Effect of a Weak Electrolyte on the Critical Micellar Concentration of Sodium Dodecyl Sulfate

The critical micellar concentration of sodium dodecyl sulfate is strongly altered bytris(hydroxy-methyl)methylammonium ions. The effect of buffer solutions containing this weak electrolyte as the counterion source has been studied using various concentrations of the acid–base system as well as modifying the pH. Results show that counterion concentrations ranging from 0 to 340 × 10⁻³M induce an appreciable diminution of the critical micellar concentration from 8 to 0.7 × 10⁻³M. The analysis of data suggests that the critical micellar concentration of sodium dodecyl sulfate depends on the concentration of weak electrolytes in a way very similar to that of strong electrolytes.     

Stability of Wetting Films of F108 Triblock Copolymer Aqueous Solutions on Quartz

Wetting films of nonionic F108 triblock copolymer aqueous solutions with concentrations below the CMC containing an electrolyte (NaCl) and formed on a quartz substrate are studied. Primary thick films are disclosed to be metastable. Their temporal stability is explained by the electrostatic repulsive forces. Film thinning and transition to a stable state occur slowly at low electrolyte concentrations (C _NaCl = 10^–5 and 10^–3 M, respectively) and instantly at its high concentrations (C _NaCl = 10^–2 and 10^–1 M, respectively). The stability of thin films is explained by the steric repulsive forces.     

Ternary [Al2O3–electrolyte–Cu] species: EPR spectroscopy and surface complexation modeling

Cu²⁺ binding on γ-Al₂O₃ is modulated by common electrolyte ions such as Mg²⁺, , and in a complex manner: (a) At high concentrations of electrolyte ions, Cu²⁺ uptake by γ-Al₂O₃ is inhibited. This is partially due to bulk ionic strength effects and, mostly, due to direct competition between Mg²⁺ and Cu²⁺ ions for the SO⁻ surface sites of γ-Al₂O₃. (b) At low concentrations of electrolyte ions, Cu²⁺ uptake by γ-Al₂O₃ can be enhanced. This is due to synergistic coadsorption of Cu²⁺ and electrolyte anions, and _. This results in the formation of ternary surface species (SOH₂SO₄Cu)⁺, (SOH₂PO₄Cu), and (SOH₂HPO₄Cu)⁺ which enhance Cu²⁺ uptake at pH < 6. The effect of phosphate ions may be particularly strong resulting in a 100% Cu uptake by the oxide surface. (c) EPR spectroscopy shows that at pH  pH_PZC, Cu²⁺ coordinates to one SO⁻ group. Phosphate anions form stronger, binary or ternary, surface species than sulfate anions. At pH  pH_PZC Cu²⁺ may coordinate to two SO⁻ groups. At pH  pH_PZC electrolyte ions and are bridging one O-atom from the γ-Al₂O₃ surface and one Cu²⁺ ion forming ternary [γ-Al₂O₃/elecrolyte/Cu²⁺] species.     

Effect of various additives on the performance of a newly developed PVC based potentiometric sensor for anionic surfactants

A new poly(vinyl chloride) PVC membrane electrode to determine monomer concentrations of dodecylbenzenesulphonate ions (DBS⁻) based on a neutral ion-pair carrier complex of dodecyltrimethylammonium–dodecylbenzenesulphonate (DTA⁺–DBS⁻), is reported here. The electrode exhibits a slope of 51.25 mV per decade for DBS⁻ ions. The DBS⁻ ion selective electrode (ISE) can determine monomer units down to concentrations as low as 3.32 × 10⁻⁴ M. The effect of three kinds of additives, i.e. alcohols, glycols and triblock polymers on the performance of the surfactant selective electrode is studied systematically. The effect of foreign anions along with primary ions on the performance of ion-selective electrode is investigated in terms of potentiometric selectivity coefficients, which were determined using the fixed interference method (FIM) at 1.0 × 10⁻² M concentration of foreign anions. The sensor responds well to the surfactant ions in the presence of additives at lower concentration. The Gibbs free energy of micelle formation (ΔG_m) of sodium dodecylbenzenesulphonate (SDBS) in the presence of various additives is calculated and found to vary differently with respect to the increase in the amount of additives. The sensor worked in the acidic pH range with a short response time of 30 s. The lifetime of the sensor is more than three months. The sensor was further used to determine the amount of DBS⁻ in local detergents. This method of determining anionic surfactants was found to be quite accurate when compared with classical methods.     

