Chemical and Biomolecular Engineering - Theses

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    The structural-functional relationship of polymer-surfactant complexes relevant to personal care product
    Bai, Tianyi ( 2020)
    Polymer-surfactant (PS) mixtures are widely used to control both solution and surface properties. The link between the molecular structure of polymers and surfactants and their associative behaviours is of great interest and it is not very well understood. The examination using several different methods in the colloidal systems is to link the function of PS complexes to their microstructure from different aspects. My thesis aims to investigate how oppositely charged PS complexes can affect the interaction and the adhesive force of drops to surfaces and link these attributes to the target functions of a formulation, including shelf life stability and drop deposition or adhesion of an emulsion formulated chemical products, for example, personal care products. This was achieved by using both novel microscopic methods to quantify adhesion interactions and probe the adsorption and microstructure of PS complexes coated on drops and model surfaces as well as correlating these data to macroscopic methods for bulk solution properties. In this work, cellulose based cationic polymer and anionic surfactants, sodium lauryl (or dodecyl) sulphate surfactants were used based on current key ingredients in personal care product formulation. We have studied when drops will stick to surfaces in the presence of PS complexes by systematically varying the components of PS complexes (e.g. polymer type, surfactant concentration and type, and electrolyte concentration) and correlating the observed drop adhesion to hydrophobic surfaces with the phase diagrams of PS complexes. This observed that polydispersity in anionic surfactant headgroup can drive different drop adhesion, which motivated studies on surfactants in the absence of polymer to see how polydispersity of head group affects the micellization of the surfactant by measuring their critical micelle concentration (cmc) as a function of polydispersity degree and added electrolyte as well as the shape and dimension of the micelle using small angle neutron scattering (SANS). These measurements demonstrated that by controlling the degree of polydispersity in surfactant headgroup, the micelle character and their interaction with polymer can be possibility predicted. The measurements of drop adhesion were then compared to the adsorption of the PS complexes in order to explain how the structure of PS complexes on different surfaces can affect drop adhesion. The adsorption of PS complexes onto model surfaces that have more complexity, relevant to skin, hair or textiles were studied by measuring the adsorbed PS layer thickness using AFM imaging as well as force measurements in combination with measures of the adsorbed amount using QCM-D. By combing the observation of the layer thickness and adsorbed mass of PS complexes upon surfactant and electrolyte dilutions, and the effect from surface character, more insights of the mechanism of the structure change of PS complexes is understood.
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    Dimensional design of the polymer/MOF composite structure for gas separation membranes
    Xie, Ke ( 2017)
    Global warming and climate change concerns have triggered global efforts to reduce the emission of carbon dioxide (CO2) to atmosphere. Post-combustion CO2 capture (PCC) is considered a crucial strategy for meeting this reduction targets. Membrane based separation technics are attractive in this field, representing the potential for a more energy efficient and eco-friendly separation process. Polymers are popular materials in gas separation membranes due to their high processability, mechanical strength and good selectivity. On the other hand, the metal-organic frameworks (MOFs) are also used in such membranes owing to their high porosity, which in turn leading to high gas permeability. In most of the current membrane studies, the MOFs merely serve as additives to polymer, i.e. the MOF particle is blended into polymer membrane to yield the mixed-matrix membrane (MMM). Therefore, the potential of MOF in gas separation applications are not fully developed. In addition, the effects of MOF morphology are not fully investigated yet. This thesis reports on several novel configurations of MOF/polymer composite structure and their applications in gas separations via membrane technology. The presentation is organized by the manipulation of MOF crystal morphologies, and the efficient use of different MOF topologies are demonstrated too. This study results in several novel membrane materials with excellent CO2/N2 separation performance. The relationship between performance and membrane architecture is investigated. In the 1st part, a novel polymer@metal-organic framework nanoparticle (P@MOF) was prepared via an in-situ ATRP on the surface of MOF