Finite Solubility Research Articles

Charge-balanced codoping enables exceeding doping limit and ultralow thermal conductivity

Materials with low thermal conductivity are applied extensively in energy management, and breaking the amorphous limits of thermal conductivity to solids has attracted widespread attention from scientists. Doping is a common strategy for achieving low thermal conductivity that can offer abundant scattering centers in which heavier dopants always result in lower phonon group velocities and lower thermal conductivities. However, the amount of equivalent heavy-atom single dopant available is limited. Unfortunately, nonequivalent heavy dopants have finite solubility because of charge imbalance. Here, we propose a charge balance strategy for SnS by substituting Sn<sup>2+</sup> with Ag<sup>+</sup> and heavy Bi<sup>3+</sup>, improving the doping limit of Ag from 2% to 3%. Ag and Bi codoping increases the point defect concentration and introduces abundant boundaries simultaneously, scattering the phonons at both the atomic scale and nanoscale. The thermal conductivity of Ag<sub>0.03</sub>Bi<sub>0.03</sub>Sn<sub>0.94</sub>S decreased to 0.535 W·m<sup>−1</sup>·K<sup>−1</sup> at room temperature and 0.388 W·m<sup>−1</sup>·K<sup>−1</sup> at 275 ℃, which is below the amorphous limit of 0.450 W·m<sup>−1</sup>·K<sup>−1</sup> for SnS. This strategy offers a simple way to enhance the doping limit and achieve ultralow thermal conductivity in solids below the amorphous limit without precise structural modification.

Design Principles for Fluorinated Interphase Evolution via Conversion-Type Alloying Processes for Anticorrosive Lithium Metal Anodes.

Over the past decade, lithium metal has been considered the most attractive anode material for high-energy-density batteries. However, its practical application has been hindered by its high reactivity with organic electrolytes and uncontrolled dendritic growth, resulting in poor Coulombic efficiency and cycle life. In this paper, we propose a design strategy for interface engineering using a conversion-type reaction of metal fluorides to evolve a LiF passivation layer and Li-M alloy. Particularly, we propose a LiF-modified Li-Mg-C electrode, which demonstrates stable long-term cycling for over 2000 h in common organic electrolytes with fluoroethylene carbonate (FEC) additives and over 700 h even without additives, suppressing unwanted side reactions and Li dendritic growth. With the help of phase diagrams, we found that solid-solution-based alloying not only facilitates the spontaneous evolution of a LiF layer and bulk alloy but also enables reversible Li plating/stripping inward to the bulk, compared with intermetallic compounds with finite Li solubility.

Enhancement of the oral bioavailability of isopropoxy benzene guanidine though complexation with hydroxypropyl-β-cyclodextrin

Isopropoxy benzene guanidine (IBG) is a novel substituted benzene guanidine analogue with antibacterial activity against multidrug-resistant bacteria. However, the bioavailability of IBG is not optimal due to its finite aqueous solubility, thus hampering its potential therapeutic exploitation. In this study, we prepared IBG/hydroxypropyl-β-CD (IBG/HP-β-CD) complex, and characterized it by differential scanning calorimetry, Fourier transform infrared spectroscopy, powder X-ray diffraction, and scanning electron microscopy. Physicochemical characterization indicated that the crystal morphology of IBG transformed into an amorphous state, thus forming IBG/HP-β-CD inclusion complexes. Complexation with HP-β-CD significantly improve the aqueous solubility, pharmaceutical properties, absorption, and bioavailability of IBG.

Substrate colonization by an emulsion drop prior to spreading

In classical wetting, the spreading of an emulsion drop on a surface is preceded by the formation of a bridge connecting the drop and the surface across the sandwiched film of the suspending medium. However, this widely accepted mechanism ignores the finite solubility of the drop phase in the medium. We present experimental evidence of a new wetting mechanism, whereby the drop dissolves in the medium, and nucleates on the surface as islands that grow with time. Island growth is predicated upon a reduction in solubility near the contact line due to attractive interactions between the drop and the surface, overcoming Ostwald ripening. Ultimately, wetting is manifested as a coalescence event between the parent drop and one of the islands, which can result in significantly large critical film heights and short hydrodynamic drainage times prior to wetting. This discovery has broad relevance in areas such as froth flotation, liquid-infused surfaces, multiphase flows and microfluidics.

