NaBr Concentration Research Articles

Measurement of Forces between Supported Cationic Bilayers by Colloid Probe Atomic Force Microscopy: Electrolyte Concentration and Composition.

The interactions between supported cationic surfactant bilayers were measured by colloidal probe atomic force spectroscopy, and the effect of different halide salts was investigated. Di(alkylisopropylester)dimethylammonium methylsulfate (DIPEDMAMS) bilayers were fabricated by the vesicle fusion technique on muscovite mica. The interactions between the bilayers were measured in increasing concentrations of NaCl, NaBr, NaI, and CaCl2. In NaCl, the bilayer interactions were repulsive at all concentrations investigated, and the Debye length and surface potential were observed to decrease with increasing concentration. The interactions were found to follow the electrical double layer (EDL) component of DLVO theory well. However, van der Waals forces were not detected; instead, a strong hydration repulsion was observed at short separations. CaCl2 had a similar effect on the interactions as NaCl. NaBr and NaI were observed to be more efficient at decreasing surface potential than the chloride salts, with the efficacy increasing with the ionic radius.

Polysulfobetaines in Aqueous Solution and in Thin Film Geometry.

Polysulfobetaines in aqueous solution show upper critical solution temperature (UCST) behavior. We investigate here the representative of this class of materials, poly (N,N-dimethyl-N-(3-methacrylamidopropyl) ammonio propane sulfonate) (PSPP), with respect to: (i) the dynamics in aqueous solution above the cloud point as function of NaBr concentration; and (ii) the swelling behavior of thin films in water vapor as function of the initial film thickness. For PSPP solutions with a concentration of 5 wt.%, the temperature dependence of the intensity autocorrelation functions is measured with dynamic light scattering as function of molar mass and NaBr concentration (0–8 mM). We found a scaling of behavior for the scattered intensity and dynamic correlation length. The resulting spinodal temperatures showed a maximum at a certain (small) NaBr concentration, which is similar to the behavior of the cloud points measured previously by turbidimetry. The critical exponent of susceptibility depends on NaBr concentration, with a minimum value where the spinodal temperature is maximum and a trend towards the mean-field value of unity with increasing NaBr concentration. In contrast, the critical exponent of the correlation length does not depend on NaBr concentration and is lower than the value of 0.5 predicted by mean-field theory. For PSPP thin films, the swelling behavior was found to depend on film thickness. A film thickness of about 100 nm turns out to be the optimum thickness needed to obtain fast hydration with H2O.

Meteoric water alteration of soil and landscapes at Meridiani Planum, Mars

The geomorphology and geochemistry data gathered by the MER Opportunity at Meridiani Planum is a rich data set relevant to soil research on Mars. Many of the data, particularly with respect to outcrops at Victoria Crater, have been only partially analyzed. Here, the previously published geochemical profile of Endurance Crater is compared to that of Victoria Crater, to understand aspects of the post-depositional aqueous and chemical alteration of the Meridiani land surface. The landsurface bears cracking patterns similar to those produced by multiple episodes of wetting and drying in expansive materials on Earth. The geochemical profiles at both craters are nearly identical, suggesting (using mass balance methods) that a very chemically homogenous sedimentary deposit has been engulfed by the apparent surficial addition of S, Cl, and Br (and associated cations) since exposure to the atmosphere. The chemistry and mineralogy at both locations is one where the most insoluble of the added components resides near the land surface (Ca sulfates), and the more soluble components are concentrated at greater depths in a vertical pattern consistent with their solubility in water. The profiles, when compared to those on Earth (and to physical constraints), are most similar those generated by the downward movement of meteoric water. When this aqueous alteration and soil formation occurred is not well constrained, but the processes occurred between late Noachian (?) to late Amazonian times. The exposure of the Victoria crater walls, which occurred likely less than 107 y ago (late Amazonian), shows the accumulation of dust as well as evidence for aqueous concentration of NaBr and/or CaBr, possibly by deliquescence. By direct comparison to Earth, the regional soil at Meridiani Planum is a Typic Petrogypsid (a sulfate cemented arid soil), bearing similarities to very ancient soils formed in the Atacama Desert of Chile. The amount of water required to produce the soils ranges from a very low (and physically unlikely) quantity of 2–4 m, to possibly (and more likely) kilometers of water that were added in small individual increments over long spans of geological time.