The Micellization and Clouding Phenomena of a Nonionic Surfactant,Poly(ethylene glycol) t-octylphenyl ether (Triton X-100): Effect of (Chloride Salt) Electrolytes

Herein, we report the micellization and the clouding of a nonionic surfactant, poly(ethylene glycol) t-octylphenyl ether (Triton X-100), in aqueous solutions in the absence and presence of (chloride salt) electrolytes. In the absence and presence of electrolytes, the critical micelle concentration (CMC) of Triton X-100 was measured by surface tension measurements. Upon increasing the temperature as well as the concentration of electrolytes, the CMCs decreased. The surface properties and the thermodynamic parameters of the micellar systems were evaluated. From these evaluated thermodynamic parameters, it was found that in the presence of an electrolyte, the stability of the micellar system is high. The cloud points (CPs) of Triton X-100 were also measured in the absence and presence of metallic ions of electrolytes. Upon the addition of metallic ions of chloride salts (electrolytes), the decrease in CP values was observed and the order was found to be: K⁺ > Na⁺ > Li⁺ > NH⁺₄.     

Conductivity of Magnesium Sulfate in Water from 5 to 35°C and from Infinite Dilution to Saturation

Conductivity data for magnesium sulfate in water from 5 to 35°C were measured at high precision covering the electrolyte concentration range from 10^–4 to 2.5 mol-dm^–3. ata analysis is based on the chemical model at low concentrations (lcCM) and on the mean spherical approximation (MSA) at moderate to high concentrations. The association constants of the MSA are compared with those from the low concentration chemical model (lcCM) calculations. Comparison is made with the data presentation bythe empirical Casteel–Amis equation.     

Electrosurface Properties of Microcrystalline Cellulose of Different Origin in 1 : 1 Electrolyte Solutions

Electrosurface characteristics (the exchange capacity and the electrokinetic potential) of the samples of cotton and wood microcrystalline celluloses (MCC) were studied as functions of the pH and the concentration of background electrolyte (10^–3–1M NaCl). It was found that the MCC samples are negatively charged over the studied pH range (3.5–10.0). The results of measuring exchange capacities were used for calculating constants of surface reactions. The values of dissociation constants of the surface groups allow us to state that the charge of the MCC surface within the studied pH range is mainly determined by the dissociation of carboxyl groups. The surface and electrokinetically mobile charges, concentrations of fixed and mobile ions, as well as Donnan's potentials were calculated for the studied samples.     

XPS investigations of the electrochemical double layer on silver in alkaline chloride solutions

The electrochemical double layer on Ag in alkaline NaCl solutions was examined ex situ with X-ray photoelectron spectroscopy (XPS). The specimens were removed from the electrolyte with hydrophobic surfaces and under potential control. The potential dependent surface concentrations of the adsorbed anions (Cl⁻, OH⁻), cations (Na⁺), the surface excess charge and the amount of adsorbed water were determined and compared to the results obtained for acidic NaCl solutions. The distinct differeness found between both electrolytes were discussed in terms of a specific adsorption of hydroxide ions in the basic Cl⁻-electrolyte; i.e., the OH⁻-surface concentration has to be considered for a proper determination of the cationic excess charge and the potential of zero charge. In addition, the initial stages of silver (1) oxide formation were examined with XPS.     

Surface film pressure of β-lactoglobulin, α-lactalbumin and bovine serum albumin at the air/water interface studied by wilhelmy plate and drop volume

The surface film pressure (II) of β-lactoglobulin, α-lactalbumin, and bovine serum albumin was studied in simulated milk ultrafiltrate (SMUF) and in water at concentrations from 10⁻⁶ up to 1% (w/v) at times from 30 s to 14 h and the results were analyzed with regard to adsorption transport and kinetics. In SMUF at low concentrations, β-lactoglobulin was the most “surface active” protein. There was little difference in the surface film pressure between β-lactoglobulin and α-lactalbumin at high concentrations. Bovine serum albumin showed the lowest surface activity, but did not reach a constant II, even after 14 h. As the pH approached the isoelectric point, the surface film pressure increased, and in the case of bovine serum albumin II increased faster. In water, however, the surface film pressures were lower than in SMUF, and for bovine serum albumin II developed more slowly. The transport to the interface was found to be controlled by diffusion only for a small concentration range of approximately 10⁻⁴%. It was controlled by initial flow disturbances at higher concentrations and free convection at lower concentrations. The rate of increase of the surface film pressure was not a simple function of surface film pressure and bulk concentration under any of the conditions studied.     

