Adsorption of polyisobutenylsuccinimide derivatives at a solid-hydrocarboninterface

The adsorption of polymer dispersants of the polyisobutenylsuccinimide seri es has been studied at the solid/xylene interface. Carbon black was studied as a model solid. Adsorption isotherms were determined, the enthalpy of ad sorption was measured by calorimetry, and the thickness of the adsorbed lay er was obtained from small-angle neutron scattering. The paper emphasizes t he structure-properties relationships with the help of a series of polyisob utenylsuccinimides having different polyamine groups and different polymer architectures, simple diblock (PIBSI) and comblike structure (polyPIBSI). T he polyamine part ensured a strong adsorption on the solid surface, which i ncreased in strength with the number of amine groups. In the same way, chan ging the diblock structure for a comblike one led to an enhanced affinity o f the polymer for the solid surface. The adsorption was enthalpic but the G ibbs free energy of adsorption remained moderate because of a large entropy loss during adsorption. There was an enthalpy-entropy compensation phenome non. Below a concentration of 70 nmol/m(3), the polymers adsorbed as a 30 A ngstrom thick monolayer and the adsorption phenomenon was irreversible, due to the polymeric nature of the polar part. A drastic increase of adsorbed amount took place for higher concentrations. The formation of reverse hemim icelles was assumed as the origin of this phenomenon. The supplementary ads orption was reversible, showing that the polymer-polymer interactions were weaker than the polymer-surface interactions.