Bulk Concentration Ratio Research Articles

A second-order phase field-lattice Boltzmann model with equation of state inputting for two-phase flow containing soluble surfactants

In this paper, we propose a phase field-lattice Boltzmann (LB) model with an equation of state (EOS) inputting for two-phase flow containing soluble surfactants. In this model, both the order parameter for the phase field and the surfactant concentration are described by second-order partial differential equations, along with Navier–Stokes equations for the flow field. Changes in surfactant concentration do not affect the order parameter distribution; hence, an unwanted sharpening effect cannot arise. Most importantly, in the existing models, the EOS of surface tension is determined by posterior simulation tests instead of being directly set as an input parameter before the simulations. Hence, it is difficult to determine the model parameters in practical applications. To address this issue, we systematically develop a fully analytical EOS for surface tension based on the Gibbs–Duhem equation. Subsequently, an approximate explicit form for EOS is provided by utilizing the Jacobi–Gauss quadrature rule. Furthermore, a multiple-relaxation-time LB scheme is utilized to numerically solve the governing equations of three physical fields. Two benchmark examples are simulated to validate the accuracy of the present model. The consistency between the numerical results and the analytical EOS is verified. Moreover, the dynamics of droplets with surfactant in simple shear flow is investigated, unveiling the profound impact of various factors, such as surfactant bulk concentration, capillary number, and viscosity ratio, on single droplet deformation and two equal-sized droplets interaction. A detailed exploration of the fluid mechanism involved in two-phase flow with soluble surfactants is presented.

Extracting mechanical and microstructural properties of Cu–Zr thin film alloys by MEMS, AFM and ellipsometer

The quantification of the atomic concentration ratios of thin-film metallic alloys having low atomic ordering is challenging, particularly if they are grown on similar metals and possess different surface chemistries. Micromechanical and optical methods have been used to correlate the elemental ratios with the mechanical and optical properties of the films. The room-temperature growth of Cu–Zn thin-film alloys with varying elemental ratios on cosputtered Si substrates was performed to obtain an amorphous film structure. X-ray diffraction patterns confirmed that the grown films exhibited a very short range ordering, suggesting an amorphous structure. The mechanical properties of the films evaluated using microelectromechanical system (MEMS) indicated that the alloy films with moderate Zr concentrations had lower surface stress compared to those with low and high Zr concentrations. Furthermore, spectroscopic ellipsometry was employed to qualitatively assess the relaxation times of free carriers. The results demonstrated a strong correlation between the relaxation times and surface roughness measurements, showing that the microstructure and resistivity characteristics of the alloys align with the Nordheim semiempirical model. The extinction coefficient of the binary alloy film linearly depends on the metallic bulk concentration ratio in a specific metallic ratio range, paving the way for realizing qualitative elemental percentage assessment in the field of metrology.

Viscous dissipation effect on forced convective transport of nanofluids in an asymmetrically heated parallel-plate microchannel

This study intends to investigate the effects of viscous dissipation on the Alumina-water nanofluids transport in an asymmetrically heated microchannel, accounting for Brownian motion and thermophoresis mechanism. An iterative algorithm deploying Runge-Kutta fourth order method was set up to solve the governing equations numerically. Viscous dissipation shifts the highest concentration and lowest fluid temperature away from the adiabatic wall and redistributes the spatial variation of thermal conductivity and viscosity, retarding the Nu as its effect strengthens. It is noteworthy that the trends of Nusselt number variation with an increasing nanoparticle bulk concentration, and Brownian and Themophoretic diffusivity ratio, N BT , highlight the competition between the enhanced thermal diffusion effect and the hindered heat convection by a larger flow resistance. A Brinkman number, Br larger than 0.02 alters the Nu pattern of variation with N BT . Viscous dissipation leads to more pronounced effects of particle migration on the concentration and temperature distribution in particular. Assuming negligible viscous dissipation, Nusselt number deteriorates beyond an Alumina concentration of 3.65 vol %. while Titania-water nanofluids showed an opposite trend. The total entropy generation, caused by fluid flow irreversibility predominantly, amplifies with an increasing nanoparticle concentration, more significantly when the concentration is below 6.5 vol %., for Br = 0.1. Conversely, an increase in Brownian to Thermophoretic diffusivity ratio, N BT , lessens the entropy generation.