Phase separation effects on a partially miscible viscous fingering dynamics

Classical viscous fingering (VF) instability, the formation of finger-like interfacial patterns, occurs when a less viscous fluid displaces a more viscous one in porous media in immiscible and fully miscible systems. However, the dynamics in partially miscible fluid pairs, exhibiting a phase separation due to its finite solubility into each other, has not been largely understood so far. This study has succeeded in experimentally changing the solution system from immiscible to fully miscible or partially miscible by varying the compositions of the components in an aqueous two-phase system (ATPS) while leaving the viscosities relatively unchanged at room temperature and atmospheric pressure. Here, we have experimentally discovered a new topological transition of VF instability by performing a Hele-Shaw cell experiment using the partially miscible system. The finger formation in the investigated partially miscible system changes to the generation of spontaneously moving multiple droplets. Through additional experimental investigations, we determine that such anomalous VF dynamics is driven by thermodynamic instability such as phase separation due to spinodal decomposition and Korteweg convection induced by compositional gradient during such phase separation. We perform the numerical simulation by coupling hydrodynamics with such chemical thermodynamics and the spontaneously moving droplet dynamics is obtained, which is in good agreement with the experimental investigations of the ATPS. This numerical result strongly supports our claim that the origin of such anomalous VF dynamics is thermodynamic instability.

NaCl-saturated brines are thermodynamically moderate, rather than extreme, microbial habitats.

NaCl-saturated brines such as saltern crystalliser ponds, inland salt lakes, deep-sea brines and liquids-of-deliquescence on halite are commonly regarded as a paradigm for the limit of life on Earth. There are, however, other habitats that are thermodynamically more extreme. Typically, NaCl-saturated environments contain all domains of life and perform complete biogeochemical cycling. Despite their reduced water activity, ∼0.755 at 5 M NaCl, some halophiles belonging to the Archaea and Bacteria exhibit optimum growth/metabolism in these brines. Furthermore, the recognised water-activity limit for microbial function, ∼0.585 for some strains of fungi, lies far below 0.755. Other biophysical constraints on the microbial biosphere (temperatures of >121°C; pH > 12; and high chaotropicity; e.g. ethanol at >18.9% w/v (24% v/v) and MgCl2 at >3.03 M) can prevent any cellular metabolism or ecosystem function. By contrast, NaCl-saturated environments contain biomass-dense, metabolically diverse, highly active and complex microbial ecosystems; and this underscores their moderate character. Here, we survey the evidence that NaCl-saturated brines are biologically permissive, fertile habitats that are thermodynamically mid-range rather than extreme. Indeed, were NaCl sufficiently soluble, some halophiles might grow at concentrations of up to 8M. It may be that the finite solubility of NaCl has stabilised the genetic composition of halophile populations and limited the action of natural selection in driving halophile evolution towards greater xerophilicity. Further implications are considered for the origin(s) of life and other aspects of astrobiology.

Analyzing Microstructural and Electrolyte Phase Limitations in Li-Air Battery Performance

Lithium-air batteries, despite having a superior theoretical performance as compared to other lithium chemistries, demonstrates poor discharge performance. The discharge product in organic electrolyte Li-air cells is lithium peroxide (Li2O2), which precipitates as a solid phase during discharge and gives rise to pore network evolution for the porous electrode. To make matters worse, lithium peroxide is electronically insulating and in turn evolves the electrochemically active interface. On the other hand, as dissolved oxygen is consumed during electrochemical discharge, additional oxygen from air is to be transported from ambient to reaction zone. Finite solubility and finite rate oxygen transport may lead to oxygen starvation for faster operation (related with electrolyte phase transport description). The relative severity of these microstructural and electrolyte phase limitations jointly determines the cell performance. Consistent and comprehensive descriptions for microstructural evolution and electrolyte phase transport are developed here, and in turn physicochemical evolution in Li-air cells investigated. Depending on the severity of these resistive modes, different strategies for cell performance improvement are highlighted.