nanoparticles. The P@MOF shows excellent pH dependent water dispersity, and used as the pH smart catalyst carrier. The investigation on the catalytic effect on 4-nitrophenol reduction clearly shows the efficient integration of the advantage from both heterogeneous and homogeneous catalysts. The 2nd part of this study directly applied the P@MOF particles in gas separation membranes. A novel approach to improve the selectivity of mixed matrix membrane (MMM) systems was developed. MOF nanoparticles (NPs) were chemical coated by a PEG based shell and then incorporated into a polymer matrix to yield a MMM. The unique design of the core-shell MOF NPs can enhance both the membrane permeability and selectivity simultaneously. This membrane material thus exhibits excellent CO2/N2 separation performance that surpasses the latest upper bound through the most direct way. This filler was also applied in the thin-film composite membrane system, showing promising performance located in the optimized zone for post-combustion CO2 capture proposed by Merkel et al. In the 3rd part, we have developed a bottom-up approach to fabricate an ultra-thin (~30 nm), continuous and defect-free polymeric membrane on a rough micro-scale MOF layer. This polymer-on-MOF architecture exhibits promising CO2/N2 separation performance with a CO2 permeance of > 3,000 GPU and a CO2/N2 selectivity of 34. To the best of our knowledge, this membrane has the best CO2/N2 separation performance compared to any membrane reported in the open literature. A novel concept of MMM is introduced in final part. This novel MMM has a unique configuration that the MOF fibres form a continuous interconnected sheet prior to the formation of polymer. Owing to this unique configuration, the permeability of the polymer is enhanced by 19 times without significant loss of selectivity, and surpasses the CO2/N2 separation upper bound.
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    Nanoparticles and macromolecules in flow
    Xie, Donglin ( 2016)
    The optimised fabrication of nanomaterials requires understanding of their behaviors in flow. Here we report on investigations into the flow induced structured changes in colloidal suspensions and polymer solutions. Fabrication of nano-devices requires understanding of the fundamental aspects of flow induced changes in suspensions or polymers. Understanding the behaviors of the dynamics of particles in flow gives insights into fluid mechanics at these length scales. In this work, rheo-optics are combined with numerical simulations to study flow induced phenomena in the colloidal systems. The rheo-optical methods are used to measure the real time optical changes of the sheared nanomaterial suspensions. The simulations are developed to derive the optical changes from the microstructure or motion changes of the suspending nanomaterials in flow. The thesis reports on three main areas of study. The first two studies are on the flow induced alignment of prolate nanoparticles in the red form poly-4BCMU solutions and gold nanorods aqueous sucrose solutions. The absorption spectra have been measured over a range of shear rates using polarized and unpolarized incident light, and the reversible optical changes indicate that the nanoparticles do not undergo aggregation during measurement. The measured absorbance anisotropy is attributed to the flow induced particle alignment which reach the limitation at high Peclet numbers. The spectral changes are consistent with the Jeffery's orbits (cooperating with the Brownian rotation) for large nanoparticles. While, for the nanorods with the long axis <100nm, the spectral shifts are no longer consistent with the modified Jeffery's orbits, but with the rods flipping between extreme orientations of the Jeffery's orbits. This indicates that the effect of the Brownian motion and hydrodynamic forces on the nanoscale rods needs being reconsidered. The viscoelastic effect on the flow-induced aggregation is studied in the dilute colloidal polystyrene nanoparticles suspensions. The real-time aggregation processes have been recorded via measuring optical absorption/scattering in flow. The observed absorbance decreases over time are attributed to the flow-induced coagulation. The aggregation processes still follow the Smoluchowski coagulation equation in a revised version. Suspensions in a series of media are studied to evaluate the effect of the media rheological properties on the particle aggregation. The data shows that elasticity reduces the aggregation while the solution viscosity increases the aggregation rate. In conclusion, the flow induced alignment and aggregation in the nanomaterials suspensions were studied using the rheo-optical method. The classical hydrodynamic theory describes the rotation of larger prolate nanoparticles in flow, but is no longer efficient for the rod like particles with the long axis 100nm. The solution viscosity accelerates the aggregation of nanoparticles while the elasticity has the opposite effect.
