CONTACT OF 2 CARBON SURFACES COVERED WITH A DISPERSANT POLYMER

Using a surface force apparatus (SFA), me have studied, first the adhe sive force between two smooth amorphous carbon surfaces in air, and se cond, the repulsive force due to the contact of two blush polymer laye rs adsorbed on carbon surfaces. Adhesion in dry air is compared to tha t due to the effect of a small meniscus formed in humid air and the pa rtial wetting of a large water meniscus. Dispersive and acid-base cont ributions of carbon surfaces are also determined, using Fowkes analysi s. The adsorption of a polyisobutenesuccinimide (PIB) in dilute soluti on with hydrocarbon solvent at 25 degrees C, and the resulting interac tions between carbon surfaces are also characterised with the SFA. Our results show that this dispersant polymer on a carbon surface forms a 5.5 nm thick anisotropic brush leger. This anisotropy is detected mec hanically and compared with that of other polymer or surfactant. The a bility of PIE molecules to adsorb on carbon particles and thus stabili ze them in the hydrocarbon solution, is of great implication in lubric ation technology. The results clarify that this additive function by s teric stabilization mechanism and not by electrostatic repulsion The r esults provide a basis for understanding the mechanism of action of of polyisobutenesuccinimides widely used as dispersant additives in lubr icants.