Synthetic Laponite-clay particles with a platelet-like shape display strong gelation when dispersed in aqueous solutions because of their positively charged rims and negatively charged flat surfaces. In this thesis, my aim was to modify the surfaces of these clay particles such that we can both access their liquid crystalline (LC) discotic phase and further build transparent and mechanically resilient coatings with a 3D "brick-and-mortar" structure that is similar to that observed in natural mother of pearl (nacre). I first introduce a simple strategy that successfully suppresses Laponite's ageing phenomenon and enables the system's isotropic-to-LC phase transition. By grafting Laponite particle surfaces with comb-like polymers, poly (L-lysine)-g-poly (ethylene glycol) (PLL-PEG), I was able to screen negative surface charges and ensure steric stabilisation. Besides using long-chain polymers, I also coated the positively charged Laponite rims with small, barrel-shaped molecules cucurbit[7]uril (CB[7]). By carefully tuning the ratio between CB[7] and Laponite, the system experienced a macroscopic phase separation into a Laponite-poor suspension and a birefringent LC gel. Inspired by the hierarchical structure of nacre, here I also demonstrate a simple approach to fabricate polymer-clay hybrid films via a water-evaporation process. In this third method, Laponite platelets were bridged by natural abundant polymers (carboxymethyl cellulose) through hydrogen bonding. This hybrid material possesses high transparency, flexibility and an outstanding fire-retardant property. After Ca2+ ion-coordination of these cellulose-Laponite composite films, the interface between the polymers and clays was further strengthened, leading to enhanced mechanical properties along with improved thermal- and water-resistance. I also present that using Dextran as a depletant, sterically stabilised Laponite can access its liquid crystal phase under low clay concentration. Finally, I show that Laponite can be coated with various polymers (PEO, chitosan, sodium alginate) for the purpose of obtaining LC gels and hybrid films. I believe that our findings on surface-modification of clay particles can open new routes to large-scale and inexpensive production of bio-inspired functional materials.