Growth, structural, spectroscopic, thermal, dielectric and optical study of cobalt sulphide-doped ADP crystals

As ammonium dihydrogen phosphate (ADP) is a popular nonlinear optical crystal, to engineer its linear and nonlinear optical properties, the chalcogenide compound cobalt sulphide (CoS) was doped and the crystals were grown by the slow solvent evaporation method. To increase the solubility of CoS in water, its nanoparticles were synthesized by wet chemical technique using ethylene diamine as the capping agent followed by microwave irradiation. The nanoparticle sample exhibited finite solubility in water and was used to dope in ADP crystals. The powder XRD patterns showed the single phase nature of the doped crystals. The FTIR spectra confirmed the presence of various functional groups and EDAX gave the estimation of Co and S elements. The EPR spectroscopy also confirmed the presence of cobalt in the doped samples. TGA indicated slightly less thermal stability of the doped crystals compared to the pure ADP. The dielectric study was carried out at room temperature in the frequency range from 100[Formula: see text]Hz to 1[Formula: see text]MHz. Also, various linear optical parameters were evaluated for pure and doped crystals using UV–Vis spectroscopy. The second harmonic generation (SHG) efficiency of Nd:YAG laser was evaluated by the Kurtz and Parry method for the doped samples, it was found to be slightly lesser than that of the pure ADP crystals.

Density profiles around A+B→C reaction-diffusion fronts in partially miscible systems: A general classification.

Various spatial density profiles can develop in partially miscible stratifications when a phase A dissolves with a finite solubility into a host phase containing a dissolved reactant B. We investigate theoretically the impact of an A+B→C reaction on such density profiles in the host phase and classify them in a parameter space spanned by the ratios of relative contributions to density and diffusion coefficients of the chemical species. While the density profile is either monotonically increasing or decreasing in the nonreactive case, reactions combined with differential diffusivity can create eight different types of density profiles featuring up to two extrema in density, at the reaction front or below it. We use this framework to predict various possible hydrodynamic instability scenarios inducing buoyancy-driven convection around such reaction fronts when they propagate parallel to the gravity field.

A model for pattern deposition from an evaporating solution subject to contact angle hysteresis and finite solubility.

We propose a model for the pattern deposition of the solute from an evaporating drop of a dilute solution on a horizontal substrate. In the model we take into account the three-phase contact angle hysteresis and the deposition of the solute whenever its concentration exceeds the solubility limit. The evaporating drop is governed by a film equation. We show that unless for a very small three-phase contact angle or a very rapid evaporation rate the film adopts a quasi-steady geometry, satisfying the Young-Laplace equation to leading order. The concentration profile is assumed to satisfy an advection diffusion equation subject to the standard Fick's law for the diffusive flux. We further use an integral boundary condition to describe the dynamics of the concentration in the vicinity of the three-phase contact line; we replace an exact geometric description of the vicinity of the contact line, which is usually assumed such that mathematical singularities are avoided, with general insights about the concentration and its flux. We use our model to explore the relationships between a variety of deposition patterns and the governing parameters, show that the model repeats previous findings, and suggest further insights.

Diffusion in a temperature gradient – A single cycle method to determine frequency factor and activation energy of solid diffusion coefficients in alloys

An experimental procedure for determining the temperature dependence of diffusion coefficients in a single diffusion heat treatment is introduced. Diffusion in a temperature gradient in samples with initially symmetric “roof-shaped” concentration profiles of a suitable length scale and concentration range yields asymmetric profiles that allow the determination of the frequency factor D0 and the activation energy QD. The binary system Al–Cu is used as an example. The procedure is applicable to alloy systems with finite solute solubility.

Direct Measurements of Colloidal Solvophoresis under Imposed Solvent and Solute Gradients.

We describe a microfluidic system that enables direct visualization and measurement of diffusiophoretic migration of colloids in response to imposed solution gradients. Such measurements have proven difficult or impossible in macroscopic systems due to difficulties in establishing solution gradients that are sufficiently strong yet hydrodynamically stable. We validate the system with measurements of the concentration-dependent diffusiophoretic mobility of polystyrene colloids in NaCl gradients, confirming that diffusiophoretic migration velocities are proportional to gradients in the logarithm of electrolyte concentration. We then perform the first direct measurement of the concentration-dependent "solvophoretic" mobility of colloids in ethanol-water gradients, whose dependence on concentration and gradient strength was not known either theoretically or experimentally, but which our measurements reveal to be proportional to the gradient in the logarithm of ethanol mole fraction. Finally, we examine solvophoretic migration under a variety of qualitatively distinct chemical gradients, including solvents that are miscible or have finite solubility with water, an electrolyte for which diffusiophoresis proceeds down concentration gradients (unlike for most electrolytes), and a nonelectrolyte (sugar). Our technique enables the direct characterization of diffusiophoretic mobilities of various colloids under various solvent and solute gradients, analogous to the electrophoretic ζ-potential measurements that are routinely used to characterize suspensions. We anticipate that such measurements will provide the feedback required to test and develop theories for solvophoretic and diffusiophoretic migration and ultimately to the conceptual design and engineering of particles that respond in a desired way to their chemical environments.