A mechanistic derivation of the Monod bioreaction equation for a limiting nutrient.

We present a quasi-steady state mechanistic derivation of the Monod bioreaction equation based upon a conceptual model involving aqueous phase diffusive transport of substrate towards a spherical microbe; transport of the substrate across its surface membrane; and reaction depleting the substrate within the microbe. The resulting Monod coefficients [Formula: see text] and [Formula: see text] are dependent upon substrate-species pairs and the mass transfer properties of the system. Two substrate transport scenarios are investigated: (1) a constant rate model that is a function of a constant flux across the surface of the microbe; and (2) a linear rate model that is the product of a constant transport velocity and the concentration of substrate in contact with the surface of the microbe. The model is verified and parameterized using benzene, toluene, and phenol depletion and biomass growth data obtained from Reardon et al. (Biotechnol Bioeng: 385-400, 2000). Calibration results indicate a normalized surface to bulk concentration ratio of nearly unity in all simulations for benzene, toluene, and phenol when paired with P. putida F1, implying that the process is not aqueous phase diffusion limited.

New Evidence of Head-to-Tail Complex Formation of SDS-DOH Mixtures Adsorbed at the Air-Water Interface as Revealed by Vibrational Sum Frequency Generation Spectroscopy and Isotope Labelling.

Details about the molecular structures of surfactant mixtures adsorbed at the air-water interface have been controversial. Using sum frequency generation vibrational spectroscopy (SFG) and isotope labeling, we show here for the first time that mixtures of dodecanol (DOH) and sodium dodecyl sulfate (SDS) adsorb at the air-water interface with the formation of a head-to-tail complex. We observed this complex formation to occur first in the aqueous subphase, followed by complex adsorption onto the interface. This new piece of evidence for the head-to-tail complex conformation contradicts the conjectured tail-to-tail adsorption of the surfactant mixtures. The SFG data also show the dominating adsorption of the SDS-DOH complex over the single molecules of SDS and DOH at the air-water interface. The interfacial DOH-to-SDS molecular ratio of approximately 2.2:1 at a DOH-to-SDS bulk concentration ratio of 10 μM/2 mM was determined by isotope labeling of the surfactants. In addition to a smaller number of gauche defects, the DOH-SDS complex was found to adopt a higher level of orderliness than the adsorbed single surfactants. These findings provide important insights into the descriptions and interpretation of DOH-SDS adsorption at the air-water interface and its properties.

Tracing root-felt sodium concentrations under different transpiration rates and salinity levels

(1) Monitoring ‘root-felt’ salinity by using rhizoslides as a non-invasive method, (2) Studying how transpiration rate, salinity in irrigation water, and root water uptake affect sodium distribution around single roots, (3) Interpreting experimental results by using simulations with a 3-D root system architecture model coupled with water flow and solute transport models. Tomato plants were grown on rhizoslides under various salinity levels and two transpiration rates: high and low. Daily root images were processed with GIMP and incorporated into a 3-D numerical model. The experiments were simulated with R-SWMS, a 3-dimensional numerical model that simulates water flow and solute transport in soil, into the root and inside root systems. Both experimental and simulation results displayed higher root-felt sodium concentrations compared with the bulk concentrations, and larger accumulation at higher transpiration rate. The simulations illustrated that the root-felt to bulk concentration ratio changed during the experiment depending both on the irrigation water salinity and transpiration rate. Changes in sodium concentrations with transpiration rates are most likely caused by root water uptake and ion exclusion. Simulation results indicate that root-scale process models are required to link root system architecture, environmental, and soil conditions with root-felt salinities.

