulking agent because it also can function as a cosolvent in solution and forms an acceptable cake after lyophilization. Addition of PEG 400 to PEG 8000 caused negligible changes in the thermogram of this bulking agent. Surprisingly, the combination of PEG 8000 and PEG 400 forms a solid lyophilized cake. The current system can be best described as the lyophilization of a miscible solution of PEG 8000 and PEG 400 resulting in a lyophile that has a crystalline structure of PEG 8000 which is able to support PEG 400.

Effect of Leachate Composition on the Adsorption Properties of Two Soils

Abstract The experimental results show that the composition of the contaminant leachate affects the adsorption behavior for the soil tested. However, this conclusion is based on the assumption that the soil adsorption isotherm is linear. To investigate this effect when the adsorption isotherm is nonlinear, a series of batch tests were conducted with a single-salt solution (KCl, CaCl2, and NaCl solution, respectively) and multi-salt solution (aqueous miscible solution containing KCl, CaCl2, and NaCl) for the selected two soils from Japan. A comparison of the test results between these two conditions indicated that for a specified cation of interest, soils adsorbed larger amounts of cations in the case of the single-salt condition relative to the multisalt condition. The Freundlich equation was adopted to fit the experimental data, and the model parameters are presented. The relative cation adsorption of soils is provided and the controlling factors are discussed.

Mobility of sulfate in forest soils: kinetic modeling.

Understanding sulfate transport and retention dynamics in forest soils is a prerequisite in predicting SO4 concentration in the soil solution and in lake and stream waters. In this study forest soil samples from the Gårdsjön catchments, Sweden, were used to study SO4 transport in soil columns from the upper three soil horizons (E, Bs, and BC). The columns were leached using a sequential leaching technique. The input solutions were CaSO4 equilibrated with forest floor material. Leaching behavior of SO4 and concentration in the effluent were measured from columns from individual horizons. Sulfate was always retained in the Bs and BC horizons, while the pattern for the E horizon varied. Attempts were also made to model SO4 breakthrough results based on miscible displacement approaches and solute convection-dispersion equation (CDE) in porous media. Several retention mechanisms were incorporated into the CDE to account for possible reversible and irreversible SO4 reactions in individual soil layers. Our modeling efforts were inadequate in describing the mobility of SO4 in the top (E) horizon. Moreover, a linear equilibrium approach was generally inadequate for describing SO4 sorption during transport in the Bs and BC horizons. In contrast, we found that the model provided good descriptions of all breakthrough results when SO4 reactivity was accounted for based on nonlinear equilibrium or first-order kinetic processes. Moreover, based on model parameter estimates, the reactivity or retention of SO4 during transport is concentration dependent. We conclude that sulfate retention during transport in this forest soil is most likely controlled by kinetic reactivity of SO4 of the reversible and irreversible mechanisms.

Dispersion de Taylor généralisée à un fluide à propriétés physiques variables

The investigation of non-reactive miscible solute dispersion in a vertical Hele–Shaw cell is considered. An asymptotic method is used to extend Taylor model to the case of the fluid density, the dynamic viscosity and the molecular diffusion coefficient are solute concentration-dependent. It is demonstrated that the averaged variables over the gap are governed by a convection–dispersion equation in which the dispersion tensor is concentration-dependent. To cite this article: C. Felder et al., C. R. Mecanique 332 (2004).

Clustering of water molecules in aqueous solutions: Effect of water–solute interaction

Clustering of water molecules in partially miscible aqueous solutions (with immiscibility gap) was studied by Monte Carlo (MC) simulations. Liquid–liquid coexistence curves were determined by MC simulations in the Gibbs ensemble. Water cluster size distributions were studied in the organic-rich one-phase region. At the coexistence curve we observe the broadest distribution of cluster sizes in agreement with the Fisher droplet model. There are no percolating water clusters in aqueous mixtures of solutions of hydrophobic particles in the studied concentration range. In contrast, in an aqueous solution of hydrophilic solutes crossing the coexistence curve approximately coincides with the 3D percolation threshold of water. An infinite water cluster (percolating cluster or droplet of the second phase) appears in an aqueous solution, when the average number of water–water H-bonds per molecule exceeds ca. 1.6.