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    The development and exploitation of highly living radical polymerizations
    McKenzie, Thomas George ( 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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    Diversification of peptide architectures by surface-initiated ring-opening polymerization
    Harris Wibowo, Steven ( 2015)
    This thesis reports the successful utilisation of surface-initiated ring opening polymerization (SI-ROP) as a versatile technique for the formation of peptide-based materials with tunable secondary conformation, architecture and applications. Chapter 1 provides an overview of the various methodologies for the synthesis and preparation of polypeptides as well as the fabrication techniques employed to create peptide-based advanced functional materials for various applications. This chapter also highlights the current synthetic limitations and challenges facing the field, and set the scene for the studies presented in this thesis. In Chapter 2, we introduced a novel approach to form cross-linked poly(L-glutamic acid) (PLGA) free-standing films (i.e., capsules) by synergistically leveraging the use of SI-ROP, hyperbranched macroinitiator, and cross-chain termination reaction to. In this assembly approach, during the SI-ROP of BLG-NCA from amine-functionalised silica particles, the propagating amine groups undergo nucleophilic attack at the carbonyl carbon of the benzyl-ester side-groups on adjacent polymer chains (i.e., cross-chain termination reactions). This event led to the formation of inactive amide groups which consequently cross-link the grafted peptide chains. Following the deprotection of remaining benzyl protecting groups and dissolution of the silica template (via hydrofluoric acid treatment), the cross-linked peptide chains formed free-standing architectures in the form of thin polypeptide capsules. While cross-chain termination was verified by conducting Maldi-Tof analysis and chain extension studies, the extensive covalent crosslinking results in stability of PLGA-capsules at various pH conditions and in the presence of H-bond breaker urea. The thickness of the capsules could be tuned by variation of the polymerization time and initial monomer concentration. Meanwhile, the composition and functionality could be tuned by using a combination of different amino acid NCA derivatives. Furthermore, despite the highly cross-linked structure, the capsules were found to be biodegradable in the presence of proteolytic enzymes. Not only did this study present a novel cross-linking approach, the results also open exciting opportunities for the development of biomedical (nano)devices with excellent mechanical stability, degradability and tunable functionality. In Chapter 3, we took advantage of SI-ROP of β-sheet forming α-amino acid N-carboxyanhydrides to form grafted polypeptides which self-assemble into β-sheet in situ. Here, we demonstrate SI-ROP as a simple, rapid, and robust strategy to form novel polypeptide β-sheet architectures with tailored shapes and dimensions that is yet to be reported in the literature. As the peptide-grafts remain anchored during SI-ROP, the formation of β-sheet-forming peptide grafts are controlled in a spatial and temporal fashion which help avoid the unconstrained random aggregation of β-sheet polypeptides formed in solution. The study reveals that after a certain SI-ROP time, H-bonding between the surface-anchored peptide grafts results in β-sheet architectures assembled in situ that possess a rigid and porous structured surface. Since both the polypeptide formation and self-assembly into β-sheet structures are surface-driven, the resulting H-bonded peptide grafts adopt the 3D shape of the template. Following template dissolution, stable and well-defined free-standing polypeptide shell architectures were formed. In this study, we found that SI-ROP time and initial NCA monomer concentration influences the morphology of the poly(L-valine) (PVal) shells. Notably, these shells are stabilised by both hydrophobic interaction and H-bonding which results in their stability under various pH conditions, high temperature and in the presence of denaturants such as urea and guanidine hydrochloride. Nevertheless, we found that the architectures are still enzyme degradable and chemical functionalities can be introduced via chain extension reaction. In the second part of the thesis (Chapter 4), we presented the diverse applications of peptide-based materials prepared by SI-ROP of NCA derivatives. First, peptide nano-coatings with tailored surface wetting properties were formed on a range of organic (cellulose and cotton) and inorganic (glass) substrates via SI-ROP of judiciously-selected amino acid NCA derivatives. In this study, the film thickness, surface roughness and wettability were tuned by controlling the polymerization time and the type of NCA derivative used (i.e., lysine or valine). While poly(L-lysine) coatings are hydrophilic, poly(L-valine) coatings exhibit water-repellent properties. The functional polypeptide nano-coatings can potentially be applied to waterproof woven fabrics, macromolecular separation technologies, biodiagnostic sensors and sustained drug-release wound dressings. Following this study, we report the unique capacity of the free-standing PVal-shells reported in Chapter 3 for the non-covalent entrapment and conjugation of various materials ranging from metal nanoparticles, to quantum dots, synthetic polymers, drug molecules and protein. Preparation of metal nanoparticles-peptide hybrid materials demonstrate potential applications in organic catalysis and diagnostic devices while entrapment of quantum dots, polymers, proteins and drug molecules open up opportunities for the convenient fabrication of biodiagnostic and drug-delivery vehicles. Finally, to further expand the diversity of peptide-based architectures we proposed future fundamental and fabrication studies that leverages the collective knowledge gained by conducting studies reported in this thesis (Chapter 5).
