| The theoretical and applied research of microemulsion has been received much attention in recent years. Due to the properties of high thermal stability, small size, and uniform distribution of microemulsion, it has been widely used to organic synthesis, extraction separation, tertiary oil recovery, biomedical engineering, etc. Investigations on microemulsion systems with special function have broad prospects. Compared with traditional organic solvent, ionic liquids (ILs) are a class of novel medium which have excellent physical and chemical properties, such as less volatile, wide electrochemical window, high thermal stability and wide liquid range. Based on the unique designability, ILs can be easily modulated by changing the composition of cations and anions and/or choosing suitable cations substituents to satisfy different research requirements. Ionic liquid microemulsion combining ILs and microemulsion has developed rapidly and become a new hot research area. Utilizing functionalized ionic liquids to build novel microemulsion systems can endow microemulsion systems with the characteristics of designability and high stability and enlarge the application range of microemulsion, which has important theoretical significance and practical application value.In this dissertation, our aims is to study the physicochemical properties of functionalized microemulsion systems which were structured by low critical solution temperature (LCST) thermosensitive ionic liquids. There are three main parts in this dissertation as follows:The first chapter mainly summarized the research background and significance of this dissertation. First, we introduced the concept of ionic liquid and microemulsion, and then we discoursed the research status of the microemulsion system involved in ionic liquids at home and abroad, which provided a solid theoretical foundation for this dissertation. Finally we present the conception of low critical solution temperature (LCST) thermosensitive ionic liquids and their developing tendency as well as the topic basis. The second chapter mainly studied the aggregation behavior of surfactant-free similar microemulsion system consisting of LCST thermosensitive ionic liquids--tetra-n-butyl phosphonium trifluoroacetic salt ([P4444][CF3COO]) and water. First, the phase behavior of [P4444][CF3COO]-H2O binary system was investigated and the phase transition temperatures of the systems with different [P4444HCF3COO] contents were determined. Then [P4444][CF3COO]/H2O (([P4444][CF3COO]content,40wt%) microemulsion system was selected as the study target, the properties and morphology characterization were examined in detail. Dynamic light scattering (DLS) and freeze-fracture transmission electron microscopy (FF-TEM) confirmed the presence of aggregates in [P4444][]CF3COO]/H2O ([P4444][CF3COO]content,40wt%) system and found that the size of the aggregates could be reversible controlled by temperature. What’s more, we noticed that [P4444][CF3COO]/H2O (40wt%) binary system displayed swelling behaviors analogous to traditional microemulsion, and possessed the ability to dissolve nonpolar substances. We confirmed the mechanism of aggregates formation is salt-inducible interaction by detecting the changes of average particle size of microemulsion droplets with the addition of NaCl and studying the interaction between [P4444][CF3COO] and water molecules by Nuclear magnetic resonance one-dimensional hydrogen spectrum (*H NMR). In practice, phase transformation between [P4444][CF3COO] and H2O results in the formation of aggregates. That is a middle transformation process between isotropic uniform system and anisotropic layered system.The third chapter investigated the microscopic property of ionic liquid-in-water (IL/W) microemulsion system formed by [P4444][CF3COO]/Triton X-100/H2O ternary systems. Initially based on the results of conductometric method and dynamic light scattering (DLS), the IL/W microemulsion is formed in the [P4444][CF3COO]/Triton X-100/H2O mixture was confirmed when the temperature exceeded the LCST. The average particle size of IL/W microemulsion droplets was found to increase with increase in temperature or R value (the molar ratio of [P4444][CF3COO] and Triton X-100). This is analogous with the swelling behavior of traditional microemulsion. Meanwhile the average particle size of IL/W microemulsion droplets enlarged with the increasing temperature, which is verified by both Small Angle X-ray scattering (SAXS) and dynamic light scattering (DLS) techniques. The experiments on the stability of carbon nanotubes in [P4444][CF3COO]/Triton X-100/H2O microemulsion systems further demonstrated the formation mechanism of IL/W microemulsion. When the temperature was raised, the number of free cation and anion dispersed in the aqueous solution would reduce, and more and more [P4444][CF3COO] molecules would access to the hydrophobic core of IL/W microemulsion, as a result of larger size of the microemulsion droplets. |
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