Study On The Surface And Interface Properties Of Room Temperature Ionic Liquids

Room Temperature Ionic Liquids (RTILs) which composed of pure ions, is a kind of new liquid materials at room temperature. These kinds of materials can be widely used in catalytic and electrochemical field, because of their unique physicochemical properties, such as extremely low vapor pressure, nontoxicity, wide liquid phase range, high thermal stabilities, highly ionic conductivities and the ability to dissolve many kinds of substances. One of most important application of RTILs is in the electronic devices, such as organic field effect transistors, super-capacitors, batteries and dye-sensitized solar cells etc. In all these applications, the surface and interface properties, which controlled the energy exchange, charge transfer and redox process, of RTILs play a certain role. In a word, it's fundamental to understand the surface and interface properties of RTILs.To get the information of RTILs surface properties, X-Ray photoelectron spectroscopy (XPS) was used to detect the chemical states of surface elements of RTILs. The quatitative analysis of RTILs surface composition shows the enrichment of carbon and fluorine elements, indicating both cation and anion are present at the surface, and the more cation alkyl chains distribution at the RTILs surface.Impedance spectroscopy (IS) was used to analyze the electrical frequency response of RTIL between flat electrodes. The device act as a capacitor when the input signal is at low frequency, while, it act as a resistor when the input signal is at high frequency. Helmholtz model was used to analyze the interface capacitance and found the ionic liquid cation was tilted to the electrodes. An easy model of a resistor and a capacitor in series or parallel is suitable to simplify the complicate interface equivalent circuit model due to the Bode plots. The contact angle of RTILs-electrode systerm can be decreased by introducing gold nano particles on electrode surface.Gold nano particles, gold clusters and gold-ionic liquids complex (Au-RTILs) were synthesized by sputtering gold onto surface of RTILs in vacuum. The scanning electron imaging (SEM) show the diameter of circle gold nano particles ranging from 26nm to 300nm, and formed dendritic structure. The binding energy of gold particles shifted to higher energy due to suface and quantum size effect. Gold clusters stabilized in RTILs lose some of their electrons, inducing the increased intensity of near edge X-Ray absorption fine structures (NEXAFS) Au L₃ whiteline and broden the resonace style.Special attention was payed to the electron structure and optical properties of gold-ionic liquids complexes. The binding energy of Au 4f for the complexes shifted to higher energy about 1.5 eV and nitrogen atoms of the cation accepted the electrons. NEXAFS of Au L₃ data show Au atoms transferred some of their electrons to the nitrogen atoms, inducing increased intense of whiteline and broden the resonace style. Extend X-Ray absorption fine structures (EXAFS) of Au L₃ data show that the length of Au-N bond is about 1.6?. The quantum yield of Au-RTILs complex reaches to 25%, and the emission energy and intensity depends on excitation energy.Platinum-ionic liquids complex (Pt-RTILs) was also synthesized by sputtering platinum onto surface of RTILs in vacuum. The Pt atoms were positive charged due to XPS data. NEXAFS of Pt L₃ data show Pt atom transferred some of it's electron to the surrounding, inducing increased intense of whiteline and broden the resonace style. The quantum yield of Pt-RTILs is lower than that of Au-RTILs complex.In a word, noble metals interacted with the RTILs cation. The properties of formed metal-RTILs related to cation and independed of anion.Sumarried our reseach data, indicating the surface and interface properties of RTILs which have many unique properties, are different from others liquid materials. Our reseach enhanced the understanding of RTILs properties and provide useful information for RTILs application.