Chan Wing Kin. / Thesis submitted in: Oct 2004. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.i / Abstract (in Chinese) --- p.iii / Acknowledgement --- p.iv / Table of Contents --- p.vi / List of Figures --- p.xi / List of Tables --- p.xv / List of Schemes --- p.xvi / Abbreviations --- p.xviii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- General Background of Phthalocyanines --- p.1 / Chapter 1.2 --- General Background of Liquid Crystals --- p.3 / Chapter 1.3 --- Structural Classification of the Mesophases --- p.6 / Chapter 1.3.1 --- The Columnar Liquid Crystals --- p.6 / Chapter 1.3.2 --- The Nematic Phase --- p.10 / Chapter 1.3.3 --- The Lamellar Phase --- p.11 / Chapter 1.4 --- Applications of Columnar Discotic Liquid Crystals --- p.13 / Chapter 1.4.1 --- General Properties of HATn Materials and Phthalocyanines --- p.13 / Chapter 1.4.2 --- Supramolecular Channels and Wires --- p.16 / Chapter 1.4.3 --- Phthalocyanine Based Gas Sensors --- p.21 / Chapter 1.5 --- General Synthesis of Liquid Crystalline Phthalocyanines --- p.23 / Chapter 1.5.1 --- Peripherally Substituted Phthalocyanines --- p.23 / Chapter 1.5.1.1 --- Octakis(alkoxymethy l)phthalocy anines --- p.23 / Chapter 1.5.1.2 --- Octa-alkoxyphthalocyanines --- p.26 / Chapter 1.5.1.3 --- Octa-alkylphthalocyanines --- p.29 / Chapter 1.5.1.4 --- Octakis-(alkoxycarbonyl)phthalocyanines --- p.30 / Chapter 1.5.1.5 --- Octa-(p-alkoxylphenyl)phthalocyanines --- p.32 / Chapter 1.5.1.6 --- Tetrakis[oligo(ethyleneoxy)] phthalocyanines --- p.34 / Chapter 1.5.2 --- Non-Peripherally Substituted Phthalocyanines --- p.35 / Chapter 1.5.2.1 --- Octa(alkoxymethyl)phthalocyanines --- p.35 / Chapter 1.5.2.2 --- Octa-alkylphthalocyanines --- p.37 / Chapter 1.5.3 --- Unsymmetrically Substituted Phthalocyanines --- p.40 / Chapter 1.5.4 --- Liquid Crystalline Metallophthalocyanines --- p.42 / Chapter 1.5.4.1 --- Copper Phthalocyanines --- p.42 / Chapter 1.5.4.2 --- "Manganese, Cobalt, Nickel, and Zinc Phthalocyanines" --- p.43 / Chapter 1.5.4.3 --- Lutetium Phthalocyanines --- p.43 / Chapter 1.5.4.4 --- "Silicon, Tin, and Lead Phthalocyanines" --- p.44 / Chapter 1.6 --- Summary --- p.45 / Chapter 1.7 --- References --- p.47 / Chapter Chapter 2 --- "Syntheses, Aggregation Behavior and Liquid Crystalline Properties of Peripherially Octaalkynyl Phthalocyanines" --- p.57 / Chapter 2.1 --- Synthesis and Characterization of Octaalkynyl Phthalocyanines --- p.57 / Chapter 2.1.1 --- Preparation of Alkynyl Fragment 22 --- p.57 / Chapter 2.1.2 --- Preparation of Alkynyl Phthalonitrile 23 --- p.58 / Chapter 2.1.3 --- "Synthesis and Characterization of [2,3,9,10,16,17,23,24-Octakis(3,4,5-tris (dodecyloxy)phenylethynyl)phthalocyaninato]magnesium(II) (29)" --- p.62 / Chapter 2.2 --- Electronic Absorption of Alkynylated Phthalocyanine 29 --- p.65 / Chapter 2.3 --- Liquid Crystalline Properties of Alkynyl Phthalocyanine 29 --- p.71 / Chapter 2.4 --- Summary --- p.73 / Chapter 2.5 --- Experimental Section --- p.74 / Chapter 2.5.1 --- General Information --- p.74 / Chapter 2.5.2 --- Physical Measurements --- p.74 / Chapter 2.5.3 --- Photophysical Measurements --- p.75 / Chapter 2.5.4 --- Experimental Procedure --- p.76 / Chapter 2.6 --- References --- p.83 / Chapter Chapter 3 --- Facile Synthesis of Liquid Crystalline Phthalocyanines Through Transesterification Reactions --- p.86 / Chapter 3.1 --- Synthesis and Characterization --- p.86 / Chapter 3.1.1 --- "Preparation of 4,5-bis(4-methoxycarbonylphenoxy)phthalonitrile (30)" --- p.86 / Chapter 3.1.2 --- Preparation of Phthalocyanines --- p.87 / Chapter 3.2 --- Electronic Absorption Properties and Aggregation Behavior --- p.91 / Chapter 3.3 --- Liquid Crystalline Properties of Phthalocyanines 31 -37 --- p.101 / Chapter 3.4 --- Summary --- p.104 / Chapter 3.5 --- Experimental Section --- p.105 / Chapter 3.5.1 --- Experimental Procedure --- p.105 / Chapter 3.6 --- References --- p.114 / Chapter Chapter 4 --- "In vitro Photodynamic Activities of Peripherially Octa-substituted Zinc Phthalocyanines with Terminal Mono-, Di- and Triethylene Glycol Chains" --- p.115 / Chapter 4.1 --- Photodynamic Therapy (PDT) --- p.115 / Chapter 4.1.1 --- Brief Introduction of Photodynamic Therapy --- p.115 / Chapter 4.1.2 --- Photophysical Mechanism Involved in PDT --- p.117 / Chapter 4.2 --- Photophysical Properties of Phthalocyanines 34-36 --- p.119 / Chapter 4.2.1 --- An overview of photochemical and photophysical processes --- p.119 / Chapter 4.2.2 --- Spectroscopic and Photophysical Properties of Phthalocyanines 34-36 --- p.122 / Chapter 4.3 --- In vitro Photodynamic Activities --- p.128 / Chapter 4.4 --- Summary --- p.128 / Chapter 4.5 --- Experimental Section --- p.129 / Chapter 4.5.1 --- In vitro Studies --- p.129 / Chapter 4.6 --- References --- p.131 / Appendix --- p.135

