Degree Of Counterion Dissociation Research Articles

Analysis of the Bromide Ion Distribution in the Water Pool of Reverse Micelles of Hexadecyltrimethylammonium Bromide in Chloroform/n-Dodecane and Isooctane/n-Hexanol by Chemical Trapping

Chemical trapping of bromide ions in reverse micelles prepared with hexadecyltrimethylammonium bromide, CTAB, in n-dodecane/CHCl3 and isooctane/n-hexanol has been obtained for 2,4,6-trimethylbenzenediazonium (1-ArN2+) and 2,4-dimethyl-4-hexadecylbenzenediazonium (16-ArN2+) tetrafluoroborates. Quantitative analysis of the reaction products of 1-ArN2+ and 16-ArN2+ with water and bromide ion, the corresponding phenol and bromo derivatives, and comparison with appropriate standard curves yielded the local concentrations of Br- in the water pool, [Br]f, and micellar interface, [Br]b, in reverse CTAB micelles prepared in n-dodecane/CHCl3 and isooctane/n-hexanol. The determination of [Br]b in reverse micelles by chemical trapping with 16-ArN2+ can be obtained after correction for probe distribution between the reverse micelle and the organic solvent, especially in the case of n-dodecane/CHCl3. This correction was possible after demonstrating that 16-ArN2+, upon dediazoniation in wet n-dodecane/CHCl3, yields exclusively the corresponding bromo derivative. A Poisson−Boltzmann (PB) equation above a water/detergent molar ratio, W/S, of 14 appropriately describes the values of [Br]f. Comparison of the experimental values of [Br]b with those predicted by PB with changing W/S suggest that 16-ArN2+ extends from the interface 0.6−1.2 nm with increasing W/S. Both PB calculations and experimental data indicate that the degree of counterion dissociation from CTAB reverse micelles in n-dodecane/CHCl3 reaches a value of ca. 0.2 above W/S 15.

Fluorocarbon Hybrid Surfactants Characterization of Admicelles and Its Solubilization

Admicelle formation of the fluorocarbon hybrid surfactant 1-oxo-1-[4-(fluoroalkyl)phenyl]-2-alkanesulfonate (FCm−HCn) on the aluminum oxide particle surface has been studied by the adsorption isotherm, ζ-potential of the particle surface, degree of counterion dissociation, contact angle, and pyrene fluorescence probe measurement. Solution properties of FCm−HCn have been compared with a dialkyl hydrocarbon surfactant, sodium 1-4-alkylphenyl-1-oxo-2-alkanesulfonate (HCm−HCn). Adsorption isotherm study and ζ-potential measurement indicate that the fluorocarbon hybrid surfactant can adsorb on the aluminum oxide surface at lower concentrations than the hydrocarbon surfactant. Furthermore, the total amount of surfactant adsorbed on the aluminum oxide surface is higher than that of the hydrocarbon surfactant. A pyrene fluorescence probe study shows that pyrene molecules are solubilized near the hydrocarbon chain of the surfactant molecules, indicating that the hydrocarbon domain exists in the fluorocarbon hybrid...

Conductance study of the thermodynamics of micellization of 1-hexadecylpyridinium bromide in (water + cosolvent)

The conductivity of (cosolvent + water) in the presence of increasing concentration of 1-hexadecylpyridinium bromide was measured at various temperatures. Acetonitrile, dimethylformamide, dimethylsulfoxide, dioxane and ethylene glycol were used as cosolvents. From the conductivity data, the critical micelle concentration c.m.c., and the effective degree of counter ion dissociation α, were obtained at various temperatures. In all the cases studied, a linear relationship between log ( [c.m.c] / mol · dm − 3 ) and the mass fraction of cosolvent in solvent mixtures was observed. The thermodynamic properties ΔH m o and ΔS m o were evaluated from the temperature dependence of the equilibrium constants for micellization of the surfactant. While the micellization process in pure water is both enthalpy and entropy stabilized, it becomes entropy destabilized in all solvent mixtures used; the values of ΔS m o being more negative with increase in the cosolvent content of the solvent mixtures. The resulting ΔH m o against TΔS m o plot showed a fairly good linear correlation, indicating the existence of an enthalpy–entropy compensation in the micellization process.

