Detergent-Polymer Interactions in Hydrocarbon Solvents: A Viscometric Study

Two common internal combustion engine lubricant additives, overbased calcium sulfonate detergents and dispersant olefin copolymer (DOCP) viscosity index improvers, are shown to interact strongly, resulting in large (ca. 50%) increases in relative viscosity in hydrocarbon solutions. This viscosity increase is believed to result from bridging interactions from either physi- or chemisorption of DOCP functional groups onto the inorganic core of the sulfonate detergent colloid, with a resulting increase in effective polymer molecular weight. Viscometric properties of the detergent/DOCP interaction products, shear stability and the effect of competitive interactions with polyisobutenyl succinimide dispersant additives are described.