Electrical percolation in micellar sodium dodecyl sulfate solutions. a phenomenological consideration

Effects of electrical percolation accompanying variations in overall surfactant concentration с have been studied by the example of micellar sodium dodecyl sulfate solutions. It has been found that, in the studied concentration range of 0.001–1.2 M, dependences of electrical conductivity K on c may exhibit at least three break points, with the dK/dc derivatives changing in the vicinities of these points. At two of these points, which are reliably identified and correspond to critical micelle concentrations (CMC₁ and CMC₂), they decrease. At the third concentration, lying between CMC₁ and CMC₂, the dK/dc derivative increases. A substantiated assumption has been put forward that this break point, at which the dK/dc derivative increases, results from the clustering of micelles and the appearance of channels with a higher specific conductivity, which is provided by the contribution from the electrical conductivity of the diffuse and dense parts of micelle electrical double layers, upon the formation of clusters. The ionic surfactant concentration that corresponds to the break point at which the dK/dc value increases has been denoted as the critical percolation concentration.     

Inclusion of the concentration dependence of the diffusion coefficient in the sand equation

The applications of the Sand equation in potentiometry of electrode and membrane systems for precise measurements of the transition time (τ) have been determined. An approach was suggested for choosing the diffusion coefficient of electrolyte (D) in the case when the concentration changes from its value in the agitated solution (where D = D_b) to the nearly zero value at the surface (D = D₀ corresponds to an infinitely dilute solution), D_b and D₀ being substantially different. The Nernst–Planck–Poisson nonstationary equations were numerically solved in a one-dimensional system including an ion-exchange membrane and two adjacent diffusion layers (for the electrode–solution system, the result is a particular case). An effective value D_ef was found, whose substitution in the Sand equation gave τ identical to that obtained by numerical solution. The neglect of the concentration dependence D(с) can lead to a nonadequate determination of the ion transport numbers in the membrane.     

The Effect of a Background Electrolyte on the Viscosity of Aqueous Dodecyltrimethylammonium Bromide Solutions

Conductometry and viscometry have been employed to study the effect of a background electrolyte (KBr) taken in concentrations of 0.03 and 0.1 M on the critical micelle concentration of dodecyltrimethylammonium bromide (С₁₂ТАB) and the dependence of relative viscosity η/η₀ of С₁₂ТАB micellar solutions on the overall surfactant concentration. It has been found that, as a first approximation, each of these dependences may be represented as the sum of two linear portions. Concentrations c* of С₁₂ТАB micellar solutions, which correspond to the inflections between the two linear portions in the concentration curves of relative viscosity, have been determined. The Einstein equation η/η₀ = 1 + 2.5p (p is the volume fraction of the dispersed phase and 2.5 is a theoretical parameter that takes into account the spherical shape of the particles) has been transformed into a form corresponding to the concentration dependence of the relative viscosity on the overall surfactant concentration to make it applicable to the consideration of low-concentration systems, which are uncomplicated by intermicellar interaction. In particular, the applicability of the above equation for estimating micelle radii has been studied. It has been shown that the (η/η₀–1) = f(c/с₀₁–1) concentration dependences represented in bilogarithmic coordinates (c is the overall С₁₂ТАB concentration and c₀₁ is the critical micelle concentration) are linear in the absence of a significant intermicellar interaction and have slopes equal to unity. This fact may be considered as a criterion for the applicability of the Einstein equation to micellar solutions.     

Simulation of electrical percolation in disperse systems at a small difference between specific conductivities of components

The possibility of development of electrical percolation upon variations in the contents of components in a disperse system has been studied in terms of Bruggeman’s ideas of an effective medium and the continual model of the electrical conductivity of composite materials. The case of a small difference between the specific conductivities of a dispersed phase K_m and a dispersion medium K_d has been considered. It has been shown that the dependence of electrical conductivity K of a disperse system on volume fraction p of a wellconducting component may exhibit an inflection in the vicinity of the p* value, which depends on the K_m/K_d ratio. Different methods for determining the p* value have been described. At low ratios between the conductivities of a dispersed phase and a dispersion medium, the inflection is very weakly pronounced. However, the representation of the K(p) dependences in semilog coordinated substantially facilitates its identification.     

