Solute Diffusion Coefficient Research Articles

The effect of water-soluble polymers on the dynamics of carbon dioxide sorption by lime sorbents

The effect of water-soluble polymers with different structure on the sorption properties of nonregenerable lime sorbents of carbon dioxide was studied. It was found that the introduction of water-soluble polymers into the sorbents could either decrease or increase the protective power time of the sorbents. To explain the revealed regularities, pore structure of the sorbents was investigated, molecular-dynamic modeling of the carbon dioxide transport was performed, and CO2 diffusion coefficients in water-polymer solutions were calculated. The results of the modeling correlate with the sorption experiment data: a high dynamic sorption capacity of the sorbent is reached after adding a water-polymer medium with a high CO2 diffusion coefficient. The results obtained can be used both to optimize the systems for the recovery of carbon dioxide from gas mixtures and to intensify mass transfer in the systems intended for photo- and electrocatalytic conversion of CO2 to useful products.

Effect of polymer/surfactant complexation on diffusiophoresis of colloids in surfactant concentration gradients

HypothesisA concentration gradient of surfactants in the presence of polymers that non-covalently associate with surfactants will exhibit a continually varying distribution of complexes with different composition, charge, and size. Since diffusiophoresis of colloids suspended in a solute concentration gradient depends on the relaxation of the gradient and on the interactions between solutes and particles, polymer/surfactant complexation will alter the rate of diffusiophoresis driven by surfactant gradients relative to that observed in the same concentration gradient in the absence of polymers. ExperimentsA microfluidic device was used to measure diffusiophoresis of colloids suspended in solutions containing a gradient of sodium dodecylsulfate (SDS) in the presence or absence of a uniform concentration of Pluronic P123 poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) nonionic triblock copolymers. To interpret the effect of P123 on the rate of colloid diffusiophoresis, electrophoretic mobility and dynamic light scattering measurements of the colloid/solute systems were performed, and a numerical model was constructed to account for the effects of complexation on diffusiophoresis. FindingsPolymer/surfactant complexation in solute gradients significantly enhanced diffusiophoretic transport of colloids. Large P123/SDS complexes formed at low SDS concentrations yielded low collective solute diffusion coefficients that prolonged the existence of strong concentration gradients relative to those without P123 to drive diffusiophoresis.

Thermodynamics and transport properties of valine and cysteine peptides in water

The study of thermodynamic and transport properties of amino acids gives access to knowledge about interactions between distinct molecules necessary to understand a variety of biological processes. In this work, we have performed molecular dynamics simulations of valine and cysteine peptides with lengths of (n) = 1, 2, 4, 8 & 16 monomers in an aqueous environment to estimate the solvation free energy and diffusion coefficients. We modeled our system using OPLS-AA parameter sets and TIP3P water at 310 K temperature. Solvation free energy of both the peptides have been reported using two thermodynamic integration (TI) based methods: TI and TI-CUBIC. The solvation free energy of both the peptides increases with the chain length. The estimated values using both methods are in good agreement with a statistical error of < 3%. The solvent accessible surface area (SASA) of solutes and hydrogen bonds between solute and solvent have also been presented to get more insights on solvation processes. The increase in solvation energy of both peptides with chain length is further corroborated by increase in the number of hydrogen bond (between peptide and water) and SASA with the chain length. In addition, the self diffusion coefficient of both solute and solvent along with their binary diffusion coefficient have been estimated for both the peptides. Furthermore, the effect of chain length on solvation free energy as well as diffusion coefficients have been studied.

