Silica-based stationary phases have been under investigation since they were first produced, and studies still continue to try to improve their morphology and porosity. A handful of reliable and straightforward synthetic procedures are used routinely for their manufacture. The most widely applied procedures are variations of the modified Stober synthesis route that allow the manufacture of relatively monodisperse particles in the nanometer range, or the sol-gel route that produces larger porous microstructures. However, the controlled manufacture of silica stationary phase with the desired physical properties is still a challenge, and most of their preparation involves multi-step preparation, adding cost and time. This dissertation outlines work that introduces a set of new protocols that were developed for the preparation of silica with controlled morphology and porosity. Herein, silica microspheres with tuneable pore size and particle size distribution were synthesised using a modified Stober method. Hydrophilic polymers were introduced into the reaction system, which acted as stabilising agent. Further altering the reaction parameters resulted in the formation of silica microspheres with controlled surface morphology, beads-on-bead silica particles. The preparation conditions were extensively studied in order to understand the reason for such phenomena. The beads-on-beads particles exhibit chromatographic potential, especially for proteins separation. Moreover, porous silica microspheres were further used for the preparation of hierarchically porous silica monoliths by a controlled freezing approach. The macropore morphologies could be tuned with the addition of surfactants in the silica colloidal suspensions during the freezing process. The engineering of porosity and improvement on mechanical stability of the silica materials were achieved through a further soaking and sol-gel process. It was also possible to enhance the mechanical stability through thermal treatment of the materials. Directional freezing approach was also evaluated to direct the assembly of silica nanoparticles. The presence of water-soluble polymers resulted in better aligned features and acted as a gelling agent in the case of charged polymer. The monolith was successfully prepared inside a fused-silica capillary column and was investigated for chromatographic applications. Preformed emulsion-templated porous polyacrylamide beads and monolith were used as a scaffold for controlled growth of silica spheres on macroporous surface. A hierarchical hybrid structure was formed. The polymer scaffold could be removed to form porous silica spheres and macroporous structures. Further investigation was considered to control the porosity and the size of the forming microspheres. This study was further extended into the preparation of fluorescent silica spheres and composite materials. Furthermore, a simple and generic method was also developed for the preparation of gradient emulsion-templated structures. The gradient could be achieved with the aid of centrifugation mechanism. This method enabled the formation of dual gradient mesoporous and macroporous composites.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:569199 |
| Date | January 2011 |
| Creators | Ahmed, Adham Saleh |
| Publisher | University of Liverpool |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.011 seconds