Interaction Between an Active Pharmaceutical Ingredient Ionic Liquid Benzalkonium Salicylate and Small Biomolecules in Aqueous Solution: UV Absorption,Conductivity, and Volumetric Study

UV absorption spectroscopy, electrical conductivity and density experiments have been used to investigate the interactions of some small biomolecules (amino acids/dipeptides) with an active pharmaceutical ingredient in ionic liquid form (API-IL), benzalkonium salicylate (BaSal), in aqueous solution. A number of useful parameters, such as critical micellar concentration (cmc), aggregation number (N_agg) and limiting molar conductivity (Λ₀) of BaSal, standard partial molar volumes (\(V_{2,\phi }^{ \circ }\)), corresponding volumes of transfer from water to aqueous BaSal solutions (Δ_trV^o), standard partial molar expansibilities (\(E_{\phi }^{ \circ }\)), hydration number (n_H) of small biomolecules, as well as the binding constants (K_b) for small biomolecule–BaSal complexes have been evaluated. The dependence of the properties on concentration, temperature and alkyl chain length of amino acids/dipeptides is examined. The results are used to identify the solute–solvent physicochemical interactions occurring in the studied systems.     

Structural investigation of salts containing ions [Pd(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>]<Superscript>2+</Superscript> and [IrF<Subscript>6</Subscript>]<Superscript>2–</Superscript>

Double complex salts (DCS) α-[Pd(NH₃)₄][IrF₆]·H₂O (P2₁/m, a = 6.3181(3) Å, b = 10.8718(5) Å, с = 7.4526(4) Å, β = 103.568(2)°), β-[Pd(NH₃)₄][IrF₆]·H₂O (P2₁/с, a = 8.5773(3) Å, b = 10.8791(4) Å, с = = 12.6741(3) Å, β = 122.497(2)°), [Pd(NH₃)₄]₃[IrF₆]₂Cl₂·H₂O (P-1, a = 7.6080(2) Å, b = 7.6274(2) Å, с = 11.8070(3) Å, β = 122.497(2)°), and [Pd(NH₃)₄]₂[IrF₆]NO₃ (Fm-3m, a = 11.21210(10) Å) have been synthesized and structurally characterized for the first time. The existence of polymorphs for the DCS has been revealed. The influence of the chemical composition of the initial reagents on the reaction course and, respectively, the products, has been demonstrated. A hypothesis on the influence of the second coordination sphere on the formation of one or the other polymorph of the DCS has been suggested. It has been shown that the series α-[Pd(NH₃)₄][МF₆]·H₂O (M = Pt, Pd) exhibits isostructurality.     

Synthesis of 3-alkylquinoxalin-2(1<Emphasis Type="Italic">H</Emphasis>)-ones via Grignard reaction

A two-step procedure has been developed for the synthesis of 3-alkylquinoxalin-2(1H)-ones from o-phenylenediamine and ethyl 2-oxoalkanoates prepared by the Grignard reaction of diethyl oxalate with alkyl bromides. Analogous reaction with α,ω-dibromoalkanes instead of alkyl bromides leads to the formation of 3,3′-(alkane-α,ω-diyl)di[quinoxalin-2(1H)-ones].     

