Search

Lupus nephritis (LN) is a significant cause of various acute and chronic renal diseases, which can eventually lead to end-stage renal disease. The pathogenic mechanisms of LN are characterized by abnormal activation of the immune responses, increased cytokine production, and dysregulation of inflammatory signaling pathways. LN treatment is an important issue in the prevention and treatment of systemic lupus erythematosus. Mesenchymal stem cells (MSCs) have the advantages of immunomodulation, anti-inflammation, and anti-proliferation. These unique properties make MSCs a strong candidate for cell therapy of autoimmune diseases. MSCs can suppress the proliferation of innate and adaptive immune cells, such as natural killer cells (NKs), dendritic cells (DCs), T cells, and B cells. Furthermore, MSCs suppress the functions of various immune cells, such as the cytotoxicity of T cells and NKs, maturation and antibody secretion of B cells, maturation and antigen presentation of DCs, and inhibition of cytokine secretion, such as interleukins (ILs), tumor necrosis factor (TNF), and interferons (IFNs) by a variety of immune cells. MSCs can exert immunomodulatory effects in LN through these immune functions to suppress autoimmunity, improve renal pathology, and restore kidney function in lupus mice and LN patients. Herein, we review the role of immune cells and cytokines in the pathogenesis of LN and the mechanisms involved, as well as the progress of research on the immunomodulatory role of MSCs in LN.

The objectives of this project are to develop novel thermotropic liquid crystalline polymers with their liquid crystalline phase ranges matching the process windows of some important engineering thermoplastics. RG 35/99

Polyhedral oligomeric silsesquioxane (POSS) is a cage-like molecule with a well-defined and highly symmetric structure having a size of 0.5 nm diagonally. The POSS material demonstrates a truly hybrid inorganic core / organic shell architecture with one or more vertexes covalently substituted by a wide range of functional groups which render materials with versatile properties for many applications. Recent studies indicate POSS incorporated conjugated polymers show improved performance due to less aggregation caused by the cubic cage which interrupts close packed linear polymers. Our previous work indicated that molecules consisting of a POSS cage and rigid organic short chains exhibit strong quantum confinement effects which imply organic-quantum-dot-like properties. In this research, a systematic study on the effect of incorporation of POSS on the properties, especially optical characteristics, of luminescent nano-particles and hyper-branched polymers was conducted in three areas: 1) Well defined blue POSS luminescent dots were designed and synthesized where conjugated oligomers are directly grafted onto eight vertexes of POSS cage. It was found that excitons are confined in each arm of emissive units and hence excitons are confined within each dot and isolated chromospheres are obtained. 2) Highly regioselective bromination of octaphenyl-POSS was achieved. The green POSS light emitting dots based on this structure were synthesized to achieve well defined nano-particles with precisely controlled structures and sizes. DOCTOR OF PHILOSOPHY (MSE)