We report the results of a series of experimental studies in two interrelated areas: homogeneous nucleation and transient heat transfer in cryogenic liquids. We report the first determination of the homogeneous nucleation temperature of liquid helium I and liquid nitrogen employing a transient superheating technique. This technique in liquid helium involved the development of a new transient magnetoresistive thermometer which relies on the strong temperaure dependence of magnetoresistance in bismuth as a thermometric property. Our measurements of the homogeneous nucleation temperature for both liquid helium I and nitrogen are in good agreement with the predictions from the Becker-Doring Volmer-Zel'dovich-Frenkel nucleation theory. On the basis of such agreement between theory and experiment in both liquid helium and liquid nitrogen we have developed a corresponding state analysis applicable to the case of homogeneous nucleation in liquid noble gases, both quantum and classical. Predictions of the homogeneous nucleation temperature and surface tension of several hydrogen isotopes are made from such a quantum mechanical law of corresponding states. We also comment on the limiting superheat temperature of liquid helium I. It is suggested that a comparison between the limiting superheat temperaure and the peak nucleate boiling temperature is meaningless and that the reported agreement between the two is largely fortuitous. In the studies of transient heat transfer in helium we find that the heat transfer from a solid into liquid helium is markedly enhanced by the application of a visible pulse of light. In liquid nitrogen we find that a transition to stable film boiling can be observed for power values as low as 40 per cent of the steady-state peak heat flux.

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The three factors of the resolution (Rs)equation(see Equation 1.1)were explored in this thesis. During the course of the research project, an important aim was to explore separation processes that would lead to an increase in productivity without sacrificing Rs. To that end, an increase in the retention factor (k)to enhance Rs was deemed detrimental to the cycle time, hence the production rate, particularly when preparative separations are involved. Consequently the primary objectives were to (i)prepare more efficient columns and (ii)investigate new strategies in manipulating selectivity. The significance of the work contained in this thesis is highlighted in 27th International Symposium on High Performance Liquid Phase Separations and Related Techniques (HPLC 2003)held in Nice, France between 15-19 June, 2003. Many of the papers presented significantly compared to chapters contained in this research / Doctor of Philosophy (PhD)

This thesis describes a developmental process required for the construction and optimisation of two-dimensional liquid chromatographic systems. The text encompasses much of the difficulties and provides a frame work for achieving positive results. The hardware requirements and the concepts for successful completion of heart-cutting and comprehensive modes of separation are addressed. Low molecular weight polystyrenes play an essential role in providing a model framework or theme for the development of two-dimensional liquid chromatographic systems. Low-molecular weight oligostyrenes were initially used to provide a theoretical assessment of combinations of liquid chromatographic systems. Interpretation of theoretical results then allowed for the development of a heart-cutting two-dimensional liquid chromatographic system for the separation of oligostyrene complex samples. This allowed for practice to be compared with the theoretical results, which are presented and provided direction as to what attributes of a two-dimensional liquid chromatographic system are beneficial. Petroleum oils are one of the most complex mixtures found in the natural environment and are included to provide a real-world application that demonstrates the potential power of comprehensive two-dimensional liquid chromatographic systems. Orthogonality is a central theme throughout the whole thesis. Separation correlation is shown to be advantageous in certain instances in the evaluation of hybrid stationary phases, as shown in the analysis of a low molecular weight polystyrene sample. The thesis finishes by the incorporation of monolithic separation media as an alternative second dimension stationary phase support. A method is discussed that allows for a substantial increase in the volume and concentration loading of two-dimensional liquid chromatographic systems that employ monolithic chromatography columns in the second dimension. This is important since volume overloading and concentration overloading in the second dimension can reduce separation performance and hence the final chapter provides a new direction for research. / Doctor of Philosophy (PhD)

Thesis (M. Sc. (Chemistry) -- University of Pretoria. 2006. / Includes bibliographical references (leaves 111-117).