THE EFFECT OF SALT CONCENTRATION ON ADSORPTION OF LOW-CHARGE-DENSITY POLYELECTROLYTES AND INTERACTIONS BETWEEN POLYELECTROLYTE-COATED SURFACES

In this investigation surface force, X-ray photoelectron spectroscopy and ellipsometry techniques have been used to study the adsorption of a low-charge-density cationic polyelectrolyte on negatively charged su rfaces. It is shown that the low cationicity of this polyelectrolyte i nduces an adsorption behavior which is limited by steric factors rathe r than by the substrate surface charge or potential. It is also establ ished that an increase in ionic strength of the solution results in de sorption of the polyelectrolyte accompanied by an increase in layer th ickness. This phenomenon is typical of a screening-reduced adsorption regime where electrostatic interactions predominate in the adsorption process. An increase in layer thickness most often occurs as a result of an increased adsorbed amount. Here, however, the increase in layer thickness occurs despite a reduction in the adsorbed amount. This can be understood as resulting from a reduced polyelectrolyte-surface affi nity and a swelling of the adsorbed layer. Finally, it is demonstrated that the employed techniques complement each other and reveal new inf ormation on the interaction forces and conformation of polyelectrolyte s at the solid-liquid interface. (C) 1998 Academic Press.