Bromide and Acids: A Comprehensive Study on Their Role on the Hydrogen Peroxide Direct Synthesis

Hydrogen peroxide direct synthesis was studied using different concentrations of NaBr and H3PO4 (promoters) with a commercial Pd/C catalyst. The aim of the study was to understand the role of the acids and bromide on the catalyst and thus the effect on the direct synthesis. The experimental work was done in a continuous trickle bed reactor (TBR) using different concentrations of promoters. The effect of the promoters on the catalyst (Pd leaching and bromide adsorption) was monitored by inductively coupled plasma (ICP) on the solution obtained from the reaction environment. ICP analysis coupled with the monitoring of conversion, selectivity, and productivity helped to understand the effect of the promoters and to check the possibility to discriminate better the reaction network mechanism with different reaction conditions. Pd leaching was correlated to catalyst activity and bromide/phosphoric acid ratio. This work provides new and original evidence on the role of promoters, allowing one to understand bette...

Activation of TEMPO by ClO2 for oxidation of cellulose by hypochlorite-Fundamental and practical aspects of the catalytic system.

Bromide-free TEMPO-catalyzed oxidation of the primary alcohols by sodium hypochlorite (NaOCl) does not proceed without a prior activation of the catalyst. Here were demonstrate an immediate in situ activation of the catalyst with an equimolar addition of chlorine dioxide (ClO2) relative to TEMPO. Sodium bromide (NaBr) had a similar role in activating the catalyst although NaBr was needed in excess and the activation took several minutes depending on the dosage of NaBr. The activation method, or the concentration of NaBr, did not affect the bulk oxidation rate. The selectivity of the ClO2 initiated oxidation remained high up to NaOCl addition of 3mol/kg bleached birch kraft pulp after which additional loss in yield and depolymerization of cellulose were emphasized with negligible increase in carboxylate content. A carboxylate content of 0.8-1mol/kg, sufficient for easy mechanical fibrillation of the pulp, was achieved under mild conditions with NaOCl addition of 2-2.5mol/kg pulp.

Influence of salt on interaction between imidazolium based ionic liquid [C 12 mim][Br] and anionic polyelectrolyte poly(sodium-4-styrenesulfonate)

Abstract The influence of alkali salt [NaBr] on complex formation between anionic polyelectrolyte poly(sodium-4-styrenesulfonate) [NaPSS] and surface active ionic liquid (SAIL) 1-dodecyl-3-methylimidazolium bromide [C 12 mim][Br] in aqueous media has been investigated by isothermal calorimetry, surface tension, fluorescence and 1 H NMR spectra. It was observed that the [C 12 mim][Br]-NaPSS complexes were effected markedly with the increased addition of salt. At lower concentration, NaBr smooth the path of formation of micelle-like aggregates between [C 12 mim][Br] and NaPSS above the critical aggregate surfactant concentration. But at high concentration of NaBr there is no [C 12 mim][Br]-NaPSS complex formation because of complete salt screening of the electrostatic attraction between NaPSS chains and the [C 12 mim][Br] micelles. A range of surface parameters akin as surface excess concentration (Γ cmc ), surface pressure at the interface (Π cmc ), minimum area occupied by single SAIL molecule at air-solvent interface (Α min ), the adsorption efficiency (pC 20 ) and surface tension at critical micelle concentration (cmc) ( γ cmc ) are calculated from surface tension measurement for both with and without NaBr. The aggregation number (N agg ) and cmc is also derived from fluorescence probe behavior and cmc obtained from all above techniques are in proper consent with each other. The interpretation of various inter-molecular interactions amid NaBr and molecules of [C 12 mim][Br] in 0.010 g/L NaPSS also have been investigated through 1 H NMR spectra.

Controllable Self-Assembly of Amphiphilic Dendrimers on a Silica Surface: The Effect of Molecular Topological Structure and Salinity.

