Concentration Of External Solution Research Articles

Coion exclusion properties of cation exchange membranes in 2:1 divalent salt solutions

The selectivity of ion exchange membranes hinges on their capacity to exclude coions. Yet, understanding how they reject coions in multivalent salt solutions remains challenging. This study presents a new molecular theory to understand coion exclusion. It examines counterion and coion condensation, including electrosteric effects. Supported by experimental data [Gokturk et al., Nat. Commun., 13 (2022)], we analyze cation exchange membrane potential in a 2:1 salt solution, revealing insights into coion selectivity and exclusion mechanisms. Notably, our theory deviates from earlier research by accommodating condensed divalent counterions that bind to one or two fixed-charged monomers. Additionally, we account for many-body electrostatic interactions, allowing the former to bind to sorbed coions. Our findings highlight the importance of coion condensation, especially in low-concentration salt conditions where coions are mainly condensed. This effect becomes less significant as the external solution concentration rises. These findings clarify the suitability of the ideal Donnan model in high-concentration salts, but its accuracy decreases in low-concentration situations. To summarize, our study emphasizes the need to account for counterion and coion condensation to understand membrane selectivity in low-concentration multivalent salt solutions.

Research on Measuring Pure Membrane Electrical Resistance under the Effects of Salinity Gradients and Diffusion Boundary Layer and Double Layer Resistances.

Forward osmosis membranes are an emerging technology with great potential applicability in energy-efficient wastewater treatments and the differentiation between two solutions. Such solutions often differ in their concentrations or compositions. In this study, the membrane electrical resistances of three different membranes, including cation or anion-exchange membranes and forward osmosis membranes, were analyzed by Luggin capillary coupled with AC impedance spectroscopy (EIS) so as to obtain the real membrane and ion transfer impedance values near the membrane interface. The results reveal that the membrane impedance obtained by both the DC and AC approaches decreased as the lowest external solution concentration increased. Furthermore, the relationship between the membrane conductivity and the internal salt solution concentration was also investigated. It can be seen that the external ion concentration is directly proportional to the free ion concentration in the membrane, and the free ion concentration in the membrane is closely related to the membrane electrical resistance.

A study of variables that affect the process of sulfate attack of cement‐based materials subjected to stray current

AbstractDurability is one of the most important considerations for subway structures. However, the cement‐based materials used in subway engineering can be jeopardized by sulfate and the stray current and therefore can be subjected to severe damage during service. This study aims to investigate the degradation process of cement‐based materials exposed to stray current and external sulfate. In particular, the effects of three key variables were evaluated: concentration of external sulfate solution, level of stray current and cement type. After exposure, the visual appearance, compressive strength, SO42− profiles and microstructure of cement‐based materials were analyzed. Moreover, the amounts of degradation products were measured to evaluate the influencing degree of different variables and further explain the degradation mechanisms. Experimental results of this study reveal that (a) sulfate attack was related to the external sulfate concentration, but the relation was changed due to the presence of stray current. One explanation is that sulfate ions can be quickly accumulated in the pores of cement‐based materials under the effect of stray current, which makes the chemical reaction of sulfate attack exchange from diffusion control to reaction control. (b) Stray current could accelerate external sulfate attack of cement‐based materials, and the greater the stray current, the more severe sulfate attack was induced. (c) Compared with P·I type cement, high sulfate resistant (HSR) cement showed a better resistance to external sulfate attack. (iv) And, the main degradation products, ettringite and gypsum, were observed in specimens after exposure. Additionally, stray current might induce the decomposition of ettringite. It should be paid more attention on the durability of cement‐based materials exposed to the coupled conditions of stray current and sulfate.

Numerical simulation of external sulphate attack in concrete considering coupled chemo-diffusion-mechanical effect

This paper proposes an extended numerical method based on Fick’s second law and second-order reaction kinetics for predicting the erosion process of concrete exposed to sodium sulphate solution. A three-phase concrete model was introduced for calculating the diffusivity of concrete to consider the effect of the interfacial transition zone (ITZ), and the diffusivities of diffusible phases were obtained based on the general effective medium equation. In addition, the effects of pore-filling and chemo–mechanical damage on the diffusivity of concrete were considered in the model, using the volume increase approach. Moreover, the expansive products, mainly gypsum and ettringite, were assumed to precipitate unevenly in the ITZ and cement paste owing to the different diffusivities and sulphate ion concentrations of these two phases. The distributions of the sulphate ions, gypsum, and ettringite in concrete, the expansion of concrete specimens, and the damage depth were determined through numerical calculations, and the simulation reliability was validated based on the comparisons with the available experimental data. Furthermore, the effects of the water–cement ratio and external solution concentration on the sulphate diffusion and specimen expansion were determined. The simulation results showed that the ITZ influenced the calculated results and should therefore be considered in the numerical model. The diffusivity of concrete decreased owing to the pore-filling effect but increased as the chemical–mechanical damage increased.