Power generation from a pH-regulated nanochannel through reverse electrodialysis: Effects of nanochannel shape and non-uniform H+ distribution

The power generated from the Gibbs free energy of mixing through reverse electrodialysis (RED) is a promising renewable energy of great potential. In this study the performance of a nanochannel having a pH-regulated surface in RED is examined, focusing on the influence of the bulk salt concentration, the distribution of H+, and the nanochannel size and its shape. Taking account of the effect of osmotic flow, we consider three types of nanochannel: bullet-shaped, conical, and trumpet-shaped nanochannels. Because the smaller the nanochannel space the more significant the degree of electric double layer overlapping the trumpet-shaped nanochannel has the best ion selectivity. As the ratio of (nanochannel length/curvature radius) varies the maximum power generated from a bullet-shaped nanochannel has a local maximum. This can be explained by the associated diffusion potential and the electric current passing through it. The results gathered provide desirable and necessary information for designing RED devices. In particular, the maximum power generation can be achieved by choosing appropriately the shape and the size of a nanochannel, and the bulk concentration ratio.

Power generation by a pH-regulated conical nanopore through reverse electrodialysis

To assess the possibility of energy harvesting through reverse electrodialysis (RED), we consider the electrokinetic behavior of the ion transport in a pH-regulated conical nanopore connecting two large reservoirs having different bulk salt concentrations, taking account of the effect of osmotic flow. In particular, we examine the influence of the ion diffusion direction, the solution pH, and the bulk concentration ratio on that behavior in detail, and discuss the underlying mechanisms. We show that the geometrically asymmetric nature of the nanopore yields profound and interesting phenomena arising mainly from the distribution of ions in its interior. Assuming a single polymeric nanopore, a power density of 18.2 W/m2 can be generated. We show that the present system has the potential of serving as an ion-selective and a salinity gradient power generation device. The maximum power efficiency which is based on assuming a linear ionic distribution in nanopore can yield appreciable deviation, especially if pH deviates significantly from 7, where the presence of H+ and OH− needs be considered.

Geochemical and isotopic evidences for a severe anthropogenic boron contamination: A case study from Castelluccio (Arezzo, central Italy)

In 2009 a deterioration of garden plants watered with domestic wells was related to high boron concentrations (up to 57 mg/L) measured in the shallow aquifer from the industrial area of Castelluccio (Tuscany, Italy), where several factories are or were using boron compounds for their industrial processes. Since 2012 a geochemical and isotopic survey of stream, ground and waste waters, and sediment samples was performed. In addition, monthly geochemical surveys were carried out from January to September 2013, during which concentrations of boron up to 139 mg/L were measured. The geochemical dataset also included raw (borax and sodium boron-hydride) and anthropogenic materials (B-rich slags and muds stored in one of the local factories), the latter being, to the best of our knowledge, analyzed for the first time in this work for bulk and leachate boron concentration and isotopic ratios. The results highlighted that the high concentrations of boron found in the local shallow aquifer had unequivocally an anthropogenic source. It was suggested that prolonged interaction between industrial (presently stored at ground level or buried) by-products and waste and meteoric waters was likely the main process responsible of the groundwater contamination as supported by the analysis of the major solutes. The dispersion of the contaminant could not clearly be observed downward the shallow hydrogeological circuit. Consequently, the presence of other sources of boron in the industrial area of Castelluccio cannot be excluded. This would also explain the reason why no univocal results were obtained by the 11B/10B isotopic ratios measured in water, sediment and (bulk and leachate) anthropogenic samples.To minimize the boron contamination a hydraulic barrier should be constructed where the highest concentrations of boron were measured.

On the meaning of the diffusion layer thickness for slow electrode reactions

A key concept underpinning electrochemical science is that of the diffusion layer - the zone of depletion around an electrode accompanying electrolysis. The size of this zone can be found either from the simulated or measured concentration profiles (yielding the 'true' diffusion layer thickness) or, in the case of the Nernst ('linear') diffusion layer by extrapolating the concentration gradient at the electrode surface to the distance at which the concentration takes its bulk value. The latter concept is very well developed in the case of fast (so-called reversible) electrode processes, however the study of the linear diffusion layer has received scant attention in the case of slow charge transfer processes, despite its study being of great interest in the analysis of the influence of different experimental variables which determine the electrochemical response. Analytical explicit solutions for the concentration profiles, surface concentrations and real and linear diffusion layers corresponding to the application of a potential step to a slow charge transfer process are presented. From these expressions the dependence of the diffusion layer thickness on the potential, pulse time, heterogeneous rate constant and ratio of bulk concentrations of electroactive species and of diffusion coefficients is quantified. A profound influence of the reversibility degree of the charge transfer on the diffusion layer thickness is clear, showing that for non-reversible processes the real and linear diffusion layers reveal a minimum thickness which coincides with the equilibrium potential of the redox couple in the former case and with the reversible half-wave potential in the latter one.