Characterisation of fully developed and equilibrium states of non-electrolyte diffusiophoretic systems via numerical simulations

Diffusiophoresis takes place when a particle in solution moves due to the presence of a solute concentration gradient. This phenomenon is often studied under some simplifying assumptions, such as negligible diffusive layer thickness or infinite diffusion coefficient. In this work we simulate diffusiophoresis without these simplifications. The goal of this numerical study is to investigate equilibrium and fully developed states of non-electrolyte phoretic systems. Simulation results show that equilibrium states depend on solute diffusivity and on a reference solute concentration far from the particle. An expression is regressed that gives the (equilibrium) diffusiophoretic velocity as a function of solute concentration gradient, solute diffusion coefficient and the reference solute concentration far from the particle. A different set of results reveals that the state of phoretic systems does not depend on the initial conditions when time goes to infinity. This motivates the definition of fully developed states, designating those systems whose properties no longer depend on initial conditions. Apart from these findings, this work also depicts the effect of solute–interface interactions on diffusiophoresis. Simulation results for two solid particles with different interaction potentials are used to illustrate particle separation via diffusiophoresis. Finally, values of particle mobility are calculated for different solute–interface attraction strengths. These results are compared with another work in the literature, which studies polymer diffusiophoresis via molecular simulations (Ramírez-Hinestrosa et al., J. Chem. Phys., vol. 152, 2020, p. 164901).

Scaled charges for ions: An improvement but not the final word for modeling electrolytes in water.

In this work, we discuss the use of scaled charges when developing force fields for NaCl in water. We shall develop force fields for Na+ and Cl- using the following values for the scaled charge (in electron units): ±0.75, ±0.80, ±0.85, and ±0.92 along with the TIP4P/2005 model of water (for which previous force fields were proposed for q = ±0.85 and q = ±1). The properties considered in this work are densities, structural properties, transport properties, surface tension, freezing point depression, and maximum in density. All the developed models were able to describe quite well the experimental values of the densities. Structural properties were well described by models with charges equal to or larger than ±0.85, surface tension by the charge ±0.92, maximum in density by the charge ±0.85, and transport properties by the charge ±0.75. The use of a scaled charge of ±0.75 is able to reproduce with high accuracy the viscosities and diffusion coefficients of NaCl solutions for the first time. We have also considered the case of KCl in water, and the results obtained were fully consistent with those of NaCl. There is no value of the scaled charge able to reproduce all the properties considered in this work. Although certainly scaled charges are not the final word in the development of force fields for electrolytes in water, its use may have some practical advantages. Certain values of the scaled charge could be the best option when the interest is to describe certain experimental properties.

Identifying structure-function relationships to modulate crossover in nonaqueous redox flow batteries.

Nonaqueous redox flow batteries (NARFBs) offer a promising solution for large-scale storage of renewable energy. However, crossover of redox active molecules between the two sides of the cell is a major factor limiting their development, as most selective separators are designed for deployment in water, rather than organic solvents. This report describes a systematic investigation of the crossover rates of redox active organic molecules through an anion exchange separator under RFB-relevant non-aqueous conditions (in acetonitrile/KPF6) using a combination of experimental and computational methods. A structurally diverse set of neutral and cationic molecules was selected, and their rates of crossover were determined experimentally with the organic solvent-compatible anion exchange separator Fumasep FAP-375-PP. The resulting data were then fit to various descriptors of molecular size, charge, and hydrophobicity (overall charge, solution diffusion coefficient, globularity, dynamic volume, dynamic surface area, clogP). This analysis resulted in multiple statistical models of crossover rates for this separator. These models were then used to predict tether groups that dramatically slow the crossover of small organic molecules in this system.

Diffusive size-structured population model with time-varying diffusion rate

&lt;p style='text-indent:20px;'&gt;This work is devoted to the study of a size-structured population model with a time-varying diffusion rate. Due to the seasonal variation, it is natural to consider the time-varying diffusion rate. Moreover, introducing the time-varying diffusion rate makes the model more challenging and requires the results of evolution operators for the analysis. Under some assumptions on the time-dependent diffusion coefficient, the existence and uniqueness of mild solution is shown. We apply the method of characteristics and evolution operators to derive our results. Positivity and boundedness of mild solution is also shown. Some examples are provided to illustrate the theoretical findings. We also solve our model numerically to study the size and spatial dynamics of population density.&lt;/p&gt;