Kinetics and Mechanism of Electroreduction of Palladium(II) Bisethylenediamine Complexes on a Dropping Mercury Electrode

Kinetics of electroreduction of complexes Pd(en)²⁺ ₂(2 × 10^–5M) on a dropping mercury electrode is studied in solutions with various concentrations of ethylenediamine and supporting electrolytes (NaF, NaClO₄) at pH 4.5–11 and different instantaneous current recording times. Diffusion coefficients for reducing complexes and kinetic parameters of the slow electrochemical stage are determined. The concentration of supporting electrolytes is found to affect the half-wave potential, which points to an inner-sphere mechanism of electrochemical stage at supporting electrolyte concentrations of 0.005 to 0.03 M and to a predominantly outer-sphere mechanism at higher concentrations.     

Residual changes in the surface charge of TiO2 (anatase) suspensions as a result of exposure to a 44 MHz radiofrequency electric field

Potentiometric titrations of TiO₂ (anatase) suspensions in solutions of 10^–2, 10^–3, and 10^–4 M NaCl prior to treatment with a radiofrequency (RF) electric field gave values of pH_pzc and pH_iep of 5.75±0.1 and 5.85±0.1, respectively, within the range of literature values. Surface charge plots versus pH for untreated samples gave curves with a common intersection point, indicating that NaCl acts as an indifferent electrolyte. Identical suspensions of anatase were then exposed for 30 min to an RF electric field with a peak-to-peak, no-load amplitude of 34V and a frequency of 44 MHz. Portions of the treated suspension were titrated after different time periods following removal of the field (2, 15, 30, and 45 min). At 2 min, the pH_pzc had shifted to 6.50±0.1, and at 15, 30 and 45 min, the curves for the three NaCl concentrations were found to lack a common intersection point, an effect which became more pronounced with time. It is proposed that RF treatment results in the formation of a porous gel layer of hydrous titanium dioxide on the surface of the anatase particles that subsequently undergoes a slow ion-exchange reaction involving ions of the supporting electrolyte.     

Investigation of adsorption behaviour of mercury in microamounts on manganese dioxide from aqueous solutions

Adsorption of mercury onto manganese dioxide was studied in relation to the concentrations of electrolyte, adsorbent and adsorbate and foreign ions. Adsorption of other metal ions under similar conditions was also measured. Adsorption decreases with increasing electrolyte concentration. Thiosulfate, thiocyanate, iodide and all cations tested suppress the adsorption; the greater the ionic potential of cation, the weaker the adsorption of mercury. Adsorption follows the Freundlich-type isotherm over a wide range of mercury concentration (10^–7–10^–8 g·ml^–1). 98% of the adsorbed mercury can be eluted from the oxide column with 60 ml of 3M nitric acid solution.     

Diffusion in dilute aqueous acetic acid solutions at 25°C

A conductimetric technique has been used to measure diffusion coefficients for aqueous solutions of acetic acid at concentrations from 0.002 to 0.02 mol-dm^–3 at 25°C. The acetic acid component diffuses more rapidly at lower concentrations where a higher proportion of the slower acid molecules are converted by dissociation to acetate ions and highly mobile hydrogen ions. The observed concentration dependence of the diffusion coefficient verifies the limiting law for weak electrolyte diffusion. A new type of conductimetric diffusion cell with several practical advantages over earlier designs is described together with an improved procedure for the conductimetric determination of accurate diffusion coefficients for weak electrolyte systems.     

Determination of thallium in the presence of large excess of lead by anodic stripping voltammetry

The paper is concerned with the determination of traces of thallium, as T1(I), in the presence of very large amounts of lead, by d.c. anodic stripping voltammetry, by adding both a complexing agent and anionic surfactant. The supporting complexing agent was 0.1M solution of EDTA (pH 4.4). The influence of the several surfactants on the signals of lead and thallium was investigated.In 0.1M EDTA at pH 4.4 at the absence of a surfactant, lead does not interfere at concentrations below 10^–4 M. When the electrolyte contains also an anionic surfactant, lead can be tolerated at concentrations up to 2 × 10^–3–6 × 10^–3 M (depending on the type of the surfactant), and the height of the thallium peak remains unaffected. This makes the determination of 10^–8 M T1(I) possible when the molar excess of lead is 2–6 × 10⁵ fold. The method has been tested by determining the thallium content of soil extracts.     

