The Effect Of Tethering Strategies Of Functional Groups And Co-solvents On The Bulk/Surface Structures Of Ionic Liquids

It is of great importance to study the bulk/surface structures and properties of ionic liquids (ILs), as they present a great impact on the transport efficiency of ILs in the applications involving the interface and heterogeneous systems. While the addition and the tethering strategies of functional groups may result in great changes of viscoisties, interfacial structures and properties of ILs, the related study is somewhat scarce. Meanwhile, the shortage of systematic research on the effect of the co-solvents on the surface structures and properties of ILs could limit the design of ILs and chemical process intensification. Therefore, in this dissertation, the effect of the tethering strategies of functional groups and the co-solvents on the microscopic properties, viscosities and air/liquid interfacial structures and properties has been studied by means of quantum chemical calculation, molecular dynamic simulation and the experiments.Two kinds of typical functionalized ILs were studied including amine-functionalized ILs and hydro xyl-fucntionalized ILs to investigate the effect of the tethering strategies of functional groups on the microscopic structures as well as macroscopic viscositites, and the relationship between the microscopic structures and viscosities was discussed. It was found that when the amine/hydroxyl group was tethered to the cation, the interaction between the cation and the anion was much stronger than that of the anion-tethered functionalized ILs, giving rise to a more compact microscopic structures and larger densities and viscosities.The structure and orientation of cation-and anion-tethered amine-functionalized ILs at the interface were investigated as a function of tethering sites and amine functionalization. When the-NH2group was tethered to the cation, strong interaction between the-NH2group and anions resulted in a compact interfacial structure, and thus no cation or anion enrichment existed in the interfacial region. However, for amino acid-based ILs with the-NH2group tethered to the anion, the interaction between the-NH2group and cations as well as between different anions was much weaker, contributing to the higher preference of the-NH2group in the outer layer of interface and the facility of the-NH2group to extend towards the vacuum or gas phase. Therefore, from the viewpoint of interfacial adsorption and transfer, the amine-functionalized ILs with an anion-tethering strategy was considered of great benefit for the CO2capture, especially when the-NH2group was on the terminal side of a relatively long alkyl chain.The surface tension of [bmim][BF4]-molecular solvent mixture was measured. It was found that depending on the kind of molecular solvent, the surface tension of the mixture could change with the [bmim][BF4] concentration in three different manners. The inter molecular interaction and surface structure of [bmim][BF4]-molecular solvent mixture were studied by molecular dynamic simulation. The hydrogen-bonding interaction of anion with ethanol was much stronger than that with acetonitrile, which probably granted the anion easier access to locate at the surface layer of the mixture, and then made the elevation of [bmim][BF4]-acetonitrile mixture more remarkable than that of [bmim][BF4]-ethanol mixture.