Thermodynamic, transport and electrochemical properties of room temperature ionic liquids

Room temperature ionic liquids (RTILs) are organic salts having melting points below 100°C. RTILs generally consist of a bulky cation and an inorganic anion. The large cation size allows for delocalization and screening of charges, resulting in a reduction in the lattice energy and thereby the melting point or glass transition temperature. RTILs exhibit many interesting properties, which make them suitable for several applications such as chemical synthesis, catalysis, electrochemical applications and gas separations. This thesis work focused on experimental measurements of thermodynamic, transport and electrochemical properties of RTILs and understanding the effects of RTIL structure on these properties.;Thermodynamic and transport characteristics of carbon dioxide in several commercially available RTILs were examined at temperatures between 10°C to 40°C. CO2 solubility was found to be higher in bis(trifluoromethylsulfonyl)imide [Tf2N] RTILs than in RTILs with other anions. Regular solution theory (RST) was applied to interpret and predict the CO2 solubilities. Eyring's reaction rate theory was successfully applied to estimate RTIL solubility parameters from the activation energy of viscosity. The solubility of CO 2 in RTILs was found to be inversely proportional to the RTIL solubility parameter.;CO2 diffusivities in RTILs were on the order of 10 -6 cm2/s. These values are an order of magnitude lower than diffusion coefficients reported for CO2 in conventional organic solvents, which can be attributed to the high viscosity of RTILs. CO 2 diffusivity was found to be proportional to the solvent viscosity with a power of -0.46. Correlations relating CO2 diffusivity to RTIL properties were successfully developed.;Novel RTILs were synthesized with different functional groups such as alkyl chains, benzyl, propionate and benzyl acetate. Density, viscosity and CO2 solubility and diffusivity for these RTILs were measured at 25°C. The density values ranged from 1.2 to 1.5 g/cm3. An increase in alkyl chain length resulted in an increase in viscosity. The viscosity of 1-alky1-3-butylimidazolium bis(trifluoromethylsulfonyl)imide [RbimTf2N1 based RTILs was affected dramatically by the choice of the functional group R. CO2 solubility was found to depend on the total number of carbons but was generally independent of the distribution of alkyl chains on the imidazolium cation.;Electrochemical windows and interfacial behavior for 1-buty1-3-methylinidazolium tetrafluoroborate and 1-buty1-2,3-dimethylinidazolium tetrafluoroborate RTILs were investigated with different electrode materials such as glassy carbon, gold, platinum and tantalum. Among the electrode materials studied, tantalum exhibited the largest electrochemical window for both RTILs. This may be explained by the robustness of tantalum towards the constituents of the RTILs. The observed electrochemical windows were related to the work function of the electrode material. The interfacial behavior of RTIL was described with an equivalent circuit consisting of a double layer and an adsorption branch.;A nano-composite material was fabricated by polymerization of 1-viny1-3-butylimidazolium tetrafluoroborate and carbon nanotubes. This material may be a potential electrode material for supercapacitor applications.