The adsorption kinetics and equilibrium of amphiphilic dendrimers based on poly(amidoamine) modified with a dodecyl chain, GnQPAMC12 (n represents the generation number), with different generation numbers at a silica-water interface have been investigated. The effect of molecular shape with different charge characteristics on the adsorption kinetics, adsorption isotherms, and the conformation of a self-assembled layer has been elucidated. For the adsorption kinetics, two steps were observed including the adsorption of individual molecules at concentrations below the critical micelle concentration (cmc) and the predominant adsorption of aggregates above the cmc. However, the adsorption isotherm, as a function of the generation number, presented an exceptional characteristic, in which a decrease in adsorption mass with different levels occurred in a high generation of amphiphilic dendrimers, depending on the balance of hydrophobic interaction and electrostatic repulsion. Atomic force microscopy imaging showed that flattened films with pores (spacing) of various shapes and roughness of 3-4 nm were formed, of which the pores (spacing) decreased obviously as the generation number increased. The addition of electrolyte (NaBr) has a great effect on the film morphology formed by the G3QPAMC12 dendrimer adsorbed at the silica-water interface, showing that the film became closer with smaller pores with increased NaBr concentration.

Effect of salts on synthesis of mesoporous materials with mixed cationic and anionic surfactants as templates

Mesoporous silica materials were synthesized using tetraеthoxysilane as precursor and liquid crystals formed in aqueous mixtures of cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) as templates, without and with the addition of NaBr or Na2SO4. For this purpose, the formation of liquid crystals as a function of the ratio of CTAB and SDS under different conditions was studied. It was found that liquid crystals formed in the mixed system of CTAB and SDS at certain mixing ratios are well-structured templates for the synthesis of mesoporous silicas. The synthesized silica materials were characterized by transmission electron microscope and nitrogen adsorption/desorption analysis. The pore size of mesoporous silicas could be controlled between 3 to 6 nm by simply changing the concentration of NaBr in solution. The mesoporous silicas exhibited lamellar structure and the order of structural arrangement was promoted with addition of NaBr. However, addition of Na2SO4 led to ink-bottle type pores of mesoporous silica with a narrow pore size distribution of around 2 nm and a higher specific surface area of 610 m2 g–1.

Interactions between pluronic block polyether and CTAB at air/water interface: interfacial dilational rheology study

The interactions between Pluronic block polyethers (L64 and 17R4) and cetyltrimethyl ammonium bromide (CTAB) were investigated by the measurement of the interfacial dilational viscoelasticity. The dilational moduli of the Pluronic block polyether/CTAB solutions firstly increased, passed through the maximum, and then decreased with the increasing concentration of CTAB. 17R4/CTAB mixed solutions have much larger dilational moduli than L64/CTAB systems, which means that 17R4 and CTAB have stronger interactions than L64 and CTAB. The dilational moduli of 17R4/CTAB systems were different from L64/CTAB systems in the presence of NaBr. The dilational moduli of the L64/CTAB mixed solutions decreased firstly, passed through the minimum value, and then increased with the increasing concentration of NaBr, while the dilational moduli of 17R4/CTAB mixed solutions increased firstly, passed through the maximum, and then decreased. These differences show that NaBr has great influence on the interactions between Pluronic block polyethers and CTAB.

Effect of Interparticle Interactions on Agglomeration and Sedimentation Rates of Colloidal Silica Microspheres.

The sedimentation half-times ts of initially monodisperse dispersions of 750, 505, and 350 nm silica microspheres were measured in water, in ethanol, and in aqueous NaBr solutions of concentration cNaBr ranging from 50 to 1000 mM, where the particles may have formed clusters. In water and in ethanol, ts was about 8, 18, and 33 h for the 750, 505, and 350 nm particles, respectively. These values were the same as the ones predicted by Stokes’ law, suggesting that the particles were monodisperse and remained so during sedimentation; ts values remained the same with increasing particle weight fraction up to 0.03, indicating no hydrodynamic interactions. Three regions of NaBr concentrations with different settling behavior were found for each size. In region I or at lower cNaBr, the ts values were the same as at no salt conditions, implying that there was no significant agglomeration before particles settled. In region II, ts decreased with increasing cNaBr, suggesting that the agglomeration and sedimentation ...

