Surface properties of poly(ethylene imine)-coated mica surfaces - Salt and pH effects

The adsorption of a branched weak polybase, poly(ethylene imine) (PEI), on the basal plane of muscovite mica was investigated using surface force measurements, electro-osmotic measurements, and ESCA. The use of this combination of techniques allows us to obtain information about adsorbed amount, interfacial charges, average structure of adsorbed layers and the most important types of forces acting between PEI-coated surfaces. The system was studied under two different conditions. The adsorbed layer adopts a flat conformation at low ionic strength and at low pH owing to the predominance of electrostatic forces. The interfacial properties of PEI;coated surfaces are compared with those of strong polyelectrolytes as well as with a linear weak polybase studied previously under similar conditions. At higher pH-values the adsorbed amount increases owing to a reduction in the polyelectrolyte charge density. This results in a thicker layer and in the increased importance of repulsive steric forces. Finally, the interaction between one polyelectrolyte-coated surface and a bare mica surface was investigated and compared with recent theoretical predictions.