Sorption and diffusion of organic acid ions in anion exchange membranes: Acetate and lactate ions as a case study

In this study, the sorption behaviour and conductivity of two anion exchange membranes (AR103 and AR204) equilibrated with sodium acetate and sodium lactate solutions are studied across a range of concentrations and pH values. The results indicate that the dissociation equilibria of the organic acids differ between the membrane phase and the external solution. There are significant concentrations of the neutral organic acid in the membranes at pH 6.5 even though the dissociation is virtually complete in the external solution. The concentration of this neutral acid increases as the pH is lowered, leading to a reduction in membrane conductivity. The diffusion coefficients of acetate and lactate ions in these membranes are determined from conductivity data. The results show that these diffusion coefficients are relatively constant but decrease slightly with an increase of external solution concentration due to osmotic deswelling. The diffusion coefficient of the acetate anion decreases as the pH falls, possibly due to dimer formation. Models extended from Manning's condensation theory have been utilized in the prediction of the co-ion concentrations within the membrane and the diffusion coefficients of the lactate and acetate anions. There is an excellent agreement between the experimental values of these parameters and the model predictions for the sodium lactate system but the model is unable to accurately fit the sodium acetate data.

Cultivation at high osmotic pressure confers ubiquinone 8–independent protection of respiration on Escherichia coli

Cultivation at high osmotic pressure confers ubiquinone 8–independent protection of respiration on Escherichia coli

Concentration-dependent Accumulation and Translocation of PFASs by Wetland Plant Alisma orientale

This study investigated the concentration-dependent accumulation and translocation of perfluoroalkyl substances (PFASs) by wetland plant Alisma orientale. The concentrations of PFASs in nutrient solution were 0, 5, 10, 50, 100, 200, 500, and 1000 μg·L-1. The electrolytic leakage of roots, Cu concentration in roots and stems, and Ca concentration in stems and leaves decreased with an increase in PFASs concentration in external solution, while the plants were growing well. The removal mass of PFASs by plants increased (0.87-116.50 μg) with an increase in PFASs concentration, while the removal efficiency decreased (20.1%-2.9%). The PFASs concentration in plant roots, stems, and leaves increased linearly with that in nutrient solution, and fitted the Langmuir adsorption isotherm and Michaelis-Menten equation well, which indicated PFASs were uptaken through passive diffusion. The root concentration factor, stem concentration factor, transpiration stream concentration factor, and partition limited quasi-equilibrium factor αpt decreased with that of PFASs in nutrient solution, probably due to the increase in the volume of transpiration water and the longer time to reach equilibrium.

Simultaneous measurement of temperature and refractive index with F–P microcavity sensor based on graded-index few mode fiber

In this paper, a Fabry–Perot (F–P) microcavity sensor based on graded-index few mode fiber is proposed and fabricated. One end of the graded-index few mode fiber is etched by hydrofluoric(HF) acid to form an air microcavity. The end with air microcavity is spliced with single-mode fiber, and another end is cut flat to make sensing head. Due to the generation of reflection surface, the F–P microcavity structure is formed between the surfaces of microcavity and the fiber tip. Simulation and experimental results show that the reflection spectrum will shift regularly with the change of external temperature, and the extinction ratio of that will also change regularly with the change of external solution concentration. The temperature and refractive index can be measured by detecting the wavelength shift and extinction ratio change in spectrum. When the temperature changes between 30∘C∼90∘C, the temperature sensitivity can be up to 10.52pm/∘C. When the refractive index changes between 1.3331∼1.3568, the maximum refractive index sensitivity is -16.03dB/RIU. This fiber F–P microcavity sensor has different responses to the change of temperature and liquid refractive index, it can be used to measure both parameters simultaneously.