Weak Micelle-Like Aggregation in Ternary Liquid Mixtures as Revealed by Conductivity, Surface Tension, and Light Scattering.

A very small concentration of NaBr is added to ternary, transparent, and thermodynamically stable mixtures of water, ethanol, and octanol. Measuring the electrical conductivity along lines with constant water to ethanol ratios reveals remarkable composition dependencies similar to those found in classical surfactant-based microemulsions. Indeed, light-scattering experiments along the same composition lines and additional surface tension measurements confirm the onset of aggregation and possibly direct, bicontinuous, and reversed structures in these surfactant-free systems such as in classical microemulsions.

Kinetic Investigations of Cu‐Mediated ATRP in Aqueous Solution

Cu‐mediated atom‐transfer radical polymerization (ATRP) is studied via on‐line vis/NIR spectroscopy in an aqueous solution of a monomer‐free model system, with CuBr/2,2′‐bipyridine acting as the catalyst, and 2‐hydroxyethyl 2‐bromoisobutyrate as the initiator, at a pressure of up to 2000 bar. Excess NaBr is added to avoid the water‐assisted dissociation of the Br–Cu(II)/L bond. The activation–deactivation equilibrium constant, Kmodel, is measured at different compositions of the water–poly(ethylene glycol) dimethylether (PEO) solvent mixture, in which PEO mimics a water‐soluble monomer. Kmodel increases by about three orders of magnitude in passing from a PEO to a water environment. The change in Kmodel is essentially due to the effect on the activation rate coefficient. Kinetic analysis of the model system upon variation of NaBr concentration in conjunction with predici simulations shows that the NaBr content has no significant impact on the activation and deactivation rate coefficients and thus on Kmodel, but on dispersity and on the degree of chain‐end functionality. image

Salt-induced counterion condensation and related phenomena in sodium carboxymethylcellulose-sodium halide-methanol-water quaternary systems.

Polyion-counterion interactions in sodium carboxymethylcellulose (NaCMC) in methanol-water media have been investigated conductometrically with reference to their variations with polyelectrolyte concentration, relative permittivity and the type and concentration of added electrolytes. The specific conductance data in polyelectrolyte-salt solutions were analyzed using an equation recently developed by us following the scaling description for the configuration of a polyion chain according to Dobrynin et al. Excellent quantitative agreement between the experimental results and those obtained with the new equation developed was observed. The results demonstrate that approximately 43-59% of the counterions remain free and that there has been a suppression of counterion dissociation in the presence of a salt in any given mixed solvent medium, the extent of which increases with increasing salt concentration. NaCl was found to be slightly more efficient than NaBr in suppressing the counterion-condensation in NaCMC-methanol-water systems. An increase in the amount of methanol in the media causes a reduction in the fraction of free counterions. The results further demonstrate that the monomer units experience more frictional resistance as the methanol content of the mixture increases or as the concentration of the added electrolytes increases. The results were discussed in terms of various interactions prevailing in these systems.

New particle formation above a simulated salt lake in aerosol chamber experiments

Environmental context Deforestation in Western Australia beginning in the mid-19th century led to a considerable change of the land surface, and Western Australia is now suffering more often from droughts. Particle formation induced by salt lakes has been identified as a potential control factor for changed precipitation patterns. This study aims to determine key factors involved in the particle formation process by simulating a simplified salt lake in an aerosol chamber in the laboratory. Abstract In recent field experiments, particle formation has been observed above salt lakes in Western Australia and related to changes in regional precipitation patterns. This work investigates the particle formation potential above a simulated salt lake in aerosol chamber experiments under various conditions. The salt lake mixture comprised fixed concentrations of NaBr, NaCl and Na2SO4, and varying concentrations of FeSO4 and FeCl3. Further, an organic mixture of 1,8-cineol and limonene was added under dark and light conditions. Both the presence of organic compounds and of light were found to be essential for new particle formation in our experiments. There were clear indications for conversion of FeII to FeIII, which suggests a Fenton-like reaction mechanism in the system. Contrary to the idea that a Fenton-like reaction mechanism might intensify the oxidation of organic matter, thus facilitating secondary organic aerosol formation, the observed particle formation started later and with lower intensity under elevated FeII concentrations. The highest particle number concentrations were observed when excluding FeII from the experiments. Chemical analysis of the formed aerosol confirmed the important role of the Fenton-like reaction for particle formation in this study. Ultrahigh-resolution mass spectrometry and Raman spectroscopy provide analytical proof for the formation of organosulfates and halogenated organic compounds in the experiments presented. Even though halogens and organic precursors are abundant in these experimental simulations, halogen-induced organic aerosol formation exists but seems to play a minor overall role in particle formation.

