The effect of cationic polyelectrolyte complexes on interactions between cellulose surfaces

The purpose of this work was to better understand the effect polyelectrolyte complexes have on the interactions in cellulosic systems. The surface forces between cellulose spheres immersed in solutions of positively charged polyelectrolyte complexes, formed by cationic and anionic polyacrylamides, were studied using an atomic force microscope. The effect of the molecular weight and the charge density of the polyelectrolytes, as well as the background electrolyte concentration were investigated. The adsorption of the polyelectrolyte complexes on the negatively charged cellulose surface had a strong influence on the interactions between the surfaces and the forces were clearly different as compared to the single polymer systems. The interactions between the adsorbed polyelectrolyte complex layers were mainly steric and repulsive, even at low polymer concentrations. The comparison between two polyelectrolyte complexes showed that the complex formed by high molecular weight and low charged polyelectrolytes induced a steric force ranging further than the one induced by the complex formed by low molecular weight and high charged polyelectrolytes. Also the pull-off forces measured on separation ranged longer in the former case but the pull-off force was weaker. The fact that the interaction forces are totally different using polymer complexes as compared to single polymer systems can have a drastic effect on, e.g. water removal efficiency, as well as flocculation during the formation of the paper web.