Miscible density fingering of chemical fronts in porous media: Nonlinear simulations

Nonlinear interactions between chemical reactions and Rayleigh–Taylor type density fingering are studied in porous media or thin Hele-Shaw cells by direct numerical simulations of Darcy’s law coupled to the evolution equation for the concentration of a chemically reacting solute controlling the density of miscible solutions. In absence of flow, the reaction-diffusion system features stable planar fronts traveling with a given constant speed v and width w. When the reactant and product solutions have different densities, such fronts are buoyantly unstable if the heavier solution lies on top of the lighter one in the gravity field. Density fingering is then observed. We study the nonlinear dynamics of such fingering for a given model chemical system, the iodate-arsenious acid reaction. Chemical reactions profoundly affect the density fingering leading to changes in the characteristic wavelength of the pattern at early time and more rapid coarsening in the nonlinear regime. The nonlinear dynamics of the system is studied as a function of the three relevant parameters of the model, i.e., the dimensionless width of the system expressed as a Rayleigh number Ra, the Damköhler number Da, and a chemical parameter d which is a function of kinetic constants and chemical concentration, these two last parameters controlling the speed v and width w of the stable planar front. For small Ra, the asymptotic nonlinear dynamics of the fingering in the presence of chemical reactions is one single finger of stationary shape traveling with constant nonlinear speed V>v and mixing zone W>w. This is drastically different from pure density fingering for which fingers elongate monotonically in time. The asymptotic finger has axial and transverse averaged profiles that are self-similar in unit lengths scaled by Ra. Moreover, we find that W/Ra scales as Da−0.5. For larger Ra, tip splittings are observed.

Hydrodynamical instability of spatially extended bistable chemical systems

Hydrodynamical density fingering of chemical fronts separating two miscible, stable steady states of different chemical composition, and hence density, can lead to complex spatio-temporal dynamics. The most striking feature of such dynamics is the disconnection of droplets of one stable steady state from fingers invading the other stable steady state. Such disconnected droplets do not exist in pure density fingering and are thus the result of the bistable kinetics. We study such dynamics by direct numerical simulations of Darcy's law for flow in Hele–Shaw cells coupled to the kinetic equation for the concentration of a chemically reacting solute controlling the density of the miscible solutions. The concentration of this solute obeys a simple cubic model leading to bistability. Experimental realization of such dynamics in spatially extended Hele–Shaw cells calls for the use of the concept of spatial bistability which implies construction of new continuously fed open reactors.

Phase behavior and structural characterization of coexisting pure and mixed clathrate hydrates.

Clathrate hydrates are crystalline compounds formed by a physically stable interaction between water and relatively small guest molecules. Under suitable conditions of guest pressure and temperature, water molecules, via hydrogen bonds, form into polyhedral cavities that connect to give space-filling frameworks. Because of partial cage filling, these crystalline compounds are nonstoichiometric. They can be divided into three distinct structural families I (sI), II (sII), and H (sH), which differ in their combination of cavities of different sizes and shapes. Although the above hydrate structures with natural gas components as guest molecules are widely known, new structures continue to be reported, such as a new, highly complex structure, known as structure T (sT) hydrate, that contains two cages of unusual geometry, and a new sII ± SH polytype. As well, a metastable sII hydrate of xenon has been observed: when a sII hydrate of tetrahydrofuran (THF) was placed in contact with hyperpolarized xenon. It is clear that many of the physical attributes of clathrate hydrates remain unknown and need to be identified in more detail. In our previous work, multiphase equilibria were measured to examine the complex phase behavior in the hydrate stability region for aqueous solutions containing carbon dioxide and methane as secondary guests. Although normally a single phase is expected to be stable in such systems, here we report the coexistence of sI and sII phases in a ternary system consisting of methane, THF, and water. This system was chosen especially to examine which structure would appear, depending on the relative concentration of the water-soluble THF molecules. THF by itself forms sII hydrate in a completely miscible aqueous solution, and in this structure, because of their size, THF guests occupy only the large 56 (H) cages. Furthermore, the mixed hydrate formed by THF and methane guests has been identified as sII, and this is independent of the THF to water ratio. However, stable hydrates in THF ±methane systems may have widely varying overall compositions, as methane may well occupy some of the large, as well as small, cages. In order to determine this, we followed two specific THF concentrations, 5.6 and 3.0 mol%, during hydrate formation. As an indirect measure of hydrate formation, the pressure ± temperature (P ± T) trajectory, which represents hydrate nucleation, growth, and dissociation stages, was measured experimentally and the resulting closed loop made by the hydrate formation and dissociation processes is shown in Figure 1a. The mixed CH4 THF hydrate started to form directly after going through the three-phase equilibrium boundary, and rapid pressure reduction occurred immediately