Synergistic barrier effect of phosphatidylcholine and phosphatidic acid on the ion transfer across a polarized liquid–liquid interface and its electrochemical stability

The synergistic effect of phosphatidylcholine, PC, and phosphatidic acid, PA, on the ion transfer at a liquid–liquid interface was demonstrated to be caused by interaction with lanthanide ions. Cyclic voltammograms of the potassium ion transfer facilitated by dibenzo-18-crown-6 were recorded at the interface between water containing lanthanide ion and 1,2-dichloroethane containing PC and PA. The mixed adsorbed layer of PC and PA enhanced the blocking effect on the K + transfer, as compared with the adsorbed layer composed of PC only. When the bulk concentration ratio of PC to that of PA was 1:2, the blocking was most effective and the potential range for the barrier layer stability was extended to the most positive potentials, i.e. the electrochemical stability of the barrier layer increased. On the contrary, an excess of PA resulted in degradation of the mixed barrier layer. The electrochemical stability of the mixed barrier layer was maintained at pH region lower than 4.0. When pH was higher than 4.0, the blocking effect disappeared. The above results are discussed in relation to the complex formation of phospholipids with lanthanide ion and to their protonation.

Source apportionment of PM2.5 organic aerosol over Europe: Primary/secondary, natural/anthropogenic, and fossil/biogenic origin

On the basis of a 2‐year comprehensive data set obtained within the CARBOSOL project, seasonal source apportionment of PM2.5 aerosol is attempted for five rural/remote sites in Europe. The approach developed combines radiocarbon measurements with bulk measurements of organic carbon (OC), elemental carbon (EC), and two organic tracers (levoglucosan and cellulose). Source types are lumped into primary emissions from fossil fuel combustion and biomass burning, bioaerosol, and secondary organic aerosol from precursors emitted by fossil and nonfossil sources. Bulk concentration ratios reported for these source types in the literature are used to estimate the source contributions which are constrained by measured radiocarbon concentrations. It has been found that while fossil‐related sources predominate EC throughout the year at all sites, the sources of OC are primarily biogenic and markedly different between summer and winter. In winter biomass burning primary emission is the main source, with sizable additional contribution from fossil fuel combustion. In contrast, in summer secondary organic aerosol (SOA) from nonfossil sources becomes predominant (63–76% of TC), with some contribution of SOA from fossil fuel combustion. The results agree well with recent findings of other authors who established the predominance of biogenic SOA for rural sites in summer in Europe. An uncertainty analysis has been conducted, which shows that the main conclusions from this study are robust.

Relationships among intrinsic properties of ordinary chondrites: Oxidation state, bulk chemistry, oxygen-isotopic composition, petrologic type, and chondrule size

The properties of ordinary chondrites (OC) reflect both nebular and asteroidal processes. OC are modeled here as having acquired nebular water, probably contained within phyllosilicates, during agglomeration. This component had high Δ 17O and acted like an oxidizing agent during thermal metamorphism. The nebular origin of this component is consistent with negative correlations in H, L, and LL chondrites between oxidation state (represented by olivine Fa) and bulk concentration ratios of elements involved in the metal–silicate fractionation (e.g., Ni/Si, Ir/Si, Ir/Mn, Ir/Cr, Ir/Mg, Ni/Mg, As/Mg, Ga/Mg). LL chondrites acquired the greatest abundance of phyllosilicates with high Δ 17O among OC (and thus became the most oxidized group and the one with the heaviest O isotopes); H chondrites acquired the lowest abundance, becoming the most reduced OC group with the lightest O isotopes. Chondrule precursors may have grown larger and more ferroan with time in each OC agglomeration zone. Nebular turbulence may have controlled the sizes of chondrule precursors. H-chondrite chondrules (which are the smallest among OC) formed from the smallest precursors. In each OC region, low-FeO chondrules formed before high-FeO chondrules during repeated episodes of chondrule formation. During thermal metamorphism, phyllosilicates were dehydrated; the liberated water oxidized metallic Fe-Ni. This caused correlated changes with petrologic type including decreases in the modal abundance of metal, increases in olivine Fa and low-Ca pyroxene Fs, increases in the olivine/pyroxene ratio, and increases in the kamacite Co and Ni contents. As water (with its heavy O isotopes) was lost during metamorphism, inverse correlations between bulk δ 18O and bulk δ 17O with petrologic type were produced. The H5 chondrites that were ejected from their parent body ∼7.5 Ma ago during a major impact event probably had been within a few kilometers of each other since they accreted ∼4.5 Ga ago. There are significant differences in the olivine compositional distributions among these rocks; these reflect stochastic nebular sampling of the oxidant (i.e., phyllosilicates with high Δ 17O) on a 0.1–1 km scale during agglomeration.

