Function Of Electrolyte Concentration Research Articles

Influence of very small bubbles on particle/bubble heterocoagulation

Very small bubbles which partially coat the surface of particles influence whether or not heterocoagulation between a particle and a bubble occurs. The electrostatic and van der Waals forces of interaction between particles and bubbles were calculated as a function of electrolyte concentration, particle size, and the size and distributions of these very small bubbles present on the particle surface. The height of the surface force barrier was compared with the hydrodynamic pressing force under conditions of flotation. The presence of these very small bubbles has a profound effect on the interaction between particles and bubbles and, in particular, strongly decreases the critical particle radius for heterocoagulation.

Structure, Surface Interactions, and Compressibility of Bacterial S-Layers through Scanning Force Microscopy and the Surface Force Apparatus

Two-dimensional crystalline bacterial surface layers (S-layers) are found in a broad range of bacteria and archaea as the outermost cell envelope component. The self-assembling properties of the S-layers permit them to recrystallize on solid substrates. Beyond their biological interest as S-layers, they are currently used in nanotechnology to build supramolecular structures. Here, the structure of S-layers and the interactions between them are studied through surface force techniques. Scanning force microscopy has been used to study the structure of recrystallized S-layers from Bacillus sphaericus on mica at different 1:1 electrolyte concentrations. They give evidence of the two-dimensional organization of the proteins and reveal small corrugations of the S-layers formed on mica. The lattice parameters of the S-layers were a = b = 14 nm, γ = 90° and did not depend on the electrolyte concentration. The interaction forces between recrystallized S-layers on mica were studied with the surface force apparatus as a function of electrolyte concentration. Force measurements show that electrostatic and steric interactions are dominant at long distances. When the S-layers are compressed they exhibit elastic behavior. No adhesion between recrystallized layers takes place. We report for the first time, to our knowledge, the value of the compressibility modulus of the S-layer (0.6 MPa). The compressibility modulus is independent on the electrolyte concentration, although loads of 20 mN m −1 damage the layer locally. Control experiments with denatured S-proteins show similar elastic properties under compression but they exhibit adhesion forces between proteins, which were not observed in recrystallized S-layers.

Electrode Polarization Impedance in Weak NaCl Aqueous Solutions

In this paper, we characterize the polarization impedance behavior of several common metals in diluted NaCl solution operated at low current densities. The objective was to provide a useful reference for those wishing to calculate the electrode polarization impedance in diluted NaCl solutions. Serial equivalent resistance (R) and capacitance (C) for silver, aluminum, gold, platinum, and medical stainless-steel were measured as a function of frequency (10(-2)-10(3) Hz) and NaCl concentration (2.4-77.0 mmol/L). The ratio of electrode polarization impedance with respect to the bulk resistance was calculated and plotted against concentration for each metal. Such a ratio shows the effect of the electrode polarization contribution as a function of electrolyte concentration when the bulk resistance of the solution changes. All metals showed a decrease of serial resistance Rp and capacitance Cp as a function of frequency. The medical stainless-steel electrode showed largest impedance values at lower frequencies compared to the other electrodes, and was concentration independent at all frequencies. Aluminum had smallest polarization impedance at low frequencies. Pure gold and platinum behaved similar with the exception that the serial resistance for gold showed a lower value at higher frequencies.

Direct measurement of molecular interaction forces in foam films from lung surfactant fraction

Molecular interaction forces, operative in microscopic foam films obtained from the isolated hydrophobic fractions of porcine lung surfactant (AS-B) are investigated by monitoring film thickness h as a function of electrolyte concentration (C el) and direct measurements of disjoining pressure/thickness (Π(h)) isotherms. The steep decrease of the common film thickness with the increase of C el evidences the action of long-range electrostatic surface forces. The experimental h(C el) curve indicates that non-Derjaguin-Landau-Verwey-Overbeek (DLVO) repulsive forces are operative at C el where common black (CBF) and Newton black films (NBF) are obtained including the physiologically relevant C el=0.14 mol dm−3 NaCl. The action of additional non-DLVO forces is corroborated by the comparison of the experimentally measured Π(h) isotherm with the DLVO theory. Considering the presence of proteins in AS-B and the formation of lipid-protein complexes it is inferred that steric type forces are operative in CBF and NBF.