Synthesis and properties of quaternary ammonium Gemini surfactants with hydroxyl groups

The article describes synthesis of four hydroxyethyl alkylene–double alkyl bromide through substitution of nucleophilic d iethanolamine, 1-bromododecane, and 1,4-dibromobutane. The structure of the new hydroxyl cationic surfactant (HDCS) was characterized by ¹H NMR and FTIR spectra. The aqueous solution of HDCS showed critical micelle concentration, i.e., 5.6 × 10^?2 mM, and could reduce oil/water interfacial tension to 3.28 × 10^?3 mN m^?1. The surface tension measurements provided a series of parameters, including critical micelle concentration (CMC), surface tension at the CMC (γ_CMC), adsorption efficiency (pC₂₀), and effectiveness of surface tension reduction (Π_CMC). In addition, maximum surface excess concentration (Г_max) and minimum surface area/molecule (A_min) at the air/water interface were obtained by the Gibbs adsorption isotherm. The influence of inorganic salts (sodium chloride, calcium chloride) and organic salts (sodium benzoate) on the surface tension of HDCS in aqueous solution was investigated. For wettability alteration measurement, contact angle measurement as a quantitative method was utilized. Meanwhile, foam ability, foam stability, and emulsifying property of the synthesized surfactant were also examined at different concentration. HDCS also had excellent viscosity property.     

Formation of mononuclear rhodium(III) sulfates: <Superscript>103</Superscript>Rh and <Superscript>17</Superscript>O NMR study

It was shown that the monomeric rhodium sulfate complexes [Rh(H₂O)₄(SO₄)]⁺, trans-[Rh(H₂O)₂(SO₄)₂]^?, cis-[Rh(H₂O)₂(SO₄)₂]^?, and [Rh(SO₄)₃]^3? were not predominant forms in aqueous solutions. The ¹⁰³Rh NMR chemical shifts of the complexes were assigned, and the conditions for their formation in solutions, concentration parameters, and acidity at which the fraction of the monomers was maximal were determined. The constants of formation of the complexes and ion pair (IP) were estimated: K _IP = 8 ± 3.5, K ₁ ≈ 8, K _2trans ≈ 1, K _2cis ≈ 1, and K ₃ ≈ 2.     

Dielectric properties of films of Ag-ED20 epoxy nanocomposite synthesized in situ. Temperature dependence of direct current conductivity

The influence of silver myristate used as a precursor of silver nanoparticles on the direct current conductivity σ _dc of epoxy polymer within the concentration range of ≤0.8 wt % was investigated. The value of direct current conductivity was determined on the basis of analysis of the frequency dependence of complex permittivity within the frequency range of 10^?2–10⁵ Hz. The temperature dependence of σ _dc is composed of two regions. The dependence corresponds to the Vogel-Fulcher-Tammann empirical law σ _dc = σ _dc0exp{?DT ₀/(T-T ₀)} (where T ₀ is the Vogel temperature and D is the strength parameter) at temperatures higher than the glass transition temperature T _g. At the same time, T ₀ does not depend on the concentration of nanoparticles. The Arrhenius temperature dependence characterized by activation energy about 1.2 eV is observed at temperatures lower than T _g. The observed shape of the temperature dependence is related to the change in the mechanism of conductivity after “freezing” of ionic mobility at temperatures lower than T _g. The value of σ _dc is increased as the concentration of nanoparticles is raised within the temperature range of T > T _g. The obtained dependence of σ _dc on silver myristate concentration is similar to the root one, indicating the absence of percolation within the studied range of concentrations.     

The frequency dispersion of dynamic transfer coefficients and elastic moduli of magnetic liquids

The analytic equations for viscosity coefficients and the corresponding elastic moduli obtained in [3] were used to calculate these values over a wide range of reduced frequency values (ω* ≈ 10^?7?10). The volume η _v (ω) and shear η _s (ω) viscosity coefficients decreased as the frequency increased. The dispersions η _v (ω) and K _r (ω) were only caused by the contribution of structural relaxation, and the dispersions η _s (ω) and μ(ω), by translational and structural relaxation. The shear elastic modulus μ(ω) and relaxation volume elastic modulus K _r (ω) increased as the frequency grew. The results obtained were in satisfactory agreement with the conclusions from general relaxation theory.     