Effect of potassium dihydrogen citrate on the diffusion behaviour of citric acid

Ternary mutual diffusion coefficients (D11, D22, D12, and D21) in aqueous solutions of citric acid (H3Cit) (component 1) plus potassium dihydrogen citrate (KH2Cit) (component 2) at 298.15 K and concentrations up to 0.040 mol dm−3 were measured using a Taylor scattering method. The obtaining of the negative values for D12 and D21 cross coefficients, mainly in dilute solutions and for the first ones, indicates that there is a strongly coupled diffusion of these components. In fact, the concentration gradients of KH2Cit drive substantial counter current coupled flows of H3Cit citric acid, indicating that each mol of diffusing potassium dihydrogen citrate can counteract the transport of up to 0.74 mol of citric acid, approximately. A better interpretation of the electrostatic mechanism for the coupled diffusion of KH2Cit and H3Cit was achieved based on the values predicted by the Nernst-Planck equations, having been verified as a good agreement between them and experimental data.

A Cleavable Self-Inclusion Conjugate with Enhanced Biocompatibility and Antitumor Bioactivity

A Cleavable Self-Inclusion Conjugate with Enhanced Biocompatibility and Antitumor Bioactivity

Effects of Co on microstructure evolution of a 4th generation nickel-based single crystal superalloys

For further composition optimization, the microstructure evolution of the fourth-generation nickel-based single crystal superalloys, which contains different Co (Cobalt) additions, is studied at three thermal exposure temperatures. Based on Lifshitz, Slyozov and Wagnerz (LSW) theory and trans-interface diffusion-controlled (TIDC) theory, the effects of Co content and aging temperatures on coarsening rate of γ′ phase are investigated in detail. The results show that the diffusion coefficient of solute is accelerated, but the γ/γ′ interfacial energy decreases with the addition of Co, thus changing the coarsening rate. Furthermore, the thermodynamic equilibrium solubility difference of elements between γ′ and γ, and the segregation of elements at the γ/γ′ interface are alleviated with increase of Co, resulting in the suppression of TCP phase after long-time thermal exposure, which guides the economical design of nickel-based single crystal superalloys.

Alloy solidification: Assessment and improvement of an easy-to-apply model

• The Gong-Chen model requires no experimental parameters and is easy to apply. • It can be used as a generic solidification model up to the solid fraction (fs) of 0.9. • When fs > 0.9, its applicability depends on both solute diffusion and partition coefficient. • The Gong-Chen model requires f s Lever > 1, which has been examined and justified. • The Won-Thomas model provides the most practical predictions but requires experimental input. It has been a central task of solidification research to predict solute microsegregation. Apart from the Lever rule and the Scheil-Gulliver equation, which concern two extreme cases, a long list of microsegregation models has been proposed. However, the use of these models often requires essential experimental input information, e.g. , the secondary dendrite arm spacing ( λ ), cooling rate ( T ˙ ) or actual solidification range ( Δ T ). This requirement disables these models for alloy solidification with no measured values for λ, T ˙ and Δ T . Furthermore, not all of these required experimental data are easily obtainable. It is therefore highly desirable to have an easy-to-apply predictive model that is independent of experimental input, akin to the Lever rule or Scheil-Gulliver model. Gong, Chen, and co-workers have recently proposed such a model, referred to as the Gong-Chen model, by averaging the solid fractions ( f s ) of the Lever rule and Scheil-Gulliver model as the actual solid fraction. We provide a systematic assessment of this model versus established solidification microsegregation models and address a latent deficiency of the model, i.e., it allows the Lever rule solid fraction f s to be greater than one ( f s > 1). It is shown that the Gong-Chen model can serve as a generic model for alloy solidification until f s reaches about 0.9, beyond which ( f s > 0.9) its applicability is dictated by both the equilibrium solute partition coefficient ( k ) and the solute diffusion coefficient in the solid ( D s ), which has been tabulated in detail.

