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The temperature-composition phase diagram of sodium cobaltate, NaxCo02, was determined over the range 0.32 < x < 0.85 and 90 < T < 500K. Sodium de-intercalation was achieved using Brz/CI-hCN as an oxidising agent, and the superstructures were determined using X-ray diffraction. A kaleidoscope of Na+ ion patterns were found, including both commensurate and incommensurate structures. The sodium ion patterning of some of the superstructures was solved via a model independent approach using Reverse Monte Carlo. Diffuse scattering was observed above the sodium ordering temperature. For high x, it was possible to reproduce the data using Monte Carlo simulations of short-range ordered 8lTangements of multi-vacancy clusters. For x :::: 0.5, the ordering consists of small regions of the superstructure confined to a single sodium plane. Old samples of sodium cobaltate are found to have de-intercalated so that the surface layer has a superstructure corresponding to a lower value of x than the bulk. The thermoelectric and magnetic properties change dramatically when the superstructures change from di-vacancies to tri-vacancies. In the case of x = 0.5 we are able to understand the resonant X-ray scattering from the electronic ordering directly from the superstructure.

This thesis reports experimental and theoretical studies on various functionalised aromatic systems in the gas phase and in solution, with an aim to understand the ways in which judicious substitution can control fundamental photochemical outcomes. The isolated gas phase experiments were undertaken using Hydroge11 (Rydberg) Atom Photofragment Translational Spectroscopy whilst those in solution were undertaken using ultrafast pump-probe experiments.

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Recently, interest has been shown in stimuli responsive microgel particles as depletants, capable of inducing entropy driven phase transitions in colloidal systems. Due to their temperature induced deswelling transition , which occurs above ~32 'c, poly(N-isopropylacrylamide) (pNIPAM) microgels present opportunities for the easy modulation of depletion interactions between colloids. The aim of the current project was to gain an understanding of the phase behaviour of colloidal particles mediated by pNIPAM microgels both below and above the volume phase transition temperature (VPTT) , for potential applications in formulation science. For this purpose, a simple model system comprising an aqueous suspension of polystyrene (PS) latex particles, stabilised with Synperonic PE/ Pl05 PEOPPO- PEO (Pl05) copolymer, and pNIPAM microgels was developed . The majority of experiments were conducted at a microgel/ colloid size ratio, q, close to 0.1 at room temperature. A phase diagram for the colloid-microgel mixture at room temperature was determined experimentally using differential interference contrast (DIC) microscopy. At sufficient microgel volume fraction, mixtures were found to separate into colloidal fluid and solid phases. At higher particle concentrations, gelation was observed. The phase diagram was compared to that for a colloid-linear polymer mixture at similar q. Similarities in the two systems were found in the position of the fluid- solid phase boundary; however , differences in the kinetics of phase separation were apparent in the earlier onset of gelation in the colloid-microgel phase diagram. This result may be due to the greater rigidity of the microgels. Interestingly, the colloidmicrogel gel line was found to coincide with the theoretical metastable fluid-fluid phase boundary calculated for binary hard sphere systems at q = O.l.

Materials under spatial confinement are subject to volume exclusion conditions differing from those of a bulk material. On reducing a system to a lengthscale of the order of a few particles onc can observe new structures, modified dynamics and phase behaviour dramatically differing from that of the bulk system. Through understanding and controlling the boundaries confining a system one can alter the energy landscape it experiences. Three colloidal model systems are realised using holographic optical tweezers to investigate confinement phenomena in quasi two dimensions. ~Whereas the bulk of existing rescarch is concerned with confinement by hard boundaries, the systems presented here employ an adaptive, deformable wall or a soft confining potential. The first system, dubbed the colloidal corral consists of a circular boundary of optically trapped colloids confining additional colloids to its interior. Despite the fact that boundary curvature inhibits hexagonal ordering within this geometry, a bistability is observed between locally favoured hexagonal structures and globally preferential configurations mimicking the symmetry of the confinement. Such behaviour is not observed with hard wall confinement and is entirely due to the adaptivity of the boundary. Additionally, a novel technique for the mechanical measurement of pressure is presented, facilitated by the deformable wall. The second system introduces shear to the colloidal corral through rotation of the boundary and is known as the colloidal washing machine. The flow behaviour in this rotating confinement is investigated for a range of rotation rates. Rigid-body- like and shear melted regimes are identified and their structural behaviours characterised. The final system confines colloids within a circularly symmetric optical potential without a boundary. The result is the assembly of two-dimensional clusters, which are characterised for a range of potential widths and depths. The absence of a curved wall allows enhanced hexagonal ordering compared to the colloidal corral.

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