School of Chemistry - Theses
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ItemProtic ionic liquids as solvents for amphiphile self-assembly and the preparation of nano-structured inorganic materials( 2013)The aims of this PhD project are: 1) to investigate the amphiphile self-assembly in protic ionic liquids and establish the phase diagrams of these systems; 2) to utilise protic ionic liquids (PILs) to synthesize nanostructured metal oxide materials, including TiO2, SiO2. The first stage is to have a careful selection of the PILs available in the literature so that suitable PILs can be chosen for the synthesis of inorganic materials. Those PILs that promote amphiphiles will be particularly of interest to create structured materials. Two key issues need to be addressed during this stage. First, a new synthetic approach needs to be developed as the synthesis of inorganic materials in PILs has not been reported in the literature up to date. However, the approaches for producing inorganic materials in aprotic ionic liquids may be used as a reference approach. Second, it has already been reported that many PILs are capable of promoting self-assembly of amphiphiles and structures such as lamellar, hexagonal and cubic phases have been observed in PILs. However, whether or not these structures can be retained after introducing an inorganic network into the system needs be investigated. TiO2 and SiO2 materials will be synthesized from the selected surfactant-PIL systems and these materials will be characterized using various analytical techniques such as BET, SAXS, and TEM. On the conclusion of the project, a comprehensive understanding of the phase formation of surfactants in PILs has been established. Two ionic and two non-ionic amphiphiles (hexadecyltrimethyl ammonium chloride (CTAC), hexadecylpyridinium bromide, HDPB), polyoxyethylene (10) oleyl ether, Brij 97 and Pluronic block copolymer, P123) were studied in three selected PILs (ethylammonium nitrate, EAN, ethanolammonium nitrate, EOAN and diethanolammonium formate, DEOAF) with different structures. The phase behaviour of these amphiphiles has been explored in these PILs in comparison with water using the small angle X-ray scattering technique. More diverse phases could be formed by the amphiphiles in EOAN and DEOAF compared to those in EAN due to the structure change of the PIL. Micelles formed by amphiphiles in a protic ionic liquid, ethylammonium nitrate (EAN), and water were analysed using various models (spherical, core-shell and cylindrical). The amphiphiles used were cationic CTAC and HDPB, non-ionic Brij 97 and P123. Spherical micelles were preferentially formed at low amphiphile concentrations, and no structure factor for intermicellar interactions was required. The micelles formed by the two cationic amphiphiles were similar in EAN and water, though different models were used due to the ionic nature of EAN. However, for the two non-ionic amphiphiles, the micelles contain a shell of ethylene oxide groups (EO) which was significantly thicker in water than in EAN, though the core radii were similar for the two solvents. At high concentrations (above 10 wt%), there was a preference for cylindrical micelles for CTAC, HDPB and Brij 97, however, the P123 micelles still remained as spheres at such concentrations. The cosolvent effects (water and methanol) on the structures formed by P123 in EAN have been investigated and two ternary phase diagrams have been established. The addition of water did not have much effect on the phase behaviour of P123 in EAN as only slightly change of the lattice spacing of the phase was observed. However, the introduction of methanol into the system changed the phase behaviour significantly. There no phases were present above 20 wt% of methanol. Interestingly, a bicontinuous cubic phase was induced with a small amount of methanol in the system. Finally, mesoporous silica materials have been synthesised using a P123-EAN template. These silica materials have ordered mesopores with disordered micropores. The amount of inorganic network could greatly affect the final structure. A sufficient amount of inorganic silica network was required to retain the structure (hexagonal) of the template. However, the preformed structure in the template could be disrupted if the silica amount was too high. The fabrication of TiO2 materials has also been attempted by using the same template. However, ordered structures were not obtained due to the crystallisation of TiO2 during the calcination process. Thus, a potential application of these PIL/amphiphile systems is the synthesis of mesoporous inorganic materials, in particular for inorganic precursors with slow hydrolysis rates.
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