| The bulk and interfacial properties of a series of water immiscible room temperature ionic liquids (RTILs) are reported. The RTILs were made by pairing 1-n-alkyl-3-methylimiadazolium cations (Cnmim, n = 6, 8, 10 and 12) with bis(perfluoroalkylsulfonyl)imide (BMSI and BETI) anions. These new RTIL materials were synthesized and characterized with respect to their bulk physical properties including: density, miscibility with water, viscosity, and conductivity. All of the properties examined were found to be highly dependent on the alkyl chain length of the cation. The properties of the RTILs were also found to be dependent on the amount of water present in the RTIL in both ambient and water-equilibrated RTILs. Because they are purely ionic compounds, RTILs are relatively conductive, upwards of 2.9 mS/cm for C6mimBMSI, and are well suited to electrochemical systems. The RTILs were also found to be electrochemically inert over a range of ∼4-5 V.; In addition to the bulk physical properties of the RTILs, the properties of these RTILs at interfaces were also examined. Ion transfer across the polarizable RTIL/aqueous interface was examined electrochemically. The RTILs have polarizable potential windows as large as 137 mV for C12mimBETI. It was found that the free energy of transfer of the RTIL cations increased by ∼3 kJ/mol per CH2 group as the alkyl chain was lengthened. Electrocapillary studies of the RTIL/aqueous interface revealed the potential of zero charge (PZC), the potential-dependent interfacial excess charge and the capacitance of the RTIL/aqueous systems. It was found that the cations of the RTIL became increasingly surface active as the alkyl chain was lengthened.; RTIL interfaces were also studied using nonlinear optical spectroscopy, namely second harmonic generation (SHG) and sum frequency vibrational spectroscopy (SFVS). SHG was used to study the adsorption of ions at the RTIL/aqueous electrochemical interface. The cations of the RTIL and water in the RTIL were found to be highly structured at the RTIL/silica interface by using SFVS. The alkyl chains of the cations were determined to be nearly normal to the interface for all of the RTILs.; Overall these studies have shed new light on to the structure and properties of a novel class of water-immiscible RTILs. This fundamental information is integral to understanding how the structure of the RTILs influence their properties and behavior in various systems. |