Solution miscibility and phase-change behavior of a polyethylene glycol-diacetate cellulose composite

Polyethylene glycol (PEG) and diacetate cellulose (CDA) exhibit good miscibility in acetone solution. The miscibility is related to the molecular weight of PEG, which increases as miscibility decreases. The phase-change behavior of PEG in composite with CDA prepared from the miscible solution was found to be completely different from that of pure PEG. When the PEG fraction in the composites was less than 85%, PEG within the composite did not melt into liquid; even when the temperature was 40°C higher than the melting point of PEG, the PEG–CDA composite exhibited solid–solid phase-change behavior. Thermal analysis indicated that the PEG–CDA composite had greater enthalpy and exhibited good thermal stability. The PEG–CDA composite that exhibited solid–solid phase-change behavior can be used as a new kind of phase-change material for thermal energy storage and temperature control. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 652–658, 2003

Polar organic solvent added to an aqueous solution changes hydrolytic property of lipase.

For developing further uses of lipase as a biocatalyst, its hydrolytic activity toward some esters was investigated in a miscible solution composed of a buffer and a polar organic solvent. Twenty percent dimethylformamide, 35% dimethylsulfoxide, 15% 1,4-dioxane, 15% dimethoxyethane, and 2% diethoxyethane promoted the hydrolysis by a lipase from Rhizomucor miehei toward some hydrophobic substrates, 4-methylumbelliferyl oleate, 4-methylumbelliferyl palmitate, and monoolein. While hydrolysis by this lipase toward the substrates with a relatively weak hydrophobicity (4-metylumbelliferyl heptanoate and 4-methylumbelliferyl nanoate) was suppressed by these solvents. A fluorometric analysis showed that the polar organic solvent in the buffer induced some conformational change around a tryptophan residue of R. miehei lipase. In addition to the influence of the miscible solvent on the solubility of the substrates, the conformational change of the protein induced by the miscible solvent would also affect the reactive properties of the lipase. Adding a polar organic solvent to an aqueous solution will be an efficient method for changing hydrolytic performance of lipases.

Dynamic mechanical behavior of the dioctyl phthalate plasticized polyvinyl chloride–epoxidized soya bean oil

The mixing of polyvinyl chloride (PVC) with dioctyl phthalate (DOP) shows two stages of gelation and fusion, but the homogeneity of each stage is influenced by the thermal stability of PVC and its rheological behavior. A torque rheometer has been used to gather almost all critical data related to the plasticized PVC in the epoxidized soya bean oil (ESBO). This study shows that, rheological data reflects the effects of DOP and epoxidization levels of SBO, in a DOP plasticized PVC–ESBO. The DOP plasticizer forms a thermodynamically miscible solution with ESBO; that reduces the rate of fusion and torque at balance of PVC. The storage modulus and tan δ of the plasticized PVC–ESBO have been used to show the extent of the homogeneity; but the dynamic mechanical behavior of PVC–ESBO is strongly influenced by DOP and the epoxidization level of SBO. The glass transition temperatures and dynamic properties of DOP plasticized PVC–ESBO are also reported and discussed in terms of the thermal stability and homogeneity of PVC.

