School of Chemistry - Theses

Permanent URI for this collection

Search Results

Now showing 1 - 8 of 8
  • Item
    Thumbnail Image
    In-situ investigations of molecular self-assembly using microfluidics
    Seibt, Susanne ( 2018)
    The general aim of this work was to study the growth kinetics of nanoparticles, self-assembly processes of hydrogelators and polymers as well as the flow-orientated alignment of anisotropic particles. This was enabled by the combination of highly optimised microfluidic devices with material-dependent analytical methods, including optical spectroscopy, fluorescence microscopy and X-ray scattering. In particular, this thesis focuses on the in-situ kinetic investigations of processes occurring during the reactions. Providing temporal resolutions down to milliseconds, direct insights in reactions were possible.
  • Item
    Thumbnail Image
    Tailor-made covalent organic-inorganic polyoxometalate hybrids: versatile platforms for the elaboration of novel molecular architectures
    Karoui, Hedi ( 2018)
    Covalent organic-inorganic polyoxometalate (POM or POMs) hybrids constitute versatile platforms for the elaboration of functional molecular architectures. This Ph.D. research project aimed to synthesize novel organic-inorganic POM hybrids using pre- and post-functionalization methods. The synthesis of organic-inorganic hybrids starting from POMs, known as direct functionalization, is a well-established synthetic procedure. However, as the complexity of the targeted functional system increases, a multi-step strategy relying on the post-functionalization of preformed hybrid POMs is necessary. Herein, both approaches are explored. Following hybridization of POM surfaces using organic units, ranging from small groups to large polymeric chains, this work provides a significant step forward in the rational design and synthesis of POMs, which permits the elaboration of POM based nanomaterials. At first, boronic acids and esters ligands were selected for POMs’ post-functionalization. Three organoboron functionalized Anderson-Evans and one organoboron functionalized Lindqvist POM were synthesized using Schiff base chemistry; with the general formulas of the Anderson-Evans POM hybrids being [MnIIIMo6VIO18((OCH2)3)CN=CHC6H4(B(OR)2)2]3− (where R = H, Me), [MnIIIMo6VIO18((OCH2)3)CN=CHC6H4(BO2(CH2)3)2]3-, with the formula of the Lindqvist POM hybrid being [VV6O13{(OCH2)3CN=CHC6H4B(OH)2}2]2-. These compounds have been characterized in the solid state by single-crystal X-ray diffraction (XRD), FT-IR spectroscopy and elemental analysis and in solution using Nuclear Magnetic Resonance (NMR) spectroscopy. This work has further been extended to organosilane functionalized mono and di lacunary Keggin POMs. Two organoboron functionalized Keggin POMs were synthesized using N, N'-dicyclohexylcarbodiimide (DCC) coupling; with the general formulas being [β2-SiW11O39{O(Si(CH2)3NHC=O-C12H17BO2)2}]4- and [γ-SiW10O36{O(Si(CH2)3NHC=OC12H17BO2)2}]4-. These compounds have been characterized in the solid state by FT-IR spectroscopy and elemental analysis and in solution using NMR spectroscopy. Later, the employment of microwave-assisted synthesis permitted the generation of novel mixed metal tris(alkoxo)molybdovanadates. The reaction of [β-Mo8O24]4- and [H3V10O28]3- with pentaerythritol or tris(hydroxymethyl)aminomethane yielded compounds with the general formula [V3Mo3O16(O3-R)]2- where R = C5H8OH or C4H6NH2. Post-synthetic esterification of the alcohol derivative yielded the acylated derivative [V3Mo3O16(O3-R)]2- where R = C7H11O2. Single-crystal X-ray Diffraction (XRD), NMR spectroscopy, High-Resolution Mass Spectrometry (HR-MS) and FT-IR spectroscopy have been used in combination to rationalize the structural isomerization observed within these systems. The rational design and synthesis of two