| Due to the extraordinary properties of ionic liquids (ILs), the self-assembled aggregates based on ILs have attracted a lot of attentions during the last ten years. As a class of tailor-made materials, the physicochemical properties of ILs can be easily modulated by choosing suitable cations and anions and/or changing the N-alkyl substituents. Due to the unique designability, it will be expected to achieve the controllability of the structures and properties of IL-based ordered molecular aggregates by tailoring the structures of ILs. Moreover, one can also realize the functionalization of traditional ordered molecular aggregates by the incorporation of functional ILs.In this dissertation, imidazolium ILs with different structures and special functional groups were designed and synthesized, and the self-assembled aggregates based on these ILs were studied systematically. Our aim is to establish the dependence of aggregation behavior of imidazolium ILs on their structures, and the unique role of functional groups on ILs in their self-assembled aggregates. Our research is helpful to achieve the controllability and functionalization of IL-based ordered molecular aggregates. There are four main experimental studies in this dissertation as follows:1. The aggregation behavior of a series of long chain N-aryl imidazolium ILs1-(2,4,6-trimethylphenyl)-3-alkylimidazolium bromide ([Cnpim]Br(n=10,12,14)), in aqueous solution and room temperature ionic liquid [bmim][BF4] was explored systematically. The effect of the incorporated N-aryl moiety in head group on the micellization was investigated compared with1-alky1-3-methylimidazolium salts [Cnmim]Br. Following results were obtained.①In aqueous solution, the CMC obtained for [Cnpim]Br is much lower than that for [Cnmim]Br, suggesting that the incorporation of the2,4,6-trimethylphenyl group facilitates the micelle formation. Although the incorporated2,4,6-trimethylphenyl groups would bring steric hindrance, the arrangment of [Cnpim]Br is slightly closer than [Cnmim]Br. The prominently enhanced π-π interactions originated from adjacent2,4,6-trimethylphenyl groups cause the [Cnpim]Br molecules arranging densely at the air-water interface. The thermodynamic results reveal that the micelle formation for [Cnpim]Br (n=10,12,14) is enthalpy-driven throughout the whole temperature range (25-45℃). The analysis of1H NMR and2D NOESY spectra indicates that the2,4,6-trimethylphenyl group slightly bends into the hydrophobie region when micelles are formed. These N-aryl imidazolium ILs present strong and stable fluorescence properties, which can extend their applications in optical fields.②In [bmim][BF4], a relatively lower CMC value was observed for [Cnpim]Br than that for [Cnmim]Br, suggesting that the incorporation of the2,4,6-trimethylphenyl group is also benefit to the micelle formation in [bmim][BF4]. The π-π interactions derived from adjacent2,4,6-trimethylphenyl groups cause the [Cnpim]Br molecules arranging densely in micelles and then induce much smaller micellar size of [C14pim]Br compared with [C14mim]Br. The CMC value for [Cnpim]Br in [bmim][BF4] is much higher than that in water, indicating the solvophobic effect in IL is weaker than hydrophobie interaction in water. Thermodynamie analysis reveals that the micelle formation process is enthalpy-driven in the investigated temperature range, similar to that in water. Due to the incorporation of aryl group, strong fluorescence properties are presented by the novel N-aryl imidazolium ILs. The current work provides a novel IL system with potential application in the field of photochemistry.2. In this part, a novel surface active IL with an aromatic anion,1-dodecyl-3-methylimidazolium β-naphthalene sulfonate ([C12mim][Nsa]) was synthesized. The self-assembly behavior of [C12mim][Nsa] was systematically investigated through POM, SAXS, FF-TEM,1H NMR, and rheological measurements. With increasing concentration, the phase transition from micelles to vesicles and then to lamellar liquid crystals occured. For the typical sample of vesicle phase at3wt%, the multilamellar and unilamellar vesicles with diameters from about100nm to500nm were observed by FF-TEM. When the concentration of [C12mim][Nsa] is increased to5wt%, multilamellar vesicles with large diameters of about2um exist mainly, coexisted with several multilocular vesicle.In addition, there is a transition from Lα phase to micelle phase with increasing temperatures. SAXS results show that the bilayers are compressed with increasing amount of [C12mim][Nsa], and the molecular arrangement in the hydrophobic region and the thickness of the hydrophobic layer become relatively stable as lamellar liquid crystals are formed. Analysis of SAXS and1H NMR results proves that β-naphthalene sulfonate anion is strongly binding to the imidazolium cation under the cooperative effect of electrostatic attraction, hydrophobic interaction, and π-π stacking interaction. The electrostatic repulsion between the imidazolium cations is then effectively screened, and the critical packing parameter is increased significantly. As a result, phase transition from micelles to vesicles and then to lamellar liquid crystals is induced.3. The aggregation behavior of surface active imidazolium ILs with different alkyl chain length, cations, and counterions, was investigated through surface tension measurements and1H NMR spectroscopy. Surface tension results show that surface properties and micellization behavior of surface active ILs in EAN are significantly affected by the structure of the cations, the basicity of counter-ions, and the hydrophobicity of alkyl chains. The CMC for [Cnmim]Br was detected only when n≥8and the CMC values decrease with the elongation of the hydrocarbon chain, indicating that solvophobic effect plays an important role in micelle formation in EAN. The CMC values are decreased when replacing Br-with [BF4]-.1H NMR results show that hydrogen bonding forms between the proton at C-2on the imidazolium ring and [NO3]-, and thus the hydrogen bonding between [CH3CH2NH3]+and [NO3]-is weakened. The interactions between the aromatic hydrogens and [NO3]-become weaker with increasing basicity of counterions and hydrophobicity of the side-chains bonded to the imidizolium cation. The conformation of the alkyl chain may be changed partially from trans to gauche conformations during micelle formation. Solvophobic effect may exist between the solvophobic portion of the EAN molecules and the hydrophobic parts of the surfactant molecules. The ethylammonium cations were found to have the tendency to penetrate into the micelles due to this solvophobic interaction.4. The effects of a series of functionalized imidazolium ionic liquids (ILs),1-carboxylmethyl-3-methylimidazolium chloride ([MimCM]Cl),1-(2-aminoethyl)-3-methylimidazolium chloride ([MimAE]Cl),1-(2-hydroxylethyl)-3-methylimidazolium chloride ([MimHE]Cl), and1-ethyl-3-methylimidazolium chloride ([Emim]C1) on the aggregation behavior of an anionic surfactant sodium dodecyl sulfate (SDS) in aqueous solution were studied in the present work. Surface tension results show the introduction of amino group makes IL more effectively to promote the micellization of SDS, while opposite tendency is observed as carboxyl group is imparted and no obvious change is induced by hydroxyl group when compared with [Emim]Cl. The addition of [MimAE]Cl produces a drastic increase in micellar size of SDS, whereas only slight increases are observed upon addition of other ILs. With decreasing pH values of [MimAE]Cl solutions, significant decrease in CMC values and increase in micellar size is observed, which is caused by the appearance of ammonium cations due to the gradual protonation of amino groups. The [MimCM]+cations are gradually changed to zwitterionic form with increasing pH, and then result in slight increase in the CMC values and decrease in micellar size. The cations of added ILs are located at the micellar surface, and the ring effect originating from the imidazolium ring result in upfield shifts of the protons of SDS. Meanwhile, the amino groups are also adsorbed at the micellar surface, while the carboxylate ions and hydroxyl groups tend to point towards bulk solutions. |
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