The development and evaluation of supracolloidal monolithic structures for applications in separation science

This thesis focuses on the development of polymer monoliths from emulsions for applications in liquid chromatography, in particular the use of high internal phase emulsions to produce monoliths with controlled morphology. An initial study focused on the preparation of hydrophilic polymer monoliths using oil-in-water emulsions. Here, the internal phase volume of the emulsion was varied to produce monoliths with improved mechanical properties under compression. A systematic study was then employed focusing on the influence of the internal phase volume, surfactant concentration and the emulsification energy on the interconnectivity of the resulting monolith. It was found that monoliths with significantly improved mechanical properties that maintained a high level of interconnectivity could be obtained by selecting an appropriate combination of these parameters. The monoliths obtained were found to be responsive to different solvent environments, with significant changes in their volume. This suggested their applicability for use as absorbents or for controlled release but made them unsuitable for liquid chromatography involving a solvent gradient. In addition, when prepared in capillary format, these monoliths were observed to detach from the capillary wall during purification as a result of shrinkage. As such, the preparation of hydrophobic polymer monoliths from water-in-oil emulsions, in capillary format, for chromatographic applications was explored, as these exhibited minimal change in volume when exposed to different solvent environments. Particular attention was paid to the effect that the preparation in capillary format had on the morphology of the resulting monoliths. It was found that when these materials were prepared in capillaries of internal diameter less than 540 ˜í¬¿m using low shear emulsification, significant alterations in their porous morphology were observed. In addition, all columns prepared possessed significant radial heterogeneity. When high shear emulsification was employed the morphology of the resulting monoliths mirrored that of those prepared within glass vials and no significant radial heterogeneity was observed. As a result these monoliths exhibited significantly improved chromatographic performance for the separation of a standard mixture of proteins using reversed-phase liquid chromatography with a solvent gradient. Given these monoliths exhibited a rigid backbone, which did not appear to be compromised by a solvent gradient, they were surface modified by simply incorporating monomers into the internal phase of the emulsion. Initial work focused on the incorporation of the hydrophilic monomer acrylamide in order to increase the hydrophilicity of the monolithic surface. The influence of the inclusion of monomer in the internal phase and choice of initiator on the resulting morphology of these monoliths was investigated. It was found that increases in the monomer content coupled with the use of either a water-soluble or oil-soluble initiator resulted in monoliths with varied morphology and surface chemistry. The increase in hydrophilicity of this scaffold was observed through the separation of some components of a peptide mixture using hydrophilic interaction liquid chromatography, which was not possible using the unmodified scaffold. Finally, a weakly hydrophilic monomer poly(ethylene glycol) diacrylate (Mw 258) was incorporated into the internal phase where it was observed to act as an efficient costabiliser resulting in an increase in the homogeneity of the column, and this material was found to be capable of separating a more complex protein mixture by reversed phase liquid chromatography. The final section of this thesis focused on the preparation of polymer monoliths using latex particles prepared from the soap-free emulsion polymerisation of styrene as a new approach for their preparation. Here, two oppositely charged latexes were combined which resulted in the formation of a colloidal gel that was porous in nature. Chemical cross-linking was then employed, by including a cross-linking monomer in the formulation, to form a rigid polymer monolith. These materials could also be prepared from a single latex by promoting the formation of the gel through the inclusion of a salt, in this case the initiator used for the cross-linking process. It was found that the pore size of these materials was predictable as it directly correlated to the particle diameter. The mouldability and freestanding nature of these gels also easily allowed for their preparation in a variety of formats, even without a mould. These materials were also capable of rapidly absorbing solvents of varying polarity though capillary action suggesting their applicability for thin-layer chromatography or for extraction.