The addition of non-absorbing polymer to a suspension of colloidal hard-spheres causes phase separation via the depletion mechanism. At high enough concentration of polymer a variety of non-equilibrium aggregation behaviour are observed. Transient gels are one such behaviour observed at the highest polymer concentrations. Transient colloid-polymer gels are metastable space-filling particle networks. They persist for some finite time before suddenly collapsing to form a dense sediment. Thus transient gels exhibit "delayed sedimentation" which is a phenomenon observed in many weakly aggregated suspensions. We have studied the collapse process occurring in the bulk of a gelled suspension using dark-field imaging and ultrasonic concentration profiling. At low polymer concentrations we observe delayed sedimentation behaviour. At the highest polymer concentration we observe a change in the settling behaviour. The suspension continuously sediment at a rate comparable to the initial slow settling rate of gels exhibiting delayed sedimentation. This is known as "creeping sedimentation". We have also investigated the effect of varying suspension height and width on the delay time of a gel. We have found a critical height below which the gel exhibits a size-dependent delay time. Above this critical height the delay time is independent of height. The same behaviour is found when width is varied. We find good agreement between the results of this experimental study and a recent theory.

Double step potential chronocoulometric measurements have been set up for the investigation of kinetics of charge transfer across the liquid/liquid interface and to study adsorption at these interfaces. Semioperation analysis of chronoamperometric and chronocoulometric data were also developed and used to evaluate the kinetic parameters. The transfer of the acetylcholine ion across the water/1,2-dichloro-methane, and water/1,2-dichlorobenzene interfaces have been studied as a function of the viscosity of both phases and the composition of the organic phases respectively. The results showed that the standard rate constant is inversely porportional to the viscosity of either phase. The potential dependence of the rate of ion transfer follows the Butler-Volmer equation. It is shown that the main difference between ion transfer and ion transport is a consequence of an entropy effect. The kinetics and thermodynamics of sodium and potassium transfer facilitated by dibenzo-18-crown-6 have been studied by chronocoulometry and its convolution technique and cyclic voltammetry. Three possible mechanisms have been examined carefully and a new terminology is being proposed. A simple way to measure the ratio of the diffusion coefficients of ionophore and its complex ion in the organic phase by using micropipette has been developed. Lithium and proton transfer across water/1,2-dichloro-ethane interface facilitated by ETH1810 have been studied and a mechanism has been proposed. Potassium transfer across water/1,2-dichloro-ethane interface facilitated by DLADB18C6 has also been observed. The adsorption of hexadecyl sulphonate anion (HDS) on the water/1,2-dichloroethane interface has been investigated by classical methodology. Finally, a new method to measure the half wave potential has been applied to the measurement of formal Gibbs energies of transfer of ions across the water/1,2-dichloroethane interface. The validity of TATB (Tetraphenyl-arsonium Tetraphenylborate) assumption is also discussed.

No description available.

No description available.

An approximate analytical expression for the current potential characteristic for charge transfer at a microdisc interface under steady state conditions is given for reversible, quasireversible and irreversible kinetics. The quasireversible expression is proposed as a simple means for analysis of experimental voltammograms thus gaining access to the potential dependent forward rate constant and the charge transfer coefficient, α. It is used to analyse simulated data and the results compared to the simulation parameters. The mathematics of the linear diffusion of cyclic voltammetry for electron transfer at the Interface between Two Immiscible Electrolyte Solutions (ITIES) is addressed, and the numerical solution of the resulting integral equation is evaluated. The results show how the cyclic voltammograms for reversible electron transfer at the ITIES vary when different ratios of reactants and products are used, and how these differ from the classical reversible cyclic voltammograms. A microhole formed by eximer laser ablation in a polyester membrane is proposed as a useful support for a micro-ITIES providing symmetrical diffusion characteristics analogous to an inlaid disc electrode. This support (and also regular arrays of microholes) has been used to obtain symmetrical steady state voltammograms for the transfer of the acetylcholine cation from water to 1,2-dichloroethane. A micro-ITIES suported at the tip of a micropipette has been used to study the transfer of alkali metal ions assisted by crown ethers which gave a lower limit for the pseudo first order interfacial transfer rate constants of 10^-2 cm s^-1, and provided data on the complexation constants of Li^+ , Na^+ , K^+ Rb^+ and Cs^+ with dibenzo-18-crown-6. The oxidations of di-n-butylferrocene and ferrocene by hexacyanoferrate III at the ITIES were investigated using both microinterfaces supported at the tip of a micropipette, and large interfaces.