Control of convective dissolution by chemical reactions: general classification and application to CO(2) dissolution in reactive aqueous solutions.

In partially miscible two-layer systems within a gravity field, buoyancy-driven convective motions can appear when one phase dissolves with a finite solubility into the other one. We investigate the influence of chemical reactions on such convective dissolution by a linear stability analysis of a reaction-diffusion-convection model. We show theoretically that a chemical reaction can either enhance or decrease the onset time of the convection, depending on the type of density profile building up in time in the reactive solution. We classify the stabilizing and destabilizing scenarios in a parameter space spanned by the solutal Rayleigh numbers. As an example, we experimentally demonstrate the possibility to enhance the convective dissolution of gaseous CO_{2} in aqueous solutions by a classical acid-base reaction.

Determination of Impurity Diffusion Coefficients in a Single Experimental Cycle

An experimental approach employing temperature and concentration gradients is presented that is suitable for determining impurity diffusion coefficients in a single experimental cycle. The Al-Cu system is used to illustrate the feasibility of the method. In a single phase α-Al solid solution, concentration gradients are generated by exposing a cylindrical sample to steep temperature gradients and by annealing until the initially formed mushy zone is re-solidified. The annealing is performed such that a symmetric, ramp shaped profile in the form of a roof is generated. The sample is then again exposed to a temperature gradient at somewhat lower temperatures for an extended time period. The symmetric profile then becomes asymmetric due to the varying diffusion coefficient along the sample. Information on the pre-exponential factor D0 and the activation energy for diffusion QD is retrieved from the asymmetry of the resulting concentration profile. The asymmetry becomes increasingly pronounced with longer diffusion times, yielding an increasing accuracy of the diffusion coefficients. The experimental approach is generally applicable to alloy systems with finite solubility.

Time and frequency dependent rheology of reactive silica gels

In a mixture of sodium silicate and low concentrated sulfuric acid, nano-sized silica particles grow and may aggregate to a system spanning gel network. We studied the influence of the finite solubility of silica at high pH on the mechanical properties of the gel with classical and piezo-rheometers. Direct preparation of the gel sample in the rheometer cell avoided any pre-shear of the gel structure during the filling of the rheometer. The storage modulus of the gel grew logarithmically with time with two distinct growth laws. The system passes the gel point very quickly but still shows relaxation at low frequency, typically below 6rad/s. We attribute this as a sign of structural rearrangements due to the finite solubility of silica at high pH. The reaction equilibrium between bond formation and dissolution maintains a relatively large bond dissolution rate, which leads to a finite life time of the bonds and behavior similar to physical gels. This interpretation is also compatible with the logarithmic time dependence of the storage modulus. The frequency dependence was more pronounced for lower water concentrations, higher temperatures and shorter reaction times. With two relaxation models (the modified Cole–Cole model and the empirical Baumgaertel–Schausberger–Winter model) we deduced characteristic times from the experimental data. Both models approximately described the data and resulted in similar relaxation times.

Metal Site Doping in the Narrow-Gap FeGa3 Semiconductor

The effects and feasibility of metal site doping of the tetragonal diamagnetic insulator FeGa3 by Fe/Co, Fe/Mn, and Co/Ni substitutions were investigated by the X-ray electron-probe microanalysis, electrical resistivity, specific heat, and magnetic susceptibility measurements. The substitution of Co for Fe in FeGa3 does not change its structural type and preserves the structure of the binary parent compound ( FeGa3), whereas the solubility of Mn in the FeGa3 -type structure is limited to 3 at.% and a finite solubility of Ni in CoGa3 is not detected.

