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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 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

Polymer/clay nanocomposites have been widely investigated over past three decades due to the dramatic boost in properties at low filler content. Although organoclay (clay modified with organic surfactants) is commonly used to reinforce the polymer, yet the reinforcing extent has yet reached the optimum performance. Besides, both organic surfactants (organic compounds with long hydrophobic tails and hydrophilic heads) and polymers are susceptible to photo-induced degradation especially in outdoor environments, making polymer/clay nanocomposites vulnerable in practical applications. In order to overcome the aforementioned problems, in this research, D-clay (polydopamine-coated clay) was studied as multifunctional filler to improve not only interfacial interactions with a wide range of polymer matrices but also stabilities of the nanocomposites. D-clay was incorporated into both elastomer (polyurethane) and semi-crystalline thermoplastic (polypropylene) systems. The structure-property relationships of the resultant nanocomposites were investigated using TEM, XRD, DMA, tensile testing, FTIR, TGA and DSC. In particular, the reinforcing mechanism of D-clay in polyurethane (PU) nanocomposites was studied with respect to surface chemistry, filler loading and filler size. On the other hand, the stabilizing function of D-clay was verified using polypropylene (PP) as the polymer matrix since PP is well-known for its poor UV stability. Firstly, D-clay was incorporated into polyether-based PU via solvent mixing and good filler dispersion was obtained. The results showed pronounced improvement in mechanical properties, such as stiffness, tensile strength and strain at break, at 3wt% clay loading. The remarkable improvement can be attributed to the excessive hydrogen bonds between D-clay and the hard segments (hard segments are made of diisocyanate and the short-chain diol) of PU. This strong interfacial interaction between D-clay and hard segments not only facilitates the stress transfer across the filler and polymer matrix, but also acts as nucleating agent for hard segment crystallization, leading to higher hard segment crystallinity. Furthermore, the impact of high D-clay loading on mechanical properties and hard segment crystallization was investigated using polyester-based PU as matrix since severe phase separation was observed in the polyether-based PU. The results showed polyester-based PU nanocomposites with D-clay concentration above 5 wt% formed percolated clay network structure, this hindered the movement of both hard and soft segments to a certain extent. Consequently, polyester-based PU/D-clay nanocomposites showed drastic enhancement in tensile modulus. On the other hand, the effect of particle size was studied using polycaprolactone (PCL)-based PU as matrix. In this case, polydopamine-modified layered double hydroxides (D-LDHs) of different sizes were used as the fillers and the shape memory performance of the nanocomposites was evaluated. It was found that D-LDH interacted strongly with hard segments, enhancing phase separation and promoting crystallization of both hard and soft segments profoundly. The nanocomposite with 2 wt% of small D-LDH exhibited good shape memory properties since most small D-LDH interacted with hard domains at low filler loading. Hence, the incorporation of small D-LDH can reinforce hard domains without sacrificing the elasticity of the system. In order to verify the stabilizing capability of D-clay, D-clay was also introduced into the PP system. This is because PP is vulnerable to degradation owing to the presence of volatile tertiary hydrogens in the polymer backbone. The results showed drastic improvement in UV resistance and thermal stability of PP/D-clay owing to the effective radical scavenging ability of melanin-like PDA layer on clays. Meanwhile, the excellent UV resistance of PP/D-clay nanocomposites can be attributed to the masking effect imposed by PDA coating. Besides, the mechanical properties of PP/D-clay were better than organoclay at similar clay loading on account of the stronger interfacial interactions. DOCTOR OF PHILOSOPHY (MSE)

Syntactic foam is a special class of light weight composite materials. It has been found useful in many areas, such as aerospace and submarine. In order to further widen its application spectrum, the enhancement in the mechanical properties of syntactic foams is essential. Besides mechanical properties, their electromagnetic interference (EMI) shielding has not been explored because of the non-conductive nature of the traditional fillers and matrices of syntactic foams. However, due to their light weight advantage, syntactic foams become an attractive candidate for EMI shielding applications, for electronic devices and electrical equipments. Therefore, developing syntactic foams with good mechanical properties and/or EMI shielding performance would expand their applications for future composite materials. In this work, hollow carbon microspheres (HCMs), instead of the traditional non-conductive microspheres, were employed to fabricate syntactic foams with phenolic resin as matrix. In the attempts to improve mechanical properties and/or EMI shielding performance of the resultant foams, three different approaches, namely coupling agent, carbonization and carbon nanofiber (CNF) reinforcement, were applied. In the first approach, the effect of coupling agent on mechanical properties and EMI shielding performance of syntactic foams was studied. Results showed that better interfacial adhesion could be induced from the coupling agent treated HCMs, which led to the enhancement in compressive strength, flexural strength and fracture toughness of the syntactic foams. Toughness mechanisms, including crack deflection, crack bowing and debonding, were proposed. However, EMI testing results showed that the introduction of coupling agent had no effect on the EMI shielding performance, because a three-dimensional electrically conductive network was not formed. In the second approach, the effect of carbonization on mechanical properties and EMI shielding performance of the syntactic foams was studied. The electrical conductivity was increased by approximately seven orders of magnitude, which resulted in a significant enhancement in shielding effectiveness (SE) by a factor of 16. The SE of 30 dB meant a shielding of over 99.9% of incident electromagnetic (EM) radiation. The shielding mechanisms were discussed in detail. However, it was also found that compressive and flexural strengths of the foams decreased due to the formation of glassy carbon and oversized internal voids after fully carbonization. The third approach encompassed the inclusion CNFs. Results showed that no enhancement in compressive strength with the addition of CNFs was observed. Flexural strength and fracture toughness were increased with increasing CNFs content and decreased beyond 1.5 vol% of CNFs. The decreasing trend was due to agglomeration and clustering of the CNFs. Toughening mechanisms, such as crack deflection, step structure and debonding of the CNFs, were proposed. It was also found SE of the CNF reinforcement syntactic foams (CNFRSFs) was increased with increasing CNFs content and was superior to those of the composites having either CNFs or HCMs only. SE of 25 dB was achieved in the syntactic foam having 2.0 vol% CNFs, which is good enough for most practical applications. The shielding mechanisms were discussed in detail. DOCTOR OF PHILOSOPHY (MSE)

