Abstract
This thesis describes an experimental and molecular modelling investigation of calcium carbonate oil soluble detergents. These are used as additives in lubricating oils, mainly to neutralise acidic by-products of the combustion process. Most of the work was carried out for phenate surfactant molecules. The work has confirmed that the detergent and calcium carbonate form an inverse micelle structure, with the diameter depending on the level of overbasing. A range of analytical techniques including, gravimetric analysis and spectroscopy assisted by 'ab initio' quantum mechanical calculation has been used to identify the chemical species present in these additives. The results of this work are discussed in chapter 2. Langmuir trough surface pressure and surface tension measurements were made to obtain information on the physical arrangement and surface properties of the overbased particles, the results of which are described in chapter 3. Molecular dynamics simulations on model structures were performed, enabling information on the molecular structure of the micelles to be obtained. These computations showed that the micelles are quite rigid structures, even at engine temperatures and that the phenates are probably discoid shaped, whereas sulphonate micelles are spherical. The bulk properties of the neat additives and in solution were investigated using dielectric spectroscopy, rheology and dynamic light scattering, and provided evidence for weak aggregation of the individual micelles into large clusters. This work is described in chapter 5. Chapter 6 concludes by bringing together the results from the experimental and modelling studies, presenting the main conclusions and suggesting topics for further research.