Protic Ionic Liquids:  Solvents with Tunable Phase Behavior and Physicochemical Properties

Abstract

The phase behavior, including glass, devitrification, solid crystal melting, and liquid boiling transitions, and physicochemical properties, including density, refractive index, viscosity, conductivity, and air-liquid surface tension, of a series of 25 protic ionic liquids and protic fused salts are presented along with structure-property comparisons. The protic fused salts were mostly liquid at room temperature, and many exhibited a glass transition occurring at low temperatures between -114 and -44 degrees C, and high fragility, with many having low viscosities, down to as low as 17 mPa.s at 25 degrees C, and ionic conductivities up to 43.8 S/cm at 25 degrees C. These protic solvents are easily prepared through the stoichiometric combination of a primary amine and Brønsted acid. They have poor ionic behavior when compared to the far more studied aprotic ionic liquids. However, some of the other physicochemical properties possessed by these solvents are highly promising and it is anticipated that these, or analogous protic solvents, will find applications beyond those already identified for aprotic ionic liquids. This series of protic fused salts was employed to determine the effect of structural changes on the physicochemical properties, including the effect of hydroxyl groups, increasing alkyl chain lengths, branching, and the differences between inorganic and organic anions. It was found that simple structural modifications provide a mechanism to manipulate, over a wide range, the temperature at which phase transitions occur and to specifically tailor physicochemical properties for potential end-use applications.

Liquid Structure and the Ion-Ion Interactions of Ethylammonium Nitrate Ionic Liquid Studied by Large Angle X-Ray Scattering and Molecular Dynamics Simulations

“…In fact, it is in agreement with the estimation of 5.3Å based on the molar volume by Atkin and Warr [17].…”

“…From the viewpoint of physico-chemical properties of EAN as liquid and/or solvent, its conductivity [15][16][17][18]21], viscosity [18,19], density [18,20,21] and phase transitions [18,21] have been reported. In addition, the acid-base property was discussed in Ref.…”

The potential contribution of organic salts to new particle growth

“…That calculated value is similar to σ m for a non-aqueous organic mixture when calculated using a simple binary approach, σ m =X acid σ acid +X base σ base . Experimental data have shown that measured σ m values for ionic liquids are typically greater than that for non-ionic organic liquids but less than that for pure water (Greaves et al, 2006). For dilute aqueous organic salt solutions, the presence of amines and NH 3 tends to lower surface tension (Mmereki et al, 2000;Donaldson, 1990), while the presence of an inorganic acid and subsequent salt formation increases surface tension (Weissenborn, 1996).…”

Ionic Liquid Lubricant with Ammonium Salts for Magnetic Media

“…(Iglesias et al, 2004;Omotowa et al, 2004;Philips & Rabinski, 2004;Reich et al, 2003) Protic ionic liquids are a subset of ionic liquids formed by the stoichiometric (equimolar) combination of a Bronsted acid with a Bronsted base. (Greaves et al, 2006;Greaves & Drummond, 2008;Yoshizawa et al, 2003) Relevant investigations into the molecular interactions of carboxylic acids and amines were conducted by Kohler et al, and the complexes of acid and amine with the molecular ratio of 1:1 can be found. (Kohler, 1981a(Kohler, , 1981b) Ionic liquids, which possess an octadecyl ammonium salt with pentadecafluoro octanate, significantly reduce the friction compared to the corresponding amide and Z-DOL.…”