Dilute nitric or nitrous acid solution containing halide ions as effective media for pure gold dissolution.

The greatly enhanced oxidation ability of dilute aqueous nitric acid (0.10-2.0 mol L(-1)) containing bromide and iodide salts as well as chloride salts has been examined based on the dissolution kinetics of pure gold at 30-60 °C. It has been found that bromide salts are more effective than chloride salts in gaining the ability of dissolving gold in dilute aqueous nitric acid solution. At 60 °C, a piece of gold-wire (ca. 20 mg) is dissolved in 20 mL of as low as 0.10 mol L(-1) HNO3 solution containing 1.0-5.0 mol L(-1) NaBr and the dissolution rate constant, log(k/s(-1)), increases linearly (from -5.78 to -4.52) with the increasing NaBr concentration. The addition of organic solvents, such as acetonitrile and acetic acid, causes acceleration of gold dissolution in LiBr and NaBr solutions. With increasing MeCN contents, for instance, the log(k/s(-1)) value of 0.10 mol L(-1) HNO3 solution containing 2.0 mol L(-1) NaBr increases linearly from -5.30 to -4.61 at 30% (v/v) MeCN. The bromide salts affect the gold dissolution rate constant in the order of KBr < NaBr < LiBr < CaBr2. With increasing NaI concentration (0.20-3.0 mol L(-1)), some acceleration in log(k/s(-1)) of 0.50 or 1.0 mol L(-1) HNO3 solution has been observed; however, the slope of acceleration as the function of NaI concentration is much smaller than that of NaCl or NaBr. The gold dissolution ability has been examined also for nitrous acid containing chloride and bromide ions at 35 °C. The NaNO2 solution containing twice or more amounts of HX (X = Cl, Br) gives the maximum efficiency for gold dissolution, according to the log(k/s(-1)) values of the mixed solutions of NaNO2 (0.10-2.0 mol L(-1)) and HX of various concentrations. The influence of oxidation by dilute nitric and nitrous acids on the gold dissolution is discussed from the standpoint of the redox potentials in "modified" aqueous solutions and not of the changes in the activity coefficients of ions.

Effect of Electrolyte and Temperature on Micellization Behavior of N-Ethyl-N,N-dimethyl-1-hexadecanaminium Bromide

Micellization behavior of aqueous solutions of N-ethyl-N,N-dimethyl-1-hexadecanaminium bromide in the presence of electrolyte sodium bromide, NaBr, was studied at different temperatures. The characterization of the surfactant solutions was done in two electrolytic concentrations of NaBr [(0.001 and 0.005) mol·kg–1] using density, viscosity, ultrasound velocity, and conductivity measurements. Several physicochemical parameters like density, apparent molar volume, ultrasound velocity, isoentropic compressibility, viscosity, Vand and Einstein hydration parameters, conductivity, and thermodynamic parameters were evaluated and compared with the corresponding parameters in aqueous solutions of the surfactant in the absence of electrolyte. In general critical micellar concentration exhibited a decrease in magnitude, apparent molar volumes exhibited an increase in magnitude, and degrees of hydration were lowered upon the addition of salt. Enthalpy of micellization registered a significant decrease in magnitude up...

Influence of halogenides on luminescence from silver molecular clusters in photothermorefractive glasses

It is shown experimentally that a rise in the sodium halogenide (NaCl, NaBr) concentration in photothermorefractive glasses increases the intensity of luminescence from silver neutral molecular clusters. Substitution of NaBr for NaCl with their concentration being the same shifts the luminescence band toward longer waves and raises its intensity. These findings can be explained by the formation of molecular clusters of type Ag n -Hal (Hal = Cl, Br) in photothermorefractive glass.