Effect of liquid film constitutional supercooling at the end of solidification on the hot cracking behavior of Al-4.0 wt.%Cu alloy

• Molecular dynamics method was used to calculate the solute diffusion coefficient. • Effect of liquid film constitutional supercooling on hot cracking was studied. • The influence of dendrite growth on hot cracking behavior was excluded. In this study, the molecular dynamics (MD) calculation method was used to calculate the diffusion coefficient of solute atoms in the liquid film (LF) at the end of solidification, and the effect of constitutional supercooling in LF on the hot cracking tendency of Al-4.0 wt% Cu alloy was investigated combined with experiments. The MD calculation result indicated that the diffusion coefficient of Cu elements ( D L ) increased as the atomic percentage of that in the LF decreased at a specific temperature within the solidification range (620 °C was chosen in this study). Supercooling degree produced by constitutional supercooling ( ΔT c ) decreased while the constitutional supercooling zone width ( Δx ) increased with D L , which facilitated extending the LF complementary shrinkage zone during solidification, and cellular grains easily formed after solidification, thus reducing the hot cracking tendency of Al-4.0 wt.%Cu alloy. The experimental results concluded that the hot cracking tendency of Al-4.0 wt.%Cu alloy decreased as the atomic percentage of Cu elements in the LF decreased, which verified the accuracy of the MD calculation results.

Fulvic and alginic acid separation during pressure retarded osmosis: Governing effects and fouling mechanisms

In this study, the performance of model foulant (alginate and fulvic acid) separation by pressure retarded osmosis (PRO) was systematically studied. At the various operating conditions tested, fulvic acid had a greater flux decline and power density loss than alginate. The results of membrane resistance test, SEM-EDX images, and the solute diffusion coefficient K demonstrated that fulvic acid was more likely to clog the inside of the porous support layer of the PRO membrane, which would exacerbate the internal concentration polarization (ICP) phenomena. Although model foulants were successfully removed by PRO (with a retention rate of about 95.0%), the presence of either calcium or magnesium ions was detrimental to the fouling process of PRO membranes. According to the XDLVO theory analysis results, the presence of calcium or magnesium ions increased foulant adhesion to the PRO membrane, thereby resulting in membrane fouling. In addition, Pearson correlation coefficient also showed that the hydrodynamic conditions (effective osmotic pressure difference as well as operating hydraulic pressure acting vertically to the membrane and parallel to the membrane cross-flow shear force) had an important effect on the degree of membrane fouling. This is attributed to the influence of the hydrodynamic conditions on the initial influence water flux and thus on the fouling of the PRO membrane.

Effect of Catheter and Stenosis on Solute Diffusion in Non-Newtonian Blood Flow through a Catheterized Stenosed Artery

The presence of stenosis at the wall of the artery lead to further cardiovascular diseases such as heart attack, stroke and many more. Treatment of a stenosed artery includes the insertion of a catheter through the artery which affects the blood flow and solute dispersion. This present study focuses on the effect of catheter radius and stenosis height on the blood flow and solute dispersion behavior. The problem is modelled using the Herschel-Bulkley fluid to represent the blood rheology, with catheter and stenosis as the boundary conditions. Analytical solutions in integral form are obtained by solving the momentum equation and Herschel-Bulkley constitutive equation. The integrals are numerically evaluated using the Simpson’s 3/8 rule and Regula-Falsi method to obtain the blood velocity. The obtained velocity is employed into the unsteady convective-diffusion equation and solved using the generalized dispersion model (GDM) to analyse the behaviour of solute diffusion. The influence of catheter radius and stenosis height on the diffusion coefficient and mean concentration of solute are observed. Results show that the diffusion coefficient decreases as the catheter radius and stenosis height increases. A decrease in diffusion coefficient simultaneously increases the solute mean concentration.