novel covalent organic-inorganic hybrid polymers via Atom Transfer Radical Polymerization (ATRP), composed of either a Lindqvist POM macro initiator of formula [V3Mo3O19{(OCH2)3CNHC=OC(CH3)2Br}]2- or an Anderson-Evans POM macro initiator of formula [MnIIIMo6O18{(OCH2)3CNHC=OC(CH3)2Br}2]3- and pH-responsive poly(2 (diethylamino)ethyl methacrylate) (PDEAEMA) polymer, was investigated. POM macro initiators were characterized using single-crystal X-ray diffraction (XRD), 1H NMR spectroscopy, FT-IR spectroscopy, UV-Vis and elemental analysis; while POM-polymer hybrids were characterized using 1H NMR spectroscopy, FT-IR spectroscopy, thermogravimetric analysis (TGA) and UV-Vis spectroscopy to assess the integrity of the POM units. These POM-polymer hybrids self-assemble into nanoparticles via copolymerization with poly(2-(diethylamino)ethyl methacrylate)-b-poly(ethylene glycol) (PDEAEMA-b-PEG), when the pH is increased above the pKa of PDEAEMA. Dynamic Light Scattering (DLS) studies were conducted to investigate the size distribution of the nanoparticles, while disassembly studies proved that they respond to biologically relevant pH variations. These observations were supported by Cryo-TEM imaging which provided valuable direct visualization of the nanoparticles. Importantly, growing polymer chains from POM macro initiators offers an excellent control over the loading of the POM clusters inside the nanoparticles.
  • Item
    Thumbnail Image
    Fundamental properties of non-wetting topography
    Simovich, Tomer ( 2017)
    The core principles of wettability were established over 70 years ago by Wenzel, Cassie and Baxter and remain the basis of present understanding of hydrophobicity. While these models are used to describe the contact angle of some functional superhydrophobic surfaces, they fail as a predictive tool. This work establishes that the Cassie-Baxter equation is limited by an inability to evaluate liquid-solid contact area. Using in-situ synchrotron based X-Ray imaging, the behaviour of water at the interface of micro-pillar arrays was observed, quantifying the effect of meniscus penetration between peaks on contact area. It was determined that the wetting line between surface asperities is governed by pillar width, spacing and height. A model was developed incorporating this relationship that predicts the contact angle of all tested superhydrophobic surfaces with a maximum error of 6.7% (average 2.2%). Microscale durability was integrated into this model to compare non-wetting topography with mechanical stability. This predicted that an ideal coating morphology would consist of over-arching microstructure with hierarchically protected nano-roughness. Combining this ideal morphology with the elastic bulk properties of nylon and epoxy, novel coatings were fabricated exhibiting both high durability (2H-6H hardness) and contact angles above 156º. A current limitation surrounding the design and fabrication of superhydrophobic coatings is the depletion of the entrapped air layer (plastron) within 24 hours. Scattered micro-droplets, stabilized by high vapor pressure, were imaged for the first time within the plastron on submerged superhydrophobic surfaces. These droplets, ranging from 20-50 μm, were also observed on the superhydrophobic hairs of the aquatic plant Pistia stratiotes. In such systems, the rate of air dissolution is reduced due to lower partial pressure of gaseous species in the plastron, resulting in increased longevity by an order of magnitude. Despite increased longevity, these plastrons still gradually decay over time. To address this, a method involving minimal localised heating (1-2ºC) was developed to replenish the plastron and indefinitely maintain superhydrophobicity. This approach is an environmentally sustainable and scalable solution for long term underwater applications.