The work described in this thesis concerns the adsorption and decomposition of small hydrocarbon molecules on the surface of an alumina supported nickel catalysts. The catalyst was prepared using a co-precipitation method and contained 25% nickel by weight. Temperature programmed reduction revealed that reduction at over 550<SUP>o</SUP>C in hydrogen was necessary in order to fully reduce the catalyst. Nickel surface area measurements were performed using hydrogen chemisorption and nitrous oxide decomposition, revealing an area of 30→45m^2/g. X ray diffraction and transmission electron microscopy showed an average nickel particle diameter of 13nm. Total catalyst surface area was measured by nitrogen adsorption at -196°C, giving a value of 250m^2/g for the as prepared catalyst. Infrared studies were performed using a combination of Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), with a standard Spectratech cell, and transmission infrared spectroscopy, with a home made infrared cell. A passivation procedure was developed so that pre-reduced catalyst could be transferred to the infrared cells and re-reduced <i>in situ</i> at 300°C. The adsorption and reaction of the two simple alkenes, ethene and propene were investigated at temperatures between 25 and 300°C. The room temperature surface chemistry of both molecules was dominated by the initial formation of alkylidyne species, ethylidyne (CCH_3) from ethene and propylidyne (CCH_2CH_3) from propene. The ethylidyne formed from ethene decayed to surface methyl (CH_3) and C_4 containing species. These were hydrogenated to methane and butane respectively. Ethylidyne itself was stable to hydrogenation. Methane was the only product released during temperature programming of the sample up to 300°C in helium. Propylidyne formed from propene decayed to ethylidyne, methyl and other C_3 and C_6 containing carbonaceous deposits. Hydrogenation produced methane and propane, leaving propylidyne and ethylidyne. Temperature programming of these species in helium produced only methane, and heating in hydrogen produced a small quantity of hexane in addition. After ethene adsorption, only 77% of the carbon deposited could be removed during re-reduction. Temperature programmed oxidation removed all of the carbon but substantial re-oxidation of the nickel catalyst occurred.

No description available.

Low-shear viscometry and visual observation are used to study the rheology and sedimentation behaviour of colloid-polymer transient gels. The delay to sedimentation (or latency time) exhibited by the transient gels increases strongly with both polymer concentration and colloid volume fraction. Two distinct categories of transient gel are discovered; those displaying a latency time independent of sample height (lower polymer concentration), and those for which latency time strongly decreases with increasing sample height (higher polymer concentration). The transient gel displays power-law fluid behaviour for low shear rates (<I>Pe </I>π 1), the viscosity strongly increasing as the shear stress is reduced. It is suggested that the strongly shear-thinning rheological behaviour of the transient gel is the principal mechanism behind the abruptness of the transient gel collapse. Rheological observations suggest that the strength of the transient gel structure significantly increases then decreases during the latency period, the decrease coinciding with the collapse. Measurements of the low shear rate viscosity of a model hard-sphere suspension are also presented. Suspension volume fractions are calibrated with respect to the thermodynamic disorder to order, or crystallization, transition. At freezing, the low-shear suspension viscosity is found to be ≈ 53 times that of the solvent, significantly different to values measured in previous studies.

An investigation into the effect of framework constituents on the sorption properties of MFI-type zeolites and AEL-type zeotypes has been carried out. ZSM-5 with different amounts of framework aluminium was readily syn-thesised. It was found that the distribution of template (tetrapropylammo-nium ions, TPA) between a low and a high temperature form, and the water capacity of the calcined zoelites both depended linearly on the aluminium content. The temperature of oxidative degradation of the template and the energy associated with this degradation were also found to depend upon the aluminium content. A series of TPA-silicalites with different alkali and alkaline earth metal ions has been prepared. The sodium and potassium forms were found to crystallise most rapidly, while the barium and the caesium ones were considerably slower. AEL-type zeotypes have been prepared from aluminophosphate gels containing different amounts of silicon. These did not produce materials with the expected Al/P ratio of one. The amount and degradation temperature of the template and the zeotype water capacity after template removal were found to depend on the framework aluminium content; in these cases this appears the dominant framework component. An attempt was made to synthesise a series of microporous silicophos-phates and, although crystalline products were prepared, their structures could not be determined and they could not be obtained in a form suitable for sorption studies. An isopiestic equilibration technique was used to study the sorption of glycerol and a series of sodium alkylsulphonates from aqueous solution. The glycerol uptake was found to depend upon the framework aluminium content; ZSM-5 with approximately 1 aluminium per unit cell was found to be most effective. The sorption behaviour was also found to depend on the cation in the silicate, the effects being larger than expected in view of the small number of inorganic ions occluded during synthesis. The framework aluminium content was also found to be important for the sorption of glycerol by the AEL materials. These zeotypes were insufficiently resilient to lattice attack for the sorption of the alkylsulphonates to be studied. The MFI materials, however, showed a gradation in sorption properties, which could be interpreted in terms of the hydrophilicity/hydrophobicity of both the zeolite frameworks and the alkylsulphonate sorbates, though the results are less clear cut than those obtained with glycerol and there may be other important considerations.

The colloidal state has long been of interest to physicists, both in its own right and as a model for atomic systems. In particular, colloidal suspensions with low size-polydispersity have been widely used as model hard spheres. Optical microscopy can resolve detail at the larger end of the colloidal length scale, and to image suspensions at an individual particle level of resolution would allow the investigation of local behaviour in a way denied to the established techniques of light-scattering. To achieve high-contrast, single-particle resolution in dense suspensions that are thick enough to show behaviour the same as would be expected in the bulk, is not a trivial exercise, however. This work builds on established advanced techniques of the light microscopy of phase objects, to develop an effective method of achieving this aim, addressing issues of imaging technique, suspension mounting and the interpretation of image data. The usefulness of this newly developed experimental protocol is demonstrated by, amongst other results, a detailed study of the structure of the colloidal crystals found in hard-sphere suspensions and an investigation of the nucleation of such crystals from the metastable colloidal fluid.