Studies On The Applications And Properties Of Surfactant-like Imidazolium Ionic Liquids In Microemulsions

Ionic liquids (ILs) are organic salts with lower melting points which are made of organic cations and inorganic or organic anions at or near room temperature. The ILs are the perfect substitutes of conventional organic solvents owing to their high thermal stability, high conductivity, wide electrochemical window, wide liquid range, negligible vapor pressure and special solubility. The studies of ILs accords with the development of green chemistry, and have received great attention by the researchers in the world in recent years.This thesis studies mainly about the physical chemical properties of surfactant-like imidazolium ionic liquids, the phase behavior and solubilization of the microemulsion formed by the surfactant-like ionic liquids. It was composed with four chapters. Chapter I, Introduction. Chapter II, Synthesis and adsorption property of the surfactant-like ionic liquids. Chapter III, Studies on the phase behavior and solubilization of the microemulsion formed by surfactant-like ionic liquids. Chapter IV, Studies on the phase behavior and solubilization of the microemulsion formed by the composite anion and cation surfactants.Chapter I. IntroductionThe definition, history, classification, synthesis, and properties of ionic liquids (ILs) were introduced in this chapter. The applications of ILs in organic synthesis, electrochemistry, separation and extraction processing, biocatalysis, and nano-materials preparation were also reviewed. The research progress on the formation of ordered molecular assembly in imidazolium ILs, such as liquid crystal, micelle, vesicle, microemulsion was reviewed. ILs can act as solvents, co-solvents, or surfactants to form liquid crystals. They also can be substituted for polar, apolar, or surfactant components in microemulsion to prepare various microemulsion systems ILs-in-oil (ILs/O), oil-in-ILs (O/ILs) and bicontinuous (B. C.).Chapter II. Synthesis and adsorption of the surfactant-like ionic liquidsThree kinds of surfactant-like ionic liquids: 1-alkyl-3-methylimidazolium bromide (C12mimBr, C14mimBr and C16mimBr), were synthesized and further purified in this chapter. All these compounds were characterized by UV spectra, and the melting points were determined. At the same time, the adsorption equilibriums of CnmimBr solutions were studied, the critical micelle concentration (cmc), surface tension at cmc were obtained, and then, the saturation adsorption capacity and the average area per molecule were calculated. The purity of all synthetic ionic liquids was examined, and no surface tension minimum was found in the surface tension curve.Chapter III. Studies on the phase behavior and solubilization of the microemulsion formed by surfactant-like ionic liquidsIn this chapter, the phase behavior and the solubilization of the quaternary microemulsion system surfactant-like ionic liquids/alcohol/alkane/brine were studied withε-β-fish-like phase diagram. The following conclusions were obtained.(1) The solubilization order of the surfactant-like ionic liquids is C16mimBr> C14mimBr>C12mimBr. With the increase in the aliphatic chain length of the surfactant-like ionic liquids, the solubilization power of the microemulsion increases.(2) It is propitious to form microemulsion with the decrease of the aliphatic carbon chain length of oils. The order of the solubilization power is n-hexane>n-heptane> n-octane> n-decane.(3) The longer the aliphatic carbon chain of the cosurfactant, the larger the solubilization power of the microemulsion.(4) The change of the temperature does not influence the phase behavior and the solubilization power of the microemulsion formed by CnmimBr.(5) The increase in the concentration of the inorganic salt could enhance obviously the solubilization power of the microemulsion.(6) The component mainly influencing theε-β-fish-like phase diagram and the solubilization power in inorganic salts is the anti-ion, namely anion such as Cl- for the CnmimBr microemulsion system. Fix the Cl- concentration, and change the kinds and charge of cations, the phase behavior and solubilization of the microemulsion was little changed. If the concentration of the inorganic salt was fixed, and the kinds of the anions were changed, the solubilization power of the microemulsion will increase with the decrease of the hydrated radius of the anions.Chapter IV. Studies on the phase behavior and solubilization of the microemulsion formed by composite anion and cation surfactantsThe phase behavior and solubilization power of the microemulsion formed by the composite anionic and cationic surfactants (AS/C12mimBr, SDS/C12mimBr) were studied by theε-β-fish-like phase diagram.(1) Synergistic effect was found between anionic and cationic surfactants in the formation of microemulsion. If anionic and cationic surfactants were mixed at non-equal mole ratio in the given mole ratio range, the solubilization power of the microemulsion increases, and no deposition appears.(2) The charge at the surface of the microemulsion droplets is mainly determined by the excessive surfactant in the mixed surfactant system. The higher the concentration and the smaller the hydrated radius of the anti-ions are, the stronger the ability for the anti-ions to compel the double electric layer is, and the larger the solubilization power of the microemulsion system is.