Unusual dispersion of the electro-optically determined electric polarizability of bentonite dispersed particles in the range 10 kHz — 1 MHz

An unusual dispersion of the electric light scattering by aqueous calcium bentonite is observed. The electro-optic effect rises with the increase of the frequency in the range 10 kHz — 1 MHz. Parallel measurements are made on suspensions of sodium bentonite and zetlizer kaolinite at different ionic strengths and particle dimensions. It is shown that the dispersion for calcium bentonite does not greatly depend on the concentration of the indifferent electrolyte (sodium chloride with concentrations 10^–4 and 5.10^–4 M/l) or on the suspension concentration. Several possibilities for explaning this unusual dispersion are considered.     

Surface charge and adsorption of Na+ and Cl− ions at the zirconium dioxide/water interface

The surface charge and adsorption densities of Na⁺ and Cl^– ions at the zirconium dioxide/electrolyte interface have been determined as a function of pH for 0.1, 0.01 and 0.001 M solutions of NaCl. Using potentiometric titration of the surface hydroxy groups, it was found that the point of zero charge occurred at pH 4.3±0.15. The results are discussed in terms of site binding model of the electric double layer. The ionization and complexation constants have also been determined.     

Viscosity of aqueous NH4Cl and tracer diffusion coefficients of ions,water and non-electrolytes in aqueous NH4Cl,KI, and MgCl2 at 25°C

Viscosities for aqueous NH₄Cl and tracer diffusion coefficients for²²Na⁺,³⁶Cl^–, HTO, and CH₃OH, acetone and dimethylformamide (all¹⁴C-labelled) in NH₄Cl supporting electrolyte are reported for 25°, together with tracer diffusion coefficients for²²Na⁺,³⁶Cl^–, and¹⁴CH₃OH in 1M KI, and for¹⁴CH₃OH in 1M MgCl₂. The diffusion coefficient of HTO in NH₄Cl solutions is slightly larger, for most of the concentration range investigated (0.05 to 4.5 M), than the value for pure water and is almost unaffected by the supporting electrolyte up to about 4M. Similar behavior is shown by CH₃OH, acetone and dimethylformamide in NH₄Cl solutions. Onsager limiting law behavior is approached by Cl^– at NH₄Cl concentrations in the 0.05–0.1M region but at much lower concentrations by Na⁺.     

The Effect of Water Addition on the Electrosurface Properties of Quartz in Solutions of Alkali Metal Bromides in Ethanol

Electrosurface properties (the -potential and surface conductivity) of quartz particles in water–ethanol solutions of CsBr, NaBr, and LiBr with concentrations C = 10^–5–10^–2 M are studied. The (log C) dependences plotted from the results of electrophoretic measurements with allowance made for the particle surface conductivity demonstrate that, when water content in the aforementioned solutions increases from 4 to 40 vol %, the -potential of quartz becomes more negative and the isoelectric point shifts toward higher electrolyte concentrations, which increase in the following series: CsBr < NaBr < LiBr. This shift of the isoelectric point is explained by a decrease in the specific interaction of the alkali metal cations with the quartz surface because of a rise in the degree of their hydration (supersolvation).     

Effects of Fe(III) ions on the electrodeposition of trace amounts of plutonium and americium

The electrodeposition of Pu and Am onto stainless steel discs from 3.2M ammonium chloride solution is strongly affected by the iron concentration of the electrolyte. At Fe(III) concentrations of more than 0.1mM (30 g Fe in 5 ml) only 30–40% of²³⁶Pu and 6% of²⁴¹Am can be deposited. Tracer experiments with⁵⁹Fe suggest that exchange processes take place between Fe from the surface layer of the cathode and from the electrolyte. Double tracer studies show increasing²³⁶Pu/⁵⁹Fe- and decreasing²⁴¹Am/⁵⁹Fe-ratios with increasing iron content of the electrolyte, which may be due to different sorption properties on colloidal iron hydroxides formed at pH<3.6.