Ion Distribution around Synthetic Vesicles of the Cat-Anionic Type

Aqueous alkyltrimethylammonium bromides, or dialkyldimethylammonium ones, were mixed with sodium alkyl sulfates and dialkanesulfonates. Depending on the overall surfactant concentration, charge and/or mole ratios, cat-anionic vesicles were formed by mixing nonstoichiometric amounts of oppositely charged species. The resulting vesicles are thermodynamically and kinetically stable. ζ-potential and dynamic light scattering characterized the systems. As a rule, cat-anionic vesicles have sizes in the 10(2)-10(3) nm range and bear significant amounts of surface charges. At fixed surfactant concentration, the vesicle surface charge density scales with mole ratios and tends to zero as the latter approach unity. Conversely, the hydrodynamic radius diverges when the cationic/anionic mole ratio is close to 1. The double-layer thickness and surface charge density are controlled by mole ratios and addition of NaBr, which plays a role in vesicle stability. The salt screens the surface charge density and modulates both vesicle size and double-layer thickness. Slightly higher concentrations of NaBr induce the transition from vesicles toward lamellar phases. The electrokinetic properties of cat-anionic dispersions were analyzed by dielectric relaxation experiments. The measured properties are sensitive to vesicle size distributions. In fact, the relaxation frequency shifts in proportion to vesicle polydispersity. Model calculations proposed on that purpose supported the experimental findings.

Effects of Sodium Bromide Salt and Temperature on the behaviour of Aqueous Solution of Cetyltrimethylammonium Bromide

The effects of sodium bromide(NaBr) salt and temperature on the aggregation behaviour of cetyltrimethylammonium bromide (CTAB) have been studied using conductivity data.Conductivity was observed to vary increasingly with both temperature and salt concentration. The critical micelle concentration (CMC) of CTAB decreased with increase in the concentration of NaBr but increased as temperature increased. For example,the CMCs of CTAB in 0.0 and 10.0mM solutionsof NaBr at 30 °C were 1.68 and 1.50 mMrespectively while those of the same concentrations at 35 °C were 1.84 and 1.63respectively.It wasalso found that both salt and temperature influenced the degree of micelle ionization as well as the free energy of micellization. Results also showedthat the stability of CTAB micelles was enhanced by adding NaBr molecules.These observations have been discussedin terms of the electrostatic repulsion of charged CTAB head group.

Characterization and stability of catanionic vesicles formed by pseudo-tetraalkyl surfactant mixtures.

The phase behavior of an ad hoc synthesized surfactant, sodium 8-hexadecylsulfate (8-SHS), and its mixtures with didecyldimethylammonium bromide (DiDAB) in water is reported. We dealt with dilute concentration regimes, at a total surfactant content of <30 mmol kg(-1) where vesicular aggregates may be formed. The high synergistic behavior of such catanionic mixtures is concomitant with strongly negative interaction parameters, β (≈-18 kBT), significant gain in the free energy of association, ΔGagg, and much lower association concentration compared to the pure surfactants. Vesicle size and ζ-potential depend on the mixture composition. Hydrodynamic diameters increase by progressive addition of oppositely charged surfactants to the one in excess. Counter-intuitively, the ζ-potential becomes more negative at DiDAB molar fractions close to 0.2. The same holds in the reverse case, the ζ-potential becomes more positive after small additions of 8-SHS; anyhow, the effect is more significant in anionic-rich mixtures. This phenomenon was explained by assuming a significant release of counterions and an asymmetric distribution of the two surfactants in the inner and outer vesicle leaflets. The equimolar mixtures form a cubic phase rather than the expected lamellar one. The effect of NaBr concentration on the stability of catanionic vesicles was also investigated. At high NaBr concentrations, all systems are destabilized. For DiDAB-rich vesicles, flocculation is observed, while for 8-SHS-rich ones, lamellar domains are formed at the bottom of the samples. The role played by NaBr depends on whether it is added before or after mixing the surfactants. In particular, preformed catanionic vesicles show a great kinetic stability towards addition of NaBr compared to those obtained by other procedures.