Competitive adsorption and thermodynamic incompatibility of mixing of β-casein and gum arabic at the air–water interface

Competitive adsorption of β-casein and gum arabic glycoprotein (GAGP) at the air–water interface has been investigated using a surface radiotracer method. Adsorption isotherms revealed that the binding affinity of GAGP to the air–water interface was about an order of magnitude lower than that of proteins. However, the saturated monolayer coverage for GAGP was about 250 mg m −2 compared to 1–2 mg m −2 for proteins. In competitive adsorption experiments involving simultaneous adsorption of β-casein and GAGP from a bulk mixture, β-casein dynamically displaced GAGP from the interface. At <8% β-casein to GAGP bulk concentration ratio, β-casein effectively inhibited adsorption of GAGP to the air–water interface. However, the ability of β-casein to displace GAGP was greatly reduced when the latter was present as a pre-formed film at the air–water interface. This was due to thermodynamic incompatibility of mixing of β-casein in the GAGP film. The incompatibility parameter, X 12, for mixing of β-casein and GAGP at the air–water interface is 0.84; this value was much greater than that for most protein mixtures. The unfavorable free energy of mixing between GAGP and β-casein at the air–water interface was about 1.3 Kcal mol −1 at 25 °C.

Dynamics of competitive adsorption of alphas-casein and beta-casein at planar triolein-water interface: evidence for incompatibility of mixing in the interfacial film.

Competitive adsorption of alpha(s)-casein and beta-casein from a bulk solution mixture to the triolein-water interface has been studied. Although the binding affinity of alpha(s)-casein to the triolein-water interface was lower than that of beta-casein in single-component systems, in a 1:1 mixture of alpha(s)-casein and beta-casein in the bulk solution the ratio of interfacial concentrations of alpha(s)-casein to beta-casein at equilibrium was about 2:1, indicating that alpha(s)-casein was preferentially adsorbed to the triolein-water interface. Furthermore, the equilibrium composition of alpha(s)-casein and beta-casein in the interfacial film at various bulk concentration ratios did not follow a simple Langmuir adsorption model. This deviation from ideal behavior was mainly due to thermodynamic incompatibility of mixing of these caseins in the interfacial region. The value of the incompatibility parameter, X(12), for these caseins at the triolein-water interface was much greater than that at the air-water interface. Displacement experiments showed that while alpha(s)-casein could dynamically displace beta-casein when the latter was in an unsaturated monolayer state at the interface, it could not do so when beta-casein was in a saturated monolayer film state. It is hypothesized that, because of thermodynamic incompatibility of mixing, the alpha(s)-casein and beta-casein mixed film at the oil-water interface may undergo two-dimensional phase separation.

Incompatibility of mixing of proteins in adsorbed binary protein films at the air-water interface.

Competitive adsorption of proteins from several binary protein solutions to the air-water interface has been studied. With a few exceptions, the equilibrium composition of the saturated monolayer of mixed protein films at various bulk concentration ratios did not follow a Langmuir-type competitive adsorption model. The deviation from ideal behavior results from incompatibility of mixing of proteins in the film at the air-water interface. This immiscibility alters the ratio of the binding affinity of the proteins in a protein 1/protein 2/water ternary film compared to that in a protein 1/water and protein 2/water binary film. A method to determine the extent of incompatibility between two proteins in a mixed protein film has been developed. It is shown that the incompatibility index derived for 19 protein 1/water and protein 2/water systems studied show a linear relationship with the absolute difference between Flory-Huggins protein-solvent interaction parameters, that is, /chi(1s) - chi(2)/, of the constituent proteins. On the basis of the evidence, it is theorized that, because of incompatibility, proteins in a mixed protein film at interfaces may undergo two-dimensional phase separation.