  • Item
    Thumbnail Image
    Interactions between inverse bicontinuous cubic phase materials and encapsulated biomolecules
    Meikle, Thomas G. ( 2016)
    The inverse bicontinuous lipidic cubic phase provides a robust, thermodynamically stable membrane mimetic, with the ability to encapsulate a wide range of biomolecules, including amino acids, peptides and proteins. The unique structural architecture and desirable properties of cubic phase lipids have led to their use in wide range of applications, including as a crystallization matrix for membrane proteins, as well as a hosting environment for therapeutic compounds, enabling the design of drug delivery materials. Within the cubic phase-biomolecule system, a complex structural relationship exists between the chemical structure of the lipid, the overall mesostructure of the system, and the structure and properties of encapsulated compounds. At present this relationship is poorly defined, slowing the further development and implementation of these materials. To investigate the structural relationship between lipidic bicontinuous cubic phase bilayers and encapsulated biomolecules, a number of different cubic phase-biomolecule systems have been examined. The encapsulated biomolecules range in complexity from free amino acids to large integral membrane proteins, and give this work relevance to a number of different end use applications, including the delivery and release of small molecule drugs and peptides, as well as the in meso crystallization of integral membrane proteins. We have examined the effects of encapsulating L-histidine and L-phenylalanine within a range of different cubic phase lipids on the mesostructure of the cubic phase. Subsequently, the translational diffusion of these compounds was measured using PFG-NMR, and a linear relationship was discovered with the diameter of the nanoscale water channels. It was demonstrated that a simple mathematical model can be used to predict in vitro release rates of small molecules based solely upon NMR determined in meso diffusion coefficients. Encapsulation of the transmembrane, anti-microbial peptide gramicidin A’ in the lipidic bicontinuous cubic phase revealed a number of interesting structural changes, both in the bilayer and the peptide itself. These changes were found to be strongly correlated with bilayer parameters such as lateral pressure profile and hydrophobic mismatch, providing further insight into the structural considerations of the system. Studies of peptide encapsulation were expanded to include a broader range of antimicrobial peptide structures, including melittin and alamethicin, which along with gramicidin A’ were encapsulated within a number of different cubic phase nanoparticle formulations. Thorough characterization and analysis of each system revealed that as in the bulk phase, the structural changes in cubosome systems were dependent on factors such as hydrophobic mismatch and lateral pressure of the bilayer, as well as peptide structure and charge. The host lipid identity was also found to significantly modulate peptide uptake. In later work, we examine the encapsulation of the integral membrane protein intimin in the lipidic cubic phase, in a study which elucidates the mesophase properties which lead to successful protein crystallization. The structural parameters of the mesophase were tracked throughout the crystallization process, providing insight into the mesoscale changes occurring during crystal nucleation. Cubic phase bilayers comprised of a range of lipids were also characterized and a strong correlation was found between properties such as protein and lipid diffusion, and successful crystallization. This body of work constitutes a significant contribution to our understanding of the interactions between encapsulated biomolecules and the cubic phase bilayer. The structural trends and considerations highlighted have implications for the further implementation of these materials, including in the rational design and formulation of drug delivery materials and in meso crystallization experiments. Information of a fundamental interest is provided through broader observations regarding the interaction of biomolecules with lipid membranes.
  • Item
    Thumbnail Image
    Solid-state thin films solar cells on polymer substrates
    DKHISSI, YASMINA DELPHINE ( 2015)
    To meet the world’s ever-growing energy needs while facing current environmental challenges, solid-state thin film solar cells offer a low-cost renewable alternative for generating electricity. Polymer substrates give thin films lightweight and flexibility, broadening their potential applications to consumer electronics and power-generating textiles. The use of solution processable materials on flexible substrates paves the way towards roll-to-roll printing of photovoltaics, taking advantage of available, low-cost manufacturing technologies. However, constructing efficient solar devices on plastic substrates remains difficult due to the substrate’s intrinsic low-temperature limitation. Furthermore, the stability of thin films needs to be addressed in order for them to become viable candidates for commercial applications. In the first research Chapter, volatile liquid electrolytes were replaced with composite polymer electrolytes to improve the stability of dye-sensitized solar cells (DSCs). On one hand, the infiltration of viscous electrolytes through the TiO2 working electrode was suspected to constitute a major limitation to producing efficient flexible devices. On the other hand, the temperature restriction of polymer substrates prevented the sintering of mesoporous TiO2 directly onto these substrates. Therefore, submicrometer-sized mesoporous TiO2 beads, that can be treated prior to the device fabrication, were investigated as a potential route to overcome the aforementioned issues. Efficient quasi-solid-state DSCs were