Brian Vincent

The synthesis of nine, nonionic, fuel-soluble poly(isobutylene)-based surfactants, and an assessment of their ability to remove and prevent carbonaceous deposit build up on light-duty vehicle engine valves, is described. Surfactants with varying surfactant head group polarity and structure, and tail length, were assessed for their potential fuel surfactant efficacy by establishing their adsorption kinetics and adsorption isotherms, from iso-octane, onto stainless steel surfaces, using both solution depletion and ellipsometry measurements. Increasing head group polarity from a simple phenol group, by the inclusion of an amine group, increased the adsorption affinity and the maximum adsorbed amount. Inclusion of additional amine groups also increased them maximum adsorbed amount, albeit only marginally. Replacing N-Me groups by N-H groups also increased the adsorbed amounts. Surfactant adsorption was found to be independent of tail length and the maximum adsorbed amount corresponded more-or-less to the surface concentration of strong acid groups on the steel surface, as determined by a Boehm titration. Additionally, all the surfactants studied appeared to adsorb onto the steel surface “irreversibly.”

In this paper, the heteroaggregation of opposite sign hard and soft colloidal particles has been studied by static and dynamic light scattering. The structure of the aggregates, as well as the aggregation kinetics, have been investigated. At low electrolyte concentration, where both long-range electrostatic repulsive and attractive forces are present, the aggregates were found to be more open than expected for diffusion-limited cluster aggregation (DLCA). However, the aggregate size time evolution is characteristic of diffusion-controlled processes. At high electrolyte concentration, where DLCA would be expected, very compacted clusters were found, as well as very rapid aggregation, leading to high polydispersity. These latter findings are interpreted in terms of the differences in the homoaggregation speeds for the hard and soft particles.