Solubility of proline–leucine dipeptide in water and in aqueous sodium chloride solutions from T = (288.15 to 313.15) K

Solubility of proline–leucine dipeptide, in water and in aqueous sodium chloride solutions, was measured at T = (288.15, 298.15, 308.15 and 313.15) K as a function of electrolyte concentration m = (0.1, 0.25, 0.5, 0.75 and 1) mol · kg −1 of water. Solubility data has been evaluated from density measurements using a vibrating tube densimeter. It has been observed that sodium chloride renders the dipeptide proline–leucine more soluble in water. Salting-in coefficients and standard free energies of transfer of proline–leucine, from water to aqueous sodium chloride solutions, have been calculated from the solubility data. Standard enthalpies and entropies of transfer have also been estimated and interpreted in terms of electrostatic and hydrophobic perturbed domains in the hydration shells of the dipeptide and of the cation and anion of the salt, as a function of temperature and salt concentration.

The role of pH and concentration on the ion rejection in polyamide nanofiltration membranes

The role of pH and concentration is studied on the ion rejection of Desal5-DK polyamide NF membranes. Various samples are used taken from two different batches (DK99 and DK02). Extensive experimentation at room temperature on HCl–water (0.001–1 mol/m 3) as well as on NaCl–water (1–50 mol/m 3) solutions is presented to characterize the membrane as a function of electrolyte concentration, at feed pH values in the range from 3 to 6.5. The applied pressure in the feed side is varied from 3 to 30 bar. The effect of feed pH is studied both on salt rejection and on total volume flux, and general trends are obtained. DK02 membranes are less pH sensitive than DK99's. Na + and H + rejections are greatly affected by pH. Na + rejection goes through a minimum value as the feed acidity increases, and correspondingly H + rejection goes through a maximum value. Minima are approximately located at pH values in the range between 4.5 and 5. Volumetric membrane charge values corresponding to each operative condition investigated are calculated through the Donnan Steric Pore Model and Dielectric Exclusion. Membrane charge is obtained as an increasing function both with pH and with electrolyte concentration in the feed side. A Langmuir-type behaviour is apparent at constant pH values; amphoteric behaviour is re-confirmed. The points of zero charge approximately correspond to the pH values at which NaCl rejections approach their minimum values.

The characterization of flat composite nanofiltration membranes and their applications in the separation of Cephalexin

We have characterized two flat composite nanofiltration membranes (NADIR ® N30F and NF PES10) by using neutral molecules and electrolytes and investigated their suitability for the separation of Cephalexin. For the first objective, the real rejection was firstly obtained by correcting the observed rejection based on the concentration polarization model. Then both irreversible thermodynamic and steric-hindrance pore (SHP) models were applied in order to estimate membrane structural parameters. It is found that the average pore radius r p are in the range 0.74–1.33 nm and the ratios of membrane porosity to membrane thickness A k/Δ x, are in the range 30,058–35,757 m −1, which are consistent with the experimental results based from the solute transport method. The effective charge density ( ϕX) of membranes, determined from the Teorell–Meyer–Sievers (TMS) model through fitting the NaCl rejection data, varies as a function of electrolyte concentration. These two negatively charged membranes express different rejection performance for single electrolytes in aqueous solutions, which in the order of R(Na 2SO 4) > R(MgSO 4) > R(NaCl) > R(MgCl 2). When investigating the ion rejection performance in the binary salt mixture solutions (Na 2SO 4/NaCl) at different pressures, these two membranes also exhibit a negative rejection to Cl − ion due to its lower valence. Through adjusting the pH of aqueous solutions, the separation of Cephalexin can be effectively manipulated up to 98% and 88% for N30F and NF PES10, respectively. In addition, increasing pressure was propitious to enhance the real rejection of solutes with higher permeate flux. N30F membrane shows higher rejection for Cephalexin due to its smaller pore size and larger charge density than NF PES10 membrane.

