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We have studied the quiescent structure of dense colloidal gels with varying strength of attraction with confocal microscopy. We have obtained high quality 3-D images that allow quantitative comparison of the different gels by the extraction of the 3-D particle coordinates and subsequent of quantitative measures of the local particle structure. We have observed that the gels have a liquid-like, although frozen in-homogeneous structure. We have found an increase in the average number of bonds per particle for decreasing attraction strength, accompanied by changes in the particle-free void regions. We developed and tested a precision linear parallel-plate oscillatory shear cell designed for light scattering-echo and microscopy experiments. This allows us to study in detail the response of gels with varying strength to low strain oscillatory shear at various frequencies will optical and confocal microscopy and light scattering-echo. We have found that the gels responds elastically to strains below a critical frequency and attraction potential dependent value. Above this critical strain the particles that make up the gel are formed to rearrange, for the strongest gels, small regions of crystal-like order can be induced by the shear and then frozen in place once the shear stops. For gels with lower potentials no ordered regions are observed in the timescale studied, however rearrangements of the voids were observed at lower strains for lower potentials. The apparent ordering is predominantly in 2-D planes and limited to small domains separated by defects or disordered particles. The amount of ordering is found to depend on strain and frequency. These results are interpreted by a simple model based on the timescale for a particle to escape from the potential well.

The integration of analytical surfactant methods with HPLC is the purpose of this study. A single separation with a similar stationary phase, mobile phase and detection was developed for faster and more convenient separation. Three different solubilising functionality surfactants (anionic, cationic and non-ionic) were evaluated in a single separation. Three surfactant standards, alcohol ethoxylate (AE), linear alkylbenzene sulphonate (LAS) and benzalkonium chloride (BAK) were investigated in the method development. The different types of reversed phase HPLC stationary phases, Cs (Exsil 80A Cs,150 x 4.6 mm, 3J.lm),endcapped Cg (Symmetry Cg, 150 x 4.6 mm, 3.5 urn), base deactivated Cg (Symmetry Shield RPg, 150 x 4.6 mm, 3.5 urn) and cyanopropyl (Genesis CN, 150 x 4.6 mm, 4J.lm) columns were studied. The following mobile phase modifiers, sodium· perchlorate, tetramethylammonium bromide (TMA) and ammonium acetate were also investigated. A mixture of two ionic surfactants (BAK and LAS) were separated using the above columns. Isocratic elutions between acetonitrile and either 0.05 M sodium perchlorate or 0.05 M TMA or 0.05 M ammonium acetate were evaluated for separation of the two components. An Exsil 80A Cs, 150 x 4.6 mm, 3 urn, column was chosen for separation of a mixture of the three surfactants. The gradient mobile phase of 0.05 M ammonntium acetate, acetonitrile and methanol was applied at a DV detection of220 nm. All homologues of linear alkylbenzene sulphonate (CIO, Cn. CI2 and Cl3), alcohol ethoxylate (C12, C14,CI6 and CIg) and benzalkonium chloride (C14) appear with k' values from 3.22 (CIO of LAS) - 9.53 (C14ofBAK). An integrated chromatographic system for the separation of these three surfactants was developed in a microbore column. An Exsil 80A Cg, 150 x 2.1 mm, 3 prn column was developed for application in liquid chromatography - mass spectrometry (LC-MS).

The aggregation and gelation of colloidal systems has been studied using confocal microscopy. For a model colloid-polymer mixture in a density matched solvent, fluid and gel were found to be the only two phases observed for sufficiently short-ranged attractions. The experimental gel boundary in this system is associated with an ergodic to non-ergodic transition line. Starting from this ‘standard model’ the effects of charge and gravity on the gelation of colloidal systems have been explored. When the colloids in this aggregating system were charged, the electrostatic repulsion was found to stabilise the clusters against further growth. This results in a stable and equilibrium long-lived cluster phase. At sufficiently high inter-particle attraction the electrostatic repulsion is overcome and the clusters form a gel. The experimentally observed gel boundary is shifted to higher inter-particle attractions due to the charge on the particles. When gravity is introduced to the system sedimentation may prevent a gel from forming. The onset of gelation is marked by the formation of small clusters which grow and eventually form a gel. If the rate of sedimentation is faster than the rate of cluster growth a sample-spanning gel is not formed. The experimental gel boundary was observed at higher inter-particle attractions due to the presence of gravity. The phase behaviour of protein solutions has been studied. The addition of salt to a protein solution causes an effective attractive interaction between the proteins, and similarly to colloid-polymer mixtures non-equilibrium behaviour is observed at sufficiently high attractions. Optical microscopy revealed four regimes: gas-liquid phase separation, non-coalescing ‘beads’, large aggregates and transient gelation. The interaction between the gas-liquid binodal and the ergodic to non-ergodic transition line is found to be essential in understanding the non-equilibrium phase behaviour.

