Developing renewable materials to reduce the dependence on fossil fuel as a feedstock for a wide range of applications is becoming increasingly acknowledged as important in society. Chitin, the second most abundant biopolymer in nature, is an ideal candidate for diverse applications because of its remarkable properties, such as abundance, renewability, biodegradability, biocompatibility, antibacterial activity, chemical functionality, and high stiffness and strength. Despite these inherent advantages, chitin is currently still underutilized mainly due to its strong molecular interactions, which make it insoluble in common solvents. Currently, its major applications are limited to biomedical engineering, such as tissue engineering, wound dressing and sutures. This thesis aims to explore and enable the potential utilization of chitin in other fields where it may serve as a renewable functional advanced material. Here, a number of novel chitin-based materials were developed successfully without employing chitin dissolution. These include chitin nanofibers (CNFs), porous chitin with tunable structures, chitin-reinforced polymer composites and chitin-stabilized aqueous foams. Moreover, the properties of these materials including interfacial, optical, thermal, and mechanical characteristics were determined, and their potential utilizations were demonstrated. Briefly, in chapter 2, CNFs with diameters of ~20 nm were successfully extracted from crab α-chitin by a high pressure homogenization process. The produced CNFs were dispersed well in water without forming strong network structures due to their electrostatic repulsions. The obtained CNF film has a high residue amount (40%) when heated up to 1000 ˚C. Meanwhile, it exhibited high optical transparency as well as great gas barrier properties. In chapter 3, on the basis of the obtained CNFs in chapter 2, versatile porous structures including oriented sheets and three-dimensional aperiodic nanofiber networks were achieved by using a freeze drying technique. Since the formation of nanofibrous structures cannot be predicted by the widely-used particle encapsulation model, a modified structure formation mechanism was proposed. In chapter 4, the structure-property relationships of the CNF/poly(ethylene oxide)(PEO) nanocomposites were established. We demonstrated that the CNFs formed network structures in PEO matrix and had hydrogen bonding interaction with PEO. The CNFs can greatly enhance the mechanical properties of PEO, such as elastic modulus and tensile strength. In chapter 5, the aqueous foams stabilized by high-aspect-ratio CNFs were developed. The created foams exhibited strong hindrance on film drainage, coalescence and disproportionation. The fibrillated CNFs alone were not able to stabilize air bubbles, but the addition of small amounts of valeric acids in CNF dispersion can make chitin foamable. The results clearly showed that valeric acid modified CNFs reduced the surface tension of aqueous dispersion and were attached at the air-water interface. Overall, this research has provided many new insights for the fabrication, characterization, and utilization of chitin, and has built a solid foundation for further exploiting chitin for diverse applications.

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This study intends to recover and expand the analytical work of Vadasz (1998) for linear and weak non-linear stability of a rotating porous media heated form below and subject to gravity and Conolis forces. It is shown that the viscosity has a destabilising effect at high rotation rate. It has been established that the critical wave number in a plane containing the streamlines is dependent on rotation. Finite amplitude calculations provide a set of differential equations for the amplitude and phase, corresponding to the stationary and over-stable convection, identifying the post-transient conditions that a fluid is subject to, i.e. a pitchfork bifurcation for the stationary case, or a Hopf bifurcation in the case of over-stable convection. The previous model (Vadasz [1998]) was extended with an additional time scale in order to represent amplitude fluctuations and a short space scale to include horizontal modes of oscillations. When the complete solution for the stream function or temperature is analysed, where left and right travelling waves are considered, we obtain a set of differential equations for the amplitude and phase. The solutions are discussed in this context. / Thesis (Ph.D.)-University of Durban-Westville, 2000.

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Commercial production and use of carbon-based nanomaterials will inevitably lead to the release of nanoscale compounds into to the environment. While fullerene nanoparticles, such as nC60 and multi-wall nanotubes (MWNTs), exhibit toxicity to certain microbes and human cell lines, their transport and deposition in subsurface environments are largely unknown. In this study, nanoparticle transport experiments were conducted in one-dimensional columns packed with water-saturated glass beads, quartz sands, or natural soil. Results demonstrated that nC60 transport was strongly influenced by electrolyte species and concentration, as well as mean grain size and flow rate. The attachment of nC60 was largely irreversible, with introduction of pH 12 water required to detach substantial quantities of retained nC60. Measured nC60 breakthrough curves and retention profiles in quartz sands suggest that the retention of nC60 was primarily due to attachment in a first energy minimum and that clean-bed filtration theory alone was not sufficient to describe the experimental data. In the presence of stabilizing agents, including surfactant, fulvic and humic acids, significant enhancement of nC60 transport in quartz sands was observed. In two natural soils, Appling and Webster soil, complete retention of nC60 was observed, even after introducing up to 65 pore volumes of nC60 suspension. However, nC60 readily transported through Appling soil in the presence of surfactant. For MWNTs with a manufacture-reported (MR) length of 50 μm readily transported through sand columns and the retention of MWNTs at higher input concentrations increased with the MR length. The data also suggested MWNTs exhibited higher mobility in quartz sands than nC60 or single-wall nanotubes under similar chemical conditions. These findings advance our current understanding of fundamental processes governing nanoparticle transport and retention in porous media and provide reliable experimental data for the development of nanoparticle transport models.

This study focuses on the effect of different experimental conditions including conventional hydrothermal synthesis and supercritical carbon dioxide (SCCO2) methods on materials characteristics in terms of particle morphology and pore geometry. Three types of mesoporous silicas were investigated by different synthesis methods, that is, MCM- 41, SBA-15 and -16. These materials were used as a target molecule due to its high volatility and strong antimicrobial characteristics. / Thesis (PhDAppliedScience)--University of South Australia, 2008.