Redox Couple Stability Studies for Thermodynamic Reference Electrodes and Fluoroacidity Investigation

A stable reference electrode is essential for electrochemical studies in molten fluoride salts, yet reference electrode design is hindered by challenges such as materials compatibility and high temperature operation. Electroanalytical studies are relevant to sensor development for molten fluoride salt systems as well as fundamental chemistry studies of salt structure and speciation. Dynamic reference electrode techniques have been used to find benchmark reference potentials, but the application of a constant current for the technique may not be feasible for sensing or high throughput studies. A thermodynamic reference electrode which is durable, stable, and reproduceable is urgently needed for both scientific studies and engineering applications of molten fluoride salts.Fluoroacidity studies are of particular interest for a fundamental understanding of molten salt speciation. The more dissociated fluoride anions present in a melt, the more of a fluorodonor it is. Thus, it is considered to have a higher fluorobasicity due to its Lewis base behavior. Fluoroacidity is related to the coordination of solvent and solute ions and, therefore, solute diffusion coefficients and viscosity. Ion solvation differs in fluoride salts of various fluoroacidities, so solvated ions have different activity coefficients in different fluoride solvents. The relationship between activity coefficients of solvated ions and a melt’s fluoroacidity is not fully understood. The electrochemical determination of these activity coefficients benefits from a stable reference electrode. In addition, quantification of fluoroacidity requires the measurement of the activity of dissociated fluoride, which can be done electrochemically. The measurement of redox potential of a given couple in various fluoride melts can lead to a classification of the solvent melts based on the Nernst equation. Therefore, the study of redox couple behavior in various fluoride melts is relevant to both the development of a robust thermodynamic reference electrode & the quantification and theory of fluoroacidity.The Ni/NiF2 and Ag/AgF redox couples have been previously investigated for use in thermodynamic reference electrodes for molten fluoride salt. Ni/NiF2 has been characterized for its stability in molten fluorides. The Ag/AgCl redox couple has commonly been used for chloride mixtures but literature on the fluoride couple is marginal. Our preliminary studies have shown the stability of the Ag/AgF redox couple in a FLiNaK melt by OCP measurement. Polarization studies will be carried out to test for reversibility, and other redox couples may be investigated. In this presentation, we present results from the Ag/AgF redox couple studies in FLiNaK, as well as their impact on current understandings of fluoroacidity.

Hydrogel Mesh Size and Its Impact on Predictions of Mathematical Models of the Solute Diffusion Coefficient

Hydrogel Mesh Size and Its Impact on Predictions of Mathematical Models of the Solute Diffusion Coefficient

Synthesis, Self-Aggregation, Surface Characteristics, Electrochemical Property, Micelle Size, and Antimicrobial Activity of a Halogen-Free Picoline-Based Surface-Active Ionic Liquid.

We present a new approach toward the design of a halogen-free picoline-based surface-active ionic liquid (SAIL) (1-octyl-4-methyl pyridinium dodecyl sulfate) [C8γPic]DS consisting of long dodecyl sulfate (DS) as an anion. The surface properties, micellization behavior, and antimicrobial activity in an aqueous solution were investigated using tensiometry, conductometry, and ultraviolet (UV) spectroscopy. Incorporating the DS group in SAIL leads to lower critical micellar concentration (CMC) and enhanced adsorption at the air/water interface of the functionalized ionic liquid compared to the C8-alkyl chain-substituted pyridine ionic liquids. The antimicrobial activity was evaluated against a representative Gram-negative and Gram-positive bacteria panel. Antibacterial activities increased with the alkyl chain length, C8 being the homologous most effective antimicrobial agent. The micelle size of [C8γPic]DS was determined by the dynamic light-scattering (DLS) study. Cyclic voltammetry (CV) measurements have been employed to evaluate the interaction between the SAIL micelle and working electrode, diffusion coefficient, and micelle size of the SAIL solution. The diffusion coefficient explored the correlation of surface properties and the antimicrobial activity of [C8γPic]DS. This halogen-free SAIL is the future of wetting agents and emulsion studies in agriculture due to its small micelle size and surface characteristics.