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    Supramolecular polymers as building blocks for the formation of particles
    Tardy, Blaise Leopold ( 2014)
    Over the last two decades, there has been a growing interest in the development of supramolecular polymers, linear macromolecules whose monomeric components are held together by non-covalent interactions. Such supramolecular assemblies are commonly found in nature and are crucial for the function of living tissues and cells. The recent development of synthetic supramolecular polymers has shown promise for enhancing the properties of polymeric materials. Indeed, studies have shown that such materials have significant benefits when compared to conventional, covalently bound, polymers. These benefits are due to the ability of supramolecular assemblies to respond to stimulus, and to dynamically rearrange their structure in a manner unachievable using conventional, covalently bound polymers. Resemblances between the dynamics of synthetic supramolecular polymers and naturally occurring supramolecular polymers are suggestive of their potential for biomedical applications. In this trend, the most promising supramolecular polymer, cyclodextrin (CD) based polyrotaxanes (PRXs), is now emerging as a potential tool to synthetically form dynamic interfaces for applications in the biomedical field. The recent popularity of these polymers in this field is not only due to their inherent, non-covalent properties but also to the low cost, high engineerability and low toxicity of the components they are made of. In this work, CD-based PRXs have been used as building blocks to form particles that were designed for developments in drug delivery. Specifically, the properties specific to PRXs have been exploited to design particles with degradation or stimuli-based response. The unique characteristics of PRXs were found to translate into similarly unique characteristics of the assembled particles. Different approaches have been studied and their advantages and limitations are highlighted. Initial investigations were aimed at designing particles fitting the requirements in properties and specific characteristics highlighted by recent in vivo and in vitro studies. In this direction, we demonstrated controlled degradation of self-assembled PRX-based structures through stimuli triggered disassembly. Such control was also shown for PRX particles dynamically formed using a templated approach, for which disassembly through judicious selection of specific building blocks is highlighted. The use of the templated approach was shown to be more straightforward and versatile in its applications, laying out a framework to form and engineer particles using PRXs as a building block. Lastly, by using CD’s molecular mobility in the PRX as an additional handle for tuning; a “one block” polymer, able to reversibly segregate into multi-blocks leading to the formation of nanoparticles, was developed. This approach is particularly interesting as many responsive polymeric materials have their response due to a stretched-to-coiled transition of individual chain while we show here a transition between a mono-block like architecture to a multi-block like architecture. The preliminary results highlight the potential of PRXs as building blocks for applications in drug delivery systems.
