Phase behaviors of poly(sulfobetaine methacrylate) in various concentrations of NaCl aqueous solutions at critical transparent state

The phase behaviors of poly(sulfobetaine methacrylate) (polySBMA) in various concentrations of NaCl aqueous solutions at critical transparent state were investigated utilizing UV–vis analytical techniques. The effects of the molecular weight and temperature on the phase behavior of polySBMA at the critical transparent state were discussed in detail depending on the relationship between the concentration of NaCl, the concentration of critical polySBMA structural unit, and the molar ratio (R_C) of NaCl to the critical polySBMA structural unit. The results demonstrate that there exists a positive polymer concentration effect on the transparency. A relationship between the molecular weight, the concentration of NaCl, and the concentration of critical polySBMA structural unit was obtained, which provides a new method for measurement of the molecular weight of polySBMA. The polymer concentration effect for the polySBMA solutions at lower temperature was remarkable, which was similar to that for the polySBMA solutions with higher molecular weight.     

Densities and apparent molal volumes of aqueous CaCl2 and MgCl2 solutions

The Pitzer ion interaction model has been used to evaluate literature data for the densities of aqueous CaCl₂ and MgCl₂ solutions between 0 and 100°C. The selected data can be adequately fitted by setting ^(1),v equal to zero. The variations of ^(0),v and C ^v with temperature have been found to be linearly correlated. The uncertainty in the calculated density is lower than 50 ppm below 1M but raises to 300 ppm at high concentrations. When plotted vs. the square root of the molality, the apparent molal volume of MgCl₂ shows a change at a concentration where a transition in the speed of sound has already been reported by Millero, et al.     

Quantitative determination of low concentrations of peptides in aqueous solutions by14C-labelling

Calibration of a counting rate method with standard solutions of¹⁴C-labelled peptides allows the accurate determination of 1·10⁻⁶ to 1·10⁻²M concentrations of peptides in aqueous solution. By the use of this method and the equilibrium dialysis technique it is shown that binding constants of different peptides to DNA that differ by as little as ΔK=|0.3|mM⁻¹ can be measured. Statistical error considerations show that such a result is significant. The use of colored complexes formed between 2,4-dinitrofluorobenzene and LYS-LYS and LYS-TRYP-LYS enabled the affinity constants of these peptides with calf-thymus DNA to be determined. The advantages of the determination of peptide concentrations, by the use of radioactive counting, over colorimetric methods as well as the importance of this highly sensitive method for the measurement of peptide concentrations and hence binding constants are discussed.     

Protonation and complex formation of 5-sulfosalicylate in NaCl,CaCl2 and MgCl2 aqueous media. Speciation in synthetic seawater

The binding capacity of 5-sulfosalicylic acid (ssa) towards cationic macro-components of natural waters has been investigated in different ionic media (NaCl, MgCl2 and CaCl2 aqueous solutions) and in the ionic strength range 0 < or = I < or = 1 mol dm-3. In order to contribute to the speciation of this multi-sites ligand, measurements have been carried out also in a synthetic seawater (SSWE) containing the major components of seawater (Na+, K+, Ca2+, Mg2+, Cl- and SO4(2-)). Measurements have been performed by potentiometry ([H+]-glass electrode), at t = 25 degrees C. A critical analysis on the experimental and literature data is also given.     

Equation of state of aqueous NaCl solutions over a wide range of temperatures, pressures and concentrations

This work describes an equation of state for calculating the density of aqueous, liquid-phase NaCl solutions, based on an analytical equation for a mixture of hard-sphere ions and dipoles in the mean spherical approximation. The equation gives reasonable accuracy at temperatures from 273 to 973 K, pressures from 0.1 to 1000 MPa, concentrations from 0 to 50 wt.%, and densities higher than 650 kg m⁻³. The observed data of Hilbert (1979), Rogers and Pitzer (1982) and Urusova (1975) are fitted with only 10 empirically adjusted parameters plus the two water molecule parameters (diameter and dipole moment) which were determined from the density and dielectric properties of water. A comparison of the calculated and observed density data is presented. Errors in the calculated values vary from 0.5 to 1.5% over the whole range of temperature, pressure and concentration. A table of densities at temperatures from 273 to 973 K, pressures from 0.1 to 1000 MPa and concentrations from 0 to 50 wt.% is presented.     