Electrochromism is a phenomenon that some materials involving reversible color changes through redox reactions under electrical stimulus. This PhD work is aimed at developing hybrid materials based on conjugated polymers (CPs) and transition metal oxides (TMOs), which combine the advantages of both materials and exhibit enhanced electrochromic properties, and understanding the underlying mechanisms. Tungsten trioxide (WO3) and poly(3,4-ethylenedioxythiophene) poly(styrene sulfate) (PEDOT:PSS) or its derivatives were employed to produce hybrid EC materials and devices. Firstly, the hybrid EC materials based on WO3 nanoparticles (NPs) and PEDOT:PSS were synthesized through the layer-by-layer (LBL) assembly method. Polyethylenimine (PEI) was applied to promote the electrostatic force between the two components. Single component films, namely PEDOT:PSS and WO3-NP films, were also fabricated as reference films through the same method. The hybrid films exhibit enhanced EC properties, especially the coloration efficiency (117.7 cm2/C), compared with the reference films. The enhancement may be attributed to the efficient charge transfer process between components, since the hybrid film exhibit enhanced electrical conductivity during switching as verified by the scanning electrochemical microscopy (SECM). According to literature and SECM results, the WO3 films experience conductive-to-nonconductive transition as applied potentials go from positive to negative, while the PEDOT:PSS presents high conductivity at its oxidized state. Therefore, in the hybrid system, the synergistic interactions between components promote the enhanced charge transfer process, resulting in improved EC performance. However, the nonconductive PEI layers involved may prohibit the redox reactions and the charge transfer process in the hybrid system, which would lower the EC performance. Secondly, to further improve the EC performance, the hybrid films based on WO3 and PEDOT:PSS were synthesized by one-pot sequential electrodeposition method without any PEI component. Single component films of same thickness were also produced as reference films. Compared with the reference films, the hybrid films exhibit significantly improved EC properties, especially the optical contrast (47%) and electrochemical stability. It’s resulted from the simultaneous switching and synergistic interactions of two components. The morphology and structure of the hybrid films can be manipulated through tailoring the electrodeposition parameters to enlarge the interfacial area, leading to efficient interactions between the components. Thirdly, the charge-balancing dopant PSS involved in the aforementioned hybrid systems is an electrical insulator, which may block the charge transfer process between WO3 and PEDOT, and lower the EC performance. Poly(4-(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl-methoxy)-1-butane sulfonic acid (PEDTS) is a self-doped PEDOT derivative bearing a sulfonate group in each repeat unit. It was employed to replace PEDOT:PSS in the hybrid systems. A hybrid aqueous suspension was obtained through mixing the EDTS monomers and WO3 NPs in acidic solutions, where the PEDTS were obtained through air-assisted chemical oxidation and spontaneously attached onto the WO3 NPs. The electrochromic devices (ECDs) assembled based on the hybrid films through air-brush spraying exhibit significantly improved optical contrast and electrochemical stability owing to the enhanced synergistic interactions between the two active components. In conclusion, the combination of WO3 and PEDOT:PSS or its derivatives is an effective way to improve the electrochromic properties owing to the synergistic interactions between the components. The polymers may act as buffer components for WO3, while the WO3 can prevent the over-oxidation of the polymers in the hybrid systems. And the combination of the two components also facilitates the charge transfer process in the hybrid system. DOCTOR OF PHILOSOPHY (MSE)

Electrochromic (EC) materials and their devices have been extensively researched over the years especially those based on conjugated polymers. Although these materials are now able to meet the key performance indicators such as high optical contrast and fast switching, there are still challenging problems faced by current EC technologies, particularly the stability of EC devices. This thesis is structured into different sections, starting from the motivation of this work, which is to explore the structural design of conjugated polymers to improve their EC properties (Chapter 1), followed by a literature review on the different types of EC materials and devices (Chapter 2) and the different experimental methodologies used (Chapter 3). In the subsequent sections, three different approaches for the design of new electrochromic polymers are proposed, and their electronic and EC properties are discussed. First, in chapter 4 and 5, a new synthetic methodology based on the inverse electron demand Diels-Alder (iEDDA) reaction has been created for the synthesis of new electron acceptors. Using this new synthetic methodology, novel electron acceptors such as pyrrolo[3,4-d]pyridazine-5,7-dione (PPD) and pyrrolo-acenaphtho-pyridazine-diones (PAPD) have been successfully synthesized and found to be highly electron deficient with very low lying lowest unoccupied molecular orbital (LUMO) energy levels. Their LUMO energy levels are lower than most of the commonly used electron acceptors. As such, this new synthetic methodology can be used to synthesize novel electron acceptors and contribute in increasing the existing library of electron acceptors available in the preparation of donor-acceptor polymers. These newly prepared electron acceptors moieties, PPD and PAPD, are then used in the synthesis of electrochromic polymers PPD1 – PPD3 and PAPD1 – PAPD5 respectively. All the polymers obtained exhibit very high solubility in common organic solvents. The PPD series of polymers displays purple to transmissive blue electrochromism while the PAPD series shows red to grey electrochromism. In particular, PAPD3 possesses very high optical contrast of 81 % in the near infra-red (NIR) region and attains high redox stability with only a 0.6 % drop in optical contrast after 800 cycles of redox cycling. Secondly, in chapter 6, the approach of utilizing 4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene (IDT) as a building block for EC conjugated polymers has been demonstrated. Due to its good performances, IDT is frequently used to prepare organic electronics, but they are rarely reported in EC materials. Herein, the IDT units are co-polymerized with dioxythiophene-based units to test its feasibility as electrochromic building block. The resultant polymers are found to exhibit a red to black electrochromism with high optical contrasts in both visible and NIR regions. As such, IDT units can be considered as potential building blocks in electrochromic materials. In chapter 7, the use of triphenylamine (TPA) as a tool to improve the redox stability of the electrochromic polymers has been demonstrated. A series of EC polymers with varying amount of TPA incorporated has been synthesized. The polymers are obtained in medium yields and highly soluble in organic solvents. High molecular weights ranging from 59 to 81 KDa are achieved and the polymers display multi-colored electrochromism. These polymers are able to transit from purple/red at reduced state, to grey at intermediate state, and then to transmissive blue at oxidized state. Notably, polymer TPA3 is able to achieve a six-fold improvement in redox stability with the incorporation of just 15 % of TPA into its polymer chains. With such significant improvement, this simple yet effective design strategy could be potentially used to modify EC polymers to enhance their redox stabilities. Lastly, a summary of my thesis is presented in chapter 8, where the three proposed design strategies are proven to be effective in creating good performance electrochromic materials. Some significant contributions made in this thesis are also being highlighted with a discussion on the suggestions for future work. DOCTOR OF PHILOSOPHY (MSE)

