Aggregation kinetics of colloidal suspensions of engine soots. Influence of polymeric lubricant additives

The aggregation kinetics of soot particles, collected from three different drain oils after engine tests and dispersed in a base oil, have been studied by static and dynamic light scattering techniques. The engine runs were performed with two different polymeric additives in the lubricating oil to probe their contribution to the soot aggregation. These polymers have the same skeleton, but one of them has a grafted dispersant function. All the aggregation kinetics have been followed for 200 hours. A Reaction Limited Cluster Aggregation (RLCA) mechanism explains correctly the experimental observations made on the three kinds of soot colloidal suspensions, with a measured fractal dimension; df, of 2.15+/-0.1. The mean values of the number of particles of an aggregate and the corresponding radius of gyration have been calculated during the whole kinetic run. In the presence of a polymer, the aggregation kinetic is slowed down and even stopped if the polymer has a dispersant chemical function. Copyright (C) 1997 Elsevier Science Ltd.