Maurizio Castagnolo

Mass action model for solute distribution between water and micelles. Partial molar volumes of butanol and pentanol in dodecyl surfactant solutions

The densities of 1-butanol and 1-pentanol were measured in aqueous solutions of dodecyltrimethylammonium bromide and dodecyldimethylamine oxide and the partial molar volumes at infinite dilution of the alcohols in aqueous surfactants solutions were obtained. The observed trends of this quantity as a function of the surfactant concentration were rationalized using a mass-action model for the alcohol distribution between the aqueous and the micellar phase. At the same time, the model was revised to account for the alcohol effect on the surfactant micellization equilibrium. The partial molar volume of alcohols in the aqueous and in the micellar phases and the ratios between the binding constant and the aggregation number were calculated. These thermodynamic quantities are nearly the same in the two surfactants analyzed in this paper but differ appreciably from those in sodium dodecylsulfate. The apparent molar volume of surfactants in some hydroalcoholic solutions at fixed alcohol concentration were also calculated. In the micellization region the trend of this quantity as a function of the surfactant concentration shows a hump, which depends on the alcohol concentration and on the alcohol alkyl chain length. The alcohol extraction from the aqueous to the micellar phase due to the addition of the surfactant can account for the observed trends.

Solute-Solvent interactions in water-rich mixtures. II. Ionic conductances in water-dimethylsulfoxide mixtures at 25°C

Conductances of sodium bromide, iodide, and perchlorate, potassium chloride, and tetraphenylboride (BPh4−) as well as triisoamyl-n-butylammonium iodide (i-Am3BuNI) have been measured in aqueous mixtures containing up to 20 mole percent dimethylsulfoxide (DMSO) at 25°C. Experimental data were analyzed by the 1965 Fuoss-Onsager-Skinner (FOS) equation. Single-ion limiting equivalent conductances were calculated by assuming that λ0 (i−Am3BuN+=λ0 (BPh4−). The variations of the limiting ionic Walden products are discussed on the basis of acid-base type interactions for cations, and on the basis of structural effects for anions.

Enthalpies of solution and dilution of butanol and pentanol in dodecyltrimethylammonium bromide micellar solutions

The enthalpies of solution and of dilution of 1-butanol and 1-pentanol were measured in micellar solutions of dodecyltrimethylammonium bromide by systematically changing the concentration of alcohols and surfactant. The enthalpies of solution at infinite dilution of alcohols at each surfactant concentration were evaluated from a linear plot. This quantity increases with surfactant concentration (up to 0.8m) with a curvature which depends on the alcohol alkyl chain length. The difficulties arising for a quantitative treatment of both the enthalpies of dilution and of solution at finite alcohol concentrations are discussed. The dependence on the surfactant concentration of the standard enthalpies of solution and the enthalpies of dilution for m→0 are rationalized. From the resulting equations the distribution constant, standard enthalpy of transfer, standard enthalpy of solution, and the alcohol-alcohol interaction parameter in the micellar phase are evaluated. The enthalpies of transfer obtained using this technique agree well with those previously reported from enthalpies of mixing. The distribution constants also agree with those reported in the literature from several approaches: mixing enthalpies, partial molar volumes, and the dependence of the cmc on added alcohol.

Excess volumes and viscosity of water—sulfolane mixtures at 30, 40 and 50°C

Abstract Densities and viscosities of water—sulfolane mixtures have been measured at 30, 40 and 50°C over the whole mole fraction range. From density data apparent molar volumes of both components and deviations from ideal volumes of mixing have been evaluated at the three temperatures. From viscosity data activation parameters of viscous flow have been computed. Data obtained seem to confirm that sulfolane acts as a structure-breaker to water even at low concentrations.

Volumes and heat capacities of binary liquid mixtures of water—sulfolane and water—hexamethylphosphotriamide

Abstract Density and heat capacity measurements of water—sulfolane mixtures at 303.15 K and water—hexamethylphosphotriamide mixtures at 298.15 K have been performed over the whole composition range. Molar, excess, apparent molar volumes and heat capacities were calculated for the two systems. The trends of these functions are discussed in terms of specific interactions between the components of the solvent mixtures and the changes caused by the organic solvents on the water structure.

Solute—Solvent interactions in water-rich mixtures. I. Ionic conductances in water—Acetonitrile mixtures at 25°C

Conductance measurements oni-Am3BuNI (TABI), NaBPh4, NaI, NaBr, NaCl, and KCl are reported for aqueous mixtures containing up to 20 mole% acetonitrile at 25°C. Experimental data were analyzed by the 1965 Fuoss-Onsager-Skinner equation. Limiting ionic equivalent conductances in water-acetonitrile mixtures were calculated assuming that the contribution to the limiting conductance foriAm3BuNBPh4 is the same for both ions involved. The trends observed for the limiting ionic conductance-viscosity products for several ions in these water-rich solvents are discussed in terms of structural effects and ion-solvent interaction.

Ionic conductances in water-sulfolane mixtures at 30°C

AbstractConductances of solutions of triisoamyl-n-butylammonium (iAm3BuN+) iodide and sodium tetraphenylboride, iodide, and bromide have been measured in water-sulfolane mixtures at 30°C. Experimental data were analyzed by the 1965 Fuoss-Onsager-Skinner equations. The limiting equivalent conductances of triisoamyl-n-butylammonium tetraphenylboride (iAm3BuNBPh4) in each solvent mixture were obtained by the equation

The effects of increasing NaCl concentration on the stability of inclusion complexes in aqueous solution

\Lambda _0 (iAm_3 BuNBPh_4 ) = \Lambda _0 ({\text{i}}Am_3 BuNI) + \Lambda _0 (NaBPh_4 ) - \Lambda _0 (NaI)