Carbon-based hybrid nanofibers, which are composites derived from incorporation of organic or inorganic nanofillers into one-dimensional carbon matrix, have attracted tremendous attention for applications in lithium ion batteries (LIBs) due to their large aspect ratio, high specific surface area and fast lithium ion intercalation/de-intercalation rate. The organic or inorganic materials could be embedded in or wrapped over the amorphous or graphitized carbon phase, depending on the preparation method. Electrospinning followed by carbonization is one of the most powerful techniques to prepare CNFs since it allows mass production, morphology and structure control, and extremely large aspect ratio. Inorganic components have been combined with electrospinning-derived CNFs to further improve the electrochemical performance, for which the morphologies and structures of the hybrid nanofibers are critical for the improvement. Although different morphologies have been formed via electrospinning, leading to varied performance, the tailoring of morphologies of carbon-based hybrid nanofibers through carbonization is not yet well understood. Thus in this work, a systematic study was conducted on the effect of carbonization on morphologies and structures of carbon-based hybrid nanofibers. Their electrochemical properties were studied as anode of LIBs and correlated to the morphologies. First of all, randomly orientated carbon-SnO2 hybrid nanofibrous mats were prepared via conventional single-spinneret electrospinning followed by carbonization. Various tin-containing salts, including tin acetate (Sn(CH3COO)2), tin chloride dihydrate (SnCl2·2H2O), tin sulphate (SnSO4), tin sulphide (SnS), were used as precursors of SnO2, and polyacrylonitrile (PAN) was used as carbon source. The morphologies and structures of the hybrid nanofibers were investigated. It is shown that under the same carbonization conditions, carbon-SnO2 hybrid nanofibers with different morphologies are formed from different SnO2 precursors. The SnO2 nanoparticles are uniformly distributed in CNFs in SnSO4 and SnS-derived hybrid CNFs, while a carbon-SnO2 core-shell morphology is achieved in Sn(CH3COO)2 and SnCl2·2H2O-derived ones. Corresponding SnO2 nanofibers with varied structures, in either solid or hollow, are also produced through simply burning out the carbon phase. When the carbon phase is completely removed, the nanoparticles touch each other, forming 1D aggregates. Thus, the hollow SnO2 nanofibers actually consist of small SnO2 nanoparticles. DOCTOR OF PHILOSOPHY (MSE)

Electrochromism is a phenomenon related to reversible color transformation of a material produced by the application of an external electric field. Electrochromic contrast and switching speed are the key performance indicators for an electrochromic material. The motivation of this work is to make use of cyclotriphosphazene (CP) and polyhedral oligomeric silsesquioxane (POSS) to synthesize novel star-like electrochromic conjugated polymers and study the synergistic effect of star-like structure and film fabrication techniques on electrochromic properties. Firstly, a new series of electrochromic hexa(4-aminophenoxy) cyclotriphosphazene-polyaniline copolymers (HACP-PANI) were synthesized. Dodecylbenzenesulfonic acid (DBSA) doped 4.0%HACP-PANI (4%HACP-PANI/DBSA) exhibits a significant enhancement in electrochromic contrast as compared with DBSA-doped homopolyaniline (PANI/DBSA). The contrast enhancement can be attributed to the easier diffusion of cations in the film of 4%HACP-PANI/DBSA, as evidenced by a significant increase in ionic conductivity, whereas the switching speed of 4%HACP-PANI/DBSA is not improved significantly due to the excessive external dopants. In order to avoid using excessive amounts of doping acid, HACP-PANI and POSS-PANI copolymers in emeraldine base form were synthesized and fabricated into multilayer thin films with poly(2-acrylamido-methane-2-propanesulfonic acid) (PAMPS) via layer-by-layer (LbL) assembly. However, the contrast and switching kinetics of 4%HACP-PANI/PAMPS is not improved compared with those of PANI/PAMPS under dynamic switching because of its densely packed structure brought by the flexible -O- linkage in HACP-PANI. DOCTOR OF PHILOSOPHY (MSE)