P.1.077 Escitalopram vs venlafaxine XR treatment ofmajor depressive disorder

In this study, twenty-five hard sphere equations of state (EOSs) were applied to evaluate the compressibility factor of fifty different single electrolyte solutions (Z1). Then by using two well-known mixing rules (Barrio Solana (BS) and Santos et al. (S)) the compressibility factor (Zm) was calculated for 1086 binary mixtures of electrolytes. The obtained results were compared with the simulation data and it was concluded that the Dehghani–Modarress (DM) EOS when applied along with the Santos et al. mixing rule has the highest accuracy (ARD%Z1DM=0.124 and ARD%ZmDM−S=0.466). Also, the mean ionic activity coefficients of a number of 1:1 electrolytes were calculated by applying the hard sphere EOSs with the mixing rules based on the mean spherical approximation (MSA) model where the concentration of cation was considered a function of electrolyte concentration. By comparing these results with reported experimental data it was found that the Ree–Hoover (RH) EOS with Santos et al. mixing rule predicts the mean ionic activity coefficients with the highest accuracy (ARD% γ(RH − S) = 0.206). In continuation of this study the compressibility factor and mean ionic activity coefficient were recalculated by means of the artificial neural network (ANN) method. The optimum architectures of ANN models for predicting the compressibility factor of single and binary mixtures of electrolytes as well as the mean ionic activity coefficient of 1:1 electrolytes were respectively obtained as 2:4:1, 3:3:1 and 3:5:1. The calculated error in the results showed that the mathematical models of the ANN method predicted the abovementioned parameters with better accuracy in comparison with the EOSs and MSA models (ARD%Z1ANN=0.047, ARD%ZmANN=0.022 and ARD % γ(ANN) = 0.014).

Enhanced electrochemomechanical activity of polyaniline films towards high pH region: contribution of Donnan effect

Enhancement of electrochemomechanical deformation (ECMD) and expansion of ECMD activity towards high pH have been simultaneously achieved in the electrolytes equilibrated with HCl and NaCl solutions for polyaniline (PANI) film. The maximum deformation has been reached to 6.7% in the mixture of 3 M HCl and 3 M NaCl equilibrated at pH 3 at ambient temperature. By comparing the fact that the ECMD magnitude is 3.2% in 1 M HCl equilibrated at pH 0.5, the simple judicious selection of electrolyte condition leads to the enhancement of ECMD magnitude by around two times. The concentration dependence on both electrical conductivity and absorption spectra elucidates the increase of protonation ratio as a function of electrolyte concentration. The results indicate that the high concentration retains both the electrochemical and ECMD activities in PANI film towards high pH region, which is the enhanced functionality of PANI supported by Donnan effect.

Ultramicroelectrode Voltammetric Investigation of Intermicellar Interaction and Micellar Growth of Sodium Dodecyl Sulfate in Aqueous NaCl Solutions

Ultramicroelectrode voltammetric measurements have been carried out to calculate the micellar self-diffusion coefficient (Ds) and intermicellar interaction parameter (Kd) of sodium dodecyl sulfate (SDS) in aqueous NaCl solutions at 298.15 K. The hydrodynamic radius ( ), the aggregation number, and the molecular weight of SDS micelles at various NaCl concentrations are also estimated. It is found that the Ds value is a function of SDS concentrations and the electrolyte concentration dependence on Ds exhibits two regions of behavior. With increasing NaCl concentration, Ds initially increases because of increasing Coulombic screening and, then, decreases linearly because of a linear spherical expansion of the micelles resulting from the increasing aggregation number. Kd is found to be a function of electrolyte concentrations. The stepwise decrease of Kd reflects that, due to Coulombic repulsion, the electrostatic interaction is gradually screened with increasing NaCl concentration. As the linear interaction theory applies rigorously over the electrolyte concentration range from 0.20 to 1.00 mol dm-3, it suggests that the micellar structure remains effectively spherical in the region, the linear spherical expansion of the micelle is occurring, and no dramatic structural changes have taken place in the micellar solutions. In addition, the micellar interaction energy is calculated, which implies that it is the Coulombic nature of the interaction between micellar particles that controls the micellar self-diffusion behavior in aqueous solutions.

Heteroflocculation of binary latex dispersions of similar chemistry but varying size

The stability of dilute bimodal (diameter:100 and 200 nm) model latex dispersions is studied as a function of electrolyte concentration and particle number fraction by measuring perikinetic aggregation with dynamic light scattering. A formally correct expression for the effective, doublet stability ratio of a bimodal system is derived that accounts for the difference in the particle size and hence, extends the derivation by Hogg and co-workers [Trans. Faraday Soc. 62 (1966) 1638]. Including the particle size ratio predicts slightly lower stability ratios for polydisperse but chemically similar systems. Stability ratios for binary mixtures of model colloidal latices are extracted from aggregation measurements in the fractal aggregation regime and are compared to predictions based on DLVO calculations of the potential. The results suggest that the composition of the aggregates is dependent on the relative stability of the two components (and consequently, on electrolyte concentration) and is richer in the least stable component.