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    Soft polymeric nanoparticles as additives for CO2 separation membranes
    Halim, Andri ( 2014)
    The use of polymeric membranes for gas separation has experienced a major expansion in the past few decades with current applications which include the separation of CO2 from flue gas. Various approaches have been explored to fabricate membranes with superior separation performance that can exceed the current upper performance limit. These include the incorporation of hard inorganic nanoparticles into polymers to form mixed-matrix membranes (MMMs). The performance of MMMs can be further enhanced if they can be fabricated into asymmetric morphology. The fabrication of asymmetric membranes, in the form of a thin film composite (TFC) membrane, is more commercially viable due to the increased flux and reduced consumption of expensive nanoparticles. TFC membranes are typically composed of a porous support coated with a highly permeable gutter layer, which is in turn coated with a thin active layer. However, the development of effective asymmetric MMMs has been limited. This is due to the difficulty in fabricating nanoparticles in a size that does not exceed the thickness of the active layer and in avoiding defects in the resulting composite structure. The fabrication of next generation mixed-matrix gas separation membranes is also hampered by the need to ensure a defect-free polymer/inorganic particle interface. A similar approach can be applied to the addition of soft polymeric nanoparticles into a selective polymer matrix. In this case, the problem of defects occurring between the particle and the matrix can be avoided through the engineering of particles that are compatible with the polymer matrix. Hence, this thesis aims to synthesize novel soft polymeric nanoparticles with well-defined architectures and utilize these as additives to be incorporated into the thin active layer of TFC membranes. The requirements for these nanoparticles include (a) a soft and CO2 permeable core and (b) a corona which is compatible with the polymer matrix. The best candidate nanoparticles are then blended with a selective polymer matrix to form the active layer of TFC membranes, which are tested for their CO2 separation from N2. The size of the soft polymeric nanoparticles are significantly smaller than the thickness of the active layer and overcome the problem of blending larger inorganic nanoparticles to form asymmetric MMMs. The first soft polymeric nanoparticles studied were based on triblock copolymers containing polyimide (PI) and poly(dimethylsiloxane) (PDMS). Well-defined difunctional PI was initially prepared via step-growth polymerization. Subsequently, PI was functionalized and chain extended with different molar ratios of PDMS-monomethacrylate (PDMS-MA) via atom transfer radical polymerization (ATRP) to form a series of triblock copolymers. Self-assembly of triblock copolymers in a selective solvent for PI, followed by cross-linking via hydrogen abstraction, resulted in the formation of well-defined nanoparticles with a soft PDMS core. The second soft polymeric nanoparticles developed in this study was based on diblock copolymers containing poly(ethylene glycol) (PEG) and PDMS. Commercially available PEG was utilized as a substitute for the PI block due to the difficulty in synthesizing well-defined polymers via step-growth polymerization. Three different molecular weights of monomethyl ether PEG were initially functionalized to form macroinitiators suitable for ATRP. These macroinitiators were then chain extended with PDMS-MA and photoactive anthracene moeities in different molar ratios to afford a series of photoresponsive diblock copolymers. Self-assembly of diblock copolymers in a selective solvent for PEG, followed by photocross-linking via [4+4] photodimerization of anthracene moeities, resulted in the formation of another well-defined soft polymeric nanoparticles with various structures that range from spherical micelles to large compound micelles. The preparation of soft polymeric nanoparticles through the self-assembly of block copolymers is generally carried out in low concentration to avoid aggregation of nanoparticles. This hinders the preparation of nanoparticles on a larger scale. The third soft polymeric nanoparticles explored in this thesis were based on PEG and PEG-b-PDMS grafted star polymers that were synthesized via the ‘core-first’ approach. This method allows the preparation of nanoparticles in high yields as the crude reaction mixture only requires separation from unreacted monomers. Various grafted star polymers with different PEG and PDMS molar ratios were synthesized in high yields and high conversions utilizing a four-arm ATRP initiator. These grafted star polymers were then utilized as additives for existing gas separation membranes. TFC membranes were prepared from commercially available selective poly(amide-b-ether) (Pebax® 2533) that was blended with a series of PEG and PEG-b-PDMS grafted star polymers. These blends formed a thin film on microporous polyacrylonitrile substrates which have been pre-coated with a PDMS gutter layer. Their ability to selectively separate CO2 from N2 was studied at 35°C and an upstream pressure of 3.4 bar. The addition of soft polymeric nanoparticles into the thin active layer of TFC membranes resulted in greatly improved flux as these particles are able to form localized, high flux, soft domains within a selective polymer matrix. These results create an interesting route to further develop and utilize soft polymeric nanoparticles as additives in membranes for gas separation processes.