The methods of determination of critical micellar concentrations of the amphiphilic systems in aqueous medium

Science is the attempt to make the chaotic diversity of our sense-experience to a logically unified system of thought. A sound theoretical basis and a rational physicochemical understanding based on experimental findings lead to a proper understanding of a topic. Colloid chemistry strengthened its footing by the extensive studies on gold sols by Michael Faraday in 1850s, however, the term “colloid” was coined by Thomas Graham in 1861. Historically, the Stone Age paintings in the Lascaux cave in France and the written records of Egyptian pharaohs were produced with stabilized colloid pigments. The part of colloid science dealing with amphiphilic molecules is so diverse on its own that it is dealt in a separate branch called the “association colloid”. A key development in the study of association colloids was the observation by James McBain that the osmotic pressure of salts of alkali metal fatty acid displayed a pronounced break in the concentration beyond a specific characteristic concentration, after which the osmotic coefficient remained almost constant (Evans and Wennerstrom, 1994). McBain attributed this fact to the self-association of these molecules among themselves (McBain, 1913, McBain, 1944) in solution. Here, we are providing a molecular as well as thermodynamic approach toward the micellization process.     

Kinetic study of barrierless coagulation of sols in electrolyte solutions

The flow ultramicroscopy method is employed to investigate the coagulation kinetics of hydrosols of α-Fe₂O₃, α-Fe00H, γ-Al₂O₃, and Cr₂O₃ with electrolytes (NaCl and KCl) under conditions corresponding to the absence of an ion-electrostatic barrier. It is found that, at pH values corresponding to pH_IEP of particles, as well as at those differing from pH_IEP, but at sufficiently high ionic strengths of coagulating electrolytes, the observed rate of coagulation is close to or above that calculated in terms of the Smoluchowski theory of fast coagulation. The data obtained are analyzed and possible reasons for the observed effect are considered with regard to the fractal structure of aggregates, the polydispersity of initial particles, and the concepts of additional interparticle attractive forces arising at high electrolyte concentrations.     

Supercooling of aqueous NaCl and KCl solutions under acoustic levitation

The supercooling capability of aqueous NaCl and KCl solutions is investigated at containerless state by using acoustic levitation method. The supercooling of water is obviously enhanced by the alkali metal ions and increases linearly with the augmentation of concentrations. Furthermore, the supercooling depends on the nature of ions and is 2-3 K larger for NaCl solution than that for KCl solution in the present concentration range: Molecular dynamics simulations are performed to reveal the intrinsic correlation between supercoolability and microstructure. The translational and orientational order parameters are applied to quantitatively demonstrate the effect of ionic concentration on the hydrogen-bond network and ice melting point. The disrupted hydrogen-bond structure determines essentially the concentration dependence of supercooling. On the other hand, the introduced acoustic pressure suppresses the increase of supercooling by promoting the growth and coalescence of microbubbles, the effective nucleation catalysts, in water. However, the dissolved ions can weaken this effect, and moreover the degree varies with the ion type. This results in the different supercoolability for NaCl and KCl solutions under the acoustic levitation conditions.     

Freezing points and related properties of electrolyte solutions. III. The systems NaCl−CaCl2−H2O and NaCl−BaCl2−H2O

The freezing temperatures of aqueous calcium chloride and barium chloride and their mixtures with sodium chloride were measured at equivalent molalities of 0.1 to 1.5 mole-kg^?1. Osmotic and activity coefficients of the mixtures were calculated at the freezing points of the mixtures. From the freezing points and calorimetric enthalpies of mixing of sodium chloride-magnesium chloride solutions, osmotic and activity coefficients were calculated at 298°K. Agreement of the calculated properties with isopiestic and electrochemical measurements at 298°K is excellent.     

Interactions of DL-serine and L-serine with NaCl and KCl in aqueous solutions

The activity coefficients at 25‡C of DL-serine and L-serine in aqueous solutions of NaCl and KC1 were measured. This study examines the effect of the nature of the cation of the electrolyte on the activity coefficients of the optical-isomers of serine in aqueous solutions for molality of serine up to 0.4 and molality of electrolyte up to 1. An electrochemical cell with two ion-selective electrodes, a cation, and an anion ion selective electrode,vs. a double-junction reference electrode was used to measure the activity coefficients of the electrolyte and the results were converted to the activity coefficients of serine in the aqueous electrolyte solution. The comparison of the results obtained for DL- and L-serine indicates that the two optical isomers have identical interactions with electrolytes in aqueous solutions and that for this amino acid the effect of the cation of the electrolyte is not significant. Comparison of these results with previous measurements for DL-alanine in aqueous solutions of the same electrolytes show the notable effect of the backbone of the amino acid.     