Theophylline‐loaded pectin‐based hydrogels. II. Effect of concentration of initial pectin solution, crosslinker type and cation concentration of external solution on drug release profile

ABSTRACTA series of drug‐loaded pectin hydrogels were prepared by mixing method in two ion types, Ca+2 or Zn+2, for wound dressing applications and their drug release performances were investigated at pH 6.4 in four different calcium ion concentrations of external solution. Pectin hydrogels were synthesized in three different concentrations of initial pectin solution and theophylline was used as a model drug. Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy were used for hydrogel characterization. Additionally, fluid handling capacity, swelling behavior, dehydration rate, dispersion characteristic, dressing pH determination, water vapor permeability, oxygen permeability, surface contact angle, flexibility, mass per unit area, and thickness were determined for selected hydrogels. One of the most valuable contributions of our study is that the concentration of initial pectin solution and calcium ion concentration of external solution are very important parameters to obtain an effective drug release. After evaluating all data, we have shown that flexible and transparent pectin‐based wound dressings can be synthesized as a controlled drug release system. Zinc‐containing hydrogel was antibacterial against Staphylococcus aureus and Escherichia coli but not suitable for cell migration. On the other hand, calcium‐based hydrogel was nontoxic on the fibroblast cells and it had no negative effect on cell migration. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48155.

Effects of solution pH on ion distribution and drug release behaviors of a weak polyelectrolyte hydrogel

A triphasic model is developed and the finite element method is adopted to investigate a weak polyelectrolyte hydrogel. The influence of HCl concentrations in external solution on ion concentrations inside the hydrogel and the evolution of water volume fraction are discussed. The conservation of charge can be satisfied everywhere in the hydrogel. Also, a drug release equation which considers both convection and diffusion effects is employed to analyze the drug release rate. The results show that the drug release rate has a very close relationship with the pH value. The simulated results are compared with experimental results of Beebe to validate the reliability and accuracy of this simulation. This work is significant for the study of oral drug controlled release in the gastrointestinal tract. © 2017 Society of Chemical Industry

An integrative modeling and experimental study on the ionic resistance of ion-exchange membranes

In many applications, the ionic resistance of an ion-exchange membrane shows a strong dependency on the external solution concentration and hydrodynamic environment. It is critical to understand the insights of ion exchange membrane process if its ionic resistance can be simulated accurately. In this paper, we have developed a new model by taking into account both the membrane properties that affect the membrane bulk resistance and hydrodynamic environment that affects the non-ohmic behavior of membrane resistance. The new model not only explains external solution concentration dependency, but also explicitly establishes a relationship between the measured membrane resistance and current density. The modeling results on the direct current (DC) and alternating current (AC) resistance of membranes are compared with experimental data measured under different external solution concentrations and applied current densities. We demonstrate that the model accurately predicts the behaviors of sulfonated polypoly (2,6-dimethyl-1,4-phenylene oxide) membranes and fumasep®-FKS and FAS membranes in all cases. The integrative modeling and experimental study provides insights into the ion-exchange membrane synthesis as well as reverse and conventional electrodialysis processes.

Isolated effects of external bath osmolality, solute concentration, and electrical charge on solute transport across articular cartilage

The metabolic function of cartilage primarily depends on transport of solutes through diffusion mechanism. In the current study, we use contrast enhanced micro-computed tomography to determine equilibrium concentration of solutes through different cartilage zones and solute flux in the cartilage, using osteochondral plugs from equine femoral condyles. Diffusion experiments were performed with two solutes of different charge and approximately equal molecular weight, namely iodixanol (neutral) and ioxaglate (charge=−1) in order to isolate the effects of solute’s charge on diffusion. Furthermore, solute concentrations as well as bath osmolality were changed to isolate the effects of steric hindrance on diffusion. Bath concentration and bath osmolality only had minor effects on the diffusion of the neutral solute through cartilage at the surface, middle and deep zones, indicating that the diffusion of the neutral solute was mainly Fickian. The negatively charged solute diffused considerably slower through cartilage than the neutral solute, indicating a large non-Fickian contribution in the diffusion of charged molecules. The numerical models determined maximum solute flux in the superficial zone up to a factor of 2.5 lower for the negatively charged solutes (charge=−1) as compared to the neutral solutes confirming the importance of charge-matrix interaction in diffusion of molecules across cartilage.

Docosahexaenoic acids activate large conductance calcium-activated potassium channels via phospholipase C- inositol triphosphate- calcium pathway in normal rat coronary smooth muscle cells