The reactions of H<SUB>2</SUB>S and COS with high purity (99.9&37 ) and doped (Ca, Cd, Cu, Ni, Na and Pd) zinc oxide absorbents were investigated using batch recycle and plug flow reactors and using DRIFTS. The absorbents were characterised by BET surface area measurement, scanning electron microscopy, thermal decomposition and atomic absorption elemental analysis. High purity ZnO was also characterised by the 1R studies of adsorption of H<SUB>2</SUB>O, CO<SUB>2</SUB> and O<SUB>2</SUB>. The reaction between ZnO and H<SUB>2</SUB>S is structure sensitive. The sulphiding mainly takes place on the Zn-polar and O-polar faces of ZnO and proceeds to its bulk through a continuous rearangement and replenishment of hydroxyls due to H<SUB>2</SUB>O on these polar faces. The surface reaction takes place in two steps; first S-H groups form on the surface and then these groups are converted into surface sulphide where the first step is fast. The second step is slow in the absence of excess H<SUB>2</SUB>O. The reaction pattern is such that the initial reaction is fast where the solid's consumption varies from 4 to 35% depending upon the pre-treatment conditions of the absorbent such as temperature and atmosphere of calcining, water saturation, etc. Doping ZnO with Cd, Co and Cu improves its sulphiding capacity and rate compared to the high purity ZnO whereas doping with Na and Ca inhibits the sulphiding. The dopants directly affect the reaction on the polar faces as well as the bulk of the solid and affect the ZnO crystallite morphology. The effect of the presence of O<SUB>2</SUB> and CO<SUB>2</SUB> in the reactant H<SUB>2</SUB>S stream on the ZnO sulphiding performance was also investigated. The possible bulk reaction mechanisms were proposed.

This thesis is devoted to the development of the interface between two immiscible electrolyte solutions as a transducer for chemical sensor design. The main detectable analyte of interest is the ammonium ion. The facilitated ion transfer of this species is reported using a variety of ionophores. Association constants of the ammonium ion with dibenzo-18-crown-6, nonactin and valinomycin are calculated along with values for the same ionophores with potassium and sodium ions. The selectivity towards these three species is such as not to enable their separation at physiological levels. A single microhole formed by excimer laser photoablation in a polyester film is used as a support for a micro liquid/liquid interface. The effect of a decrease in the supporting electrolyte concentrations of both the organic and aqueous phases is investigated with regard to ion and facilitated ion transfer reactions. It is shown that it is possible to study ion transfer reactions using simply pure water as the aqueous phase electrolyte. The ITIES is used as a transducer to follow enzymatic reactions. The ammonium ion produced in the urea/urease and creatinine/creatinine deiminase enzymatic decompositions is detected by facilitated ion transfer using dibenzo-18-crown-6. The adsorption/transfer of the polyelectrolyte Nafion at the ITIES is investigated. The two characteristic transfer phenomena observed are attributed to the adsorption/transfer of Nafion in its dissolved form and a restructured form of the polyelectrolyte. A biosensor for urea is proposed where the ITIES has been 'solidified' in the form of polymeric films.

We have modelled epioptic systems using semi-empirical methods. We apply one such theoretical technique, Berreman’s 4x4 matrix formalism, to simulate and compare the results of various epioptic spectroscopies when applied to model systems. We place particular emphasis on 45° reflectivity spectroscopy (45DR), and demonstrate its potential for the study of systems with surface regions of mixed isotropic and anisotropic character. We also demonstrate the superior surface senstiviity of 45DR when compared to spectroscopic ellipsometry (SE) and show that 45DR is inherently more stable with regards to inaccuracies in bulk data. However, we also reveal that practical considerations lessen the potential impact of this technique. We continue the application of this matrix formalism to simulate the absorption of molecular species onto model surfaces. We show that reflection anisotropy spectroscopy (RAS) is sensitive to both molecular orientation and substrate properties, and that a simple polarisable dipole model, omitting local field contributions, enables us to reproduce the experimental spectra of Goletti <i>et al</i> and Weightmann <i>et al</i>, who studied porphyrin and DNA base molecule absorption respectively. We also assess the effect of optical activity on RAS spectra. Finally we apply the derivative model, in which surface optical spectra are related to perturbations of bulk electronic transitions, to noble metal (110) RAS spectra. We demonstrate that this model describes, consistently and accurately, the spectra of these intrinsically anisotropic systems. Furthermore, we show that observed transition broadening in ion-bombarded systems can be explained in terms of quantum mechanical uncertainty derived from roughness induced localisation of near-surface electrons.