Electrostatics of B-DNA in NaCl and CaCl2 solutions: ion size, interionic correlation, and solvent dielectric saturation effects

The epsilon-modified Poisson-Boltzmann (-MPB) equations ( J. Phys. Chem. B, 2007, 111, 5264) have been solved on a three-dimensional grid for an all-atom geometry model of B-DNA. The approach is based on the implicit solvent model including finite sizes of hydrated ions and a dielectric approximation of the ion hydration shell. Results were obtained for the detailed geometry model of B-DNA in dilute and moderately concentrated solutions of NaCl and CaCl(2). All -MPB parameters of ions and dielectric medium were extracted from published results of all-atom molecular dynamics simulations. The study allows evaluations of the ion size, interionic correlation, and the solvent dielectric saturation effects on the ion distributions around DNA. It unambiguously suggests that the difference between the -MPB and Poisson-Boltzmann distributions of ions is low for Na(+) counterions. Such a difference in the case of divalent counterions Ca(2+) is dramatic: the dielectric saturation of the ion hydration shell leads to point-like adsorption of Ca(2+) on the phosphate groups of DNA. The -MPB equations were also applied to calculate the energy of interaction between two B-DNA molecules. Results agree with previously published simulations and experimental data. Some aspects of ion specificity of polyelectrolyte properties are discussed.     

Wetting and spreading of molten NaCl and CaCl2 over polycrystalline hydroxyapatite

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Electroinjection determination of aluminum in aqueous solutions

A procedure is proposed for determining aluminum(III) in water over a concentration range of 0.1–2.0 mg/L in the presence of commensurable amounts of iron(III) using electroinjection analysis. The following parameters were varied in the experiments: the composition and pH of a working buffer solution, the reagent-to-metal concentration ratio, the time of sample injection, the composition of a buffer solution in sample preparation for analysis, the concentration of the reagent (Xylenol Orange), and the reaction time. As a result of this, the sensitivity and selectivity of determining aluminum were improved as compared with the currently available procedures.     

Anomalies in supercooled NaCl aqueous solutions: a microscopic perspective

In this work we studied the effect of NaCl on the thermodynamic and dynamic properties of supercooled water, for salt concentrations between 0.19 and 1.33 mol?kg(-1), using molecular dynamic simulations for TIP5P∕E water model and ion parameters specially designed to be used in combination with this potential. We studied the isobaric heat capacity (C(p)) temperature dependence and observed a maximum in C(p), occurring at T(m), that moves to lower temperature values with increasing salt concentration. Many characteristic changes were observed at scaled temperature T∕T(m) ～ 0.96, namely a minimum in the density of the system, a reduction of the slope of the number of hydrogen bonds vs. temperature, and a crossover from Vogel-Tamman-Fulcher to Arrhenius dynamics. Finally, at low temperatures we observed that water dynamics become heterogeneous with an apparently common relationship between the fraction of immobile molecules and T/T(m) for all studied systems.     

Electrochemical corrosion kinetics of tin and tin amalgams in NaCl aqueous solutions

Electrochemical techniques were used to determine the corrosion rate of pure tin metal as compared to 80 Sn/20 Hg tin amalgam. X-ray diagrams showed that this amalgam was a crystalline γ₂ phase, whereas a 50 Sn/50 Hg amalgam contained liquid alloy embedded in the same γ₂ phase. Open circuit potential measurements, combined with narrow range potential scanning voltammetry, lead to the conclusion that amalgamation resulted in enhancement of the corrosion current, mainly by increasing the cathodic electron transfer reaction kinetics both in deaerated and in oxygen-saturated NaCl solution. When maintained at zero current potential in a solution containing dissolved O₂ gas, the samples were gradually covered with an insulating oxide layer which was identified by a series of electrochemical impedance diagrams recorded at different time intervals. The oxide layer was firmly adherent to the bulk tin metal but was poor at protecting the amalgam electrode. Finally, at potential values where the anodic current reached a few mA/cm², the pure tin metal surface was suddenly deteriorated by the formation of extremely deep pinhole corrosion pits, while this effect was smoothed down by amalgamation. Electronic Publication