Interfacial Tension and Electrocapillary Measurements of the Room Temperature Ionic Liquid/Aqueous Interface

Abstract

The surface and aqueous interfacial tensions for a series of water-immiscible room-temperature ionic liquids (RTILs) have been measured. The RTILs used in this study were based on 1-alkyl-3-methylimidazolium cations (Cnmim, n=6, 8, 10, and 12) and bis(perfluoromethylsulfonyl)imide (BMSI) and bis(perfluoroethylsulfonyl)imide (BETI) anions. It was found that the surface tensions of the RTILs increased with an increasing cation chain length similar to the behavior of n-alkanes. Interfacial tensions of the RTILs with aqueous solutions, however, were found to decrease with the cation chain length, which has been attributed to the increased surface activity of the longer chain cations. We have also demonstrated the first use of electrocapillary measurements to study the polarizable RTIL/aqueous interfaces. From the electrocapillary data, the potential of zero charge (PZC) for these RTIL/aqueous interfaces was determined, as well as the relative surface excess charge and capacitance. The PZC was found to be dependent upon the structure of the anions and cations with PZC values ranging from -357 mV for C6mimBETI and -161 mV for C10mimBMSI. The electrocapillary results also show that the cations of the RTIL are becoming increasingly surface-active as the alkyl chain on the cation is lengthened, thereby modulating the interfacial potential.

Electrovariable gold nanoparticle films at liquid–liquid interfaces: from redox electrocatalysis to Marangoni-shutters

“…40,41 The resistance is independent of D w o f, whereas an increase in RC at positive and negative potential differences reects the increase of the capacitance with the polarisation of the interface. The RC time constant is a property of the interface and is not directly involved in the redox reactions; thus, the discussion will be limited to the other parameters.…”

Surface tension measurements of imidazolium-based ionic liquids at liquid–vapor equilibrium

“…Methods for the determination of equilibrium thermodynamic and transport properties of ILs have been investigated both experimentally and theoretically [1][2][3]. Enthalpies of vaporization [4,5], viscosities [6], thermal conductivity [7], aggregation behavior [8], and liquid-liquid interfacial tension [9] of imidazolium-based ILs have been investigated widely. These ILs are also used in multiphase homogeneous catalysis [10].…”

Potential dependent structure of an ionic liquid at ionic liquid/water interface probed by x-ray reflectivity measurements

“…[41][42][43] Local ion concentrations in EDLs are generally different from those in bulk. Electrocapillarity (dependence of surface tension on the phase-boundary potential) studies [44][45][46][47][48][49] at the IL|W interface confirmed fundamental features of the EDL such as surface excess and specific and non-specific adsorption of IL ions at the IL|W interface. These studies suggested that the EDL at the IL|W interface is not far from the view of the Gouy-Chapman-Stern model [50][51][52] that has long been the theoretical basis for EDL at the electrochemical interfaces such as electrode|electrolyte solution interface.…”