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Chemical Engineering Approaches to the Fabrication of Uniform Polymeric Particles and Structures

Student thesis: Doctoral ThesisDoctor of Philosophy

This thesis aims to investigate different approaches to fabricate well-defined and uniform polymeric materials, with sizes ranging from micrometre to nanometre.
We first developed a simple approach via which the size of polymer microparticles resulting from conventional suspension polymerisation could be satisfactorily controlled. The approach employed a two-stage stirring protocol in which a conventional emulsification was conducted in the first stage at a higher agitation speed, followed by polymerisation at reduced stirring speed. The proposed policy led to the formation of more uniform particles, depending on the stabiliser concentration, than those obtained from the one-stage conventional method.
The two-stage stirring protocol was extended to include membrane emulsification as the precursor to polymerisation. The use of a stirred-vessel membrane emulsification, by which the size of drops could be controlled with more accuracy, followed by a shear-controlled suspension polymerisation significantly improved the uniformity of products. The effects of various governing parameters in membrane emulsification, such as the feeding policy, stirring speed, stabiliser concentrations, and flowrates were studied in order to find the optimum conditions under which the one-to-one copy of the initial drops and polymer microparticles could be achieved.
In the next stage, both emulsification and polymerisation stages were replaced by the state of art microfluidics and UV polymerisation, respectively, to produce complex microparticles with highly ordered and well-defined interconnected windows. Uniform water/oil/water (w/o/w) double emulsion, with controlled number of inner water droplets, was first produced and then used as precursor before it was consolidated into porous microparticles through UV photopolymerisation. The sizes and number of cores, porosity and the morphology of the porous microparticles were precisely tuned by the flowrate, confinement offered by the geometry of the channel and packing structure of the inner droplets.
The study was then extended to fabricate 3D porous structures known as polyHIPE. Uniform w/o, in which the internal phase ratio (water phase) occupies more than 74.05% of the total volume of the emulsion, was produced by co-flow microfluidics device. A centrifugal-step was also attempted to further increase the phase ratio and thus the resultant porosity of the structure. Polymerisation of the external oil phase resulted in the formation of open polyHIPE structures with distinctive morphology and porosity.
The final aim of this thesis was to synthesis uniform polymer nanoparticles with a high solids content. Emulsifier-free emulsion polymerisation was chosen as the technique, but a mixture of acetone and water was used as the reaction media to increase the solubility of the monomer phase. The particle size, number of particles and the uniformity were controlled by the concentration of acetone as well as the monomer concentrations. The combined effects of co-monomer and acetone were also investigated and sub-100nm uniform nanoparticles with high solids content were obtained.
Original languageEnglish
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Award date2018

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