Study of host–guest interaction between ß-cyclodextrin and alkyltrimethylammonium bromides in water

Cyclodextrins were found to play important roles in self-assembly systems of surfactants. The interactions between host molecule ß-cyclodextrin (CD) and model cationic surfactants, alkyltrimethylammonium bromides with different alkyl chain length: dodecyl-(C₁₂TAB), tetradecyl-(C₁₄TAB) and hexadecyl-(C₁₆TAB) are studied by means of conductivity measurements at 313.2 K. The data obtained indicate that inclusion complexes (CD:S⁺) had formed, and apparent critical micelle concentration (CMC*) is equivalent to the combined concentrations of surfactant monomers complexed with the CD and that of a free dissolved monomer in equilibrium with the micellized surfactant without CD. Inclusion complexes were characterized by an equilibrium binding constant K ₁₁, which value increases as the length of alkyl chains, and consequently the hydrophobicity, increases. From mathematical model the concentrations of the uncomplexed cyclodextrin, uncomplexed surfactant ion, and inclusion complex in the submicellar, as well as in the micellar range were calculated. The competition between the micellization and complexation processes leads to the existence of a significant concentration of free CD in equilibrium with the micellar aggregates. The percentage of uncomplexed cyclodextrin in equilibrium with the micelles is independent on cyclodextrin concentration for a particular ternary system and is 31, 37, and 34 % for C₁₂TAB/water/ß-CD, C₁₄TAB/water/ß-CD and C₁₆TAB/water/ß-CD, respectively. By using standard Gibbs free energy for micellization and surfactant complexation by CD, we can explain the observed behavior.     

Stereodirected reactions of salicilaldehyde derivatives with <Emphasis Type="Italic">tert</Emphasis>-butyl 3(4)-hydroxy-2(3)-(3-methylbut-2-enyl)- piperidine-1-carboxylates as an efficient preparation procedure of tetrahydropyran derivatives fused with a piperidine ring

Reaction of salicilaldehyde and its derivatives with unsaturated cis-, trans-alcohols of the piperidine series in the presence of methyl orthoformate and p-toluenesulfonic acid led to the formation of a new heterocyclic system connecting four fuzed rings (two tetrahydropyrans, a piperidine, and an aromatic ring), 6,6-dimethyl-6а,7,7а,8(9),10,11,11а,12а-octahydrochromeno[3′,4′:5,6]pyranо[3,2-с(b)]pyridine.     

Small-angle X-ray scattering in sodium dodecyl sulfate solutions and micelle clustering

The small-angle X-ray scattering (SAXS) in micellar sodium dodecyl sulfate solutions has been studied in the range of overall concentrations c from 8 mM (CMC₁) to 300 mM and the absolute values of scattering vector q from 0.07 to 3.0 nm^–1. The total intensity of isotropic scattering has been revealed to increase with solution concentration. At c > 27 mM, the SAXS spectra have been found to exhibit an interference peak, which testifies a correlation in the arrangement of micelles in the bulk solution. This peak corresponds to the magnitude of q close to 1.55 nm^–1. Using the position of this maximum, average distance r₀ between the centers of micelles has been determined, which is equal to 4.1 nm and remains almost unchanged upon an increase in the overall concentration of sodium dodecyl sulfate. The observed regularities have been explained in terms of the DLVO theory taking into account the electrostatic and molecular intermicellar interaction.     

New Phosphate-Sulfates with NZP Structure

NaZr_2–xB_x(PO₄)_3–2x(SO₄)_2x (0 ≤ x ≤ 1.25, B = Mg, Co, Ni, Cu, Zn), and NaZr_2–xR_x(PO₄)_3–x(SO₄)_x (0 ≤ x ≤ 1.25, R = Al, Fe) phosphate-sulfates series have been prepared by a sol–gel process. These compounds belong to the NaZr₂(PO₄)₃ (NZP) structure family and crystallize in hexagonal crystal system, space group R\(\bar 3\)c. Limited solid solution series were found to exist; their formation temperatures and thermal stability limits were determined. Particle sizes as determined by microstructure observation were 50–200 nm, and for Cu- and Zn-containing samples, 200–500 nm. The thermal expansion of phosphate-sulfate NaZr_1.25Cu_0.75(PO₄)_1.5(SO₄)_1.5 was studied in the range 25–700°C. Thermal expansion coefficients and thermal expansion anisotropy were found to be α_a =–5.40 × 10^–6 °C^–1, α_с = 18.88 × 10^–6 °C^–1, α_avg = 2.69 × 10^–6 °C^–1, and Δα = 24.28 × 10^–6 °C^–1.     