First-principles study of the effects of solutes on long-range order degree, self-diffusions and antiphase boundary energies in ordered FeCo alloy

The brittleness of FeCo alloy is generally caused by the B2 ordering behaviors. Alloying elements V, Nb, Ta, Mo and W were experimentally found to be effective in improving the toughness and plasticity of FeCo alloy. In this work, first-principles calculations were carried out to reveal the toughening mechanism of solutes in ordered FeCo. We used the antisite defect energy as the link to establish the relation between long-range order (LRO) degree and temperature, and successfully predicted the temperature dependence of LRO degree. These considered solutes of V, Nb, Ta, Mo, and W can effectively reduce the maximum LRO degree reached at a specific temperature. We computed the self- and solute diffusion coefficients in ordered FeCo alloy, and found these solutes exhibit faster diffusion characteristics than Fe and Co atoms. Nb and Ta were found to prominently reduce the self-diffusion coefficients in the process of atomic ordering, giving a contribution to the retardation in ordering kinetics. Also, these solutes can substantially reduce the antiphase boundary (APB) energies by repairing the metal bonding along 〈111〉 direction broken by APBs, effective in improving the dislocation mobility. In FeCo alloy, the toughening mechanism of these solutes can be summarized as the following two aspects. First, the atomic ordering can be effectively suppressed by reducing the LRO degree and self-diffusion coefficients. Furthermore, dislocation slip is enhanced by the solute-induced low APB energies. These findings provide some reference significance for improving the ductility of intermetallics.

Enhancing Some Mechanical Properties (Compression, Impact, Hardness, Young modulus) and Thermal Conductivity, Diffusion Coefficient of Micro Epoxy Composites.

In this research, the study effect of additive titanium dioxide powder (TiO2) as a lone composite ( Ep+TiO2) and a mixture of (TiO2) and silicon oxide (SiO2), ( Ep+ TiO2+SiO2)as a hybrid composite on the mechanical and physical properties for epoxy coating. Thescompsiteswere prepared by (Hand Lay- the molding) method. The samples were tested for compressive strength, surface hardness, modulus of elasticity, thermal conductivity and diffusion coefficient, from the results obtained showed improvement in mechanical properties after adding ceramic powders, as the alone composite (EP+ TiO2) had the highest compressive strength ( 53.738 ) ᴍPa, the hybrid composite ( EP+TiO2 +SiO2 ) had the highest surface hardness (79.65), modulus of elasticity (1166.66 ) ᴍPa, impact strength ( 8.48) ᴍPa, thermal conductivity (0.4961 )watt/ m.c◦. As for the diffusion coefficient in the acidic solution ( HCL), the epoxy without adding the highest diffusion coefficient ( 31.3x 10-10) m2/ sec while for immersion in ordinary water, the one composite material (Ep+ TiO2) had the highest value of the diffusion coefficient (7.56x10-10)m2/sec.

Through Diffusion Measurements of Molecules to a Numerical Model for Protein Crystallization in Viscous Polyethylene Glycol Solution

Protein crystallography has become a popular method for biochemists, but obtaining high-quality protein crystals for precise structural analysis and larger ones for neutron analysis requires further technical progress. Many studies have noted the importance of solvent viscosity for the probability of crystal nucleation and for mass transportation; therefore, in this paper, we have reported on experimental results and simulation studies regarding the use of viscous polyethylene glycol (PEG) solvents for protein crystals. We investigated the diffusion rates of proteins, peptides, and small molecules in viscous PEG solvents using fluorescence correlation spectroscopy. In high-molecular-weight PEG solutions (molecular weights: 10,000 and 20,000), solute diffusion showed deviations, with a faster diffusion than that estimated by the Stokes–Einstein equation. We showed that the extent of the deviation depends on the difference between the molecular sizes of the solute and PEG solvent, and succeeded in creating equations to predict diffusion coefficients in viscous PEG solutions. Using these equations, we have developed a new numerical model of 1D diffusion processes of proteins and precipitants in a counter-diffusion chamber during crystallization processes. Examples of the application of anomalous diffusion in counter-diffusion crystallization are shown by the growth of lysozyme crystals.