FORCES BETWEEN POLYELECTROLYTE-COATED SURFACES - RELATIONS BETWEEN SURFACE INTERACTION AND FLOC PROPERTIES

The forces acting between negatively charged mica surfaces in the presence of some different cationic polyelectrolytes have been measured using a surface force apparatus. The different polyelectrolytes used have between 10% and 100% of the monomers charged. Particular emphasis has been given to the forces acting between the polyelectrolyte-coated surfaces when the ionic strength of the solution is low, i.e. when electrostatic forces predominate the interaction between the surface and the polyelectrolyte. Under these conditions the most highly charged polyelectrolytes adsorb in a very flat conformation and only a weak recharging is observed even at polyelectrolyte concentrations considerably above that needed to neutralise the mica surface charge. The surface force data are discussed in relation to the flee structures and properties obtained when latex particles are flocculated by polyelectrolytes. These studies are carried out by using a device that is based on three photometric dispersion analysers. The flee structures formed in the presence of various polyelectrolytes can to a large extent be rationalised by considering the interactions measured in the surface force apparatus provided that the difference in charge density of the mica surface and the latex surface is kept in mind.