Thermodynamic Study of Self-Assembly Behavior of Propranolol Hydrochloride in Aqueous Solutions as a Function of Electrolyte Concentration and Temperature

Density and ultrasound measurements of propranolol hydrochloride in aqueous solutions were carried out as functions of the drug molality, in the presence of different concentrations of added electrolyte (0.00, 0.01, 0.03, and 0.05) mol kg-1 NaCl and at the temperatures (288.15, 293.15, 298.15, 303.15, 308.15, and 313.15) K. The critical micelle concentrations were determined using the Phillips definition. To calculate changes in the thermodynamics properties of micellization, the mass action model was applied.

Colloid stability and coagulation rate of polystyrene latex particles in a turbulent flow

We measured the rate of coagulation in a turbulent flow to clarify the effectiveness of result of trajectory analysis of the collision efficiency between colloidal particles in flow fields. Experiments were performed in a mixing vessel filled with a dispersion of monodisperse polystyrene latex spheres as functions of electrolyte concentration and mixing intensity. It was found that dependencies of the critical coagulation concentration and the capture efficiency on ionic strength and effective shear rate qualitatively agreed with the numerical prediction based on the trajectory analysis of two spheres in a laminar flow.

Cyclic voltammetric and electrochemomechanical characteristics of freestanding polypyrrole films in diluted media

Cyclic voltammograms and electrochemomechanical deformations (ECMD) in freestanding polypyrrole (PPy) films have been investigated as a function of electrolyte concentration. It was found that both the oxidative and reductive peaks shifted towards lower potential with the dilution of the electrolyte in PPy films deposited from dodecylbenzene sulfonic acid. In the case of PPy films deposited from p-phenol sulfonic acid, the oxidation and reduction peaks tend to shift towards higher and lower potentials, respectively. These results indicate that the ion contributing to the redox reaction determines the polarity of the potential shift according to the Nernst equation. The ECMD magnitudes were also changed with electrolyte concentration. However, the efficiency of the deformation per degree of doping did not change much over 0.01 M. This indicates that the decrease in ECMD magnitude is not attributed to degradation of the ECMD behavior, but that a decrease in doping quantity for the film essentially effects the decrease in deformation magnitude in diluted media.

Volumetric and Viscometric Studies on Sodium Nitrate and Potassium Nitrate in Aqueous and H 2 O-urea Solutions

Density and viscosity of NaNO3 and KNO3 in aqueous and in H2O-urea solutions were determined as a function of electrolyte concentrations at 308, 313, 318, 323, and 328 K, respectively. The apparent molal volume (φv) of the electrolytes were found to be linear functions of the square root of the solute molality (b). The φv and \(\) data were fitted to the Masson equation [1] by the least square method to obtain the apparent molar volume at infinite dilution (φv^), which is practically equal to the partial molar volume \(\). The viscosity coefficients A and B were calculated on the basis of the viscosity of the solutions and the solvent concerned using the Jones–Dole [2] equation. The activation parameters for viscous flow (ΔG≠, ΔS≠, and ΔH≠) were calculated according to Eyring [3]. The values of \(\) for the two systems were also calculated from B-coefficient data. The results were found to be of opposite nature in the two electrolyte systems. Where sodium nitrate showed structure making behaviour both in aqueous and in H2O-urea solutions, KNO3 showed structure breaking behaviour in aqueous solutions and structure making behaviour in 5 molal H2O-urea solutions in the studied temperature range. The behaviour of these two electrolytes in aqueous binary and in aqueous-urea ternary systems are discussed in terms of charge, size, and hydrogen bonding effects.

Water activity in aqueous solutions of homogeneous electrolytes: the effect of ions on the structure of water.

An unconventional method, based on the spectrophotometric measurements of solution absorbance during hydration of aldehydes into diols, was applied for the determination of water activity in aqueous electrolyte solutions. The obtained values of the activity coefficient fW as a function of electrolyte concentration were used to estimate water structure ordering around ions. This method does not suffer from the weaknesses of X-ray diffraction and neutron scattering techniques applied in complementary studies.