To investigate the mechanisms of docosahexaenoic acids (DHA) on activating large conductance calcium-activated potassium channels (BK channels) in normal rat coronary smooth muscle cells. Normal coronary smooth muscle cells were isolated by enzyme digestion from Sprague-Dawley rats. BK currents were recorded by patch clamp in whole cell and single channel configurations, respectively. The effects of DHA on cytosolic calcium concentrations were examined by recording the changes of fluorescence intensity ratios. DHA (1 μmol/L) could activate BK channels. Open probabilities (NP0) of BK channels at test potential 60 mV, and calcium concentrations in external solution at 0, 0.01, 0.1, 1, 3, 10, 50 and 100 μmol/L were 0.002 7±0.000 4, 0.006 0±0.001 4, 0.097 2±0.010 6, 0.137 9±0.032 9, 0.468 7±0.163 7, 2.097 1±0.310 4 and 3.120 4±0.242 7, respectively (P<0.05, n=4). Before DHA perfusion, the fluorescence intensity ratio was 0.51±0.01, and the ratios were 0.53±0.02 and 0.55±0.01 after 0.001 and 0.01 μmol/L DHA perfusion, respectively (P>0.05, n≥5). The ratios were 0.64±0.01, 0.65±0.01, 0.70±0.01, 0.69±0.01, 0.68±0.01 and 0.67±0.02 after 0.1, 0.3, 1, 3, 5 and 10 μmol/L DHA perfusion, respectively, and EC50 was (0.04±0.02) μmol/L(P<0.05, n≥4). They were all higher than that before DHA perfusion. After incubating with phospholipase C (PLC) blocker U73122 and inositol triphosphate (IP3) blocker 2-APB, the ratios were 0.52±0.01 and 0.49±0.02 on the setting of 0.1 μmol/L DHA, respectively. Compared with control group(0.64±0.01), the ratios decreased after incubating with blockers (P<0.05, n≥4). Docosahexaenoic acids can activate large conductance calcium-activated potassium channels by the pathway of PLC-IP3-Ca(2+) to increase cytosolic calcium concentration in normal coronary smooth muscle cells, dilate the coronary vessels and bestow protective effects on cardiovascular system.

Effect of ionic concentration on drug release from polyelectrolyte hydrogel carriers analyzed via triphasic mechanism model

In different parts of the gastrointestinal tract, the rate of drug release from polyelectrolyte hydrogel tablets is highly affected by variance of ionic concentration. This research aims at revealing clearly how the drug release from a hydrogel matrix is affected by ionic concentration of external solution through the finite element simulation and triphasic mechanism model. The coupled relationship of the motions including the polyelectrolyte hydrogel swelling, the water flow and the ion diffusion, is illustrated in the present work. In order to simulate the drug controlled release from a swollen polyelectrolyte hydrogel carrier, the mathematical model was built on the basis of the multiphasic theory of polyelectrolyte hydrogels. Finally, the reliability of the simulation method was verified qualitatively by experimental results. The results reveal that when the initial concentration of fixed anions of polymer network is higher than the concentration of free anions in the external solution, the drug release rate increases with increasing the ionic concentration of the external solution. The research is helpful for the optimal design of oral drug release in gastrointestinal tract.

Non-destructive radiotracer technique in characterisation of nuclear grade anion exchange resins Tulsion A-30 and Dowex 550A LC

The present study deals with the application of non-destructive radio isotopic tracer technique to evaluate the performance of nuclear grade resins Tulsion A-30 and Dowex 550A LC. The evaluation was made by testing the performance of the two resins during iodide and bromide ion-isotopic exchange reactions. It was observed that at a constant temperature of 30°C, as the concentration of labelled iodide ion solution increases from 0.001 mol/L to 0.004 mol/L, the percentage of iodide ions exchanged increases from 66.90% to 74.10% for Dowex 550A LC resins and from 60.70% to 67.80% for Tulsion A-30 resins. Similar trend was observed for the two resins during bromide ion-isotopic exchange reaction. The overall results indicate superior performance of Dowex 550A LC resins over Tulsion A-30 resins under identical operational conditions of temperature and ionic concentration of external solution.

Magnetic field controlled particle-mediated growth inducing icker-like silver architectures

An unusually anisotropic growth or quasi-one-dimension growth of silver architectures can be achieved when an external magnetic field is applied to a simple replacement reaction. The external magnetic field greatly promotes the growth of trunks along 〈111〉 directions but weakens the growth of branches along 〈311〉 directions, resulting in a silver icker-like architectures. The influences of the external magnetic field, solution concentration and reaction time have been investigated in detail. The formation of silver icker-like architectures could be attributed to shape magnetic anisotropy and fast complex micro-magnetohydrodynamic (MHD) convection effects induced by the external magnetic field of the nanoparticles possessing a truncated octahedron structure. Moreover, the magnetic field effect on the crystal growth of nanostructures generally involves the ion-mediated growth process or the aggregations of numerous nanoparticles along the magnetic field directions because of dipolar interactions. Our experiments and discussions, however, indicate that metal crystals are grown through a multistep particle-mediated growth process with the nanoparticles as basic building blocks.