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    Assembly of polymer matrices enveloping cubic lyotropic liquid crystalline nanoparticles for drug delivery applications
    Driever, Chantelle Dana ( 2012)
    Cubic lyotropic liquid crystalline nanoparticles (cubosomes™) exhibit great potential as drug delivery vehicles due to their nanoscale size, biocompatible constituents, and high loading potential for hydrophobic, hydrophilic, and amphiphilic agents. However, they also suffer from some limitations which have restricted their clinical effectiveness. For example, they release their cargo in a rapid, uncontrolled manner— a phenomenon known as burst release. In addition, the lipids which form reverse cubic phase typically do not contain surface functional groups for the immobilisation of targeting or stealth providing moieties. Polymeric capsules, in particular those made with the layer-by-layer technique, are able to modify the release properties of a loaded drug according to the number and nature of polymer layers. Many of the polymers employed also contain available functional groups for additional chemistry. However polymeric capsules can be difficult to efficiently load with therapeutic agents, particularly when the drugs are lipid soluble. Additionally, the removal of the capsule core template often requires conditions that can cause instability. This thesis examined the use of polymers to modulate the properties of cubosomes with the intention to aid stability, limit burst release, add potential functionality, and increase the payload. Different methods used to prepare stable, well dispersed amphiphilic cubosomes (high pressure homogenisation, extrusion, and ultrasonication) were analysed and compared. The effect of an additive to the aqueous environment (such as sodium chloride or phosphate buffered saline (PBS)) was also investigated. Certain additives to the amphiphile matrix such as the charged lipids cetyl trimethylammonium bromide (CTAB), dioctadecyl-dimethylammonium bromide (DODAB) or sodium dodecyl sulphate (SDS) were found to cause structural changes to both bulk and dispersed cubic phase but could be tolerated up to a certain quantity before complete destabilisation occurred. Integrating cubic nanoparticles and polymer matrices was first accomplished by coating silica microparticles. This resulted in a multilayered polymer coating representing an embedded layer of cubosomes surrounded by poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) polyelectrolytes. Upon removal of the silica core, stable polymer microcapsules containing embedded cubic nanoparticles were obtained. A diversity of molecular encapsulation matrices is offered through the capsule core, polyelectrolyte layers, and the embedded cubosomes of these sub-compartmentalised, nanostructured microcapsules. Individual cubic nanoparticles surrounded by polyelectrolyte multilayers were prepared next. The polymers were able to interact with the non-charged cubic lipid nanoparticles by utilising a polyelectrolyte modified with hydrophobic side chains (poly(methacrylic acid-co-oleyl methacrylate), PMAO) as an initial layer. Three bi-layers of poly(L-lysine) (PLL) and poly(methacrylic acid) (PMA) were then sequentially added. In order to separate accrued polymer aggregates from the coated lipid nanoparticles, a simple technique was developed whereby centrifugation separated the less dense cubosomes for collection. Modulation of the drug release properties and attenuation of the burst release from coated cubosome particles was demonstrated using two model drugs (fluorescein and perylene). The modified polymer PMAO was then utilised as an alternative stabiliser for lyotropic liquid crystalline nanoparticles. The charge-stabilised particles were tested against the most commonly utilised steric stabiliser Pluronic F127 for stability and drug release characteristics. Although PMAO-stabilised nanoparticles still exhibited burst release, improved particle stability was observed over time and over a range of temperatures, including storage under refrigeration. A lesser amount of PMAO stabiliser and less energy input were also required to disperse the bulk lipid into discrete, uniform nanoparticles compared to Pluronic F127. These studies demonstrate the viability of combining layer-by-layer polymer matrix technology with cubic lyotropic liquid crystalline nanoparticles to enhance the future of drug delivery.