An Environmentally Friendly Process Involving Refining and Membrane-Based Electrolysis for Magnesium Recovery from Partially Oxidized Scrap Alloy

Magnesium is recovered from partially oxidized scrap alloy by combining refining and solid oxide membrane (SOM) electrolysis. In this combined process, a molten salt eutectic flux (45 wt.% MgF2–55 wt.% CaF2) containing 10 wt.% MgO and 2 wt.% YF3 was used as the medium for magnesium recovery. During refining, magnesium and its oxide are dissolved from the scrap into the molten flux. Forming gas is bubbled through the flux and the dissolved magnesium is removed via the gas phase and condensed in a separate condenser at a lower temperature. The molten flux has a finite solubility for magnesium and acts as a selective medium for magnesium dissolution, but not aluminum or iron, and therefore the magnesium recovered has high purity. After refining, SOM electrolysis is performed in the same reactor to enable electrolysis of the dissolved magnesium oxide in the molten flux producing magnesium at the cathode and oxygen at the SOM anode. During SOM electrolysis, it is necessary to decrease the concentration of the dissolved magnesium in the flux to improve the faradaic current efficiency and prevent degradation of the SOM. Thus, for both refining and SOM electrolysis, it is very important to measure and control the magnesium solubility in the molten flux. High magnesium solubility facilitates refining whereas lower solubility benefits the SOM electrolysis process. Computational fluid dynamics modeling was employed to simulate the flow behavior of the flux stirred by the forming gas. Based on the modeling results, an optimized design of the stirring tubes and its placement in the flux are determined for efficiently removing the dissolved magnesium and also increasing the efficiency of the SOM electrolysis process.

Kinetic Control of Catalytic CVD for High-Quality Graphene at Low Temperatures

Low-temperature (∼600 °C), scalable chemical vapor deposition of high-quality, uniform monolayer graphene is demonstrated with a mapped Raman 2D/G ratio of >3.2, D/G ratio ≤0.08, and carrier mobilities of ≥3000 cm(2) V(-1) s(-1) on SiO(2) support. A kinetic growth model for graphene CVD based on flux balances is established, which is well supported by a systematic study of Ni-based polycrystalline catalysts. A finite carbon solubility of the catalyst is thereby a key advantage, as it allows the catalyst bulk to act as a mediating carbon sink while optimized graphene growth occurs by only locally saturating the catalyst surface with carbon. This also enables a route to the controlled formation of Bernal stacked bi- and few-layered graphene. The model is relevant to all catalyst materials and can readily serve as a general process rationale for optimized graphene CVD.

Controlling the Abruptness of Axial Heterojunctions in III–V Nanowires: Beyond the Reservoir Effect

Heterostructure nanowires have many potential applications due to the avoidance of interface defects by lateral strain relaxation. However, most heterostructure semiconductor nanowires suffer from persistent interface compositional grading, normally attributed to the dissolution of growth species in the common alloy seed particles. Although progress has been made for some material systems, most binary material combinations remain problematic due to the interaction of growth species in the alloy. In this work we investigate the formation of interfaces in InAs-GaAs heterostructures experimentally and theoretically and demonstrate a technique to attain substantially sharper interfaces. We show that by pulsing the Ga source during heterojunction formation, In is pushed out before GaAs growth initiates, greatly reducing In carry-over. This procedure will be directly applicable to any nanowire system with finite nonideal solubility of growth species in the alloy seed particle and greatly improve the applicability of these structures in future devices.

Surface adsorption and vesicle formation of dilauroylphosphatidylcholine in room temperature ionic liquids

Surface chemical properties of a phospholipid, dilauroylphosphatidylcholine (DLPC), in two ionic liquids (ILs), 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4) and hexafluorophosphate (bmimPF6), were investigated by means of surface tension, dynamic light-scattering, and freeze-fracture transmission electron microscopy. It was found that DLPC shows finite solubility in the ILs and spontaneously forms vesicles with size distribution around 400nm in diameter above the critical vesicular concentration (CVC) of 0.040wt.% (in bmimBF4) and approx. 0.08wt.% (in bmimPF6). Other than the CVC value, anion specificity of the ILs was also seen in the temperature effect on the vesicular aggregation; that is, a temperature-induced reversible aggregation was observed in bmimPF6, but not in bmimBF4. The differences in the vesicular stability against the temperature-induced aggregation could be attributed to differences in the interaction between anion species of the ILs and zwitterionic phosphatidylcholine head groups. The apparent molecular area occupied by DLPC at the air/solution interface was estimated to be 0.37nm2 in bmimBF4 and 0.20nm2 in bmimPF6 by applying the Gibbs adsorption equation. These values are much smaller than the molecular area of 0.69nm2 reported for the hydrated DLPC bilayer of lamellar liquid-crystalline phase. This result is not consistent with the traditional Gibbs adsorption model, but can be interpreted in terms of a picture for the surface adsorption of soluble amphiphiles proposed by Moroi et al. Differential scanning calorimetric study is also reported regarding the phase transition behavior of DLPC bilayer solvated by the ILs.