Interactions between adsorbed lactoferrin layers measured directly with the atomic force microscope

Lactoferrin is an important protein found in tear fluid and has been implicated in the fouling of contact lenses. The interaction forces between lactoferrin layers, adsorbed onto hydrophobic model substrates, as a function of electrolyte concentration, solution pH and protein concentration were investigated using an atomic force microscope (AFM) where the geometry of the scanning tip was modified by attaching a colloid particle. Bovine lactoferrin adsorbed strongly and modified the interaction forces to include both a long-range electrostatic repulsive force, which could be described using the DLVO theory, and a short-range additional repulsion due to compression of the adsorbed protein layers. The adsorption of lactoferrin was verified by XPS analysis of the surfaces and the adsorbed layer was determined to be present as a full monolayer by AFM imaging. At smaller separation distances, deviations from theoretical predictions indicated that there was an adsorbed layer of at least 5 nm on both surfaces. DLVO theory could be used successfully to describe the longer ranged interaction forces in background electrolyte concentrations of 0.0002 and 0.001 M KNO 3, at various solution pH values. This analysis yielded effective diffuse electrical double layer potentials, which when plotted against the solution pH, suggested that the point of zero charge (pzc) of the protein coated surfaces was around pH 8, in agreement with literature values of the pI for lactoferrin. At higher electrolyte concentrations, 0.15 M KNO 3, the interaction forces could no longer be described using DLVO theory. The interaction forces between the adsorbed lactoferrin layers were purely repulsive, and the range and magnitude varied as a function of solution pH. Variations in the forces as a function of solution pH reflected conformational changes that depend on short ranged electrostatic interactions between the peptide residues within the protein molecules and the peptide residues and the substrate as well as van der Waals and hydrophobic interactions. The range of the interaction forces and the high compressibility of the adsorbed layers indicated that a significant number were present in an end-on orientation.

Electrokinetic Characterization of Poly(N-isopropylacrylamide) Microgel Particles: Effect of Electrolyte Concentration and Temperature

A fundamental study about the characterization of a poly(N-isopropylacrylamide), poly(NIPAM), microgel, cross-linked with N,N′-methylene bisacrylamide (BA), has been carried out. The anionic charge of this system was increased by copolymerization with 2-acrylamido-2methylpropanesulphonic (AMPS) acid. The electrokinetic behavior of these aMPS/NIPAM microgel particles has been investigated. First, the surface charge density was determined by conductimetric titration, and the particle size was obtained by transmission electron microscopy under several conditions. Electrophoretic mobility measurements were carried out as a function of electrolyte concentration and temperature. The hydrodynamic diameter of the particles was also measured by photon correlation spectroscopy as a function of electrolyte concentration and temperature. These size data have been taken into account in order to explain the mobility behavior by using Ohshima's theory for soft particles, with very good agreement between experiments and theoretical predictions.

Thermodynamics of Transfer of Amino Acids from Water to Aqueous Sodium Sulfate

The solubilities of amino acids at 288.15, 298.15 and 308.15K in water and aqueous sodium sulfate have been determined as a function of electrolyte concentration (0.5, 1.0, 1.5 mol/kg of water). It has been observed that sodium sulfate renders amino acids less scluble. The free energies of transfer of amino acids from water to aqueous sodium sulfate have been calculated from the solubility data. The enthalpies and entropies of transfer have also been estimated. The solubility and the thermodynamics of transfer data manifest that sodium sulfate generates favourable interaction between nonpolar groups of amino acids. If applied to proteins, it seems to stabilize the protein native globular structure by enhancing the intramolecular nonpolar-nonpolar group interactions.

Electrolyte-Induced Structural Evolution of Triton X-100 Micelles

The long-time self-diffusion coefficients of Triton X-100 micelles have been determined as a function of surfactant and electrolyte concentrations using rotating disk electrode voltammetry in conjunction with ferrocene acting as an electroactive probe. Micellar diffusion conforms to the linear interaction theory and yields micellar hydrodynamic radii values and interaction parameters as a function of electrolyte concentration. The interaction parameters varied from 3.4 to 3.6 over the electrolyte concentration range 0.01−0.8 mol dm-3 KCl, which is consistent with excluded volume interactions and indicated the absence of significant micellar shape changes with the addition of electrolyte. Micellar hydrodynamic radii varied linearly with respect to [KCl] from 4.22 to 6.21 nm, indicating the progressive evolutionary growth of the oblate micelles due to increasing aggregation number and “hydration”. The semimajor to semiminor axial ratio (a/b) increased from 2.0 to 3.5, indicating evolution to a more asymmetric structure. Micellar molecular weights increased from 77 700 to 326 000 over the electrolyte concentration range studied, which is predominantly due to water entrapment at the periphery of the self-assembled structures. Intrinsic viscosities were found to decrease from 6.09 to 4.61 cm3 g-1, indicating a decrease in specific micellar volume, which may be attributed to ethylene oxide chain collapse due to dehydration. The decrease in micellar specific volume was found to correlate precisely with the electrolyte induced decrease of the cloud point.