| Three series of ionic liquids were designed and prepared, their tribological properties were investigated. The following main conclusions are reached:1. Alkyl-4-[5-(alkylsulfanyl)-1,3,4-oxadiazol-2-yl] pyridinium tetrafluoroborate derivatives were synthesized and their thin films were prepared on silicon wafers by means of spin-coating. Under low load, the films sliding against AISI 52100 steel ball display good tribological properties. The wear life increases when the chain length decreases, which is closely related to the interaction between ILs and substrate surface. The wear and friction reduction performance of the films decreases when the load rises to a higher value. The best result is obtained for the film of 1-ethyl-4-[5-(ethylsulfanyl)-1,3,4-oxadiazol-2-yl] pyridinium tetrafluoroborate. The friction coefficient is about only 0.14 and the wear life is above 4000 sliding cycles under the load of 0.5 N. So this kind of ionic liquid can be potentially applied in ultra-thin film lubricant.2. A series of novel dicationic symmetrical and asymmetrical ionic liquids based on tributylalkyl phosphonium and alkylimidazolium were synthesized. The thermal stability was improved dramatically compared with their pure counterparts with single cation. The decomposition temperature of 1-(1-tributylphosphine-yl-hexyl)-3-methylimidazolium dihexafluorophosphate reached to 445℃, which is able to be used under high temperature conditions. Asymmetrical bis-substituted ILs with double hexafluorophosphate anions have the best tribological properties among the tested lubricants, i.e. PFPE, corresponding ILs with single cation, the counterparts with tetrafluoroborate anions and symmetrical bis-substituted ILs. The anti-wear life of the film increases with the increment of chain length and the friction coefficient decreases with increment of the loads. The best result is obtained for the film of asymmetrical 1-(1-tributylphosphine-yl-hexyl)-3-methylimidazolium dihexafluorophosphate: the friction coefficient is about only 0.12 and 0.1; the wear life is above 10000 and 3500 sliding cycles under the load of 0.5 N and 1.0 N, respectively. This kind of asymmetrical double ionic liquid can be potentially applied in ultra-thin film lubricant.3. A series of hexaalkylguanidinium salt ionic liquids (HGILs) were synthesized. The thermal stability, contact angles and tribological properties of their films were investigated. HGILs have high thermal stability. The lipophilic properties of HGILs largely depend on the structure of them, especially their anion. The tribological behaviors of HGILs were dependent on both the anions and the side-substituted alkyl chains. Under the same friction condition, the tribological performance of them increases with the increment of chain length. And the hexafluorophosphates are better when the cations are same. Compere with conventional ionic liquids B106 and PFPE, HGILs have better tribological properties.4. The tribological properties of the HGILs as the lubricants for a steel/steel sliding system were evaluated at room temperature and high temperature. It was found that the HGILs had better friction-reducing and anti-wear ability for the steel/steel sliding system. Especially, they had higher load-carrying capacity than ionic liquids B106, X-1P and PFPE.5. The tribological properties of the HGILs as the lubricants for a steel/aluminum sliding system, steel/copper sliding system, Si3N4/steel sliding system were evaluated at room temperature. It was found that the HGILs had better friction-reducing, anti-wear ability and load-carrying capacity than ionic liquids B106 and conventional lubricants. |