Electrochromism is a phenomenon that materials are able to change its color reversibly under external potential. The mechanism of electrochromic materials is redox reactions in most of the cases. Composite materials have been widely used for electrochromic applications, as they have the potential to exhibit the advantages of both components. Conjugated polymer-based composite is a popular option due to the conductivity and flexibility of conjugated polymers. The challenge in design of a high-performance composite material is to achieve synergistic effects in desired aspects instead of getting average performance of the components. The design guidelines of electrochromic composite are not well established. Thus, the aim of the thesis is to design new conjugated polymer-based composite systems in which the conjugated polymers and the other components are complementary in certain aspects, and study how interfacial interactions affect synergistic effects of the complementary components in conjugated polymer-based electrochromic composites. The key hypothesis is that with proper structural design, strong interfacial interactions between conjugated polymers and the other components may induce significant synergistic effects, positively influencing electron transport, oxidation/reduction potentials, electrochemical stability, and/or mechanical robustness. To verify the hypothesis, two composite systems have been studied are molybdenum trioxide/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (MoO3/PEDOT:PSS) and polyaniline-carbon nanotube (PANI-CNT). The components have complementary properties in conductivities or mechanical properties. The interfacial interactions in each composite are electrostatic interaction and covalent bond, respectively. Both composites show enhanced electrochromic and electrochemical properties. It is proved that strong interfacial interactions between these two pairs of components induce significant synergistic effects. This conclusion provides a rationale for designing high-performance composite materials for electrochromic applications. Doctor of Philosophy

The conventional, linear, take-make-waste economy which was a by-product of the industrial revolution is not a viable option anymore. Environmental concerns are driving the development of a new circular model in which reduce, reuse, and recycle are key. Since this circular model would keep materials in commerce for longer, safer product designs that would reduce the amount of hazardous materials are vital. In this work, the aim is to implement this design philosophy in producing polymer/graphene nanocomposites as a rapidly emerging class of materials. The design philosophy is based on two strategies: first, to substitute conventional, synthetic components by their naturally-occurring counterparts and, second, by eliminating chemicals by assigning their roles to other multifunctional components. Graphene and, by extension, polymer/graphene nanocomposites have seen huge interest in academia and industry. Among different methods to produce graphene, liquid-phase exfoliation (LPE) is one of the most commonly used. LPE is a low cost, industrially-friendly, high-yield process in which graphite flakes are exfoliated into their 2D constituents, i.e., graphene, and stabilized in a liquid medium. Water is the most desirable medium for LPE but graphene needs stabilization with surfactants or stabilizers because of the huge mismatch between the surface energies of water and graphene. There have been a myriad of synthetic surfactants and stabilizers studied for this purpose, but natural surfactants have seen less attention. Here, lignin, an abundant, undervalued, byproduct of paper industry, will be used as a naturally-occurring stabilizer for graphene. Lignin-modified graphene (LMG) is non-covalently modified meaning its sp2 structure, which is the reason for its amazing properties, is unperturbed. Different polymer/graphene systems based on this sustainable design philosophy are produced. In the first work, LMG is added to waterborne polyurethane (WPU) to produce conductive films for antistatic coating applications. Since durability against environmental damage is an important factor for these coatings, functional properties such as self-healing and UV-resistance are required. However, instead of using self-healing agents and synthetic UV blockers, LMG is tasked with enabling self-healability and improving UV stability. Thanks to its multifunctional properties, LMG can act as a photothermal converter creating heat after being illuminated by near-infrared (IR). This increases the rate of polymer diffusion at the site of damage which results in fast self-healing of the damage. Due to the anti-UV properties of LMG and lignin, these nanocomposite coatings show remarkable UV resistance as well. The combination of self-healing and UV-stability renders these films highly durable. In the second work, graphene was used to produce multi-functional sensors. Commercially-available polyurethane (PU) sponges can become conductive by dip-coating in aqueous LMG suspensions. These sponges show electrical sensitivity to compression, and thanks to their high mechanical stability, they are able to accurately sense pressure with high accuracy over 5000 compression-release cycles. Since LMG acts as a negative temperature coefficient thermistor, these sensors can measure temperature with high sensitivity as well without the need for any temperature-sensitive component. Finally, this design philosophy is taken to the next level by completely removing lignin in the third work. Here, WPU can be used as a stabilizer to produce WPU-modified graphene (PMG). In contrast to the WPU/LMG system, WPU/PMG nanocomposites have no external stabilizer. These highly conductive nanocomposites are electromechanically sensitive and show huge electromechanical responses to deformation. In addition to being the polymer matrix and stabilizer, WPU endowed the sensors with shape conformality too, which significantly increased the real-life sensitivity of the sensors in monitoring biomechanical deformations and reproducing blood-pressure waveforms. This innate shape-conformality obviated the need for an additional skin-conformal layer. By adopting these strategies, organic liquid media and synthetic surfactants/stabilizers can be substituted by water and naturally-occurring lignin, or in case of the last study, lignin can be eliminated. Other functional additives such as self-healing agents, synthetic UV-stabilizers, or active materials are not required thanks to the multifunctional and multi-stimuli responsive nature of graphene. Doctor of Philosophy