Micelle Formation by Anionic and Cationic Surfactants in 18-Crown-6 Ether +β-Cyclodextrin + Water Systems

The conductances of sodium decyl sulfate (SDeS), sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), and trimethyltetradecylammonium bromide (TTAB) have been determined in 18-crown-6 ether + water (CR + W), β-cyclodextrin + W (CYC + W), and in CR + CYC + W mixtures with fixed 0.0151 mol dm−3 of CR and varying the amount of CYC with the overall change in the mole–fraction range of CYC from 0.0 to 0.5 in a CR + CYC + W mixture at 30 °C. From the conductivity data, the critical micellar concentration (cmc), degree of counter ion dissociation (β), free energy of transfer of the surfactant hydrocarbon chain from medium to the micelle (), and free energy of transfer of surface contributions () of SDS, SDeS, DTAB, and TTAB have been computed. It has been found that the micelles of anionic surfactants are stabilized in a CR + W mixture in comparison to that in pure water, whereas micelles of cationic surfactants remain more or less unaffected. Micelles of all of the above surfactants are denatu...

Electrochemical Study of the Micellization of Hexadecylpyridinium Bromide in the Presence of Some Crown Ethers

AbstractA membrane electrode selective to hexadecylpyridinium bromide was used to study the micellization of the surfactant in the presence of varying concentrations of crown ethers 15‐crown‐5, dicyclohexyl‐18‐crown‐6 and dicyclohexyl‐24‐crown‐8 at 27°C. The critical micelle concentration of surfactant was largely influenced by the crown ethers used, indicating their participation in the structure of the resulting micelle. The degree of attachment of crown ethers to the surfactant in the micellar structure was found to be 1. An estimation of the Kf for the 1:1 surfactant‐crown interaction in the micellar region is reported. The degree of counter ion dissociation was found to increase with the crown ether concentration, and with the nature of macrocyclic ligands in the order 15‐crown‐5 < dicyclohexyl‐ l8‐crown‐6 < dicyclohexyl‐24‐crown‐8. There was also some evidences for a rather strong interaction between dicyclohexyl‐24‐crown‐8 and the surfactant in the submicellar concentration ranges in solution.

Cetylpyridinium chloride[ndash ]tetradecyltrimethylammonium bromide mixed micelles in ethylene glycol[ndash ]water and diethylene glycol[ndash ]water mixtures

The conductances of cetylpyridinium chloride (CPyCl)–tetradecyltrimethylammonium bromide (TTAB) mixtures over the entire mole fraction range of CPyCl (xCPyCl) have been measured in water, ethylene glycol–water (EG–W) and diethylene glycol–water (DEG–W) mixtures consisting of 20, 40 and 60 wt.% EG and DEG in their respective binary mixtures at 30 °C. From the conductivity data, the mixed critical micellar concentration (cmc), degree of counter-ion dissociation (χ), standard Gibbs energy of transfer of the surfactant hydrocarbon chain from medium to the micelle (ΔGHP°), and Gibbs energy of transfer of surface contributions (ΔGs°) for mixed micelles were computed. The non-ideality in the mixed micelle formation was evaluated by using the regular solution theory extended by Rubingh. It was observed that the non-ideality decreases with increase in the amount of EG or DEG. This was attributed to the solvation of the surfactant hydrophobic tail by EG or DEG molecules owing to EG or DEG–hydrocarbon interactions.

Thermodynamic studies on water-β-cyclodextrin-surfactant ternary systems

Conductance measurements are reported for double chain surfactants like N,N,N-octylpentyldimethylammonium (OPAC) and N,N,N-octyloctyldimethylammonium chlorides (OOAC) in water-β-cyclodextrin solution. From the specific conductivity data, the apparent critical micelle concentration (cmc ∗) and the degree of counterion dissociation (β) were obtained at a fixed β-CD concentration ( m βCD = 0.01190 mol kg −1, besides from the cmc ∗ value and that in water (cmc) the stoichiometry of the surfactant-β-CD complex was calculated. Densities, heat capacities, enthalpies of dilution at 298 K and osmotic coefficients at 310 K were measured for the same systems; the apparent molar volumes, V λ , and heat capacities, C λ , of two surfactants in β-CD solution, calculated as functions of surfactant concentrations m s, have made possible to obtain the properties of transfer of the surfactant from water to β-CD-water solutions.