A general introduction to zeolites and aluminophosphate based molecular sieves is followed by a more detailed review of EU-1 and AlPOj-S, the two molecular sieves studied in this work. The synthesis and characterisation of these molecular sieves is described. The characterisation techniques gave details of the framework structure and composition, surface area, and morphology. A time study of the crystallisation of AlPO4-5 from an aluminophosphate gel containing two organic templates showed the formation of a hydrate phase before the AlPO4-5 phase, the change in pH during hydrothermal crystallisation, and the transformation of the Kaiser alumina spheres to give the spherical morphology of A1PO.4-5 associated with this synthesis procedure. Volumetric adsorption and subsequent desorption of but-n-ene isomers on both molecular sieves at room temperature showed that some strong adsorption of the molecules occurs, which could be removed at higher temperatures. The effect was more pronounced with EU-1. Gravimetric adsorption of various organic compounds on AlPO4-5 showed pore filling values and rates of uptake consistent with the kinetic diameters of the organic molecules. The Langmuir model, found to give the best fit for the adsorption isotherms, was seen to break down at mid-range values of P/P0. Thermal desorption of pyridine from H-EU-1 showed that the acid sites probably exist in or close to the side pockets in the EU-1 channel system, and that a side pocket may contain more than one acid site. The A1PO4-5 samples of spherical morphology were found not to have strong acid sites. The framework of calcined A1PO4-S was seen to be degraded to a denser phase by aqueous salt solutions, whereas as-synthesised samples remained intact The extent of the attack was dependent upon the anion and the solution concentration. A1PO4-11 and AlPO4-25 samples were also attacked but to a lesser extent. EU-1 and A1PO4-S samples acted as acidic catalysts in the isomerisation of but-1-ene. Only but-1-ene, cis and trans but-2-ene were observed in the gaseous phase. A strongly bound residue was detected on the surface of EU-1 by TGA. This residue was seen to deactivate the catalyst in the first instance, but heating the sample with the residue in a vacuum was seen to change the catalytic nature of the zeolite. The activity of the A1PO4-5 samples was lower than EU-1 under identical conditions. However, samples of the AlPO4-5 spheres were seen to have a higher activity than the usual barrels. Investigations gave no solid evidence for the seat to this increased activity, but it is thought that framework defect sites may be responsible.

A gravimetric balance and the frequency response (FR) technique have been used to investigate the adsorption and the mass transfer behaviour of the normal alkanes, from methane to n-hexane, and the cyclic hydrocarbons, benzene, toluene, ethylbenzene, p-xylene, cyclohexane and cis-1,4-dimethylcyclohexane, in silicalite-1, ZSM-5 and theta-1 respectively. The range of the experimental conditions covered by the FR measurements has been extended and the frequency response data have been improved considerably compared to earlier studies using the FR technique. Most of the isotherms of the systems studied in this work can be reproduced well by the Langmuir model. Deviations of the isotherms for n-pentane and n-hexane in silicalite-1 from this model at low temperatures, however, have been observed. These deviations have been attributed to sorption site heterogeneity of the sorbent and to the immobilisation of these molecules in the sinusoidal channels of the zeolite. Distinct steps were observed in the isotherms of benzene and toluene in silicalite-1 at loadings > 4 m./u.c., which were reversible, while a hysteresis loop was found in the isotherms of p-xylene at loadings > 4 m./u.c. in silicalite-1 but not in the isotherms of p-xylene in ZSM-5. In contrast with some explanations in the literature, the heterogeneous sorption sites which are present in the MFI samples and sorbate-sorbate interactions have been invoked to explain these anomalous results. The mass transfer of benzene and cyclohexane molecules in MFI zeolites is controlled by a pure micropore diffusion process, whereas the diffusivities of ethylbenzene and cis-1,4-dimethylcyclohexane in these sorbents may be hindered by the rotation of the methyl groups in these molecules. The effect of the structure defects of the framework on the diffusivities of aromatics inside the pores of siliclite-1 has been found. The diffusivities of the four aromatics decrease in the order of p-xylene > toluene > benzene > ethylbenzene, and the diffusion coefficients of the two cyclic alkanes are at least one order of magnitude smaller than the values for benzene. The diffusion coefficients of propane in theta-1 are about two orders of magnitudes smaller that those of propane in silicalite-1. Such a result arises from the single-file diffusion process which is occurring in this system. The activation energy for diffusion of propane in theta-1 is close to the heat of adsorption and is more than twice that found in silicalite-1 where three-dimensional diffusion is involved. This finding provides, for the first time, experimental evidence to support the assumption proposed in single-file diffusion theory that the rate of adsorption and desorption of sorbate molecules at pore entrances of one dimensional channel sorbents may be the rate-controlling step. The results obtained in this study reveal the importance of the effect of the pore structure of zeolites and specific features of the sorbate molecules on the dynamic processes involved in the adsorption and diffusion of these molecules in the zeolite networks.

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