This research investigates the theoretical basis of a new photo-fabrication system. By this system, optical and thermal effects are used, together or separately, to locally induce a phase change in a liquid resin. This phase change phenomena is used to "write" three-dimensional shapes. In addition, a thermal-kinetic model has been developed to correctly simulate the physical and chemical changes that occur in the bulk (and surroundings) of the material directly exposed to radiation and/or heat, and the rates at which these changes occur. Through this model, the law of conservation of energy describing the heat transfer phenomena is coupled with a kinetic model describing in detail the cure kinetics in both chemical and diffusion-controlled regimes. The thermal-kinetic model has been implemented using the finite element method. Linear rectangular elements have been considered and the concept of isoparametric formulation used. The Cranck-Nicolson algorithm has been used to integrate the system of equations, resulting from the finite element discretisation, with respect to time. Three different photo-fabrication processes were investigated. The first process uses ultraviolet radiation to cure a thermosetting polymer containing a certain amount of photoinitiator. The radiation generates free radicals by cleavage the initiator molecules, starting the chemical reaction. The second one uses ultraviolet radiation to start the curing reaction of a liquid thermosetting polymer containing a certain amount of photo-initiator. In this case, a heat source is also used to increase the temperature, and consequently, to increase the rate of gel formation and the fractional conversion, decreasing the necessary exposure time. Finally, the third system uses a thermosetting material containing small amounts of both thermal and photo-initiators. In this case ultraviolet radiation and heat are used to simultaneously start two types of chemical reactions: thermal-initiated and photo-initiated curing reactions. Moreover, the heat source is used to increase the rate of gel formation of the photo-initiated curing reaction. This third process has been found to be advantageous because: the generation of radicals is more efficient, small concentrations of initiators can be used and consequently light can penetrate deeply inside the polymer, the curing reaction is more localised and the system has more tunability. Finally, in order to test the proposed photo-fabrication principles, a device has been constructed. This uses the mask-based writing method, in which an image is transferred to a liquid polymer by irradiating through a patterned mask. Various polymer shapes have been produced. The initial conditions to produce these shapes have been established from the understanding of the physical and chemical transformations of the selected resin under thermal and photo-initiated curing reactions and from simulation. In addition, the device has been used as a platform to test the thermal-kinetic model in real situations. The correlation between the experimental and predicted results is excellent.

The laser powered homogeneous pyrolysis (LPHP) technique was used to promote chemical reactions. The temperature and the geometry of the temperature produced in the reaction cell by a continuous wave IR CO2 laser were photographed and measured using chemiluminescence, spectroscopic (IR diode laser source spectrometer) and chemical standard techniques. The distribution of the temperature over the volume of the cell was found to be inhomogeneous, and the diffusion effects on the reaction rate were negligible. The mechanism of the decomposition of CH3I, d3-CH3I and their mixture was investigated using the LPHP technique. The rate of the decomposition of d3-CH3I was faster than that of CH3I. No significant amount of mixed isotopes of the products were observed during the irradiation of the mixture. The reactions of (CH3)4Sn (TMT) and (CH3)3SnSn(CH3)3 (HMDT) showed they decomposed, and the major products were CH4 and metallic layer deposited on the walls of the reaction cell. A significant amount of CH3D was observed during the reaction of TMT in presence of D2 at a relatively high laser power. The reaction of (CH3)3Al (TMAL) was investigated using LPHP technique and the mechanism of its reaction was presented. A monomeric TMAL form was detected during the reaction using FTIR spectrometer scanning of the reaction zone perpendicularly with the incident CO2 laser beam. A (CH3)2A1 (DMAL) radical was found as a result of the decomposition of TMAL. The DMAL radical was trapped and isolated as stable compounds: (CH3)2AIF (DMAF) in dimeric and tetrameric forms, and (CH3)2AICI (DMAC) in dimeric form, using SF6 and CCI4, CHCI3 and CDCI3 as radical scavengers, respectively. The presence of H2 and D2, which are widely used as carrier gases in the metal organic chemical vapour deposition (MOCVD) technique, did not have major effect on the mechanism of the reaction, but were shown to have isotopic effects on the thermal conductivity of the reaction cell, slowing down the reaction. A new photoacoustic spectroscopic technique, based on the change of the resonance frequency of the reaction cell (r.f.), was introduced to follow and examine the chemical reactions, revealing the change of the cell composition. The results obtained by this technique were fairly comparable with those obtained by IR spectroscopic methods.

The kinetics of reaction and solvation properties of binary aqueous mixtures are discussed from different theoretical standpoints. Kinetic data are reported for reactions involving several Iron (II) complex cations in binary aqueous mixtures. The Savage-Wood Additivity Group Scheme (SWAG) is applied to kinetic data for the aquation of [Fe (5-nitro-1, 10-phenanthroline) 3]2+ in binary aqueous mixtures. Limitations of the theory are examined. The theory works well for reactions in alcohol-water and some carboxylic acid-water mixtures but not for reactions in urea-water and cyclic ether-water mixtures. The conclusion is reached that this theory can only be applied to relatively simple solutions. Otherwise, the assumptions made in the theory are not valid. Attention is then turned to the Kirkwood-Buff theory which can be applied to reactions in mixtures containing significant amounts of the cosolvent. Few assumptions are made in its derivation. This theory is used to probe the properties of a wide range of binary aqueous mixtures. Kinetic data describing reactions in these binary mixtures are then examined, leading to a consideration of preferential solvation. Finally, the possibility of monitoring chemical reactions under isochoric conditions is considered. A meaningful isochoric volume is defined. Kinetic and equilibrium reaction data are then analysed under these isochoric conditions.

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