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Title: Fabrication and applications of nanoporous alumina membranes
Author: Lee, Kah Peng
Awarding Body: University of Bath
Current Institution: University of Bath
Date of Award: 2013
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The performance of membranes in various processes is largely dependent on their morphological properties. Thus, membrane structure has been continuously optimised for different applications. Anodic alumina membranes (AAMs) exhibit self-ordered pore structure and the pore size can be tuned in the sub-micrometre range. The aim of this PhD project is to propose and develop AAMs for the applications of membrane filtration and emulsification with potential for scale-up. In the project, the AAMs were initially fabricated in flat sheet form to optimise the process parameters to obtain membranes with a high quality of pore structure. The membrane pore diameter can be readily controlled by the anodization voltage. While AAMs are normally symmetric, by manipulating the anodization voltage, asymmetric AAMs consists of stem pores and active pores have been successfully made. After that, the flat AAMs with symmetric and homogeneous structure were used as a platform to study for surface modification and fluid transport in nano-channels. The surface chemistry and wettability of the membranes has been altered by grafting of silane molecules and carbon coating by chemical vapour deposition. Fluid flow measurement through pristine AAMs with pore diameter in the 20 nm to 100 nm range shows flow enhancement effect, experimentally for the first time, can occur in hydrophilic materials. Subsequently, tubular AAMs were fabricated using aluminium alloy tubes, to be assessed for ultrafiltration and membrane emulsification processes. The pore structure of the tubular AAMs was analogous to flat membranes. Despite the reduced pore circularity and hexagonal arrangement originated from the presence of impurities in the starting materials, the narrow pore size distribution was not compromised. In a selectivity-permeability analysis, the asymmetric tubular AAMs outperformed most of the commercial ceramic membranes but their flux was very low when compared to polymeric membranes. A bovine serum albumin filtration test showed that complete pore blocking-cake filtration model can be used to describe the fouling behaviour. Finally, symmetric tubular membranes were used to study dead-end and cross-flow emulsification processes. The resulting emulsions show low polydispersity. Using a membrane with 25 nm average pore diameter, the obtained average droplet size was as low as 120 nm during a cross-flow emulsification. This is by far the smallest achieved average droplet size by cross-flow membrane emulsification.
Supervisor: Mattia, Davide ; Arnot, Thomas Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: membranes ; flow enhancement ; Ultrafiltration ; emulsification ; ceramic