Percolation in the model of random successive adhesion of anisotropic particles

Numerical studies of random successive adsorption (the RSA model) of rectangular particles on a flat substrate are performed and the dependences of saturation concentration and the percolation threshold on the parameters of a model are determined. The dependences of saturation concentration φ _j∞ on the particle diameter-to-length ratio r and the parameter of orientational order S are found. Correlations between the ? _j∞(r) function and excluded surface area are discussed. It is revealed that for highly ordered systems (S ≈ 1), the saturation concentration φ _j∞ is equal to 0.557 ± 0.005 and is virtually independent of r. For partially ordered systems, the ? _j∞ value decreases with an increase in r and in the r → ∞, ? _j∞ → 0. Percolation transition and electrical connectivity for the systems studied can take place only under the assumption of the tunnel mechanism of conductivity through gaps with finite thicknesses. The minimum thickness of tunnel gaps, at which percolation can occur, rises with increasing r and decreasing S.     

Calculating Permittivity and Dielectric Loss Frequency Spectra for Aqueous Electrolyte Solutions

Analytic expressions for dielectric permittivity factor ε₁(ω) and dielectric dissipation factor ε₂(ω) of electrolyte solutions are obtained, based on the ratio between complex factors of dielectric permittivity and specific conductivity. The range of frequency dispersion of dynamic factors ε₁(ω) and ε₂(ω) for aqueous solutions of LiCl, NaCl, KCl, and CsCl is considered. Numerical calculations are performed for friction coefficients β _a and β _b ; relaxation times τ _a , τ _b , and τ _ab ; and factors ε₁(ω) and ε₂(ω) in a wide range of variation for ρ; concentration c; temperature T; and frequencies ω. The resulting theoretically calculated ε₁(ω) and ε₂(ω) values and the Cole–Cole diagram are in quantitative agreement with experimental data.     

Evaluation of the stability of dye heteroassociates formed in aqueous solutions

The additive tetraphenylarsonium-tetraphenylborate model of interactions was found to be applicable to the problem of “preexperimental” evaluation of the stability of associates formed by dye cations (Ct⁺) and anions (An^?) in aqueous solutions. The possibility of predicting equilibrium association constants K _as from preliminarily calculated ΔG(Ct⁺) and ΔG(An^?) and of solving the inverse problem was analyzed. The invariability of the ΔG(Ct⁺) and ΔG(An^?) values and the problem of bringing calculation results in consistency with the experimental K _as values are discussed.     

Sulfonamidation of halogen-substituted electrophiles with <Emphasis Type="Italic">N</Emphasis>-(2,2,2-trichloroethyl)arenesulfonamides

Reactions of N-(2,2,2-trichloroethyl)arenesulfonamides with primary alkyl bromides and iodides, allyl bromide, chloroacetonitrile, and benzyl chloride in acetonitrile on heating in the presence of potassium carbonate gave the corresponding N-alkyl-N-(2,2,2-trichloroethyl)arenesulfonamides.     

Promising membrane materials based on strontium titanate

Electroconductivity of SrTi_1?x Fe _x O_3?δ(x = 0–0.5) specimens was studied by four-probe method. An opportunity was studied to produce hydrogen by high-temperature electrochemical conversion using SrTi_0.5Fe_0.5O_3?δ as the membrane material of the best conductivity. The effective ambipolar conductivity values calculated for SrTi_0.5Fe_0.5O_3?δ from the leakage experiment were found different from the ambipolar conductivity values calculated by the four-probe data processing because ambipolar conductivity corresponds to bulk transfer of complex oxide particles, taking no surface phenomena into account.