Physicochemical Properties and Structures of Room-Temperature Ionic Liquids. 3. Variation of Cationic Structures

Abstract

A series of room-temperature ionic liquids (RTILs) were prepared with different cationic structures, 1-butyl-3-methylimidazolium ([bmim]), 1-butylpyridinium ([bpy]), N-butyl-N-methylpyrrolidinium, ([bmpro]), and N-butyl-N,N,N-trimethylammonium ([(n-C(4)H(9))(CH(3))(3)N]) combined with an anion, bis(trifluoromethane sulfonyl)imide ([(CF(3)SO(2))(2)N]), and the thermal property, density, self-diffusion coefficients of the cation and anion, viscosity, and ionic conductivity were measured over a wide temperature range. The self-diffusion coefficient, viscosity, ionic conductivity, and molar conductivity follow the Vogel-Fulcher-Tamman equation for temperature dependencies, and the best-fit parameters have been estimated, together with the linear fitting parameters for the density. The relative cationic and anionic self-diffusion coefficients for the RTILs, independently determined by the pulsed-field-gradient spin-echo NMR method, appear to be influenced by the shape of the cationic structure. A definite order of the summation of the cationic and anionic diffusion coefficients for the RTILs: [bmim][(CF(3)SO(2))(2)N] > [bpy][(CF(3)SO(2))(2)N] > [bmpro][(CF(3)SO(2))(2)N] > [(n-C(4)H(9))(CH(3))(3)N][(CF(3)SO(2))(2)N], has been observed, which coincides with the reverse order to the viscosity data. The ratio of molar conductivity obtained from the impedance measurements to that calculated by the ionic diffusivity using the Nernst-Einstein equation quantifies the active ions contributing to ionic conduction in the diffusion components and follows the order: [bmpro][(CF(3)SO(2))(2)N] > [(n-C(4)H(9))(CH(3))(3)N][(CF(3)SO(2))(2)N] > [bpy][(CF(3)SO(2))(2)N] > [bmim][(CF(3)SO(2))(2)N] at 30 degrees C.

Structural effects of polyethers and ionic liquids in their binary mixtures on lower critical solution temperature liquid-liquid phase separation

“…The ILs were synthesized by using the methods described in literature. [5][6][7] The details of preparation and characterization The water content in the ILs was measured using the Karl-Fischer titration method and was found to be o110 p.p.m.…”

“…In a previous study, we systematically investigated the effect of cationic and anionic structures on the basic physicochemical properties of ILs, such as viscosity, ionic conductivity and ionic diffusivity. [5][6][7] ILs have been successfully used in various fields; 1-4 for example, they have been applied to separation technology and catalysis, and they have been used as reaction media for organic syntheses and as electrolytes for electrochemical devices. Thus, ILs, a new class of solvents, are gradually replacing conventional organic solvents.…”

Design and Materialization of Ionic Liquids Based on an Understanding of Their Fundamental Properties

“…21 Surprisingly, ILs based on aromatic cations have lower ionicities than those based on aliphatic cations. 22 In addition, interestingly, ILs having different alkyl chain lengths on imidazolium cations exhibit lower ionicities with increasing alkyl chain length, as shown in Fig. 2.…”

“…17 ILs having high ionicity are categorized as "good ILs", whereas those having low ionicity are classed as "poor ILs". 17 By using PGSE-NMR, we systematically examined the ionicity of a variety of ILs [19][20][21][22][23][24][25] having different anions with the same cation, 19 different cations with the same anion, 22 and different alkyl chain length on imidazolium cation with the same anion. 20 As shown schematically in Fig.…”

“…21 Nevertheless, the ionicity of ILs having different cations with the same anion does change to some extent. 22 This behavior can be interpreted as arising from differences in the directionality of ion interactions. 21 When the interaction energies of an ion pair of an IL change significantly depending on relative position of the cation and anion, the directionality of interactions is considered to be large.…”