In this work, thin films of poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) were prepared via two routes, spin coating and electrospinning. It was found that electrospinning of PVDF from its N,N-dimethylformamide/acetone solutions can induce molecular orientation of PVDF chains and hence promote the formation of ?-phase. The addition of 3 wt.% of tetrabutylammonium chloride (TBAC) into the polymer solutions can effectively improve the morphology of the electrospun fibers due to the great increase in the conductivity of the solutions, and lead to almost pure ?-phase in the fibers. TBAC, a hygroscopic salt, could retain water in the fibers, which may led to hydrogen bonding between the water molecules and the fluorine atoms of PVDF and induce more trans conformers, while electrospinning induces chain orientation, which promotes inter-chain registration and hence stabilizes ?-nuclei. Modification of the rotating disk collector allowed the collection of thin films of aligned electrospun PVDF and P(VDF-TrFE) fibers, enabling the measurement of the hysteresis loops of these thin films. Electrospun PVDF performed significantly better than P(VDF-TrFE) which differs from the trend observed from spin-coated films. The degree of crystallinity and the contribution of other polar phases in electrospun PVDF fibers were believed to be the main reason for this phenomenon. The blending of PVDF and P(VDF-TrFE) across various compositions did not give rise to significant co-crystallization, regardless of the processing method used. Preliminary results of treatment of PVDF with hydrogen peroxide yielded spin-coated films with high polar phases (both ?- and ?-phase) with impressive a-phase suppression, allowing a one step method to produce films with high polar phase content. Master of Engineering (SME)

222 p. Hydrogen-bonded liquid crystalline polymers have unique properties that combine many attractive features that are characteristic of conventional polymers and liquid crystals. Additionally, they have the ability to respond to external stimuli due to the reversibility of the hydrogen bond. The diverse properties of these materials have therefore opened up a multitude of promising applications and disciplines. Consequently, in order to attain a deeper understanding and aid the exploration of potential technological advancements in such materials, new hydrogen-bonded main chain liquid crystalline polymers were prepared. The structure-property relationships were reviewed and their thermal and liquid crystalline properties were examined. Master of Engineering (MSE)

This work is focused on the preparation of PEN/clay nanocomposites and the characterization of their structures and properties. The preparation of the nanocomposites by in-situ polymerization and melt intercalation was investigated, and the extent of clay dispersion at various length scales was examined by x-ray diffraction, polarizing optical microscopy and transmission electron microscopy. The dynamic mechanical properties and thermal stabilities of the nanocomposites were studied and correlated to their hierarchical structures. In addition to the direct stiffening effect of clay, it was found that the modified crystalline morphology, and the clay-induced orientation of the PEN lamellae/crystallites can also lead to additional reinforcement in the nanocomposites. Finally, the polymorphism behavior of the nanocomposites was investigated. The studies revealed that the temperature-dependent polymorphism behavior of the PEN/organoclay nanocomposites arises because the organoclays could simultaneously exert a hindered heterogeneous nucleating and plasticizing effect. DOCTOR OF PHILOSOPHY (SME)

Maleic anhydride modified polypropylene (MAPP) was compounded with commercially available surface modified montmorillonite in a twin screw extruder. Re-compounding ensured the removal of visible tactoids from extrudable while TEM and WAXD techniques showed non-uniform dispersion of clay platelets, however, quite a few nanometer-thick clay layers can be identified. Master of Engineering (SME)

This study was carried out to design and synthesize new liquid crystalline polymers, which have broad mesophase range matching processing temperature windows of some common engineering plastics, aimed at exploiting their applications as processing aids for the thermoplastics. Master of Engineering (SME)