Exploitation of tandem streams for carry-over compensation in flow analysis: I. Turbidimetric determination of potassium in fertilizers

Tandem flow is the essence of a novel modality of flow analysis. This unique stream initially comprises several neighboring slugs of miscible solutions that undergo fast mixing while flowing through the analytical path. When overlap of the slugs is partial, the identity of the initial slugs can be preserved although with some carry-over. If to each slug corresponds a processed sample zone, carry-over can be efficiently exploited. Carry-over exploitation as means to enhance sampling rate and/or reagent consumption is demonstrated in designing an improved turbidimetric determination of potassium in fertilizers using sodium tetraphenylboron. Sampling rate undergoes a remarkable increase and other favorable characteristics are maintained. Potentialities and limitations of the approach as well as dependence of measurement repeatability on the carry-over degree are discussed.

Slightly compatible polymer mixtures at equilibrium: phase composition, interfacial and diffusional properties

An approximate solution is presented to the phase equilibrium problem for the case of a partially miscible polymer solution or a binary heteropolymer blend. It is based on the Flory–Huggins theory and is valid for mixtures well into the phase-separated region. Analytical expressions are derived for the extent and composition of each of the two coexisting phases as a function of the component molecular size and interaction strength. These results are combined with Helfand's model to provide estimates for the interfacial tension and thickness and, therefore, a measure of the quality of the interfacial bonding in a polymer/polymer blend. They are also utilized in conjunction with a free volume theory approach for calculating the mutual diffusion coefficient of a penetrant, migrating through a polymer.

Hydrothermal synthesis, structure and property of nano-BaTiO3-based dielectric materials

A series of Ba 1- x Sr x Ti 1- y Zr y O 3 (0≤ x ≤0.5, 0≤ y ≤0.4) and Ba 1- x Sr x Ti 1- y Sn y O 3 (0≤ x ≤0.3, 0≤ y ≤0.3) solid solutions were synthesized by low-temperature/low-pressure hydrothermal method below 170℃, 0.8 MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible solid solutions based on BaTiO 3 . Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of those powders doped by Sr 2+ and Zr 4+ or Zn 2+ and Sn 4+ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO 3 phase at room temperature.

Particle formation by mixing with supercritical antisolvent at high Reynolds numbers

A precipitation process is considered in which completely miscible solution and supercritical antisolvent are passed through premixing and diluting zones of a turbulent flow. The influence of flow velocity on particle size and nuclei concentration is discussed in terms of mixing and precipitation time constants and their supersaturation dependencies. The proposed model allowed the major process parameters such as supersaturation profile, mixed fluid fraction and mean particle size to be calculated and compared with experimental data. For the crystallization system paracetamol/ethanol/CO 2 studied, the supersaturation profile becomes established at Re≅10 4. The particle size and shape are defined, firstly, by increase of supersaturation and relative volume of mixed (on molecular scale) fluid with increase of flow velocity and, secondly, by decrease of residence time available for nucleation with increase of flow velocity. These competitive processes can result in minimum particle size at a defined flow rate.

Solubilization of rapamycin

The solubilization of rapamycin, a poorly water soluble investigational immunosuppressive drug, by facilitated hydrotropy is presented. Partially water-miscible aromatic solutes (such as benzyl alcohol, benzoate, or benzoic acid) can be solubilized by water-miscible cosolvents, such as ethanol and propylene glycol. Once solubilized, the partially miscible aromatic solute becomes a solubilizing agent. This technique yielded a dramatic (>1000-fold) increase in the aqueous solubility of rapamycin.

Synthesis, structure and dielectric properties of Ba1-xSrxMyTi1-yO3 (M = Zr, Sn)

A series of Ba1-xSrxMyTi1-yO3 (M = Zr, Sn, 0⩽x⩽0.4, 0⩽y⩽0.3) solid solutions were synthesized with the soft chemical method below 100 °C. XRD pattern and cell parameters-composition figures of the prepared powder demonstrate that they are completely miscible solid solutions based on BaTiO3. Furthermore, TEM shows that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of the powder doped with Sr2+and Zr4+ or Sn4+ have dielectric constant eight times higher and dielectric loss thirty per cent lower than those of pure BaTiO3 phase at room temperature.