Electrical double layer properties of hexadecyltrimethylammonium chloride surfaces in aqueous solution

The effect of aqueous KCl concentration on the electrical double layer properties of hexadecyltrimethylammonium chloride (CTAC) surfaces has been investigated. For self-assembled CTAC bilayers adsorbed onto amorphous silica surfaces, flat plate streaming potentials ( ζ s potentials), electrostatic potentials obtained from the electrophoretic mobility of colloid microspheres ( ζ e potentials) and diffuse layer potentials ( ψ d) derived from the force versus separation curves for the interaction of a colloid microsphere with a flat plate (measured with an atomic force microscope) have been analysed. Trends and differences in the ζ s and ζ e potentials have been attributed to incomplete electrical neutralisation of the silica surface by the inner adsorbed monolayer of CTAC, and differences in the silica surface charge density for the colloid and flat plate. It is considered that derived ψ d values highlight the problem created by surface roughness for atomic force microscopy force curve analysis. CTAC micellar surface potentials ( ψ o), which have been determined by a solvatochromic acid-base indicator technique, are greater than the ζ potentials for the planar adsorbed CTAC surfaces. Analyses in terms of a site-binding model and classical electrical double layer theory suggest that the degree of counterion dissociation from the surfactant headgroups (α) is significantly different for highly curved and planar surfaces; α is in the range 0.10–0.15 for the adsorbed CTAC bilayers and in the range 0.41–0.66 for spherical CTAC micelles when activities are used in the calculation. The CTAC critical micelle concentration and the minimum area per CTAC molecule at a planar interface as a function of KCl concentration have been ascertained from air/aqueous solution surface tension curves. The hydrophobic contribution to the free energy of CTAC micellisation has been calculated on the basis that CTAC micelles behave as Nernstian objects in KCl solution with the surfactant monomer acting as a potential determining ion. The results for the CTAC KCl systems have been compared with the results obtained for similar hexadecyltrimethylammonium bromide KBr systems.

Electrochemical Study of the Micellization of Hexadecylpyridinium Bromide in Binary Methanol–Water Mixtures

Abstract A membrane electrode selective to hexadecylpyridinum bromide was used to study the micellization of the surfactant in various methanol–water mixtures at 25 °C. There is a linear relationship between log cmc and the weight percent of methanol in solvent mixtures. The degree of counter-ion dissociation at different solvent compositions is reported. The degree of methanol attachment was found to be 2.04. The charged phase-separation model was used to express the mechanism of the mixed micelle formation.

Apparent Molar Volume and Apparent Molar Adiabatic Compressibility Studies of 2,6-Di- tert-butyl-4-methylphenol and 2- tert-Butyl-4-methoxyphenol in Aqueous Micelle Solutions of Hexadecyltrimethylammonium Chloride as a Function of Surfactant Concentration and Temperature

Ultrasonic velocities and densities of aqueous solutions of cetyltrimethylammonium chloride have been measured at concentrations below 0.35 mol kg -1 at 25, 35, and 45°C. Apparent molar volume and apparent molar adiabatic compressibility properties of the aqueous surfactant solutions were derived from these data. Apparent molar volumes and apparent molar adiabatic compressibilities of 2,6-di- tert-butyl-4-methylphenol and 2- tert-butyl-4-methoxyphenol dissolved in aqueous micellar solutions of cetyltrimethylammonium chloride were determined as a function of surfactant concentration and temperature. The results obtained for the binary and ternary systems are compared with those previously published for binary aqueous cetyltrimethylammonium bromide systems and for ternary systems of this surfactant containing the same additives. The degree of counterion dissociation from the micelles and the effect this has on the extent of hydration of the head group region of the micelle are shown to have an effect on the solubilization sites of hydrophobic-like additives in these micelles.

Equilibrium and kinetic studies associated with the interaction between sodium dodecyl sulfate and polyvinylpyrrolidone in aqueous solution

Binding isotherms for various sodium dodecyl sulfate–polyvinylpyrrolidone mixtures have been constructed from electrochemical measurements involving a dodecyl sulfate-selective membrane electrode. It was found that once the surfactant starts to bind to the polymer, small surfactant aggregates are formed. These aggregates grow in size until the polymer becomes fully saturated after which ‘free’ micelles are formed in solution. The degree of counterion dissociation was also measured using an electrode selective to the sodium counterion. The surfactant concentration at the start of binding and at the onset of the formation of free micelles was also determined using gel filtration. Finally the kinetics of the binding process were measured using ultrasonic relaxation measurements.

Thermodynamic properties of N-octyl-, N-decyl- and N-dodecylpyridinium chlorides in water

Densities, heat capacities and enthalpies of dilution at 25°C and osmotic coefficients at 37°C were measured for N-octyl-, N-decyl- and N-dodecyl-pyridinium chlorides in water over a wide concentration region. Conductivity measurements were performed in order to evaluate the cmc and the degree of counterion dissociation. Partial molar volumes, heat capacities, relative enthalpies and nonideal free energies and entropies at 25°C were derived from the experimental data as functions of the surfactant concentration. The changes with concentration of these properties are quite regular with the exception of the heat capacities which display anomalies at about 0.9, 0.25 and 0.12 mol-kg−1 for the octyl, decyl and dodecyl compounds, respectively. At these concentrations there were also changes in the slopes of the specific conductivity and of the product of the osmotic coefficients and the molality vs. concentration. These peculiarities can be ascribed to micelle structural transitions. The thermodynamic functions of micellization were graphically evaluated on the basis of the pseudo-phase transition model. These data have been compared to those for alkyltrimethylammonium bromides and alkylnicotinamide chlorides. It is shown that the introduction of the hydrophilic CONH2 group lowers the hydrophilic character of the pyridinium ring.

