【作者】 陈烨；

【导师】 王华平；

【作者基本信息】 东华大学 ， 材料学， 2011， 博士

【摘要】 离子液体作为化工分离、材料制备、化学反应等的新兴溶剂体系,其应用过程中都不可避免地遇到与水、有机溶剂、大分子等的混合与分离,研究离子液体多元体系的聚集行为,可以充分说明离子液体多元体系中微观相形态、结构及其随动力学条件的变化情况,有利于指导建立离子液体多元体系混合与分离的技术方法。本论文主要采用激光光散射技术系统研究了离子液体多元体系的聚集行为,包括离子液体/水体系,离子液体/有机溶剂体系以及离子液体/高分子体系,探讨了离子液体与不同分子之间的相互作用机理,为离子液体的实际应用提供理论支撑。首先,为了说明离子液体与水分子的相互作用,我们主要研究了离子液体/水体系的聚集行为。选取1-丁基-3-甲基咪唑四氟硼酸盐[C4mim][BF4]为模型分子,研究了O-100wt%全浓度范围内的聚集行为,发现体系中除了有1nm左右的胶束峰外,还存在尺寸在几百纳米左右的异质结构峰。这种离子液体水溶液中出现的异质结构与在一些有机溶剂与水的混合体系中出现的异质结构相似。离子液体本身阴阳离子间的强相互作用、烷基链的疏水性以及水的三维氢键结构是形成这种异质结构的根本原因。阴离子氢键碱度越大的离子液体在水中形成的异质结构尺寸越小,而烷基链越长的离子液体在水中越不稳定,越容易形成异质结构甚至出现相分离。离子液体的浓度以及滴加的次序对异质结构的尺寸和形貌有很大影响。用0.22μm的膜过滤能有效去除异质结构,而胶束能被完整地保留下来,但随时间推移异质结构又会在体系中重新形成。同时过滤前后体系的离子数目没有改变,说明异质结构的存在并不影响体系的物化性质。另外,降低温度有利于异质结构的形成。其次,为了说明有机分子的极性对其与离子液体相互作用的影响,我们系统研究了二甲基亚砜(DMSO)、乙腈、乙醇、甲苯等极性完全不同的溶剂分子与离子液体混合后的聚集行为。结果表明强极性的DMSO能与各种离子液体均匀混合；而极性最弱的甲苯与离子液体不能互溶,混合后发生宏观相分离。在乙腈、乙醇等混合体系中出现了尺寸较大的异质结构,异质结构的性质与离子液体水溶液中出现的异质结构的性质相似。浓度、混合次序、阴离子的性质、阳离子烷基链的长度对异质结构的形成都有影响。可以推测异质结构的形成与离子液体本身的性质以及溶剂分子的极性有关。最后,为了说明离子液体对高分子聚集形态的影响,我们系统研究了带电性质不同的高分子在1-烯丙基-3-甲基咪唑氯化盐[AMIM][Cl],1-丁基-3-甲基咪唑甲酸盐[BMIM][COOH],1-乙基-3-甲基咪唑甲基磷酸酯盐[EMIM][(CH3O)HPO2]等离子液体中的聚集行为。结果发现,与中性高分子相比,带电的高分子与离子液体的相溶性更好。如带负电的脱氧核糖核酸DNA、聚苯乙烯磺酸钠PSS都以单分子的形式分散在离子液体中；而电中性的聚乙烯醇PVA、聚芳砜酰胺PSA在离子液体中都会发生一定程度的聚集。纤维素在离子液体中的溶解表现出独特性。作为中性高分子的纤维素溶于[AMIM][C1]后,链上的羟基因吸附Cl-而使纤维素链表现出类似聚电解质的性质。离子液体溶解高分子的能力与阴离子和高分子的相互作用能力有很大关系,当高分子和离子液体中形成的氢键或极性力的相互吸引作用不能克服阴阳离子本身的吸引作用时,则容易发生大分子聚集甚至产生沉淀导致相分离。更多还原

【Abstract】 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.更多还原