Incompatibility and Phase Separation in a Bovine Serum Albumin/β-Casein/Water Ternary Film at the Air–Water Interface

Thermodynamic incompatibility and two-dimensional phase separation in a bovine serum albumin (BSA)/β-casein/water ternary film at the air–water interface has been studied using an epifluorescence microscopy technique. The incompatibility between BSA and β-casein at the air–water interface was deduced from deviation of the experimental equilibrium composition of the proteins in the mixed saturated monolayer film from that predicted by the Langmuir-type competitive adsorption model at various bulk concentration ratios. Fluorescence microscopy of the mixed monolayer film showed distinct phase-separated BSA-rich and β-casein-rich regions coexisting with inhomogeneous mixed regions. BSA always tended to be the dispersed phase and β-casein the continuous phase. It is suggested that because the free energy at the “interfaces” between the phase-separated regions is generally higher than at other regions of the film, they may act as zones of instability in protein-stabilized foams and possibly emulsions.

Phase Separation in Two-Dimensional αs-Casein/β-Casein/Water Ternary Film at the Air−Water Interface

Two-dimensional phase separation in αs-casein/β-casein/water ternary film adsorbed at the air−water interface has been studied using an epi-fluorescence microscopy technique. The equilibrium composition of saturated mixed monolayer films of αs-casein/β-casein at the air−water interface at various bulk concentration ratios did not follow a Langmuir-type competitive adsorption model. This was due to a change in the binding affinity of the proteins to the interface as a result of incompatibility of mixing of the proteins in the mixed monolayer. This manifested itself in two-dimensional phase separation of αs-casein and β-casein in the mixed protein film. αs-Casein always tended to be the dispersed phase and β-casein the continuous phase in the film. Also, phase separation occurred only when the film at the air−water interface was aged for several days, suggesting that the process was kinetically limited by lateral diffusion of the protein components in the viscous film.

Voltammetric Measurement of [Cu(II)]/[Cu(I)] at a Platinum Rotating Disc Electrode and Control by Electrolysis at a Platinum Net Electrode in Chloride Solutions

ABSTRACT A method has been described to measure and control the [Cu(II)]/[Cu(I)] bulk concentration ratio in aqueous chloride solutions. A variation of the ratio is achieved by controlled potential electrolysis at appropriate reducing or oxidizing potentials. The concentration ratio can be monitored by a repetitive double potential step amperometric method at a platinum rotating disc electrode. The amperometric signal can be used to control the electrolytic process in order to obtain and maintain a predetermined bulk concentration ratio. Diffusion coefficients of respectively 6.2 10−6 and 5.6 10−6 cm2 s−1 have been determined for Cu(II) and Cu(I). Potential applications of the method are the control of polymerisation reactions, of the reduction of textile dyes with the aid of a mediator system and of the colour characteristics of different kinds of glass.

Study of local structure around zirconium ions in grain boundaries of polycrystalline α-alumina by X-ray absorption spectroscopy and chemical analysis of thin foils

The chemical state and local structure around zirconium ions in doped α-polycrystalline alumina (300 wt ppm ZrO 2) was studied by X-ray absorption spectroscopy measurements at the zirconium K edge and by scanning transmission electron microscopy on thin foils. The zirconium segregation in alumina grain boundaries depends on alumina grain size: for a mean grain size of about ∼3·5 μm, the grain boundaries are saturated with zirconium. The zirconium grain boundaries to bulk concentration ratio, calculated from energy dispersive X-ray spectrometry measurement on thin foils is equal to ∼(5±3)×10 3. The zirconium located in grain boundaries forms nanocrystalline tetragonal zirconia particles. This allotropic zirconia form is stabilised at room temperature because of the important contribution of the surface free energy. ©