The crystallization kinetics of diphenylhydantoin (DPH) has been studied at constant conditions in a small mixed suspension mixed product removal (MSMPR) crystallizer. Supersaturation is created by changing the pH of a DPH solution in the crystallization vessel. Crystal size distributions (CSD's) are measured by an in situ zone sensing method. Effects of pH and supersaturation on crystallization kinetics and CSD are summarized. The effect of an additive on the crystal growth of DPH has been studied in a batch system. Avoidance of nucleation in the early stages of crystallization is essential to the effect investigated.

X-ray diffraction has been used to investigate the structure and structural behaviour of several inorganic solids under variable pressure and temperature conditions. A brief description of the diamond anvil cell (d.a.c.) and its applications to the high- pressure investigations is given. A spectroscopic system built for pressure calibration is discussed, plus an account of powder diffraction data analysis including a detailed description of a software package engineered for the specific reduction of powder data obtained under variable pressure. Potassium nitrate (KNO3) has seven polymorphs in the pressure range 0.0-4.0 GPa. This material has been studied with energy dispersive powder diffraction (EDXRD) to 9.3 GPa. The structure of the non-ambient phase IV refined by neutron diffraction at 0.36 GPa has been confirmed, the compressibility of the high-pressure phase measured and found to be anisotropic with axial compression ratios a:b:c = 1.0:0.64:0.50. The valence induced structural transition at 0.8 GPa in EuPd2Si2 has been studied using EDXRD and uni-axial compressibilities calculated. A basic explanation of the electronic theory which accompanies the subtle shortening of the a lattice parameter in the tetragonal asymmetric unit is also given. The structures of two compounds CH3HgX (X = I, Cl) have been investigated using single crystal and angle-dispersive powder techniques respectively. The crystal structure of methyl mercuric iodide is reported. CH3HgCl has been observed above and below the temperature induced I/II phase boundary at 162.5 K. A hypothesis detailing the iso-structural nature of CH3HgCl low temperature phase II and the ambient phase I of the analogous methyl mercuric bromide is also tested.

This work reviews the current knowledge of the synthesis , properties , structures and biological activities of isatogens. The unequivocal 2 C NMR assignment of 2-phenylisatogen 1S reported and used to assign the spectra for a range of 2-(4-substituted-phenyl)isatogens. Molecular dynamics of 2-phenylisatogen in chloroform are reported and indicate that there is little if any inter-ring mesomeric resonance in this compound. 1~C , ~N NMR and UV-Visible spectroscopic data are reported for a range of 2-(4-substituted-phenyl)isatogens. Analysis of this data indicates a small but significant degree of inter-ring mesomeric resonance is present in these compounds especially those with strongly electron donating or withdrawing substituents. An interesting correlation is found between ~sN substituent chemical shifts and molar absorbtivity of the visible transitions. The X-ray crystal structure of 2-(4-chlorophenyl)isatogen is reported and shows a small but significant shortening of the inter-ring bond length compared to 2-phenylisatogen , further supporting the hypothesis of inter-ring mesomeric resonance in these compounds. 1 H and ~C NMR data are reported for the 2-(pyrid-2-inium)isatogen cation and indifate the presence of intramolecular interaction between the ~---H and N~O groups in the molecule. The X-ray crystal structure of the perchlorate salt of the cation and the ~H solid state NMR spectrum both support this conclusion. The molecular structure indicates that the intramolecular interaction is comprised of coulombic and hydrogen bonding interactions leading to a near coplanar structure for the cation compared to the noncoplanar structure for the parent base, 2-(pyrid-2-yl)isatogen. A hypothesis is put forward to explain molecular packing and configuration differences in 2-heteroarylisatogens. The molecular packing and configuration is controlled by a balance of intermolecular dipole attraction and repulsion. Predictions of molecular packing and configuration are made for a number of 2-heteroarylisatogens. The X-ray crystal structure of 2-(pyrid-3-yl)isatogen is reported and found to be in complete agreement with the predictions of the hypothesis. Further studies are proposed involving the synthesis of ~N and ~~O labelled isatogens , the study of inclusion complexes with cyclodextrins and the study of isatogens with the potential for increased mesomeric interactions. ,

This thesis presents a study of colloidal particles dispersed in thermotropic liquid crystals. It has a specific focus on colloids in the presence of an interface between the liquid crystal and an isotropic fluid. Three systems are studied: colloids trapped at a planar interface between a cholesteric liquid crystal (CLC) and an isotropic oil, nematic emulsions with interfacial colloids and the influence of colloids on the phase transition kinetics of the cholesteric blue phase. Experiments are carried out using polarising optical and confocal microscopy. By combining these techniques, the director field of the liquid crystals could be imaged in combination with precise observation of the colloid locations. Custom image analysis algorithms are developed to extract the information. In the first system, we create an interface between a cholesteric liquid crystal and an isotropic liquid. Homeotropic anchoring leads to a well aligned cholesteric layer and the formation of the fingerprint texture. Fluorescent colloidal particles with planar surface anchoring are dispersed in the CLC. A majority of these particles decorate the interface. The final distribution of particles perpendicular to the interface has a clear dependence on the particle size. In the plane of the interface, surface defects form a template for the colloids. The second system is a particle dispersion within a short pitch CLC which exhibits a blue phase. The colloidal particles and associated defects act as nucleation sites for the blue phase in the cholesteric to blue phase transition. Colloidal particles cause localised melting from the blue phase to the isotropic phase and lead to a larger temperature range for coexistence between isotropic and blue phases. Furthermore, the isotropic regions can be faceted, their shape and size is controlled by the blue phase elasticity. In the final system, a nematic emulsion is created. Droplets of nematic LC are dispersed in water. Colloidal particles initially mixed into the liquid crystal decorate the interface between the two fluids. The addition of a surfactant switches the liquid crystal alignment at the fluid-fluid interface from planar to homeotropic. This forces a change in defect structure, from two boojums at the poles to a hedgehog defect in the droplet centre. The presence of colloids affects the switching dynamics and alters the final liquid crystal alignment preventing the droplets from forming a central radial defect. There is a symbiotic relationship between the particle properties - size and anchoring at the surface - and the elastic properties of the liquid crystal in the bulk and in the presence of an interface with an isotropic fluid. How the systems respond when the balance of these factors is altered is explored throughout the thesis.

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