Surface forces between adsorbed polyelectrolytes in salt solution

Abstract

Highly charged cationic polyelectrolyte was adsorbed onto mica from 10⁻⁴ M KBr and 10⁻⁴ M K₂SO₄ solutions. The results show that the structure of the adsorbed layer and the total amount adsorbed is dependent on the anion valency. Both the layer thickness and the adsorbed amount increase when the salt anion is of higher valency. — Desorption over several days into 10⁻⁴ M K₂SO₄ solution was followed. This indicates the adsorbed layer initially overcompensates the mica lattice charge. After some time, the sign of the charge is re-reversed, due to desorption. Adhesion between the adsorbed layers increases during the desorption process. This adhesion is attributed to bridging of entropic origin.