successfully fabricated on plastic substrates, and studies on the infiltration of the electrolyte through the electrode were conducted. Then, efforts were focused on photovoltaics utilizing inorganic-organic perovskites, an emerging technology with reported efficiencies rivalling existing commercial solar cell technologies. Solution processed, these hybrid materials can be prepared at low temperature, thus becoming a potential candidate for application to polymer substrates. Nevertheless, the majority of these solid-state devices constructed on glass employ a high temperature processed inorganic hole blocking layer (≥450 °C), non-compatible with flexible applications. In this regard, efforts were directed towards the development of methods to fabricate efficient flexible solid-state perovskite devices on polymer substrates with a range of low-temperature processed hole blocking layers. As a result of the moisture and temperature sensitivity of these hybrid perovskites, a perovskite deposition method was developed and optimized, in order to improve the reproducibility of these devices. In Chapter 4, power conversion efficiencies (PCEs) over 13 % were attained for TiO2-based flexible planar perovskite devices, with an average efficiency of 11.8 ± 1.8 %. In Chapter 5, ZnO was chosen as an electron selective material given its advantages for printing, and PCEs over 10 % were achieved for spin-coated ZnO-based perovskite solar cells on polymer substrates. Exacerbated degradation of CH3NH3PbI3 was observed when deposited on ZnO, therefore the correlation between the annealing conditions and the decomposition of the perovskite film was examined. In Chapter 6, practical industrial concerns such as the stability and the manufacturing processability of these devices were considered. PCEs over 10 % were obtained for flexible perovskite devices with a printed TiO2 layer, but the device reproducibility was affected by the fabrication protocol. Finally, the stability of TiO2-based perovskite devices on polymer substrates was assessed, and encapsulation of flexible devices was performed to extend the device lifetime. To understand the origins of the degradation of CH3NH3PbI3-based solar devices, a range of storage conditions was used, and their impacts on the perovskite film were investigated. The following research questions will be addressed throughout the thesis: -Is the infiltration of the electrolyte through the TiO2 film critical? -Can the low temperature processing restriction on polymer substrates be overcome by developing a low temperature inorganic blocking layer synthesis? -Can solid-state solar cells on polymer substrates be made commercially viable? -What are the parameters that affect the degradation of CH3NH3PbI3-based perovskite solar cells?
  • Item
    Thumbnail Image
    Excitation energy transfer in nanocrystal systems
    Beane, Gary ( 2014)
    The development of sensing platforms capable of accurately and sensitively detecting toxins, small molecules and DNA, has been an area of intense interest by researchers in defence, medicine and public safety. The photophysical phenomenon of Förster Resonance Energy Transfer (FRET) provides a route to achieving a high quality transduction signal for analyte detection, and the creation of next-generation sensing platforms. However, whether this model is valid to describe energy transfer in nanoparticle-dye systems has yet to be satisfactorily proven. A detailed background to FRET in general, and its application to nanoparticle fluorophores specifically, will be provided in Chapter 1. A detailed description of experimental protocols for both the synthesis of semi-conducting nanocrystal fluorophores, so called ‘Quantum Dots’, and a number of rigid, dye labelled polyproline peptides will be detailed in Chapter 2. Back- ground information about specific experimental techniques, including peptide synthesis and single particle spectroscopy, is also provided. In Chapter 3 energy transfer between Quantum Dots (QDs) and molecular dye molecules, is detailed. Using rigid polyproline spacers to controllably vary the separation it is found that, in contrast to simple dye-dye systems, the ratio of dye adsorbed to each QD must be explicitly accounted for by the Poisson distribution. Moreover, it is found that dye fluorescence quantum efficiency is also distance dependent, which obscures enhancements to the dye fluorophore due to energy transfer. However, accounting for both of these effects, it is found that the efficiency of energy transfer from QDs to adsorbed dye molecules obeys an R−n dependence with n = 6, as predicted from Förster Resonance Energy Transfer (FRET). In Chapter 4 energy transfer between ZnO nanoparticles to adsorbed dye molecules, is detailed. Remarkably, energy transfer in this system is found to occur from an intraband electronic state. It is found that the entire broad emission from radiative decay of this state, is uniformly reduced upon dye adsorption with a concomitant enhancement in the dye emission. These observations demonstrate that energy transfer from ZnO involves a single electronic state coupled to the phonon modes of the crystal lattice. It is also found that this energy transfer to the adsorbed dye molecules is very efficient, regardless of the orientation of the dipole moment of the dye molecule and the distance to the defect state. Finally in Chapter 5, a novel parameter for quantifying fluorescence intermittency, ‘blinking’, in QDs is presented. As energy transfer at the single particle level is often confounded by this phenomenon, additional insight that leads to its suppression is desirable. The parameter is essentially a measure of the total fractional correlation of single QD time-trajectories, which is found is related to the ensemble photoluminescence quantum yield and effectively independent of the manner in which the time-trajectory is binned.
