Studies On The Aggregation Behaviors Of Ionic Liquids Multicomponent Systems By Laser Light Scattering Technique

As one of the new kind of solvents in the aspects of chemical separation, material preparation and chemical reaction, ionic liquids (ILs) mixing with water, organic solvents or dissolving the macromolecules are inevitably encountered during their applications. Investigation on the aggregation behavior of ILs multicomponent systems is helpful to understand the interaction between ILs and other components, which is conducive to guide the establishment of mixing and separation techniques in ILs multi component systems.In this work, laser light scattering (LLS) was used to investigate the aggregation behaviors of ILs multicomponent systems, including ILs/water systems, ILs/organic solvent systems and ILs/polymer systems.Firstly, as an example of the aggregation behaviors of IL/water systems, a miscible ionic liquid 1-butyl-3-methyl-imidazoliumtetrafluoroborate ([C4mim][BF4]) was used to mix with water at the ratio ranging from 0wt%to 100wt%. LLS results indicated that besides the aggregates (micellar structure) with size about 1 nm, large-scale heterogeneous structures with several hundred nanometers were observed in the mixture. The heterogeneous structures in ILs aqueous solutions were similar to that in the mixtures of some organic solvents and water. The formation of heterogeneous structures was attributed to both the 3-D hydrogen-bond network of H2O and the local structure of ILs. The size and the property of the heterogeneous structures were closely related to the mixing orders, as well as the IL concentrations. Filtration by a 0.22μm filter was able to effectively remove the heterogeneous structures, while keeping the nanoscale aggregates intact. No change in conductivity was observed after filtration. Interestingly, the heterogeneous structures were reformed with the time. An acceleration in this reformation had been observed by decreasing temperature. The size of large-scale structure was found to be dependent on hydrogen basicity and length of alkyl chains of IL.Secondly, the aggregation behaviors of ILs with different polar solvents including dimethylsulfoxide (DMSO), acetonitrile, ethanol and toluene were investigated. Homogeneous mixture was formed when ILs mixed with the organic solvent with strong polarity such as DMSO while ILs was immiscible with toluene. The large-scale heterogeneous structures in ethanol or acetonitrile solutions were similar to that in ILs aqueous solution. The formation of large-scale heterogeneous structures was influenced by the ILs concentration, the mixing order, and the property of anions, as well as the length of alkyl chain. The weak interactions between organic solvent molecule and IL compared with anions and cations would lead to the heterogeneous structures formation. The organization pattern of ILs also had effect on the formation of heterogeneous structures. The different polarity results in the different properties of mixtures as in the case of water which is a strong polar solvent but mixed inhomogeneously in microscopic, due to the 3D hydro-bonding network.Finally, the aggregation behaviors of different polymers in 1-allyl-3-methylimidazolium chloride ([AMIM][Cl]),1-butyl-3-methyl imidazoliumformate ([BMIM][COOH]) and 1-ethyl-3-methylimidazo liumphosphite ([EMIM][(CH3O)HPO2]) were investigated. The charged polymers were easier to dissolved in ILs than neutral polymers. For polyelectrolyte carrying negative charge, such as DNA and polystyrene sulfonate (PSS), single chain conformation was observed for both polymers in ILs. While for neutral polymer, such as polyvinyl alcohol (PVA) and polysulfonamide (PSA), aggregation occurred. Cellulose in particular, was neutral polymer but dissolved well in [AMIM][Cl] resulting in single chain conformation. LLS and zeta potential analysis indicated that cellulose exhibited the feature of polyelectrolyte after dissolution in IL. The solubility of polymer in ILs was closely correlated with the interactions between anions and polymer, if the attractive forces between polymer and ILs gained by hydrogen bonding or polar interactions, cannot counterbalance the intractions between cation and anion, aggregation or precipitation of polymers would commonly occur.