Studies On The Microstructures And The Properties Of Ionic Liquids At The Solid/Liquid Interface

Room-temperature ionic liquids (ILs) are a special class of liquids solely composed of cations and anions. Even though bulk properties of ionic liquids are still under intense investigations, the study of the microstructure of ionic liquids in low dimensional system is an exciting challenge and has attracted great attention due to their relevance in catalytic processes, separation, lubricants, electrochemistry, biomass conversion, etc. Herein, the microstructures and the melting points variation of ILs immobilized on the outer surface of MWCNTs are presented.The major work and results for this dissertation are listed as follows:(1) Two imidazolium-based ionic liquids (ILs), i.e.[Bnmim][BF4] and [Bmim][AuCl4], were adsorbed on the outer surface of multi-walled carbon nanotubes (MWCNTs) via physical method. In order to understand the molecular packing of ILs immobilized on the MWCNTs surface, the composite samples with different weight ratios of ILs were characterized by using X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), respectively. It was found that the rings of imidazolium cations of ILs are nearly parallel to the MWCNTs surface, and the packing orientation is determined by the substitute groups on the imidazolium-ring. Both the anions ([BF4]-and [AuCl4]-) occupy an adjacent area with imidazolium cation to form neutral surface layer. Furthermore, for the immobilized ILs, the melting point (Tm) of [Bmim][AuCl4] rises slightly, while the Tm of [Bnmim][BF4] gets depressed. The molecular rearrangement and the melting points change of the immobilized ILs result from the complex interfacial interactions between the ILs and the MWCNTs surface.(2) It was found that some long-alkly-chain functionalized ILs could soublize carbon nanotubes in solvent, the role of the ILs similar with that of surfactants. By choosing [C12mim][Br] as a protype ILs, we studied the molecular packing of the [C12mim][Br] on the outer surface of MWCNTs by XPS. It was found that the rings of imidazolium cations of ILs are nearly parallel to the MWCNTs surface, the carbon chains prefer to perpendicular to the horizontal plane of the imidazolium ring and MWCNTs surface. For distinguishing the function group is imidazolium ring, carbon chain or imidazolium cation. The ionic liquids [Cnmim][Br](n=2,4,6,8,10) with different carbon chain length were adsorbed on the MWCNTs surface. We found that with the increase of alkyl chain length, the tilt angle between carbon chain and MWCNTs surface becomes smaller and smaller. And for [C12mim][Br]/MWCNTs, the function group is imidazolium cation. In addition, the melting point of the immobilized ILs is different from the ILs in bulk, the melting points variation is dependent with the structure of ILs.