Cadmium accumulation and strategies to avoid its toxicity in roots of the citrus rootstock Citrumelo

In order to assess implications of Cd-induced oxidative stress in roots of the citrus rootstock Citrumelo, seedlings were hydroponically exposed to two relatively realistic Cd concentrations during 7 days. Our results showed that increasing Cd concentrations in external solution were associated with higher Cd accumulations in roots. At 5μM Cd the accumulation of Cd in roots was over 70-f higher than in aerial part (stem+leaves). Malondialdehyde (MDA), superoxide radical (O2−), hydrogen peroxide (H2O2) and lipoxygenase activity (LOX) increased in Cd-exposed roots, suggesting a metal-induced oxidative stress. The Cd treatment enhanced the activity of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and guaiacol-type peroxidase (G-POD), as well as the content of secondary metabolites i.e. soluble phenolics (SPs) and lignin. Histochemical analyses of roots showed that Cd, H2O2, (O2−), lignin and G-POD displayed a similar location pattern. Almost all analyzed parameters showed a similar dynamic tendency with increases under 5μM Cd followed by decreases under 10μM Cd, suggesting that a complex coordinated Cd-defensive mechanism is operating in Citrumelo roots exposed to environmental realistic Cd concentrations.

Electroresponsive behavior of 2-hydroxypropyltrimethyl ammonium chloride chitosan/poly(vinyl alcohol) interpenetrating polymer network hydrogel

An interpenetrating polymer network hydrogel composed of 2-hydroxypropyltrimethyl ammonium chloride chitosan and poly(vinyl alcohol) was prepared. Its swelling properties and electroresponsive behavior in aqueous NaCl solutions were studied. The results indicated that the water uptake ability of the hydrogel decreased with increasing ionic strength of aqueous NaCl solution. The Young's modulus, elongation at break and tensile strength of the hydrogel swollen in deionized water were 4.29 MPa, 76.5% and 3.26 MPa, respectively. The hydrogel swollen in the NaCl solution bent toward the anode under non-contact direct current electric fields, and its bending speed and equilibrium strain increased with increasing applied voltage. The electroresponsive behavior of the hydrogel was also affected by the electrolyte concentration of external NaCl solution, and there was a critical ionic strength of 0.10 where the maximum equilibrium strain of the hydrogel occurred. By changing the direction of the applied potential cyclically, the hydrogel exhibited good reversible bending behavior. Copyright © 2011 Society of Chemical Industry

Electroresponsive Behavior of Sulfonated Benzal Poly(vinyl alcohol) Hydrogel Under Direct-Current Electric Field

A novel sulfonated benzal poly(vinyl alcohol) (S-B-PVA) hydrogel was prepared by sulfonating benzal poly(vinyl alcohol) hydrogel with concentrated sulfuric acid, and its swelling properties, mechanical properties, and electroresponsive behavior in Na2SO4 solutions were studied. The results indicated that the water take-up ability of the hydrogel decreased with the increasing ionic strength of Na2SO4 solution. The Young's modulus, elongation at break and tensile strength of the hydrogel swollen in deionized water is 8.38 MPa, 22.2% and 3.14 MPa, respectively. The hydrogel swollen in Na2SO4 solution bent toward the cathode under non-contact dc electric fields, and its bending speed and equilibrium strain increased with the increasing of applied voltage. The electroresponsive behavior of the hydrogel was also affected by the electrolyte concentration of external Na2SO4 solution, and there is a critical ionic strength of 0.1 at which the maximum equilibrium strain of the hydrogel occurs. Under a cyclically varying electric field, the hydrogel exhibited a good reversible bending behavior.

Electroresponsive Behavior of 2-Hydroxypropyltrimethyl Ammonium Chloride Chitosan Hydrogel Under DC Electric Field

A novel polycationic chitosan hydrogel, 2-hydroxypropyltrimethyl ammonium chloride chitosan hydrogel (HACC hydrogel), was prepared by the introduction of quaternized groups with glycidyltrimethylammonium chloride (GTMAC) and epichlorohydrin as crosslinker, and its swelling properties and electroresponsive behavior in aqueous NaCl solutions were studied. The results indicated that the water uptake ability of the hydrogel decreased with the increasing ionic strength of aqueous NaCl solution. The hydrogel swollen in the NaCl solution bent toward the anode under the non-contact dc electric fields, and its bending speed and equilibrium strain increased with the increasing of applied voltage. The electroresponsive behavior of the hydrogel was also affected by the electrolyte concentration of external NaCl solution, and there is a critical ionic strength of 0.15 where the maximum equilibrium strain of the hydrogel occurs. By changing the direction of the applied potential cyclically, the hydrogel exhibited good reversible bending behavior.