Thermodynamic properties and conductivities of some dodecylsurfactants in water

Densities, heat capacities, enthalpies of dilution, osmotic coefficients and conductivities are reported for dodecylamine hydrochloride, dodecyldimethylammonium and dodecyltrimethylammonium chloride in water over a wide range of concentration. The last two properties were also measured for dodecyltrimethylammonium bromide. From the thermodynamic data partial molar volumes, heat capacities and relative enthalpies and nonideal free energies and entropies were derived as a function of the surfactant concentration. The cmc's and degree of counterion dissociation were also calculated from the transport properties. It is shown that the trends of volumes, enthalpies, free energies and entropies are quite regular whereas heat capacities present maxima and minima at concentrations which depend on the nature of surfactants. Corresponding changes were observed in the osmotic coefficients and specific conductivities. The thermodynamic functions of micellization were evaluated on the basis of the pseudo-phase transition model. Finally, the effects of the introduction of methyl groups in the hydrophilic moiety of the surfactant and of the nature of the counterion on the thermodynamic properties of monomers and micelles are examined.

Equilibrium and kinetic properties of alkylpyridinium sulfate micelles

Equilibrium and kinetic measurements on tetradecyl- and pentadecylpyridinium sulfate micelles have been carried out. The value of the degree of counter ion dissociation α is seen to be highly dependent on the method used for its determination. The critical micelle concentrations and the mean aggregation numbers are close to those of the corresponding bromides. The fast and slow relaxation times for the two substances were also measured and the different values of α were used for the calculation of the parameters obtainable from the relaxation times. The rate constants and the width of the micelle size distributions determined from the fast relaxation time are seen to be rather insensitive to the value of α, while the parameters characterizing the submicellar aggregates are highly dependent on the degree of dissociation. Furthermore, an explanation is given for the very different concentration dependences of the slow relaxation time for the alkylpyridinium sulfate and sodium alkyl sulfate micelles.

Influence of chirality on micelle formation of sodium N-acylalanates and sodium N-lauroylvalinates

The critical micelle concentrations (cmc) of the optical isomers of sodium N-acylalanates and sodium N-lauroylvalinates were measured. The optically active isomers had the smallest cmcs in all NaCl solutions and at all temperatures. The degrees of counterion dissociation from the micelle (α) were determined and found to be identical for the optically active isomers and the racemic mixtures. The effective coefficients of electrostatic interaction ( K g ) and the free energy of transfer per methylene group from water to micelle (ω), respectively, are identical in both solutions. The thermodynamic parameters of micellization for the optically active surfactants were smaller than those for the racemic ones. It was concluded that the difference between the cmc values of the racemic and the optically active isomers results from the difference of the conformation of amino acid part in the surfactant molecule on the surface of the micelles.

Effect of counter-ions on the thermodynamic properties of alkali dodecyl sulfates in monomeric and micellar dispersions.

In order to elucidate the behavior of ionic portion as well as hydrophobic one of surfactant at solution and micelle formation with the view-point of enthalpy and heat capacity changes, the molar standard enthalpies of solution and micelle formation of lithium, sodium and potassium dodecyl sulfates (generically abr. as DMS), ΔsolH^- and ΔmH^- , were determined by calorimetry at various temperatures from 20° to 50°, and also their critical micelle concentrations, CMC's by electric conductivity measurement. The molar standard Gibbs free energy and entropy of micelle formation as well as the degree of counter-ion dissociation in micelle were calculated using thermodynamic relations from the values of CMC at various temperatures and ΔmH^- . On the basis of Born's theory, ΔsolH^- was expressed in the terms, explicitly containing the ionic radii of both dodecylsulfate anion and counter-cation, Li+, Na+, and K+, in MDS crystal and in water, and the terms, representing the hydrophobic contributions of MDS to lattice and hydration energies. The substitution of experimental and literary values into the above-mentioned expression gives, e.g. 2.2 A and 2.0 A as ionic radii of dodecylsulfate ion in crystal and in water, respectively. Also, ΔmH^- and its corresponding heat capacity, ΔmC^- , were analyzed with respect to the hydrophobic and ionic contributions to micelle formation.