This thesis describes an experimental study of calixarate overbased detergent oil additives, used to neutralise acidic by-products of engine combustion. Aspects of interest in this study include experimental synthesis of calixarenes and overbased detergents, physical and structural characterisation and monitoring of the synthesis process. Two types of calixarenes were prepared (6 and 8 phenolic units). A synthesis procedure of the calixarate overbased detergent was set up, basedono adaptation of existing procedures used for other classes of overbased detergents. The procedure was also modified to suit a lab-scale. 13C NMR and UV-Vis spectroscopy have provided strong evidence for a precursor of the overbased detergent. The ionisation of the surfactants (stearic acid carboxylic group, and phenolic units) was clearly established. The synthesis process was monitored at the molecular and macroscopice level. The use of 13C -labelled compounds enabled a semi-quantitative study of the concentration evolution of each chemical during the synthesis. Langmuir-t rough measurements and dynamic light scattering showed a decrease of particle size during the synthesis of the overbased detergent. The final calixarate overbased detergent was then fully characterised by these two methods. Based on the various information gathered (starting and final material characterisation, monitoring of the process),a mechanism was suggested. This involved a progressive solvation of calcium hydroxide, and breakdown of mixed calcium hydroxide and calcium carbonate.

The interaction between a single polystyrene particle and a polystyrene substrate has been previously reported by a number of investigators. However, the effects of relative humidity, applied load and contact time on the adhesion of polystyrene surfaces have not been investigated and these effects are poorly understood. It is the primary aim of the current work to characterise the effect of the aforementioned parameters on the adhesion of polystyrene surfaces using atomic force microscopy. The polystyrene used in this study contained 1% of divinyl benzene as a cross-linking agent. The adhesion forces between an individual polystyrene particle, normally 12-14 mum in diameter, and the surface of a compacted tablet of the same material have been measured at various relative humidities using a custom-built instrument and a commercial AFM. The commercial instrument has the capability of scanning the sample surface, and allowing greater control over the relative motion between the sample and probe. One of the achievements of this work is that a technique has been developed whereby an image of the surface of the tablet can be obtained using the attached particle as a probe scanning in non-contact mode. From the work conducted using the custom-built instrument, the dependency of adhesion forces on the relative humidity is greatest at relative humidities above 60% where capillary forces cause a sharp increase in adhesion with increasing relative humidity. Hysteresis was observed in the solid-solid contact gradient of the accompanying force curves, suggesting non-elastic behaviour at the contact area of the surfaces. Using the commercial AFM it was observed that adhesion values are consistently higher than results obtained from the custom built instrument across the range of relative humidity from 2% RH to 50% RH. This is due to the selection of smooth, single particle contact sites in the commercial AFM experiments. The measured adhesion forces from the custom-built instrument were found to be significantly lower than predictions for adhesion from the contact mechanics theories of JKR and DMT. This can be attributed to the effect of surface roughness and multiple contacts, which are not taken into account in either the JKR or DMT contact mechanics theories. At humidites below 60% the results obtained from the commercial AFM are in much better agreement with the predicted pull-off forces from the JKR model, because smooth, single particle contact regions could be selected. Using the custom-built instrument and the AFM Explorer, the effect of applied load on the adhesion force between a polystyrene particle and a polystyrene substrate was studied at low, medium and high relative humidity. Increasing the applied load has little effect on the measured adhesion forces at low and medium relative humidity but at high relative humidity of 60 to 65% RH, a transition was observed at an applied load of 1000 - 1200 nN. Above this transition the adhesion force increased steadily with applied load due to the yield stress of the material in the contact region being exceeded. The experimental values of applied load have been coupled with published values of Young's modulus, Poisson's ratio and hardness to predict the contact area from contact mechanics models of JKR and Maugis-Pollock. When coupled with the published value of yield stress for the material, the applied load for the onset of plastic flow is predicted. The value of 1508 nN predicted by the plasticity-based MP model agrees approximately with the observed transition in behaviour.

The effects of counterion on the lyotropic liquid crystalline phase behaviour of some quaternary ammonium salts of perfluorodecanoic acid in water have been studied using a combination of optical polarising microscopy (OPM), deuterium nuclear magnetic resonance (211 NMR) and cryo-transmission electron microscopy (cryo-TEM). The results from the phase diagram studies flill into two groups. Firstly the ammonium (A) and tetramethylanmionium (TMA) counterions show a phase behaviour with nematic (N) and random mesh (MJi 1 (0)) phase which possess non-uniform interfacial curvature. The second group of surfactants with counterions, butyltrimethylammonium (BTMA), dibutyldimetylammonium (DBDMA), and tetrabutylammonium (TBA), form only a classical lamellar phase (La). For both DBDMA and TBA lower consolute behaviour has been observed. At fixed concentration in all five systems cryo-TEM visualises isotropic liquid phase structures that vary from sphere / rod micelles for A and TMA to vesicles / bilayer pieces for the other surfactants. These results are consistent with a reduction of the interfacial curvature of the aggregates, a phenomenon explained by a closer association of the counterion with the micellar surface. This is postulated to be driven by an increase in the size and hydrophobicity of the counter-ion from A to TBA. The correlated mesh phase (Mh i (R3 m)) is unique to the TMA surfactant of this series. It is extremely stable, both thermally and in surfactant concentration, when compared to such phases formed in other surfactant systems. To further elucidate the effect of countenon and investigate the mechanisms that stabilise mesh intermediate phases the effects of additives on the Mh 1 (R3 m) have been studied. The evolution of the phase behaviour and lyotropic phase structures formed in the TMA system have been studied upon the addition of salt (tetramethylammonium chloride, TMAC1), cosurfactant (111,1H-perfluoro-I-decanol, CiooI) and oil (perfluorooctane, C goil) using OPM, 211 NMR and small angle X-ray scattering (SAXS). Upon addition of a third component the Mh1(R3 m) is lost and a Mii j (0) stabilised. Further addition of the third component drives the formation of L. phase in the TMACI and C 10o1 addition systems. The structure of Mli 1 (R 3 m) phase is essentially unaltered over that of the binary phase irrespective of the amount or type of third component added. In the case of TMAC1 addition the formation of the Mh 1 (0) is driven by a reduction in the electrostatic interlayer interaction via a screening effect of the added counter-ions. In the C10o1 and C8oil addition systems the phase transition is driven by an alteration in the packing of the hydrophobic interior of the aggregates, which is termed a 'hydrophobic packing constraint'. SAXS experiments show that upon the transition from the Mh 1 (R3 m) to Mh1 (0) phase the surface area per molecule is conserved (within experimental error) and occurs more rapidly in the presence of C 10o1 and Cgoil indicating that the stability of the former over the latter requires a well defined intra-layer topology. The Mh 1(0) to L. transition is driven by a closure of defects as the additive concentration decreases the surface area per surfactant molecule via enhanced counter-ion binding in the TMACI experiments, or surface charge dilution in the C 10o1 addition systems.

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