Chemical and Biomolecular Engineering - Theses
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ItemThe development and exploitation of highly living radical polymerizations( 2016)The synthesis of polymers with controlled molecular weights, designed topology, and defined chemical functionality is becoming increasingly important for high value applications where the improved properties that polymers with well-defined (macro)molecular structures can provide are desirable. Development of chain-growth radical polymerization technologies that allow for the synthesis of polymers of low dispersity with a high degree of chemical fidelity (i.e., retention of the α and ω chain end functionalities) has accelerated in the recent past, with the improvements in chemical fidelity opening new avenues to the application of these techniques for the synthesis of complex and multi-functional macromolecular architectures via relatively simple synthetic pathways. In this thesis, a novel photocontrolled radical polymerization technique is presented and investigated. This technique combines many of the desirable features of a modern controlled polymerization process, including: i) propagation via an active radical species, allowing for a wide range of compatible functional groups and a diverse solvents under relatively simple reaction conditions; ii) the ability to control the polymerization via an external stimulus (i.e., light), allowing for potential spatial and temporal control; and iii) the production of polymers of low dispersity and with high chemical fidelity. The exploitation of this, and other recently developed synthetic technologies is demonstrated via the facile synthesis of (mulit)block and star (co)polymers in simple one-pot reactions. Highly complex chemical structures are attained through a variety of approaches, however the key to the success of all of these is the degree to which chemical fidelity is maintained throughout the course of the polymerization reaction. This research therefore introduces new strategies toward the synthesis of polymers of high chemical and structural fidelity, and presents ways in which these desirable features can be exploited for the straightforward synthesis of complex polymeric architectures with higher orders of chemical and structural complexity.
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ItemCharacterisation of suspensions in settling and compression( 1997-06)The concentration of fine particle suspensions is a crucial step in many industrial processes, two major processes that depend on this are the disposal of mine tailings as highly concentrated slurries, and the wet casting of ceramic components from highly concentrated suspensions. The thickening and filtration operations in these processes are still not completely understood. The successful design and operation consolidation equipment must be based on the properties of the target suspension. The quantitative characterisation of suspensions in settling and compression was the prime objective of this thesis. In a general consolidation model, the behaviour of suspensions in settling and con1pression is fully defined by two parameters; the compressive yield stress function and the hindered settling function. The compressive yield stress quantifies the strength of the suspension network in compression and determines the maximum concentration achievable for any given applied force. The hindered settling function quantifies the hydrodynamic drag forces experienced by consolidating particles in the suspension and determines the settling velocity and the time scale for the consolidation process. These suspension consolidation parameters were determined using a variety of techniques. For measurement of the compressive yield stress, two centrifuge based techniques and a pressure filtration technique were evaluated both independently and with each other - with good results. It was thus verified that the compressive yield stress is a material property of suspensions in compression. For measurement of the hindered settling function, two pressure filtration techniques were developed using a custom built apparatus. Measurements were successfully made using these techniques for the first time. The materials used in the study were three aqueous metal oxide suspensions systems; Zr02, Ti02 and A120 3. The shear and compression rheology of these systems is fully controlled by manipulation of the particle surface chemistry which changes the suspension micro-structure. The validity of the general consolidation model was systematically studied using suspensions prepared under various conditions. Factors studied were the effects of flocculation state, initial concentration, steric stabilisation, suspension preparation methods and prior shear and compression history. These factors affected the compression rheology to varying degrees and were quantified. The conditions for maximum consolidation were determined. A correlation between shear and compression rheology also generated a useful empirical relationship that can be used in design and operation of consolidation equipment. Finally, the measurement of the compressive yield stress and hindered settling function of a suspension was applied to the prediction of the concentration profile and sediment height in an operating continuous thickener. With some refinement, the model and techniques used in this study are a viable means for design and optimisation of continuous thickeners based on the material properties of the suspension.
