Self-Assembled Structures Of Ionic Liquids And Their Applications In The Synthesis Of Nanomaterials

As a new kind of solvents, ionic liquids (ILs) have attracted a lot of attentions due to their unique properties. For short alkyl chains, they can be used as solvents to replace traditional organic solvents in the fields of catalysis, organic synthesis, chemical extraction separation, electrochemistry, and molecular assemblies. Meanwhile, as a kind of salt with alkyl chains, it can be also used as the surfactant, their aggregation behavior in water is another extensively studied subject.A large number of ions have led to the great species of ILs. People can design and synthesize a certain IL to satisfy their own needs by changing the ions and the alkyl chain length. Such investigations can enrich the species of ILs and also establish the basis for their application in different fields, which are quite interesting and of great importance.So in this dissertation, we carried out the following work:Investigations on the self-assembled aggregates formed by N-alkyl-N-methylpyrrolidinium bromide (CnMPB) in different solvents. Then, we prepared varied materials by using the self-assemblies as templates. Finally, we employed a much facile ionic self-assembly (ISA) route, through the complexation of CnMPB, MO and PB to construct supramolecular microfibers with the aid of various non-covalent interactions.1. Investigations on the self-assemblies formed by long chain CnMPB. The work can be divided into two parts:Investigations on the micellization behavior of CnMPB in water; Investigations on the LLC phases formed by CnMPB in two different solvents, water and ethylammonium nitrate (EAN), the results are described below.(1) CnMPB can be self-assembled into micelles in water, the critical micelle concentration (cmc) values decrease with increasing alkyl chain length, which is in accordance with traditional cationic surfactants. Then, we have compared the cmc value of CnMPB with that of CnmimBr and CnTAB. The results show that, the cmc value of CnMPB is a little higher than CnmimBr, but lower than CnTAB. This may be due to the following reasons:the alkyl chain length of CnMPB head group is longer than CnTAB, which results in higher surface activity. Even though the alkyl chain length of CnMPB head group is the same as that of CnmimBr, the conjugated bands in the latter can increase the interactions between different molecules, which also results in higher surface activity. According to the results of the static luminescence quenching experiments, we have calculated the aggregation number (Nagg) of CnMPB micelles, which is close to that of CnmimBr, but less than that of CnTAB. This phenomenon indicates that, the head group has the significant effect on the micelle formation. The temperature dependence of the thermodynamic parameters (?Gm0,?Hm0 and?Sm0) of the micelle formation shows the micelle formation process is entropy-driven at lower temperature, but enthalpy-driven at higher temperature.(2) Both hexagonal (H1) and reverse bicontinous cubic (V2) phases can be formed by C16MPB in water and EAN. POM pictures have showed that, the H1 phases formed are with obvious fan textures, while the V2 phase is isotropic and the POM images are occupied by a dark background. Results from SAXS technique have indicated that, C16MPB molecules arranged more tightly in H1 phases formed in water than in EAN, which can be attributed to the solvent effects. Through comparison of rheological properties of H1 phase formed in different solvents, we can find that, the H1 phase formed in EAN displays a Maxwell behavior. However, the H1 phase formed in water shows a gel-like behavior, unlike traditional cationic surfactants. Such results can help us better understand the solvent effects on the properties of the LLC phases. Results from DSC technique show that, the LLC phases formed in EAN is high temperature resistant, which can enlarge their application fields.2. Investigations on the synthesis of nanomaterials by using the aggregates formed by ILs as the templates. The work can be divided into three parts: Investigations on the hollow spherical and worm-like silica materials templated by the aggregates of C12mimBr. Investigations on the hollow silica materials and nanoparticles prepared by using the IL microemulsions as templates, the effects of catalysts on the morphologies of the materials are explored. Investigations on the LLC phases formed in C14mimCl/EAN binary system, then we use the LLC phases as a medium to disperse the multi-walled carbon nanotubes (MWCNTs). The results are listed below.(1) With the aid of C12mimBr, we have prepared various silica materials. Their morphologies can be tuned by controlling the stirring time and evaporation temperature. Results from SEM and TEM show that, both hollow silica microspheres and hollow worm-like materials can be prepared through such a method. A possible emulsion droplets fusion mechanism is proposed. Further investigations by the HRTEM and nitrogen adsorption-desorption techniques indicate that, the micropores can be found on them. Besides, they both show suitable ability as controlled release systems, which can enlarge their applications.(2) The O/IL microemulsion droplets formed in the system composed of TX-100, benzene, and BmimBF4 are selected as the templates to synthesize the silica nanomaterials. The results show that, hollow silica microspheres can be prepared in the absence of catalysts. Then we investigated the effects of the catalysts and found that the ellipsoidal silica nanoparticles can be prepared in the presence of HCl, while hollow microspheres are prepared in the presence of alkali. Such results suggest that the catalysts have great effects on the shape of nanomaterials.(3) Both H1 and V2 phases can be formed in C14mimCl/EAN binary system. Then, we use the H1 phases as a medium to disperse the MWCNTs and the LLC/ MWCNTs composite material can be obtained. Results from POM and SAXS techniques show that, the MWCNTs can be well dispersed in the H1 phases and the ordering of the H1 phase has not been destroyed during the dispersing process. Rheological results show that, the viscosity of the H1 phase increases after the dispersion of the MWCNTs.3. The supramolecular microfibers are prepared by mixing the solutions of C14MPB, MO, and PB. Results from SEM, OM, and AFM techniques show that, the supramolecular microfibers formed in the present system is about 1-5 micrometers in width and about several millimeters in length. Results from 1H NMR show that, the stoichiometry between C14MPB and MO in the complexes is determined as a 1:1 molar ratio in all samples and has no relation with the initial amount of them. As for the relative small content, the amount of PB in the microfibers is very difficult to be determined by 1H NMR technique. The formed complex has fluorescent properties and may have potential applications in some specific fields. The electrostatic interaction,?-?stacking interaction, and hydrophobic interaction are regarded as the main driving forces for the supramolecular microfibers formation. This has break through the traditional ones, the different dyes used in the present system have strengthened the molecular interactions, which can favor the formation of ordered structure.