Investigation On The Physical Properties Of Ionic Liquids

In this paper, two methods (macroscopic thermodynamics and spectroscopy) were used to explore the chelate-based ILs and the protic ILs, respectively. The former has received widespread attention and regarded as a potential new material for its dual char-acteristic of ILs and metal. As later is formed by the proton transfer, ionicity has also been a hot research topic. This study tried to explore the physical characteristics and provides experimental support for the design of ILs.In view of the first kind of ILs, densities, viscosities and conductivities of four chelate-based ILs [Li(DOBA)][Tf2N],[Li(HDA)][Tf2N],[Li(DEA)][Tf2N], and [Li(EA)][Tf2N], and their binary mixtures with water were determined. The excess mo-lar volume (VE) and viscosity deviations (Δη) were calculated by density and viscosity and fitted by a Redlich-Kister equation. Physical properties of [Li(DEA)][Tf2N] were calculated by empirical equations over a temperature range from313.15to333.15K in order to study the effect of temperature change. The excess molar volumes show nega-tive deviation from ideal solution and two different behaviors between water-rich and IL-rich regions. Most viscosity deviations show negative values, except for the binary mixture of [Li(DOBA)][Tf2N]/water. The effect of chelate state on the above physico-chemical properties has been discussed. Furthermore, the Walden rule was used to eval-uate the relationship of molar conductivity and dynamic viscosity of these ILs, which indicates all of them have good ionicity.In view of the second kind of ILs, the ionicity value, which is a key property of protic ILs, was obtained by the attenuated total reflection Fourier transform infrared spectroscopy (ATR-IR) and nuclear magnetic resonance (NMR) respectively for a pro-tic ILs:n-propylammonium acetate. Spectroscopic approaches were for the first time successfully applied in quantitatively measuring ionicity of protic ILs. The method of potentiometric titration is found not suitable for such kind of ILs as the ApKa of the compositing acid and base is relatively small. In the IR spectrum, molecular species can be directly observed from the range1200-1800cm"1, and the ratio of ionic and molec-ular species can be quantitatively calculated by the area of characteristic absorption peaks calibrated by NaAc/HAc solutions. The results show that93%components in n-propylammonium acetate are ionic species. NMR method was also introduced to test and verify the result and the calculation results fit well with IR approach. It indicates that for a protic ILs whose ApKa value is relatively small. Spectroscopic methods such as IR. and NMR could be applied to determine the ionicity.