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    Drinking water treatment sludge production and dewaterabilityф
    Verrelli, D. I. (D. I. Verrelli, 2008)
    The provision of clean drinking water typically involves treatment processes to remove contaminants. The conventional process involves coagulation with hydrolysing metal salts, typically of aluminium (‘alum’) or trivalent iron (‘ferric’). Along with the product water this also produces a waste by-product, or sludge. The fact of increasing sludge production — due to higher levels of treatment and greater volume of water supply — conflicts with modern demands for environmental best practice, leading to higher financial costs. A further issue is the significant quantity of water that is held up in the sludge, and wasted. One means of dealing with these problems is to dewater the sludge further. This reduces the volume of waste to be disposed of. The consistency is also improved (e.g. for the purpose of landfilling). And a significant amount of water can be recovered. The efficiency, and efficacy, of this process depends on the dewaterability of the sludge.In fact, good dewaterability is vital to the operation of conventional drinking water treatment plants (WTP’s). The usual process of separating the particulates, formed from a blend of contaminants and coagulated precipitate, relies on ‘clarification’ and ‘thickening’, which are essentially settling operations of solid–liquid separation.WTP operators — and researchers — do attempt to measure sludge dewaterability, but usually rely on empirical characterisation techniques that do not tell the full story and can even mislead. Understanding of the physical and chemical nature of the sludge is also surprisingly rudimentary, considering the long history of these processes. The present work begins by reviewing the current state of knowledge on raw water and sludge composition, with special focus on solid aluminium and iron phases and on fractal aggregate structure. Next the theory of dewatering is examined, with the adopted phenomenological theory contrasted with empirical techniques and other theories.The foundation for subsequent analyses is laid by experimental work which establishes the solid phase density of WTP sludges. Additionally, alum sludges are found to contain pseudoböhmite, while 2-line ferrihydrite and goethite are identified in ferric sludges. A key hypothesis is that dewaterability is partly determined by the treatment conditions. To investigate this, numerous WTP sludges were studied that had been generated under diverse conditions: some plant samples were obtained, and the remainder were generated in the laboratory (results were consistent). Dewaterability was characterised for each sludge in concentration ranges relevant to settling, centrifugation and filtration using models developed by LANDMAN and WHITE inter alia; it is expressed in terms of both equilibrium and kinetic parameters, py(φ) and R(φ) respectively.This work confirmed that dewaterability is significantly influenced by treatment conditions.The strongest correlations were observed when varying coagulation pH and coagulant dose. At high doses precipitated coagulant controls the sludge behaviour, and dewaterability is poor. Dewaterability deteriorates as pH is increased for high-dose alum sludges; other sludges are less sensitive to pH. These findings can be linked to the faster coagulation dynamics prevailing at high coagulant and alkali dose.Alum and ferric sludges in general had comparable dewaterabilities, and the characteristics of a magnesium sludge were similar too.Small effects on dewaterability were observed in response to variations in raw water organic content and shearing. Polymer flocculation and conditioning appeared mainly to affect dewaterability at low sludge concentrations. Ageing did not produce clear changes in dewaterability.Dense, compact particles are known to dewater better than ‘fluffy’ aggregates or flocs usually encountered in drinking water treatment. This explains the superior dewaterability of a sludge containing powdered activated carbon (PAC). Even greater improvements were observed following a cycle of sludge freezing and thawing for a wide range of WTP sludges. Further aspects considered in the present work include deviations from simplifying assumptions that are usually made. Specifically: investigation of long-time dewatering behaviour, wall effects, non-isotropic stresses, and reversibility of dewatering (or ‘elasticity’).Several other results and conclusions, of both theoretical and experimental nature, are presented on topics of subsidiary or peripheral interest that are nonetheless important for establishing a reliable basis for research in this area. This work has proposed links between industrial drinking water coagulation conditions, sludge dewaterability from settling to filtration, and the microstructure of the aggregates making up that sludge. This information can be used when considering the operation or design of a WTP in order to optimise sludge dewaterability, within the constraints of producing drinking water of acceptable quality.