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ItemNovel and reactive surface coatings via plasma polymerisation( 2012)The work in this thesis investigates the plasma polymerisation of bromine-containing monomers with the aim of functionalising a wide variety of material surfaces with a bromine-functionalised plasma polymer film (BrPP) that is both robust and amenable to secondary reactions. The focus of these reactions has centred upon the copper catalysed alkyne-azide cycloaddition (CuAAC) reaction, a paradigm of click chemistry; a modular synthetic concept referring to reactions that are wide in scope and occur with high specificity and efficiency. Systematic studies were carried out in order to optimise the plasma deposition of a BrPP film coating that is both robust and adherent to the surface on a variety of materials when exposed to both aqueous and organic environments. Optimised thin film deposition conditions were obtained with the monomer 1-bromopropane. The BrPP film was characterised by X-ray photoelectron spectroscopy (XPS), Fourier transform infra-red spectroscopy (FTIR), water contact angle and atomic force microscopy (AFM). The 1-bromopropane plasma polymer film was further characterised using a novel technique developed in this thesis whereby the PP film is first deposited onto a sodium chloride crystal followed by delamination with double-sided tape. This allowed the top- and underside (substrate-plasma polymer interface) of the film to be directly analysed by XPS and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The chemical composition and molecular orientation of the film were different on the topside compared to the underside and this indicated a heterogeneous film structure. The results provided useful insights into the early stages of film formation and chemistry of the 1-bromopropane plasma polymer film. The bromine groups in the 1-bromopropane PP film were substituted by nucleophilic exchange with sodium azide to create surface-bound azide groups (N3PP) suitable for immobilising functional alkynes via the click reaction. The click reaction was verified by XPS and FTIR analysis, which revealed that the reactivity and efficacy of the reaction were influenced by the subtle variations in the BrPP film chemistry across the different substrates. The micropatterning of a fluorescent alkyne via click microcontact printing was also demonstrated. Following recent developments on the photoinitiation of the click reaction, a photolithographical process was developed to click graft and cross-link alkyne-functionalised poly(ethylene glycol) (PEG) onto the N3PP film to fabricate patterned PEG hydrogels. The hydrogels exhibited tuneable thicknesses, resistance to cell attachment and reactivity towards further click reactions. The versatility and functionality of the BrPP film was further demonstrated by the toposelective and robust deposition onto monolayers of silica microparticles. This resulted in the formation of particles with two distinct regions of different chemistries, which are also commonly referred to as Janus particles. The Janus character of the modified particles was verified by azide nucleophilic exchange and subsequent click reactions with fluorescent alkynes. The formation of discrete half shell structures of the BrPP film following dissolution of the silica template provided further evidence of selective film deposition onto the microparticles. Toposelective deposition was also carried out on a monolayer of silica microparticles that were pre-functionalised with multi-layers of layer-by-layer assembled polymer films. This procedure resulted in the formation of polymeric Janus particles and subsequent dissolution of the silica core resulted in the formation of polymeric Janus capsules.
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ItemThe effect of shear on dewatering of flocculated suspensions( 2005)The ability to separate a suspension into its respective solid and liquid constituents is an important requirement in the chemical, wastewater and mineral industries. Typically, separation occurs in open, large diameter tanks known variously as thickeners, settlers or clarifiers. The design and operation of these devices have been based, until recently, on kinematic models and macroscopic mass balances. The problem with these approaches is that consolidation in the bed is not described accurately and consequently, the area required for thickening is often grossly overestimated. Recently, Buscall and White [24] proposed a 1−D phenomenological theory of dewatering that encompasses both sedimentation and consolidation, providing a more solid grounding for understanding, simulating and optimising dewatering in a range of devices, including thickeners. This theory identifies two important rheological parameters; a concentration dependent yield stress, Py (φ) and hindered settling function, R(φ). Despite representing a significant improvement over a kinematical approach, Buscall and White’s dewatering theory involves a number of simplifications so that in practise, simulations often underestimate dewatering in full sized thickeners [97, 153]. One aspect of thickening that is poorly understood is the effect of raking. At the base of the thickener, a rake transports the thickened sediment to the outlet. An additional effect from raking is to increase the average solid concentration in the underflow [33, 46]. Raking introduces normal and shear stresses, which cannot be described within a one-dimensional framework. Therefore, observed differences between predicted and measured thickener underflow concentrations are attributed to the action of the rake. The aim of this thesis is to develop a better understanding of how shear stresses effect compressional dewatering in both pilot and full scale thickening operations. Before attempting to quantify the effect of shear on dewatering, it was considered necessary to first establish that the 1-D model was capable of predicting dewatering in the absence of shear. Up until now, no known studies have been undertaken to validate the model under controlled conditions. To approximate one-dimensional flow with no shear, a tall narrow column with no moving parts was used. Two solid fluxes and several bed heights were studied, and the outputs from the column were compared with the 1-D model predictions. The results show that under ideal conditions, the model predicted the underflow solid concentration to within 10 %. The effect of shear on dewatering was investigated using a Couette shear device. Couette geometry was chosen to provide uniform shear. Since in Couette flow, no normal stresses act in the direction of rotation, the mechanism behind dewatering can investigated. These experiments showed that shear caused dewaterability to improve up to a critical shear rate, beyond which dewaterability was adversely affected. The relationship between this critical shear rate and flocculation conditions was investigated by using different flocculant dosages. The shear modified Py (φ,γ) and R(φ,γ) can be input to the 1−D model, thereby incorporating shear indirectly. As a result, the model predicted an order of magnitude increase in solids flux. The above procedure was used to characterise the dewaterability of a real thickener feed as a function of shear rate. The optimum shear rate was determined by finding the minimum R(φ,γ). Then, Py(φ) and R(φ) were input into the thickener model. The predicted underflow concentration could then be compared against plant data. Even when shear is taken into account, the model still under predicts the performance of the thickener. To understand this result, the pilot column work was revisited since the control over experimental conditions was far greater. To introduce shear, concentric cylinders were installed in the column and rotated at a fixed speed. Thus, the effect of shear and bed height on underflow density were determined at different rates of shear. This showed that the underflow concentration increased with bed height; a result not expected based on the model prediction. The effects of shear on underflow density were secondary to bed height. The bed height dependence can only be explained if dewatering is not steady but changes over time. For a four metre bed height the residence time is eight times longer than a one metre bed. Improvements in dewatering could be related to time dependent restructuring of aggregates which would result in an associated change in R(φ). By fluidizing suspensions for times corresponding to the residence times in the tall column, R(φ) and Py(φ) could be determined, as functions of volume fraction and time. Aggregate properties including structure and density were measured before and after fluidization using focussed beam reflectance measurement (FBRM) and floc density analysis (FDA).