Anti-biofouling aims to prevent the acculumulation of biological organisms like proteins and micro-organisms on surfaces. This can be achieved by applying anti-biological and fouling release non-toxic polymeric coatings on surfaces. Conventional production of polymer composites is a time consuming process which involves a long thermal curing step of the monomers into thermosets. An attractive cost saving and environmentally friendly alternative is to perform curing via UV radiation. It shortens the curing time greatly, lowers the curing temperature and requires little or no solvent. Thus, it is increasingly popular in the coating and microelectronic industries. Acrylates and other radical initiated monomers are widely studied and used in industry. However, they are highly sensitive to oxygen and have poor adhesion strength on many surfaces, making them poor coatings. By contrary, epoxides are more stable in oxygen and have good adhesion properties, establishing them as good coatings for many surfaces. Unfortunately, they are not as well studied and hence not widely used. It is desired to create an IPN of both epoxides and acrylates to retain the advantages of the individual polymers while increasing the hardness, impact strength and chemical resistance to produce a good antibiofouling coating. Nanofillers are commonly added into polymer matrix to improve various properties of the materials. Hence, nanocomposites of TMPT(EO)A added with different nanofillers were UV-cured and studied kinetically. DPC was used to carry out the curing with the analysis of curing kinetics and photoreactivity simultaneously. Surface energy, tensile strength and hardness of the IPNs were analyzed via static water contact angle measurement, tensile test and Vicker micro hardness test. In this study, TMPTA, TMPT(EO)A, PEGDA, TPGDA, CN8003, CN104 and Epolam® 5015 were used in the investigation of the formation of simultaneous IPNs with TMPT(EO)A, PEGDA and TPGDA as the most reactive monomers among the seven monomers and oligomers. The effects of composition of individual monomers and temperature were investigated under optimum photoinitiator concentration. The highest percentage conversion and highest rate of reaction was when the experiment was conducted at 70°C with the highest acrylates proportion. The activation energies of the IPNs were found to be either between or lower than that of the monomers. IPNs containing CN8003 were suitable for fouling release purposes due to their low elastic modulus and surface energy. Its flexibility allows it to be an inner coating of the antibiofouling system. IPNs containing TMPT(EO)A had high surface energy, tensile strength, elastic modulus and hardness, making it a good candidate as an anti-fouling resistive outer layer. Unmodified nanoclay-TMPT(EO)A nanocomposites had the highest photoreactivity and percentage conversion at 1 'wt% unmodified nanoclay. Master of Engineering (MSE)

Fibre reinforced composite materials have become an alternative to many structural materials such as steels and alloys and some have become the dominant form of structural material. A major challenge faced by the fibre-reinforced composites industry is the presence of volatile organic compounds (VOCs) in hardener and solvent and the time taken for thermal curing is considerably long. Radiation curing offers an increased in speed of curing yet eliminates or reduces the VOCs. Additional advantage of radiation curing in fibre-reinforced composites is the absence of gel time since cross-linking in a resin formulated with photo-initiator will only commence upon exposure to UV light. Therefore, the removal of the gel time constraints could lead to improved laminate quality; for example, there is more time for precise fibre placement and orientation, complete fibre wetting and the removal of entrapped air. The aim of this project is to study the feasibility of employing radiation curing in the fabrication of glass fibre reinforced composites using epoxy based matrices. Commercial Bisphenol F epoxy resin (Epolam 5015) used widely in resin transfer molding has been used as the based material. Thermal curing kinetics of Bisphenol F epoxy resin was investigated with differential scanning calorimetry (DSC). Master of Engineering

This work is focused on the effect of polyhedral oligomeric silsesquioxane (POSS) compounds bearing reactive and non-reactive groups on the properties of resultant epoxy-anhydride hybrids and the underlying mechanisms. With rapid developments in nanotechnology, there has been great interest in polymer nanocomposites such as epoxy-based hybrids. POSS compounds have been incorporated in amine-cured epoxies for property improvements. In contrast, POSS/epoxy hybrids based on anhydride cure agents are seldom studied due to challenges such as the kinetically-controlled cure process and the requirement of catalysts for effective curing which may lead to complex reaction kinetics. However, the benefits of longer pot lives, better controlled curing, higher thermal and dimensional stabilities may outweigh the detriments. Kinetics, morphological and thermal studies were carried out to elucidate the effect of a POSS-epoxy on the properties of an epoxy-anhydride system in which the epoxy has self-catalytic sites. The POSS tether length difference on the cure kinetics was investigated. Tailoring POSS tether chemistry to reduce the cure kinetics difference between resin components was also studied with a novel POSS-anhydride. Anhydride-cured epoxy hybrids containing POSS-imidazolium (POSS-IMC) surfactants and corresponding modified clays have been prepared. Their catalytic effects were examined with correlation to the resultant morphologies and impact on the thermal properties. Interfacial interactions of non-reactive POSS on the thermal properties of epoxy-anhydride hybrids have also been investigated with octa-phenyl POSS (OPS) and its brominated derivatives. DOCTOR OF PHILOSOPHY (MSE)

Formulate thermoplastic composites that offer high thermal conductivity and good electrical insulating properties for electronic packaging purposes. Examine other important properties such as rheological properties (ease of processing) and the mechanical properties (end use performance). Master of Engineering (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)