Novel Ionic Liquid Crystal Based On Trifluoromethylsulfonylimide Anions: Synthesis,characterization And Properties

Ionic liquid crystals are a kind of liquid-crystalline materials composed of only ionic species at ambient temperature. Ionic liquid crystals combine the advantages of ionic liquids(nonflammability, negligible vapor pressure, wide electrochemical window, etc.) and liquid crystals(anisotropic properties, etc), and thus can be used as anisotropic ion-conductive materials. Recently, fan-shaped ionic liquid crystals have attracted increasing attention as anisotropic ion-conductive materials, because they can form relatively stable one-dimensional conductive channels by self-assembly of columnar phases. In this thesis, a series of alkali metal salts based on fan-shaped trifluoromethylsulfonylimide anions, which show highly negative charge delocalization, were synthesized and characterized. The effects of the ionic structure on the liquid-crystalline properties were investigated. The main contents are as follows:First, 3,4,5-tris(alkoxy)benzoyl chloride was synthesized from ethyl gallate. Then, four kinds of potassium [3,4,5-tris(alkoxy)](trifluoromethylsulfonyl)imide were synthesized by nucleophilic substitution reaction of 3,4,5-tris(alkoxy)benzoyl chloride with CF3SO2 NK. The other eleven alkali metal salts(M= Li, Na, Rb and Cs) were prepared by the metathesis reaction of potassium salts.Second, the structures of the obtained salts both are characterized by 1H NMR, 13 C NMR, 19 F NMR and so on. The fundamental properties(phase transitions behaviors, liquid-crystalline properties, anisotropic ionic conductivities, etc.) of the obtained salts were investigated by differential scanning calorimetry(DSC), plarized optical microscope(POM) and so on, and the influence factors of the formation of liquid crystalline mesophase are discussed. The results show that seven ionic liquid crystals were observed to show columnar liquid-crystalline mesophase at room temperature. It is more likely to form crystalline mesophase phase when the cation is K+ or alkyl chain length is n-tetradecyl, and the most wide temperature range of liquid-crystalline mesophase is 119.2 °C. It is also found that addition of propylene carbonate solvent is not perferable for the formation of liquid crystalline mesophase. It is revealed by conductivity tests that aligned columnar crystals can form continuous one-dimensional ion conductive channels, which is advantageous for the migration of cations. The ion-conductivity of the ionic liquid crystals increases with increasing cation size, and decreases with increasing the length of alkyl size chain. The highest ion-conductivity is observed for C14 Cs, and its σ∥ can reach 9.44×10-6 S cm-1 at 100 °C.