  • Item
    Thumbnail Image
    Interfacial effects on aqueous sonochemistry and sonoluminescence
    Sostaric, Joe Zeljko ( 1999-06)
    The dissolution of quantum sized CdS and MnO2 particles in water was conducted using 20 kHz ultrasound. CdS particles were found to dissolve chemically via an oxidation process while MnO2 particles dissolved via a reductive process. It was found that the dissolution of the colloids could be controlled via the addition of surface active chemicals to solution and by varying the saturation gas type. In the presence of Na2S or propan-2-ol and argon gas, the dissolution of CdS was inhibited, whereas the addition of alcohols (methanol, ethanol, propan-2-ol, butan-1-ol and pentan-1-ol) to the MnO2 system led to an increase in the amount of dissolution for a given time of sonication. This increase in dissolution was found to be dependent on the ability of the surface active radical scavenger to accumulate around the bubble interface during the cavitation process. Eventually, at higher alcohol concentration there was a plateau or a limiting value reached for the efficiency of colloid dissolution which was common for each alcohol. (For complete abstract open document)
  • Item
    Thumbnail Image
    Cubic phase lipids as novel biosensing surfaces
    FRASER, SCOTT ( 2011)
    Sub-micron particles, called cubosomes, formed from the fragmentation and steric stabilization of inverse bicontinuous cubic phases (QII) of lipids have a microenvironment reminiscent of biological lipid bilayers, making them promising class of material for a number of applications. The phase behaviour of the amphiphile phytantriol (3,7,11,15-tetramethyl-1,2,3-hexadecanetriol) is well characterised and we describe studies of cubosomes formed from the QII phase of phytantriol/water systems. Cubosomes tailored for specific applications require additional components, which can alter the structure and phase behaviour of the system, for example the incorporation of ligands such as a receptor lipid or protein for biomedical applications. Hence, a study of the effect of additives on the phase behaviour of cubosomes was undertaken. Data obtained using the small-angle X-ray scattering (SAXS) beam line at the Australian Synchrotron showed that addition of non-functional amphiphiles to the matrix of phytantriol/water cubosomes affected the lattice parameter of the cubosomes and, hence, the cubosome microstructure. Oleic acid and monoolein stabilized the Pn3m cubic phase of the cubosomes, whilst CTAB and SDS caused a loss of structure at lower temperatures/molar concentrations of additive. Synchrotron SAXS was also used to investigate the effect of functional additives, the ganglioside receptor, GM1, and the biotinylated phospholipid, bDSPE, on the matrix of the phytantriol/water cubosomes. The results of these studies indicated that both systems would yield stable double diamond Pn3m cubosomes at low – medium molar concentrations of additive. To further investigate the viability of these systems for biomedical and biosensing applications we screened their binding capacity against their natural ligands. Using a combination of enzyme-linked immunosorbent assay (ELISA), surface plasmon resonance (SPR), and quartz crystal microbalance (QCM) techniques, we showed that GM1 containing cubosomes specifically bind to cholera toxin (CT) with an IC50 of 1.6 nM, which is more potent than any currently available inhibitor. Specific targeting of bDSPE containing cubosomes to avidin-modified surfaces was visualised using cryogenic transmission electron microscopy (cryo-TEM), as was the ability of surface-bound bDSPE cubosomes to specifically bind ligands from solution. Further QCM results demonstrated how bi-functionalised cubosomes, containing GM1 and bDSPE, could be targeted to a surface via one functionality, then sense a secondary ligand via a separate functionality. The results presented in this thesis provide insight into the effect of additives on the phase behaviour of cubosome systems and factors, which affect their potential biomedical and biosensor applications.