The purpose of this study was to investigate the effect of polyelectrolytes on the adhesion forces between polyelectrolyte-coated surfaces and to relate the observed phenomena to the performance of dry strength additives in papermaking systems.
The adhesive properties (pull-off forces) between polyelectrolyte-coated surfaces in air were determined as a function of the polymer charge density and the number of contacts. We found
strong adhesion energy for model systems coated with polymers of the highest (cationic) charge density, which suggests that electrostatic surface-polyelectrolyte-surface bridges are the main cause of the adhesion. At low charge density another force contribution due to entanglement of polymer chains gives rise to a significant contribution to the adhesion forces. The disruption of the contact leads to irreversible changes in the adsorbed layers when either the number of electrostatic bridges formed is large or when entanglement effects are important for polymers with a relatively low binding strength to the surface. These results are discussed in terms of our current understanding of development of dry strength in fiber systems.