1-Ethyl-3-methylimidazolium Ethylsulfate in Water, Acetonitrile, and Dichloromethane: Molar Conductivities and Association Constants

Molar conductivities, Λ, of dil. solns. of the ionic liq. 1-ethyl-3-methylimidazolium ethylsulfate in water, acetonitrile (AN), and dichloromethane (DCM) were detd. as a function of temp. (AN: T = (273.15 to 313.15) K; DCM: T = (273.15 to 308.15) K; water: T = (278.15 to 313.15) K) in the concn. range c = (≈ 0.25 to ≈ 5) × 10-3 mol/dm-3. The data were analyzed with Barthel's low-concn. chem. (lcCM) model to obtain the limiting molar conductivities, Λ∞(T), and assocn. consts., KA°(T), of this electrolyte in the investigated solvents. From Λ∞(T) the Eyring activation enthalpy of charge transport was detd. and found to be slightly larger than the corresponding value for viscous flow of the solvent. Strong ion pairing was found for the electrolyte in DCM (KA° ≈ 6/104 mol-1/dm3), whereas ion assocn. in AN is rather weak (KA° ≈ 40 mol-1/dm3). From the temp. dependence of KA°(T) the enthalpy and entropy of the ion-pairing process were calcd., and ion assocn. was found to be entropy-driven for both nonaq. solvents. In water the salt is fully dissocd

Hydration and ion association of aqueous choline chloride and chlorocholine chloride

The choline ion (Ch(+)) is ubiquitous in nature and also its synthetic homologue, chlorocholine (ClCh(+)), is widely used. Nevertheless, surprisingly little information on the hydration and counter-ion binding of these cations can be found in the literature. In this contribution we report effective hydration numbers, determined by dielectric relaxation spectroscopy, and ion-pair association constants with Cl-, determined by dilute-solution conductivity measurements. In combination with RISM calculations the obtained data suggest that for Ch(+) water is bound to the hydroxy group via hydrogen bonds whereas for ClCh(+) a rather stiff clathrate-like shell around the chlorine atom seems to be formed. With Cl- both cations form contact ion pairs with association constants of only B2 to 3 M-1

Light, neutron, X-ray scattering, and conductivity measurements on aqueous dodecyltrimethylammonium bromide/1-hexanol solutions

Ternary systems of dodecyltrimethylammonium bromide (C12TAB)/1-hexanol/water are examd. for series with const. surfactant/alc. molar ratios of 8:2, 8:4, 8:6, and 8:8 at surfactant concns. of 6.167-61.67 g/L (0.02-0.20 mol/L). The methods used are cond. measurements, differential refractometry, static and dynamic light scattering, small-angle neutron scattering, and X-ray scattering. Crit. micelle concns. and the degree of dissocn. of the micelles are detd. by cond. measurements. The refractive index increment is given for each series as well as static and dynamic light-scattering intensities plotted as a function of the surfactant concn. From small-angle neutron-scattering expts. a detailed picture of the size and the geometry of the micelles could be obtained, whereas small-angle X-ray scattering allowed information about the thickness of the interfacial film to be inferred. A hypernetted chain calcn. with solvent plus ion-averaged screened Coulombic potentials combined with an ellipsoidal core/shell model permitted a simultaneous and coherent description of all scattering results